4150 Carburetor Accelerator Pump Tuning

[@johnsawyer8180]

What Keith said is very important and needs to be corrected in the video, .015 clearance to the accelerator pump arm is a WOT adjustment, if you are trying to select which color cam to use while you already have .015 clearance in the pump arm you will choose the wrong cam every time! (and the cam that you already have might already be the correct cam if adjusted correctly)

[@keithiverson6687]

With the accelerator pump arm adjustment, what I’ve read and done is to rotate the accelerator to WOT, then measure the .015 clearance to make sure the arm still travels and doesn’t bottom out. David Vizard’s book also says to preload the arm by 2 flats while still having the .015 clearance at WOT for instant throttle response. I haven’t tried that as as I got pretty good results by just taking up all the slack, better than the Q-jet accelerator pump adjustments results I’ve gotten in the past.

[@MuscleCarSolutions]

Whatever you’ve gotta do to make sure that pump diaphragm doesn’t bottom out and get damaged!

[@SmooveBee1]

Keith - that is the method according to Holley. And that is how I do it as well.

[@ricknorrington2211]

Thanks for the cam information!! Definitely something that is not talked about at all Nicely done sir!!👍👍👍🏁🏁🤘

[@stephenmitchell3569]

Thank You for Sharing this !!! I am rusty and this dust off my love of tuning the Holley carb back in the 70-80s... Yep old guy but running a 520 bbc on the street including delivering auto parts was a hoot !!! Yes old guys still say hoot...😊 Now last hotrod 540 bbc nitrous blower street car to drive to Kroger...my last hoot...lol !!!

[@davelowets]

@@stephenmitchell3569 I make 800h.p. with just a plain ole N/A 547" big block Oldsmobile....

[@johnc7431]

Excellent demonstration. I'm all ears and learned more about my 4150 that I did not know. I honestly did not think that it was a long demonstration very informative. Thank you for your time. Keep the videos coming😊

[@MuscleCarSolutions]

Glad to hear that! I try to include all the details on a topic so full understanding of how something works and how to use it is understood. Sometimes that goes too long for folks. Glad you enjoyed it! Thank you!

[@pacbrian3809]

that still gets me on the nozzles being a measurement of time and not volume. i always just assumed it was a bigger shot of fuel. makes perfect sense your the only one who has talked about this

[@MuscleCarSolutions]

It’s not talked about. For whatever reason it just assumed it’s a bigger shot of fuel, not how quick or how slow it’s delivered!

[@BPattB]

I'm pretty sure you knew I would be visiting this video, lol. Anyhow, I got everything set just about to factory setting. The secondaries were way to far opened. So the car runs pretty well. I have a slight bog/hesitate just off idle. I was hoping to have more time this weekend on the car, but my old dog needed my attention. Dog trumps car every time. She's looking a lot better so hopefully, the long weekend I'll be able to get some more tuning time!

[@MuscleCarSolutions]

Million times out of a million, the dog trumps everything else! No need to explain that bud! I’m right there with ya. Hope your pup feels better soon.

[@jacobrusso9522]

Man I know a fair amount about basic carb tuning but did not know about that screw. My new carb runs great but if I just slightly touch the gas off idle, it bogs. If I hit the peddle faster, it's fine. THANK YOU SO MUCH DUDE!

[@barefootbandit1]

Awesome video mate. I've been learning a lot over the last 12 months but this video really takes the cake. I keep having take off hesitation in my ski boat.

[@GorhamWorks]

Great video, tuning a 870 cfm Holley vacuum secondary on a bbc 540 right now in my c10. Baby stepping through the circuits. You confirmed something in the sequence of tuning I’ve never heard verbally really well. Great information. The secret is combination together! Loved the video.

[@MuscleCarSolutions]

Tuning is a process. It’s not overly complicated, but too few folks actually take the time to work through it and leave so much power, drivability and economy on the table. Love that process!

[@davelowets]

An 870 vacuum secondary on a 540 is giving up a LOT of power....

[@schultzmotorsports8034]

Best information I've seen yet on carb adjustment..thanks for the video. Now I can get my carb tuned.

[@MuscleCarSolutions]

Nice! Make it happen! 😃

[@gabrieldimarco9646]

Great video as always. You make me miss tuning carbs.

[@demartinsm8479]

Excellent tuning reference video. I always watch this before I jump into a tuning scenario with my 4150 style carburetor.

[@davelowets]

Before tuning ANY carb, also make sure that the t-slot to throttle butterfly ratio IS correct before moving forward. The T-slot, when looking at it from the bottom side of the throttle bores, should be covered up by the primary butterflies enough so that it looks like a perfect square ⬛️ shape when the throttle is at idle. If the slot is exposed much more than this, the throttle MUST be closed more in order for the carb to operate properly at an idle, tip-in, and light throttle cruise. If the engine will no longer hold an idle with the primary throttle butterflies closed far enough to get the proper square t-slot appearance, then one must adjust the secondary throttle butterflies open a little further to make up for the primary being closed that far, OR one can drill a small hole I'm each of the primary throttle butterflies in the middle of the bottom edge of each butterfly between the throttle shaft and the edge of the butterfly. Then retest. If the idle still isn't high enough, then drill the hole slightly larger until it. does. Having the t-slot exposed to far WILL take a large chunk of performance out of your tip-in and light throttle cruise throttle positions along the sweep.

[@demartinsm8479]

​@@davelowets thank you for the insights. I've made huge leaps forward and tuning my carb. But, it still has a hesitation that I cannot tune out of it. I think I will remove the carb and reduce the slot slightly and see if that helps. Thank you again!

[@charlielitz6395]

Thank you so much. This was so helpful. I'm starting to get a clue on how to build and tune my carb. I will have some questions when I start my project. Until then thank you again

[@MuscleCarSolutions]

Glad it’s been helpful! Just let me know if you have any questions. Always eager to help if I can.

[@twr064]

As others have said, you are incorrect with the .015. There should be no slack in the pump AT ALL, and the .015 is measured as Additional pump arm travel at WOT.

[@jaygooch1190]

You are correct

[@cpa2132]

@@twr064 fuck, I completely forgot this 🤦🏼‍♂️, glad you commented this, bc I'm going to go readjust mine now

[@davelowets]

YES! If there is ANY slack in the pump arm that allows the throttle to move even the tiniest bit without depressing the pump diaphragm, there WILL be a stumble in the area of the throttle movement until the slack is taken up in the system. The INSTANT that throttle lever moves just the tiniest bit, the pump diaphragm SHOULD be moving also, and fuel SHOULD be coming out of the squirter.

[@BlitzFreak369]

Absolutely correct. Many people miss read the Holley book. It’s .015 to .019 of additional travel at Wide Open Throttle, so as not to bottom out the diaphragm. This clearance at idle will cause a hesitation or stumble / bog when you stab the throttle. ✌🏻

[@jeaniejpeck-barge5778]

Thank you for this. This WAS my problem and now I can correct it. I didn't even realize this made a issue for start up... SUCH a difference!

[@chrisherrmann9627]

I will watch this a few more times. This is exactly what I needed

[@MuscleCarSolutions]

Cool! Hope it’s useful for you!

[@1986argy]

Definitely like the videos. I'm still learning carbs, and videos like this are incredibly helpful.

[@timgroleau1612]

Great video. Another piece of the puzzle acquired.

[@MuscleCarSolutions]

Good deal! Glad it was useful to you.

[@braddenning1617]

I BUILT A 292 INLINE CHEVY 6, 12.1. 525/505 SOLID SCHEIDER CAM 108 OVERLAP, no budget !!! all machine work doe by professionals that know these inline chevys !! But its gonna be street driven to shows and some drag racing. HEI dist. M-21 close box 430 Dana 60 9 years to build it !!!! First pull on the dyno with a MAN A FRE 3X2 It shot almost to 370HP . AND CRISP !!! The rear carn took a crap and we slapped on a brand new 2x4 complete set up. It Made 383HP. 418 TORQUE. We had some time left and changed jets ,1 maybe 2 sizes bigger.and it lost power. we drilled and tapped the rear plate for a jet and it worked best stock jet size. But this 2X4 will tear ass, but it bogs, has flat spots Im stumped !!! Look on you tube for " 2 DR Checker Marathon Hot Rod,Thanks

[@VinoRatRodbuilds]

Thanks for the info you always share. 👍

[@MuscleCarSolutions]

Thank you sir! Always appreciate you stopping by.

[@stevenbongiorno9277]

I’m not sure, but I’ve read, from a bunch of articles in magazines, and from books I’ve bought about Holleys. They pretty much say that you should open the throttle all the way, then make sure that you have at least .015 clearance, so the pump doesn’t bottom out at full throttle. What’s your thoughts on that? I’ve been setting my pump arm like that for years. I still check to see that there’s no play in the linkage, and the pump reacts as soon as any movement is made with the throttle. Could I be limiting any shot from fully being used?

[@MuscleCarSolutions]

Absolutely yes. One of the poor parts of that carburetor. If the diaphragm gets punctured, hello fuel on a hot intake manifold or distributor! So yes for sure it’s a good practice. The amount it would limit fuel is negligible. Some math might be able to calculate how much of that full 3 CC shot is affected. It’s an interesting question.

[@StanleyNakasone-ss1le]

Thanks for the information on the pump size. I will change back my pump from a 50 to a 30. My 750 vacuum secondary is for the street. My friend has a problem with his 750 vacuum secondary carburetor. When he does wot and let's go of the gas. The engine would die, but would start up after this happen.

[@davelowets]

Probably too lean at an idle, OR the t-slot is exposed too far.

[@benjaminnawrocki489]

Awesome video very instructive and precise. What would be the typical symptom of an accelerator pump found to be slightly pre loaded ?

[@havebenthere]

Great video, but accelerator adjustment needs to be touching at idle. The .015 clearance is for all the way open clearance, otherwise you delay the shot for a few degrees throttle which could give a slight hesitation off idle hit. On the 30 cc pumps, I've never used a larger 50 cc even with E85 and had a great throttle response. At the same time I've tuned the idle air bleeds and mab's along with jetting to get the right mix. The best tool for carbs are a good o2 sensor, but realize unless you video the gauge and tach while driving or just hitting the throttle wot then you won't see exactly what's going on. At the same time a vacuum gauge in video is needed to determine the power valve. Wrong power valve is hard to solve with pump corrections!

[@hunterburge7878]

You should do a video on setting ignition timing, I’ve done it multiple ways and I don’t know what’s right but what I think works the best is sitting at idle with a vacuum gauge hooked up I just turned it till the gauge was the smoothest reading

[@MuscleCarSolutions]

@@hunterburge7878 at some point I’ll cover the basics and how I do it. It’s pretty simple but everyone seems to have their own way of doing it.

[@johnk1532]

Greetings from Australia, many thanks for the info 👍

[@MuscleCarSolutions]

You’re very welcome!

[@CashMopar]

Awesome video! I needed this! I have the 650 double pumper. I put hollow screws in the squirters. The solid screws barely let out the gas? Its better but a slight bog into the secondarys. I also have 31 squirters. 340 Chrysler, x heads.

[@MuscleCarSolutions]

Sounds like a different cam to tune in when the engine is experiencing that hesitation. Keep tuning!

[@mickangio16]

You only need the hollow screw when using a squirter over .040".

[@davelowets]

7:26... You'd NEVER want to have be using position 2 on ANY "street car". If the idle screw has had to be cranked in THAT far to get the engine to idle, that would mean that your T-slot setting IS going to be totally out of whack, and that NEEDS to be corrected before you move any further. Whether it's drilling holes in the primary butterflies, or adjusting the secondary butterflies open a little more, the T-slot setting HAS to be adjusted properly, or else your idle, tip-in, and light throttle cruise performance WILL suffer big time. The #2 pump cam setting would ONLY be used for a radical race style engine where idle, part throttle, and tip-in performance is not needed and is non-existant. What I have found throughout my many years of tuning Holley style carburetors is that the pump shot squirter size is way more important than the pump cam profile is. 99% of the time, I can get the accelerator pump circuit operating flawlessly on any vehicle by adjusting the squirter sizes, and using the box stock pump cam. There have been very few instances where I have gained any noticeable improvement by changing the pump cams. In the few cases where I have had to play with the pump cams to get the throttle response 100% crisp and instant, it has been on a large cubic inch engine with a radical camshaft, and a somewhat tight torque converter.

[@Fastlife660]

Do you have any carb tuning videos or books ! I like your delivery!!

[@davelowets]

@Fastlife660 Thank you! Unfortunately I do not. Just 30 years of knowledge stuck inside my head. I can help you with any questions you may have though... I have thought about writing a book, but as soon as I sit down and try to start, the words totally just vaporise out of my thoughts. I've ALWAYS had a problem with this ever since school. If a person can ask me a direct question, I can always answer it with detail, but if I try to organize all my thoughts and ideas into a list (book) forget it, I get lost... 🤷🏻

[@fazawah2933]

Still waiting for Billy Godbold , concerning tappet fails. Some have whispered bud lighting and targeting comp cams on the internet webs .

[@MuscleCarSolutions]

I interviewed him on Friday. Scheduled for next Sunday.

[@davelowets]

Stay away from flat tappet cams... there every reason to use a roller, and no reasons not to.

[@killtraccskill_onthe_beat1824]

Great video. I am currently running the pink cam, which came with the carburetor. It appears that the duration of my 1st shot is not long enough, and the stumble occurs between the 1st and 2nd shots. Which color cam would give me a longer shot duration?

[@davelowets]

@killtraccskill_onthe_beat1824 You need a set of cams that overlap between the primary running out before the secondary starts. Usually the cams do overlap just a bit. Sounds like you could use a set of greens in both ends

[@menoaz]

In foot brake racing and I'm at 1800 roms for 5 sec waiting for the green. Am I using my squirters or still on the idle circuit?

[@davelowets]

@menoaz Squirters are LONG gone by that point. Depending on how far you have the throttle opened to reach the 1800 RPM's, you could be anywhere from the idle circuit on up to the boosters. With my 800h.p. big block, 1800 rpms is only like 1/40th of the throttle travel.

[@hybridmusclegarage4590]

Awesome. Great info as always!!

[@MuscleCarSolutions]

Thanks man! Appreciate it!

[@knightranger1783]

Great info. I need to get back to my projects.

[@brandonprater6934]

I see you have the new Edlebrock Double Pumper on the bench! I have one in my 78 bronco and am in the middle of tuning it. I love it so far. I have an new MSD box and AFR gauge and have swapped jets a couple of times(before the MSD box fixed a LOT of issues). Right now I'm working on getting a vaccuum gauge in cab to help tune the power valves. It seems good in the primaries but WOT is a bit wet. A question for you - Since the new VRS 1450 has thicker throttle shaft, can I swap out the cams on it with a holley unit? I've not gotten to the cams or air bleeds or PV restriction channels just yet but I do like digging into the details. I may even get another set of metering plates to make the hot swaps even hotter/faster. Dig the channel! Keep WOT!

[@MuscleCarSolutions]

Yes. That than the bowl and metering block gaskets, the rest is mostly the same. Power valves, jets, emulsions and air bleeds are all the same, to include the cams. At least from what I’ve seen so far. There are larger diameter shaft cams available out there. I’m told Edelbrock now has a cam kit, but not the part number 12403. That the smaller shaft version. Hoping to have all their new part numbers soon.

[@MuscleCarSolutions]

And thank you! Glad you’re enjoying the videos.

[@jordanisles9767]

What motor in your 78? I just dropped a brawler 750 in my 79 with a fresh 460.

[@tmc.318]

So if I'm interpreting the pump cam chart correctly, most cams will not deliver 1/10th of 30cc with a full sweep. They will deliver less. The colors tune how much is delivered to the squirters and by when and I guess it's up to the spring to hold the tension on the diaphragm in the chamber as the squirters flow out what they can in the time they are pressurized. The cam's action on the arm can't outrun the squirters rate of flow.

[@TargaWheels]

Its weird that I've never had an issue with a right-out-of-the-box 4150. There's formulas to use to find the right cfm for your application. Other than the float level and air bleeds...out of the box was perfect. I'm talking about 90's "gold" holleys, not the silver/polished versions that came out in the late 90's and after. Always had problems with those. I guess people think "bigger is better", and in certain situations, that's true. But MOST of the time, for all-around trouble-free operation, compromises have to be made. But before that silver/polished era of holleys, those gold carbs were trouble free. Even today I look for older used carbs and grab those 4779, 3310, or 1850 carbs from back then.

[@MuscleCarSolutions]

That’s generally the issue. You’re absolutely correct on getting the right CFM for the application. Covered that in a past video. But right out of the box is practically mathematically impossible. There’s close. There’s “that will do”. There’s “I can tolerate that”. But extremely rare to be perfect, right out of the box. Hey I covered that in a past video too! 👍

[@adammic16]

In regards to the secondary side...hole #2 if idle is above 850rpm or just leave it in #1??? Im thinking its more so just the primary side for that initial take off???

[@josephnubile1970]

thanks for explaining but the one thing you left out is wich way to install the pump cam. from the pictures I can see that the flat side faces the throttle lever. nobody ever starts the video with this is how to install the cam...... Great video.

[@mechanknuckle]

So when your tuning the secondaries on a double pumper, they could be set very differently than primaries? Like I could have a 28 squirter in front and a 35 in back? Same with cams?

[@MuscleCarSolutions]

@@mechanknuckle sure. It’s about timing and volume. At WOT that volume can look a lot different than at part throttle or even that time that the throttle initially opens as it’s on its way to WOT. Same with the timing. That timing can look a lot different depending on the type of driving you’re doing. Squirters are about timing. Cams are about timing. That’s how important it is to the tuning process. The right amount of fuel at the right TIME!

[@These-nutz]

When you say slot numbers 2 do you mean the bottom hole closer to the base of the carb? I got it

[@reevesautomotivefarm9614]

I love your videos but you do need to correct the part about adjusting the pump arm. it should touch at idle, the .015 or more is the play at WOT. We also start with squirters and use cams only for fine tuning. Not trying to be a hater, keep up the good work!

[@tylerjohnson254]

So does the accelerator pump cam have anything to do with idling problems?

[@PawnShopRockers]

My Holly 650 is having issues on cold start up. It has been great for over 2 years. I could Tap pedal, and car starts right up in cold idle position. Recently my throttle return spring popped off pulling on to the freeway a full acceleration. Engine reved up quite high before I could shut it off. Cold idle setting has not worked since this event. Any idea if the two are connected? How to test for this? Car runs well when warm but not as peppy as before. Also smells rich at idle or while driving. Thank you.

[@davelowets]

Not connected...

[@PawnShopRockers]

Super!! Thank you.

[@Jonathan-bk9vb]

A small question. for a mercruiser boat caburator. because I barely start the engine. uncontrollably begins to supply gasoline to the cylinders. And when I turn off the engine, it is still supplying gasoline. It does not have an electric fuel pump.... greetings from rome..thanks

[@jeffreyurbain9604]

Does the rules for the cams apply to the secondary side? Only put on the second position if your idle is over 850

[@cosimosanfilippo9050]

I live in Sydney, and I have a full Bronco 1986 with a 351 Cleveland with (15' Rim, tyre size - 31-10-15 . Diff ratio 3.5), Engine bean rebuild no so long ago, but it was up to now dedicated LPG, with 18 Degrees static advanced because of the type of fuel. Now back to Petrol, ( what you guys call it "GAS"), I mounted a 600 Vacuum secondary manual choke Holley carburetor with external adjustable needle valves. The Bronco is mainly use for occasional trips going camping, and fully loaded. I was wandering if you could please give me an initiation setting of the carburetor , jets , power valve. I know that longer fuel delivery for a heavy vehicle and a slow curve of a distributer advance, is ideal. I had it all worked out for LPG over the years, I actually learned a lot. in my younger days, I experimented a lot also with petrol system, but just as an inexperience young man with no disasters results , otherwise I would had contacted the specialist. Would it be possible to have some help with carburation and distributer timing general idea to start with?. I know I'll have to experiment to finally pin point the best possible result, but it would be hard to tune and tray with an empty truck, with very different result once loaded. I fallow you tutorial videos and I enjoy your detailed explanations. Knowing stuff is one thing , but having the ability to transmit knowledge is another, and in my opinion you have both. Your reply would be very much appreciated, and very important to me as I will be start tuning soon. At the moment the carburetor is very stock ( as far as I know), with probably a 6.5 power valve. Thanks again for your splendid work. I am sure many of us have beneficiated from your videos. Kid Regards... Cos.

[@MuscleCarSolutions]

Hey Cos. Sounds like you’ve had some good experiences with the Bronco. My grandfather ran an LPG converted truck in the 70s and 80s. Wish I had more interest in it at a young age. I think there’s a lot to learn from it. As far as a guess on a calibration to start with, I will always start with the base calibration. That 600 is likely close on the jets for the size engine you have and I’m assuming you won’t be running it at a high RPM, even though the Cleveland engines tend to like the higher operating ranges with their larger intake runners. The thing you’ll need to adjust for initially is the power valve size. I did a video recently on sizing and how to tune with the PV that might be helpful to you. Hopefully the rest of your build is focused around lower end torque. Ignition timing is extremely critical here! 12-14 initial is a good starting point. You can adjust from there based on what the engine wants. Hope that was enough to get you started. Let me know if you have other questions or want to discuss any other options. Thank you very much for the kind words. It’s very much appreciated. Cheers mate!

[@shawnstevenson9252]

Any way I can email you a afr video of mine? I've been stuck with this proform 650 I have. My afr is all over

[@MuscleCarSolutions]

If you go to the about section of the channel you’ll find a link to my website. You can send me an email through the contact form. Can’t put the link here, YT blocks it for some reason.

[@Dodgecummins529]

I put a 50cc accelerator pump with brown cams and #45 nozzles now my pedal is hard to press in when i try to go full throttle, there’s a definite hard spot going into secondary’s….whats the fix for the hard pedal?

[@laurensvanpeperstraten9294]

Hi my friend. Great video. I am almost there with the tune of my 4150 edelbrock 750 cfm carb. I got all the right afr’s in all the right rpm ranges. But now i have the following problem. When i go quickly to wot it gets way lean. When i gradually press the throttle it stays on point. So I figured the accelerator pump needs some tuning. I dont think the pump cams for these carburetors are available yet, and i think i need a longer and maybe faster shot of fuel. Do you think enlarging the nozzles could help my issue?

[@MuscleCarSolutions]

You can try a different nozzle to shorten the time the pump shot is delivered. Cam change would also be a good idea. Any of the 1/2” throttle shaft cams will work.

[@laurensvanpeperstraten9294]

@@MuscleCarSolutions allright thanks! I will try that.

[@laurensvanpeperstraten9294]

@@MuscleCarSolutions do you know where i can get the pump cams for a 1/2 inch throttle shaft. I search the entire internet and havent found them

[@fxstsharley]

Great info. Thanks.

[@stevebottrell9154]

I don't know if you are still looking at comments, but I have a question I hope you can help me with. I have a 1982 Dodge Ramcharger, with a 360. I put a new 600cfm 4 barrel Holley on it, and it seems to run fine except for it stumbles off idle when it's in gear. It'll stall if I give it too much gas. So I have to feather the throttle to get going. Once I'm going, no problem. Also, starts fine. I thought maybe I have too small of a carb, but I read up on it before I bought it and guys where saying 600 was big enough. I was trying for better milage. Thing is a gas pig. Anyway, do you think just changing the cam might solve that stumble?

[@MuscleCarSolutions]

@@stevebottrell9154 what is your ignition timing set to?

[@stevebottrell9154]

@@MuscleCarSolutions I took it into a performance shop to see if they could fix it, and they said they set it to 10 degree advance? I'm not a serious mechanic unfortunately, don't have a timing light and I'm not sure I understand timing well enough anyway. They spent a couple hours on it, and still didn't fix it. The cost of mechanics really makes that option a tough pill to swallow. It's a $1000 carburetor now :)

[@MuscleCarSolutions]

@@stevebottrell9154 what part of the country are you located? Or specifically, at what elevation do you live and operate the vehicle in?

[@stevebottrell9154]

@@MuscleCarSolutions I live in Lethbridge, Alberta, Canada. 910 meters elevation, or 2985 ft. according to Google.

[@MuscleCarSolutions]

@@stevebottrell9154 nice! I’ve spent a lot of time in Alberta. Mostly between Edmonton and Calgary but a few trips in your neck of the woods. Ok, 10 isn’t enough. Adding a few more degrees of timing will help the entire range and help the carburetor manage that demand for power off idle or through out the engines rpm range. Now, your decision needs to be, is it getting too much fuel or not enough? That’s generally simple to determine. Tail pipe black and sooty? Smell like fuel at idle and or cruise? Pull the spark plugs and see if they are black and sooty (old plugs can be a little deceptive as they’ll tell you the long term condition of the engine as a whole, but sometimes difficult to read if it’s from a rich condition). If the plugs smell like fuel, it’s likely too rich a condition. As far as the CFM size goes, really depends on how the engine is configured? Bone stock? Stock cam, stock manifold, stock compression ratio? Then yes you could consider going to a smaller carburetor. I did a video on selecting CFM size. Go give that one a watch and see what you come up with.

[@vicc6744]

I hope you can help I have this type of carb (actually a summit carb 650) -I rebuilt it and now I don't remember seeing a check valve ball and I don't see it on an exploded view chart.

[@davelowets]

Some models don't have a check ball, but they have a needle and seat shaped piece under the nozzle.

[@vicc6744]

@@davelowetsThanks I was going crazy- I searched the whole room and couldn't find anything and as I said it didn't show up on the diagram. you reassured me thanks.

[@psycho6542]

If anybody can help, im having that dead spot coming off from idle and i put brand new accel pump, jetting is two up from stock, 35's, timing is ok and no vac leaks, its a holley4150, single meter block, vac secondries, on 289 sbf, any pointers would help, thanks

[@ZedThirtyOne_Z31_]

Thank you Sir.

[@tonygoldense763]

I have a holley 650 double pumper I bought off someone. It has a major stumble when I take off. I changed the nozzles from 28 to 33 and adjusted the accelerator pump. Still no change. I see it has a red cam should I change it and to what color?

[@MuscleCarSolutions]

Try a heavier cam. Like anything else. Small changes. Try the green one next.

[@MuscleCarSolutions]

What engine are you working on? Share some details? Stumble occurs when going WOT from a dead stop or just easing away from a stop light?

[@ricknorrington2211]

Make sure you have the correct power valve for the vacuum of your engine first thing! If you have 17” vacuum at idle you would want a 8.5 power valve. Chances are you may have a 6.5 in your carburetor right now and will cause a stumble. Good luck sir

[@joshkeasler512]

So if u have a brown on the primary would you need brown on secondary?

[@MuscleCarSolutions]

Not necessarily. Tune them independently.

[@josephfriedrich9792]

What would cause a slight leak from the accelerator gasket area? I don't want to over torque the four p2s, but there is the slightest leak even after sitting? Are the blue gaskets not good for oil? Mines on a rotary application so I have to premix with 2stroke

[@MuscleCarSolutions]

Did you replace the pump diaphragm yet?

[@josephfriedrich9792]

@MuscleCarSolutions yes sir

[@MuscleCarSolutions]

@@josephfriedrich9792 that’s usually the culprit. Might just verify with a file that the pump cover is flat. Same with the mounting surface on the bowl. Don’t need to take off a ton of material. The witness marks will tell you if you’ve got any warp. Or if your eyes are good you can lay them on glass and verify that way. Guess it’s just some investigating till you can find where the leak is and what is causing it.

[@josephfriedrich9792]

@@MuscleCarSolutions that's what I was thinking, but hoping was just bad material/gasket. I have a good L square to check it with. Thanks for the replay

[@MuscleCarSolutions]

@@josephfriedrich9792 as long as it’s a good name brand pump diaphragm, it should deteriorate very quickly. Got to be something else causing that issue. Hope it’s an easy find!

[@kellymontoya3258]

When adjusting accelerator pump the choke needs to be open or closed I assume open?

[@MuscleCarSolutions]

Wide open!

[@kellymontoya3258]

@@MuscleCarSolutions on the smaller pump what if its adjusted almost all the way to the end. Do I need a 50 cc or is something wrong with the setup idles at 1000 cant get it lower have a decent cam not above 500 so not radical any ideas or I'm sure you need more info timing around 34 no advance locked in starts fine has hesitation of idle adjusted to 15 thousands still hesitation have the biggest cam on second hole. So I just got a wideband 02 to help will put in this weekend

[@bobjones37450]

It needs to be open. That way there is no chance the fast idle cam is holding the throttle part of the way open.

[@SmooveBee1]

Nozzle size is about the duration of the squirt, not the 'time' of the squirt, right?

[@MuscleCarSolutions]

Total time to deliver the shot is determined by the size of the nozzle. Total volume is determined by the total pump stroke and diameter of the bore.

[@sam-oh5wj]

Carbs are amazing, what a freakn rabbit hole. Learn to tune....!!!!!! A/F gauges and carbs should be sold together as a package... Mandatory..!!

[@MuscleCarSolutions]

It would make the tuning time much shorter and far more accurate on its conclusion. But it’s still no guarantee that the user would take full advantage of it. Still get hundreds of questions a month from folks who have made no tuning changes. Only basic functionality adjustments.

[@katykab00m]

What are those bright colored plastic looking things?

[@tonygoldense763]

He explained it in his video. If you watch his video you will know what they are.

[@forged_billions2]

Mines cut off when I try to do a burn out

[@mickangio16]

Hole #1 and hole #2 has to do with throttle position at idle, not engine rpm.

[@shelbyavant5081]

In throttle position at idle is related to rpm, isn't it? That's why it's not an exact formula, just a rule of thumb.

[@freddietellez8737]

I just picked up my stock 82 bronco 351w I added a jegs 4bbl intake and bought a Holley 4bbl carburator I just pick it up from the shop the guy told me its running to rich when in park it will rev fine but when I put it in drive it starts to bogg after little presses on the peddle its fine but still running to rich. So my shop guy told me its a bat carburator and it has a flat spot so I need to send it back. But is was new or rebult when I bought it. Cost me 500 bucks for the dam thing. What whould u suggest I do

[@freddietellez8737]

The Holley is 600cfm