Tuning and Balancing Zenith-Stromberg and SU Carburetors in Your British Sports Car

Assuming your ignition system, engine internals, and carburetors are in good condition... learn how to balance and tune your carburetors. We'll make another video getting into more detail on the various setups, but after a few G&Ts we thought this basic guide could help you set up your carbs for your engine after they've been properly rebuilt. Subscribe to our channel to see future videos, and make sure to comment if there's something specific you'd like to see!

[@OllyBarker95]

i have watched countless videos about doing my carbs on and off for a long time now, thank you for making it easier :)

[@midwestmotoring]

We'll be doing a video specifically about pulling apart the Stromberg carburetors on a TR6 soon. You'll see disassembly, some explanation of how things work, and putting everything back together. Let us know if there's anything else you're curious to see and it'll go higher on the priority list of videos to edit!

[@bluegoo5341]

Can’t thank you enough for such a great video! Was able to finally tune up my Strombergs thanks to you👍🏻. Cheers!

[@midwestmotoring]

Glad to hear I could help!

[@BuilditUK]

Nice and simple video. Best bit of tunning advice for these types of carbs. Cheers

[@midwestmotoring]

Thanks! Sorry for the poor video production, but hopefully the videos help!

[@bobspeller2225]

Sounds good to me, thanks for an easy review to carb adjustment. Cheers Bob

[@midwestmotoring]

You bet! I'm considering re-shooting the video with a bit more focus on the distributor since you really shouldn't set the carburetors before dealing with the ignition.

[@jononeil500]

Wow. That was a great video. Thank you!

[@midwestmotoring]

Glad you liked it! If there are any issues, check out the distributor video. Most carburetor problems are actually ignition problems....

[@kenstephens5121]

keep the videos up great job!!

[@midwestmotoring]

Thanks, will do!

[@nestorbeckmann]

Nice and easy, helped me with my Dodge 1500. Greetings from Argentina

[@midwestmotoring]

Glad it helped!

[@Paulzimmermanroses]

Is the Uni-Syn tool you use a specific model for Strombergs? Mine are dual carbs. 1994 Morgan Plus 4 with a TR4 engine. Great video. Very clear and easy to follow.

[@midwestmotoring]

No, it can be used for other carbs as well, like SUs. Basically as long as it covers the opening completely it'll work.

[@Paulzimmermanroses]

@@midwestmotoring thanks!

[@youtubecopyrights]

This is a wonderful video. My manual says for the TR4 it should be adjusted to around 500RPM. But I can’t even turn the idle down that much. The engine struggles a lot and stays at about 600-700 unsteady. Engine stabilizes at about 1000 RPM. SU Carbs

[@midwestmotoring]

500 sounds super low. Even the TR6 I think is about 650 or 700, and it won't do it unless everything else tune-wise is perfect. Which manual are you using?

[@joecorrie1]

I wonder if your throttle shafts are worn or another vaccum leak letting in to much air which would need more fuel to be smooth running causing a higher rpm? just a thought. I'm in know way as knowledgeable as Midwest Motoring, just thinking about your issue.

[@fezziwig47]

Thank you for these videos and hope you can clarify the steps for tuning the carbs once back on the car (1969 S2 E type, 175 CD2 carbs, original to car, fixed needle, no mixture tuning). I warmed the car, took off the air cleaner and set my UniSyn to the rear (firewall) carb. Adjusted US to get a reading and then placed the US on front (radiator-side) carb. The rear carb had a reading to the first mark, but on the front carb, the little cup went all the way to the top. Watching your video again, it looks like I should turn the front carb's idle screw CCW (down) ??? The car started fine, ran fine before I replaced the Strom seals/gaskets/etc. After putting them back on the car, the idle went from 750 to about 1250. Then the part that is confusing... after setting the carb balance, you turn the same idle screw to adjust the idle??? won't that throw the balance off then? or do you then turn the screws the same amount to maintain the balance?

[@midwestmotoring]

Yes, exactly! You're on the right track. Since the idle is too high, you would balance the carbs by lowering the front one as the cup in the unisyn is too high. If the idle were too low, then you would adjust the rear carb to be higher instead. Remember to make sure the linkage is disconnected, otherwise adjusting the front carb will also accidentally adjust the rear carb and vice versa. You can adjust the unisyn if you need so that the range it measures in stays useful. As for setting the idle once the carbs are balanced, so long as you move the throttle screws by the same amount (for example turn both 1/8 of a turn in the same direction), then you won't throw off the balance. You can always check the balance after moving the idle in this way. It shouldn't have changed, but it's an easy adjustment if it did. I hope that helps! Beautiful car--make sure you drive it!

[@bodieb.1239]

Huge help for me. Thanks. Why are so many people afraid of touching these carbs? Great video

[@midwestmotoring]

No idea. They aren't complicated. Just different. Really intuitive once you understand them.

[@66ManFromUncle66]

Great video and I'm a complete beginner with doing my own maintenance. I'm just a little confused as you undid the nut for the throttle linkage but didn't show or say when it should be re tightened it? and by adjusting the throttle stop is that what changes the idle speed ?

[@midwestmotoring]

Hello! Yes, adjusting the throttle stop is what changes the speed. The more "in" the screw is, the more the butterfly is open, so it lets in more air and fuel and the engine speeds up. The idea behind keeping the linkage loose is that you can operate each butterfly independently. Otherwise, if you open one, it's going to open the other one slightly more too--so you're not changing the balance. The time to tighten the linkage back up is after you're happy with the balance, have adjusted the mixture if required, and checked the balance again. From that point, go ahead an tighten, and then just adjust both carbs the same amount if you need to fine tune the idle speed.

[@MAL-Collector]

Thanks for the video. I will try getting my saab 99 adjusted. Its sounds like a tractor when its cold. But warm nothing. I think its too rich. Im gonna buy that tool!

[@midwestmotoring]

If the rough running is only when it's cold, that's not necessarily the mixture being off--it could be your cold idle mixture is where the problem is.

[@patrickpieri8108]

Thanks for your excellant video. I tried it on my Strombergs...the left carburetor, everytime I put the syncronizing tool on the mouth, the red float goes all the way up the tube quickly and the engine stalls. I tried the idle screw both ways and can not get any change on the float ball level ? The engine always stalls. The right carb I have adjusted at 60% of the float level up the tube. I double checked the linkage, and its not getting binded up. Any thoughts from anone would be greatly appreciated. Much Thanks, Patick vehicle is a 1970 Jaguar XJ6

[@midwestmotoring]

Hi Patrick, If the float goes to the top of the tube and the engine stalls, you need to adjust the tool. The center "cone-shaped" bit rotates, which opens up the gap for air to go through. It's adjustable to allow for different strength and size engines. You need to unscrew it to allow more air to flow. Once you get the float somewhere in the middle (the actual location isn't important--just where it is relative to the other carburetor), it shouldn't change the RPMs much. If it does drop significantly (a little is okay, but it definitely shouldn't be stalling), then the carb is burning way too rich.

[@JoseFranco-mw4hu]

thanks for all

[@midwestmotoring]

You're welcome!

[@jamcdona]

I have a question about balancing- I noticed that you balanced to the lower air flow indication; is there a specific air flow that you should be looking for? Could you have adjusted the lower one to match the higher flow carb instead? I have the same unisyn that you are using, but it doesn't register very easily. I think it's calibrated or different carbs, or it's faulty. Amazon purchase, $9 or so...

[@midwestmotoring]

Good question! If you have the same unisyn, then by turning the round bit in the middle you can make the gauge more or less sensitive to airflow. Screw it in and the float will fly higher, for example. The actual levels are somewhat arbitrary. As for whether to adjust one carb up or the other down, that depends on your RPM at idle. If your RPM is 2200, you'll want to adjust one carb down. If it's 550, you'll want to adjust the weaker carb up. Ideal idle in a TR6 is like 800 or 850 if memory serves. Again... that's with a completely stock engine and soforth. Once you put in a hot cam, swap to triple webers, raise the compression etc.... all bets are off.

[@user-le5xb5cp3y]

I have a volvo c304 with 2 stromberg carbs. At 1 point the quantity of fuel consumed aumented twice and power diminished. Any guess? Your video was very nice

[@midwestmotoring]

Carburetors usually don't act that way suddenly, except for maybe a sticking float valve. I'd guess your distributor needs service--especially if you have points.

[@charlesbaker4508]

Thanks for this. What is your preferred weight of oil in the dashpots of ZS carburetors? I rebuilt mine recently and put 20/50 in the wells and with the rod installed they are very difficult to move but do move smoothly. I won’t be able to do any tuning until spring… Thanks in advance

[@midwestmotoring]

I have an oil can with 30w in it, but the shop manual says engine oil like what you're doing.

[@sunchoi9250]

Adjusting mixture from the top with the special tool, to lean the mixture, which way do you turn? It would seem clockwise would move the needle deeper into the jet, restricting fuel and leaning out the mixture. Or should I turn counterclockwise?

[@midwestmotoring]

Counterclockwise. The threads are in the same direction as most bolts at a hardware store, so by turning clockwise you would be threading the adjuster into the needle--bringing everything close together. Since the needle isn't allowed to turn, and since the adjuster can't move up or down, this draws the needle up into the air piston and out of the jet (making the mixture richer). Turning the adjuster counterclockwise has the opposite effect. You're unthreading the adjuster, which makes the assembly longer and forces the needle farther down and out of the air piston. This puts the wider portion of the needle into the jet and makes the mixture more lean. I hope this helps!

[@user-le5xb5cp3y]

Functioning in idle is perfect

[@midwestmotoring]

It's so nice when it sounds right!

[@patrickbitton4198]

Thank you for your great videos. I am having a hard time getting my rpm's below 1000. I unscrewed the idle screws so that they don't touch the throttle, and still above 1000rpm's. Is there anything I should be looking at to get my rpm's down? Thanks Btw, I have a 73 TR6.

[@midwestmotoring]

Your bypass valves are out of adjustment.

[@patrickbitton4198]

@@midwestmotoring thank you. I’ll take a look at that.

[@rizalsaiful6058]

Hi sir..in your video shoot at 3.15 mentioned that too rich or too lean symptoms..if so, which part to be adjusted then? Jet height to be in which level or idle port screw once to be.adjusted and how it could be? Thanks so.much. .👍

[@midwestmotoring]

Hello, there are only 2 ways to adjust the mixture. Early carburetors have adjustable jets. You'll know the jets are adjustable because underneath the carburetor will be what appears to be a bolt that you can put a wrench on. That will raise or lower the jet. Later carbs have adjustable needles (the screw on the side of the carb is the idle trim screw, and you'll need specialized equipment to tell if it's doing anything). The needle is adjusted with a special tool down the top of the carburetor. For about a year in 1968 or so, neither jet nor needle was adjustable. These carbs require disassembly to adjust, by physically moving the needle up or down and then re-tightening everything.

[@fauzanadiem6259]

Great video! I have stromberg 175cd Mercedes 1978, I've try to adjust mixture but when I try to lift the valve up the idle drop & engine is shut off. The rpm is already on the high idle. Is there other screw to adjust the idle? I have no problem with the power of my engine but when I checked the spark plug its full of carbon (Back then my spark plug is brown & fuel economy is great)

[@midwestmotoring]

You may be lifting the needle too high. Very slightly is all you need. But if your plugs are black, it might be too rich. Whether it's too rich while driving or just at idle is a different question though....

[@fauzanadiem6259]

@@midwestmotoring Im sure I lift it very slightly, it is possible the carb too lean but the spark plug too rich?

[@midwestmotoring]

Yes, the plugs you have could play a role as well. So could the timing.

[@robertgagnon3336]

I also have watched quite a number of videos on this topic and this guy is far and away the clearest to my ear. And I have an issue and I hope he will respond. My jet readjusts itself, it seem to me. The tension or torque needed on one 175 CD is almost none to the point it's not clear if I even have the allen bit on the Stromberg tool truly inserted. How is this addressed? Obviously I will have to remove the air valve from the carb. I suppose I will have to remove the jet and adjustment parts from the air valve. Please describe how to make adjustment on these more tight. Thanks!

[@midwestmotoring]

There are a couple pieces that could have worn or that aren't correctly installed. Most often, if the allen key seems too easy to turn, you have a worn o-ring (so it offers little resistance to turning). You could possibly also have a set screw that is missing or broken, so the needle will unscrew itself. Or, perhaps the threads on the needle or the adjuster are worn. It's also possible someone has opened the carburetor before and has replaced adjustable parts with non-adjustable ones. The best way to find the problem is to disassemble the needle / air piston and see what you have to work with. Have an o-ring handy (I think these come in the re-build kits) as that's the likely culprit. PS, if you're having to top up the dashpot oil fairly frequently--that's another clue that points to a worn or improperly sized o-ring. I hope this helps!

[@midwestmotoring]

Also, just to clarify... it's common to use wrong part names in forums and online, so when you say "jet" I assumed you were referring to the mixture needle (the majority of carbs I've owned adjust this way, but that's down to the cars I've bought). Technically, using the word "jet" to describe the mixture needle would not accurate though, since the jet is actually the brass tube in the base of the carb (the thing the needle slots into). Early ZS carbs and most SUs adjust by moving the jet up and down, and the mixture needle is fixed in position in the air piston. If you have a fixed needle and an adjustable jet, you may have worn threads somewhere underneath the carburetor, or the spring may be missing or broken (there's a spring that holds everything tight).

[@robertgagnon3336]

@@midwestmotoring Yes it surely helps!

[@robertgagnon3336]

@@midwestmotoring Yes, I mean the metering needle. I have the variation where the Stromberg mixture adjusting tool is used to prevent the air valve from turning whilst turning the allen keyed screw on the needle. I mean to replace the o-rings as a first step, I think that is exactly the answer. Another question point: when placing the screw/o-ring etc back into the damper cylinder, how does one know how far to insert the six (?) pointed keeper? Seems if one pushed it in too far, you could hence not adjust the needle. Again, many thanks!

[@midwestmotoring]

Hi Robert, sorry for the delay--I don't get notified except for the first question for some reason. The answer is to push the keeper all the way down. You don't want the threaded adjuster to move up and down--just the needle. The keeper will hold the adjuster in place so that only the needle will move when the threads are turned.

[@andrewep2816]

Thank you for helpful video. My Stromberg 175 has another mix adjustment screw and plastic nut on the firewall side (MGB-79). In fact the sticker still under the hood only points to those the screw as the adjustment location. Could you help me understand how that screw and nut interplay with the adjustments made internally using the adjustment tool down the barrel?

[@midwestmotoring]

Hi Andrew! Stromberg carbs had a number of variations with different bits that were attached. For example, there is often an idle trim adjustment screw on the side for very fine tuning. Yours might have an idle circuit in lieu of other parts such as the bypass valve or temperature compensator that would be on most Triumph setups. Are you able to post a photo? Or can you email it to [e-mail]?

[@andrewep2816]

@@midwestmotoring Thank you! I sent a pic of that engine bay sticker with the carb illustrated and the adjustment screw highlighted. I will follow with an actual photo this eve. Very kind of you to assist.

[@midwestmotoring]

@@andrewep2816 got the photo. Looks like you have an idle circuit on your carb. With the throttle closed and the engine at idle, there isn't enough fuel and air going through the carb to make everything run properly. This is a separate path for the air and fuel that only comes into play at idle. I would suspect (though I'm not sure) that you can also adjust the needle, float height, etc. to actually adjust your fuel mixture. That's where the special tool down the top comes in. The idle circuit, then, is mainly to control emissions with the throttle closed while you're at a red light--but if your main mixture is off you'll never have enough adjustment in that idle circuit to make a difference. Also, it would have no affect with the car moving. I'd recommend a shop manual if you have one for your car, but there's also a Zenith Stromberg manual that I own that's been very helpful for me. These are stupid money on Amazon and ebay--just wait until you find one cheaper or for free at a garage sale or something, but here's a link. www.ebay.com/itm/Zenith-Stromberg-Manual-by-Haynes-BUK22/303398508667?hash=item46a3f5d87b:g:8vIAAOSwAepd8CUG

[@midwestmotoring]

@@andrewep2816 Just consulted my ZS book. Seems like I was correct. The adjustment screw on the side is for fine tuning and should be done using a CO meter in the tail pipe. For larger adjustments, you should use the allen key tool in the dashpot. That'll at least get you pretty close. Let me know what you think about the Tuning & Balancing video.

[@andrewep2816]

@@midwestmotoring Thank you. And the video was great. I tuned the carb over the weekend... I believe successfully. I took that screw and nut down most of the way, but not entirely. Then I focused on using the tool and adjusting the needle. I was able to get the carb to the point that a slight lift on the needle had essentially not effect on idle. Later I read an article by J Twist and at the end of which he states, "When adjusting the carb at home, tighten the MGB air bleed screw so no air passes through this circuit." Too late unless I do it again. I figure what I obtained thru needle adjustments compensated for however much the air bleed screw was short of full tightening. Please let me know if you disagree. And thank you again for the guidance.

[@randygibson7538]

Good morning. I own a 1971 TR6 with ZS 175s. I was driving yesterday and the engine seemed to “boog” down under acceleration. It would correct itself when I feathered the throttle. Also, it did not happen every time i got on the gas. When you have a minute would you please let me know your thoughts? Thanks. Randy Gibson

[@midwestmotoring]

First thought is to make sure the oil in the dashpots are full. Low or no oil and the air valve will rise too quickly, and you'll have a lean mixture on acceleration. Second thought is under the distributor cap--your timing might not be advancing correctly.

[@trrobbins4518]

I have a 74 TR6 some of my spark plugs are black, others are white, I have quite a bit of carbon build up. The car runs and idles fine. Do I need to adjust the mixture?

[@midwestmotoring]

Maybe. It depends on why the plugs are different colors. First, I'd check to see whether you're looking at some cylinders burning rich or if it's something different, such as leaking oil. Assuming it's a rich/lean condition, I'd then make sure your timing is working properly, that you have good compression, the rocker clearances are set correctly, and so forth. There's a dozen or so things that can throw off your mixture, and if you set the carburetors now, your best case scenario is that you'll just have to adjust it again later. This video does a little better of a job showing you the order to do your checks in: kzbin.info/www/bejne/hJ25f6psgLieitk. Good luck! Keep us posted if you have more questions!

[@chrisrao9647]

My adjustment tool from Moss didn’t fit my 2 stromberg zeniths 175CD-2 on my 68 e type. Thoughts?

[@midwestmotoring]

In 68 the carbs might adjust from the bottom. Check for a hex nut on a sort of post sticking out from the bottom of the carb. If you have one then it's got an adjustable jet. If not, then you might have a non adjustable set. They used those for about a year.

[@blakenorman4822]

so when you took apart the throttle linkage that allowed you to measure each carb separately with meter and adjust screw to match idles then rehook carbs back together with reattaching throttle linkage? Its just that one bolt on throttle linkage you have to loosen to unpair carbs? Put in electric ignition in place of points but my vacum outlet coming out of bottom of distributor isnt connected to anything, should it be connected with tube or hose to something to make it run better? takes forever to get to where it wont die when its just started my dad rebuilt carbs couple years ago tr6, thanks for video

[@midwestmotoring]

Hi Blake! Yes, to disconnect the throttle linkage only takes 1 nut. Technically, you could disconnect it from both carburetors, but there's no need. You only have to loosen it enough on one side or the other so that they can operate independently. As for the distributor... yes, the vacuum should be connected to one of the carburetors. If it's a vacuum retard it should be connected to the top of the carb or manifold vacuum. if it's a vacuum advance it should be connected to the bottom of the carburetor. It's also important to make sure that the vacuum capsule doesn't leak--many of them do! For this, you'll need a vacuum pump like I use in one of the other videos. They're only about $30-$40 if I remember, but it's a tool that's definitely worth having. Sometimes the vacuum capsule is disconnected to try and "fool emissions," but that doesn't work, and usually makes things worse. It's important to have the vacuum capsule working in a road-going car if you want to get full use of the distributor's advance curve.

[@midwestmotoring]

If you're not sure about the distributor... there are companies that will rebuild it for you for $150 or so. They vary in quality, though, and with a vacuum pump and some elbow grease it's not difficult to do most of the work yourself. You'll need a distributor machine to actually test it accurately, but if the weights are free, you have an electronic ignition, and the vacuum capsule works... there's really good odds it's going to be close to where you need it to be anyway.

[@blakenorman4822]

@@midwestmotoring Was able to get carbs to stay at same idle speed when lifting piston up about 1/4 inch had to turn needles all the way in to do it seemed a little weird, was able to get meter to read the same by adjusting idle screws, car is idiling at about 1100, the outside of the distributor shaft does rotate freely a little bit around the inside shaft so i didnt take out distributor, im still not sure where i should connect vacum pot to, coming out of bottom of one carb is a vacum hose with a bolt in it sealing it off, just bled the brakes after totally rebuilding all four corners of suspension last month and a half, got it on the road feels great and seems to be running pretty smooth might try adjusting timing a little this weekend, thanks for the advice, saw your new video from yesterday on troubleshooting car not starting, good stuff

[@midwestmotoring]

@@blakenorman4822 I'm happy to hear you're on the right track! If the needles are all the way in, then that means you're all the way "rich." If your ignition system is working properly and you have the correct needles, that might mean your float height is set a millimetre or two more than it out to be. The float height is sort of the "coarse" mixture adjustment, and then the needle used to fine tune things. You may want to find out since it's better to run a little too rich than a little too lean! As for the vacuum port, that depends on whether your distributor has a vacuum advance or a vacuum retard. If it's a TR6 and you have one capsule, chances are good it's a vacuum retard as original. You would connect to the port on the bottom of the carb (where they've sealed it off) and seal off any ports on the top of the carb. Technically, this will retard your timing at idle (high vacuum to the distributor) and you'll have the benefit of vacuum advance (by way of "less vacuum retard") and mechanical advance. AKA more performance! Before pulling the carbs apart though, you really should check your timing with a strobe. They're only like $30 at an auto parts store. Check it's correct at idle, and then check it again with the engine running about 4000 RPM. The timing should have advanced. If it doesn't, your advance is not working and you need to fix that before adjusting the carburetors. Anyway, keep at it. I'm hardly an expert, but it's learning from those who knew what they were talking about that's been keeping my cars on the road. I just happen to be the one with a decent camera and rugged good looks to film it! :)

[@neurus2671]

Dear, i have these same carburettors on a dodge 1500 (hilman avenger made in south america) they both choke on idle. As the piston goes up, it accelerates. when I work with the registry it is still drowning. the fuel reservoir is level. Do you know another reason why there may be a very rich mixture?

[@midwestmotoring]

Hello! If the mixture is too rich and you can't make it lean, then the most likely cause is the float is not set to the correct height. If that's not it, then it could be the altitude you're at. Higher altitudes have thinner air, so the mixture will be more rich to begin with.

[@TheAbsoluteJedi]

Where can I buy the Synchronization Tool and the adjustment tool? Also, is there a possibility that the carbs on my 1979 Triumph TR-7 don't have an Allen Key down underneath where the plunger sits? I'm pretty sure that I've looked before when I took the dashpots off and it looked like it was a solid piece, no adjustment screw.

[@midwestmotoring]

Moss Motors sells the tools you need, or I believe you can find them on Amazon as well. A TR7 should always have the carbs that adjust from the top unless you don't have the original carbs.

[@TheAbsoluteJedi]

@@midwestmotoring yeah, I got the Sync and Adjustment Tool a while back. I actually just had the carbs professionally rebuilt, I got them back onto the intake manifold and got it all put back together, but I haven't had a chance to dial them in yet.

[@geoffdunstan8567]

Thanks for this series on the strommy carbs. I've just bought my latest TR6, third since 1980! It's US spec and has the 175 CD 2s. It's running very rich, doesn't need choke to start or run, drives off from cold no choke, after a good run the plugs show running rich also. I've checked and adjusted the electrics, they were pretty well ok, then after balancing air flow went to adjust the mixture, on one carb it was tight to turn the adjuster, the other wouldn't turn at all (no adjustment left??). Would appreciate comments / suggestions! thanks and best regards, Geoff D from Merimbula Australia

[@midwestmotoring]

The adjuster is sort of a fine adjustment, but the float height is the coarse adjustment. If it's not set correctly, you'll run out of adjustment just like you're saying. If the timing is working properly, correct plugs, good spark, etc... then I'd suspect your floats are letting in too much fuel before shutting off the valve.

[@geoffdunstan8567]

Thanks very much, thought I might have to head that way.... will let you know what I find, regards, Geoff D

[@midwestmotoring]

@@geoffdunstan8567 good luck! Let me know if you get stuck

[@geoffdunstan8567]

:)👍thanks, ended up changing them for a pair of S.U.s I've had sitting around for decades! Running not too bad, will do for now and will have a good go at the strommies later on. regards Geoff D (A.U.)

[@mst__mem8620]

Hi, how are you? I have a pierburg 175cd carburetor with a fixed needle on a volvo b230 engine. How can I adjust the mixture ratio correctly? Is the level of the needle height equal to the surface of the piston? Is there a fixed measurement of the main jet?

[@midwestmotoring]

That depends. If the needle is fixed, the jet can move up and down. Both actions will accomplish the same thing, since the mixture is determined by the relationship of the needle to the jet. In other words, raising the needle is the same thing as lowering the jet. If you do not have an adjustable jet, then the only option is to manually raise or lower the needle, test, then shut the car back off and adjust a little more. It's a painstaking process, but the only option in about 1968 and 1969.

[@mst__mem8620]

@@midwestmotoring OK thanks. I have a fixed needle and the main jet is adjustable, so I have to fix the needle at the level of the piston and start adjusting the main jet?? And a second question, does the descent and ascent of the plane affect the speed of the car, because at first I was struggling with the fact that the car could not exceed 135 km with chopping After that, I modified the jet by lowering it down, and now the speed does not exceed 148 km, and at some times the engine is unstable, especially in the morning run

[@Ar_classic_portugal]

Hello, how.can I Start from the basis? I HAVE a SU the early ones but Im Lost from where to start

[@midwestmotoring]

You need to set up the carburetor to a neutral setting. The needle should be flush with the air piston, and the bridge needs to be raised to be flat, then screwed down a couple turns. From there, you can raise or lower as required, but it should be close if you've rebuilt the carb correctly.

[@Kudec1979]

Where I can get This air flow meeter and This ajusting tool?

[@midwestmotoring]

Good question. Most of the British car parts suppliers will carry them. Moss, Rimmer Bros, Victoria British, TRF... you can also find them on ebay or with smaller distributors if you like to shop local. Make sure you have adjustable needles before buying the mixture adjusting tool as not all carburetors have that feature. Naturally, the airflow meter will only be useful for multiple carburetor setups. The airflow meter should be around $30 and the carb tool somewhere under $10.

[@jessecastro8898]

Hello. I have a 1975 MG midget single carb. What is the fuel ratio?

[@midwestmotoring]

14.7:1, with exceptions based on engine load and temperature.

[@phildavis9504]

I just did this test and my rear carburetor sucked the measurement tool and the engine rpm dropped and almost stalled. The front carburetor was fine. Can you tell me how to fix this? Thanks

[@midwestmotoring]

Your measuring tool is closed off too much. Most of them have an adjustment to open them up. The rear carb is the one doing all the work, and they are almost certainly out of balance.

[@phildavis9504]

How open should I adjust it?

[@midwestmotoring]

Hi Phil, "as open as you need" is the correct answer. I'm assuming you have the same air flow meter that I have, which is a sort of disc with a tube on one side. The tube has a red floating bit in it. If that's the case, what you want to do is pick the stronger carburetor (the rear one in your case) and keep opening the adjustment on the air flow meter until the floating indicator is somewhere in the middle of the gauge. The actual reading on the gauge is less important than the idea that both carburetors have the same reading. Make sure you disconnect the throttles from the carburetors because you need them to operate independently of the linkage. If you don't disconnect the throttles, your balancing will not work properly. It will give false readings and you'll need to start again. If you look closer at the tool, there is a smaller disc inside the larger one on the outside (the outside ring has a foam lining to press against the carburetor body, the inside disc has a spring pressing against it and screws in and out to allow for adjustment).

[@midwestmotoring]

Some other air flow meters have rubber plugs in the body of the meter. Simply open some of these plugs if it's restricting the air flow too much. The gauge should not be cutting off air to the engine, just reading it. If the gauge is indicating somewhere in the middle, but the engine is still dying, then that carburetor is much too lean and needs to be richer. You know this because reducing the air flow on an already lean carb will starve the engine even more. You can confirm this by looking at a spark plug of one of the cylinders that is fed by the carb in question. White means too lean, black means too rich, and a light ashy brown is just right.

[@midwestmotoring]

DEFINITELY make sure your distributor is in good order first though. The carburetors should be the very last thing you touch. They don't really go out of tune, and they won't need adjustment or rebuilding unless you've changed altitude dramatically or if the car has been sitting for long periods of time and the fuel has gummed up.

[@allenslocumb8278]

I finally was able to move my needles. Had to use a little heat and then replaced with new needles. Set them flush. Car runs very hot now, and I can't equalize the airflow using my synch tool. I put on one carb and get it set but then I go to put it on the 2nd and the car dies, not enough air I assume. That shouldn't happen. What am I doing wrong? The carbs are delinked, btw. Made that silly mistake already.

[@midwestmotoring]

Depends on where the idle is. You might have a vacuum leak preventing one carb from working properly, or possibly an incorrectly set bypass valve. It could also very likely be a distributor issue or a number of other problems. If you can't get it to balance, you either have the mixture waaaaay off on one carb (ie a vacuum leak) or the idle speed waaaaay off on one carb (sticking linkage, improperly assembled, obstruction somewhere, etc). Best bet is unfortunately to disassemble and double check everything. If you can't figure it out, I do carb rebuilding for people and can help further.

[@allenslocumb8278]

@@midwestmotoring Good advice. I ordered a vacuum gauge earlier today. I think timing is fine but it's easy to double-check so I will do that. These carbs worked fine before I changed the needles. I had to change the needles b/c the O-ring was bad and I was burning the dashpot oil. Changed spark plugs b/c they were coated but used same kind. I even checked the floats, which didn't change so all good. I have to believe my mixture is waaaaaay off. More to come once I get the vacuum gauge. Pls make more videos!

[@allenslocumb8278]

So it was 3 problems. First, it was running very lean. Had to adjust both needles 5/8 of a turn. I also had a tear on the underside of a hose. And finally, we had put on a bottom nut but never went back to tighten it. Doh!

[@jasonbirch1182]

Used some of your techniques to tune my 230c with a cdt175. Thanks. You mentioned the hate for the auto choke in anoutger video. What a stupid idea, mine has coolant circulation to it and just cooks the whole carb. How can i delete this nonsense? I know when it needs choke and can handke that myself just fine.

[@midwestmotoring]

There are kits available to switch to a manual choke, but I'm not sure where to source one for a 230c. The important thing if it's not working right is that you often need to bleed the coolant to make sure it's not just air in the auto choke. Otherwise, yeah, I like just pulling a knob too. So much simpler.

[@jasonbirch1182]

@@midwestmotoring it's real obvious there's water in it. It's hot as shit. I don't want my carb at 180+ degrees when I'm romping on this thing.

[@stephaneauger1036]

hello!...thank you!..am canadien and i buy a triumph :( hahaha--thank you

[@midwestmotoring]

You're welcome! Glad to be helpful!

[@kkayson]

Can you narrate in a British accent in the future?

[@midwestmotoring]

If I make a new video with just the mustache, I'll definitely pull out an accent to go with it. :)

[@TheAbsoluteJedi]

​@midwestmotoring your video provides good instruction, but us very confusing in actually performing the operation. You say at the end of the video to do the fuel/air mixture first, but do it last in your video instruction, then balancing them first, but should be done last by implication. Also, you state that ".......other than that, you'll really only need a screwdriver to change the idle speed, and something to take apart the Throttle Linkage." You can't "take apart the Throttle Linkage" on my 1979 Triumph TR-7, at least not as far as I can tell, so can I even adjust them without undoing the Throttle Linkage? Some clarification would be nice.

[@midwestmotoring]

Balancing the carbs should be done first, but after you change the mixture you could very well upset the balance and will need to do it again. Technically, it's not a first or second thing so much as a needing to do one, then the other, then repeat. As for the throttle linkage, if you have twin carbs, there will definitely be a way to disconnect the linkage between the two. You are not able to adjust them without loosening the throttle linkage so the throttles can be acted upon independently. Your shop manual should have a blown up image that may help to identify the parts and how they come apart. Good luck!

[@TheAbsoluteJedi]

@@midwestmotoring yeah, no, there's not. When the carbs are bolted onto the Intake Manifold, there are little claw-like things that are like a curved Y-shape that goes over the Throttle Linkage, and the only way to disconnect one from the other is to take them off of the Intake Manifold, but then they're off the car, and the car isn't going to run with them off the Intake Manifold, hate to break it to you. There's no simple thing that you can do to disconnect one from the other without taking them off the Intake Manifold, and this is the stock setup from the factory.

[@midwestmotoring]

Can you send a picture to [e-mail]?