How To Tune & Sync Weber DCOE Carburetors

Having trouble tuning your carbs? Not entirely sure how they work? Don't know who to ask?
In this episode, John (@thegroundlevel) provides a comprehensive walk-thru on just how DCOE sidedraft carburetors work. From outlining the various parts of the carburetor & how they function to complete tuning & syncing - we tackle all aspects of what it takes to get some sidedraft Weber Carbs running right on your vehicle.
For those looking to edge up their tuning capabilities or if you're simply curious about how a Triple Carb setup works - this video is for you!
Enjoy!
01:16 - Explaining Carburetor Components Using A Weber DCOE 40mm Carb
09:04 - Introduction To Carb Tuning
09:47 - Step One: Zero Out Idle Adjustment & Idle Speed Screws
10:32 - Step Two: Reposition Idle Speed Screws
11:18 - Step Three: Back Out Idle Mixture Screws
12:26 - Step Four: Prepare To Tune (Reconnect Linkage & Turn Car On)
12:42 - Carb Tuning Part I: Adjusting The Idle Mixture
14:34 - Carb Tuning Part II: Initial Syncrometer Readings
16:17 - Carb Tuning Part III: Adjust Air Flow Through Progression Holes
18:11 - Conclusion: Have Patience & Happy Tuning!
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[@braddrake4426]

Tuning my carbs today based upon your excellent guide. Should be able to fire her up for the first time in 20 years this week because of this. Thanks!

[@TheCurbCut]

@@braddrake4426 Exactly what we love to hear

[@jordancollins4577]

Best carb explanation on KZbin. Fantastic. Keep up the good work

[@dillpickle7468]

Love the old stuff where you need to tweak and alter the carbs until your are happy with it. Keeps you in touch with your machine and it is a satisfying task when you achieve improvement. Keep up the good work and wish you great success with your channel. Paul (Australia).

[@sullivantravis1566]

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[@bronsondavion466]

@Sullivan Travis instablaster =)

[@sullivantravis1566]

@Bronson Davion Thanks for your reply. I found the site on google and Im trying it out atm. Seems to take a while so I will reply here later with my results.

[@sullivantravis1566]

@Bronson Davion it worked and I finally got access to my account again. Im so happy! Thanks so much, you really help me out !

[@bronsondavion466]

@Sullivan Travis Glad I could help :)

[@Afcknbum]

You guys don’t understand how much I needed this video THANK YOU!!!

[@unigateman]

God sent you.. I have a TR6 with 3 WEBER 45s need this

[@traxxi2003]

These carbs hold a very special place in my heart. I’m my opinion, nothing compares to the sound of well tuned Weber carbs!!!

[@TheCurbCut]

Couldn’t agree more, friend! 💯

[@andrewb3497]

One of the best dcoe explanations out there. I liked how you specifically explained about the position of the throttle plate at idle with regard to the first progression hole. However, from memory, Weber states it should cover the first progression hole. Once this is set then , in my opinion, the idle speed screw should not be adjusted again as each carb should flow at the same rate. Only use the idle mixture screw to adjust the idle rpm.

[@TheCurbCut]

Andrew B Thank you! And yes, as far as prelim tuning is concerned, all incremental adjustments should be made with your mixture screws to find the best idle without the motor stumbling down. However, once this is established, it is ultimately necessary to balance the carbs within fine adjustments along the idle speed axis, be it with interlink adjustments or the method shown here.

[@andrewb3497]

@@TheCurbCut @5:25 I should add that at idle the Weber Tuning Manual states that the progression holes should NOT be exposed. The early Spanish made DCOE carbs had issues regarding obtaining good idle hence people seem to have to adjust the throttle plate position that can expose part of the first progression hole. The later Weber DCOE 45 152G model seemed to fix this and added a 4th progression hole. @5:40 - so at idle, the fuel/air mix from the idle jet should only be entering each barrel via the idle hole. The amount of this mix delivered is adjusted by the idle mixture screw as you then say at @7:05. It is the idle jet that determines the mix of fuel/air that is delivered to the idle hole AND the progression holes.

[@MindDezign]

Those carbs with horns, a " uni-sync " tool allows you to keep the air horns on.....the air horns are an itergral part of the side drafts.. Put you are the only channel to explain these carbs ,which are Black Magic to most people that buy them. Great job.

[@TheCurbCut]

Fair point! And if I had a uni-sync handy, that would have been the way to do it! That being said, a good later-note to this syncing process would be this: - if you're syncing at idle without your horns in place, bear in mind that the longer your stacks are, the richer your AFR will read without them at idle - sync a little richer sans horn because intake velocity will be higher when reinstalled, thusly leaning out the mixture a bit - conversely, the shorter your horns = less intake velocity at idle; your idle syncing will remain closer to your sans-horn readings By this process in the video, I was functioning off of some pre-existing knowledge of what is needed for this particular application. And thanks for the kind words! We value all the feedback

[@MindDezign]

@@TheCurbCut and as to trumpet length it's to help tune power range. Short for low to mid range Cams and long for mid to high rpm power bands. I always find amusing when people run their side drafts on looks alone. Let's get the long ones they look Bad-Ass. Fine for show. But you need to MATCH ,to go. Again I've seen tons of videos.....no body has taken the time to explaining chokes and such and then show how to sync side drafts. Your the first.. so that's very cool. I've run a SPORTS CAR only Restoration shop for 20 yrs ,20 yrs ago I love side drafts of all kinds, I always had both tools in my tool box ,for monitoring intake air. I keep both my Z cars in CARBS. And Happy to do so. Again a well done video !

[@JAZZZZZ8]

Best Video on these Webbers ever and the way you explain this is real cool and understandable for a beginner like me working on my 260 X with 40s If I am in New York after this Covid shite I would love to visit your yard. I love the small businesses . Well done

[@TheCurbCut]

Happy to help! And good luck with your 260! Drop us a line if you're in town sometime. Godspeed, Eddie!

[@CJkofoed]

Great video - even though they aren't covered this gives me a lot of insight into my Mikuni 44s.

[@gustavonash8361]

I thank you very much for the information very well explained in summary but very clear, what is missing is the explanation of the emulsion tubes.

[@GMJ]

well done. super easy to understand

[@jgraham8248]

Thank you for a detailed, experienced and respectful explanation of tuning these carbs. I have tuned the dual Weber downdrafts to the Nth degree on my 260Z. I plan to get triples soon along with installing a Stahl header I purchased a few years back. I have never touched DCOE carbs but I expect to get versed at it. Videos like yours help take away the intimidation! Thanks again!

[@potkas7]

Thanks. I needed a refresher on tuning the Triple Weber DCOE 48s on my '69 MGC.

[@mirianiautoworks749]

You have no idea how bad I needed this, I’ve never gotten my 260z with Spanish 40’s dialed in. The slightly low compression doesn’t help but this tutorial should put me in range! Thanks for doing this!

[@TheCurbCut]

Excited for you! When dialed right, nothing is more rewarding than triples on a Z car. Good luck!

[@petergiourelas3753]

Best webers made in Italy not Spain

[@CoolGuyClub]

Bad ass video... I'm in the middle of trying to fire up my 4age with webers and boy does this video help.

[@TheCurbCut]

That's what we love to see on 4AGE's!

[@novakenss]

I watched this video again today. I got my street performance 260S Comp Cam installed and broken in. I had to have the rocker arms ground a little. Idle now is smooth and I have put in 45 F9 idle jets to get my AFR numbers to 13:1 at idle which is about 900 rpm. I did have to loosen all the throttle arms so I could get the throttle plates the same. Idle mixtures about 5/8 turn out for 13:1. I sent my distributor to Advanced Distributors in Minnesota for a rebuild and recurve. I want more initial timing, like 16* and no more than 35* above 3,000. Should have it back next week. The cam change raised all cylinders compression 25 psi from the shorter duration. I look forward to taking it out for a test drive with the new cam and jetting. Thanks for the help and info.

[@TheCurbCut]

This sounds like it's sure to be a good time! Good luck and enjoy! Happy to be of help.

[@KevinSmith-xt8xr]

Love it dude keep up the good work

[@victorbencosme5715]

Great video 👍

[@Follett2121]

Great video!!

[@HayPOWER-PR]

Thanks

[@josephebarnes95]

Redline pump, malpassi regulator. Thanks bud dig your vids.

[@apathy01]

Yerrr! Whats up dude!

[@Adz093]

Will be setting up a pair of 40 DCOEs on my A15 soon. This was helpful.

[@TheCurbCut]

Glad to hear it! Good luck

[@iaindoole4060]

Great video thank you . I have 40 DCOE on my Elan and really value your approach to set up and tune.

[@itisshlerman3079]

i want to put 4 of these on a 327 csb. Planning on then putting in an FB Rx7

[@BeastFromTheEast79]

Thank you thank you.. Definitely needed this for my one off build 💪🏻💪🏻😎

[@klonoa310]

Extremely helpful video! I'm so close to getting mine drivable so I can at least drop it off to get dyno tuned further. Conventional wisdom tells me both barrels of a single carb should be synced with each other. My foremost one is lopsided with one barrel reading about 7 and 5 on the syncrometer, respectively. Weirdly enough the airbleed screw has no effect on the rich barrel...

[@chrisroach9459]

Do you have one barrel per cylinder? Or one DCOE feeding more than two cylinders? If air bleed screw has no effect, it's possible your shaft is twisted. Do both throttle plates line up equally with progression holes? If so, then likely mixture screws need adjustment, or one is damaged, or jets aren't matched from left to right on one carb.

[@unigateman]

I have triple webers on my TR6 ex PI, the car has always spluttered at low revs, followed this and basta, what a difference, idling at 900 rpm just right,, thanks

[@AdamsAnalysis]

Awesome video! Thanks for putting it together.

[@slanginnoodles9865]

This is excellent info, just what I was looking for. I'm working on a tripple set of Solex on a Skyline, id love to get into contact at some point

[@hajimarigarage9861]

This video was great 🙏🏾

[@anthonycavanagh9448]

Very helpful

[@VitosFix]

Awesome!

[@garyyasaki9226]

Excellent explanation on how to sort Webers. It's taken me 2 years of playing around and a box of jets so I wish I would have seen this back then. My 2000 Datsun Roadster with DCOE 40's runs great now but has always been a bit reluctant to start when cold but after a few minutes is fine. Any things I should look for or suggestions? Nature of the beast? Thanks.

[@TheCurbCut]

Nature of the best, really! It's more important to have the car properly tuned for idle / runout when the engine is warmed. You could install a manual choke across your carbs to help with warming the car up to temp when you start it, but chokes (by design) tend to run the car extremely rich when they're activated. I tend to air on the side of feathering the throttle enough to get the car to op temp within the first few minutes of starting before taking the car out for a rip. And again, always advisable to stay away from needling the redline until your engine is warmed up.

[@jasonmiller72]

❤ dude I would buy you beer if I were close!! Thank you!!! The only question I have is at the end when you were adjusting the air. I only noticed you did this on the left portal of each. Why do you not also do the 3 right portals ?

[@TheCurbCut]

Definitely do it on all! An oversight in shooting / editing. Hopefully it’s implied enough 🙏🏻

[@novakenss]

I'm a new owner of a '72 240Z with triple Weber 40 DCOEs. These are my first set of Weber side drafts. I've leaned the idle jets to 45 F9's to get me about one turn out on the idle mixture screws. Runs pretty well and the plugs look light brown not black as before. I'm also about to change from a race spec cam to a performance street cam this week. I will see how the jetting requirements change then with better vacuum and more compression from less duration. I do have the short taper idle screws. Do you think I could put in the long taper thinner ones for finer adjustment? Thanks for the tune tips.

[@TheCurbCut]

novakenss The longer enrichment screws wouldnt work the way you think by just installing them on your earlier carbs. I get your theorizing, but I wouldn’t attempt this. These screws only help with the idle circuit, so once your in the power range of the car on your main circuit, it almost doesnt matter. Also, they would seat completely differently and the “tuning” here isnt going to net the results you’re after. ALSO! I would wait til you install the new cam and assess where a rejet is needed or perhaps you can simply adjust on your present hardware. Good luck!

[@novakenss]

@@TheCurbCut I'm putting in the street cam tomorrow. I'll see how the air fuel ratios change. I have two O2 sensors in the header twin pipes before the collector. 2 AFR gauges in the console. I'll see all the ranges and what I'll need to do. Lastly, I didn't think that the long tapered idle needles would be compatible with older 40DCOE carbs. Thanks for that info.

[@doraibu.garage]

I cant see what screw you're adjusting to close off the progression holes?

[@clydecotton]

At the end you didn't show the critical step of adjusting the balancing. You said to turn the screw "in" to richen it up, which is the opposite of what you should do.

[@steelofcrom]

Do you want the synchrometer to be st 5 or was it just at 5? Mine shows 10 from the baseline.

[@israelrosario2896]

Hi! Very good detail explanation . I have toyota corolla 1.8 -3TC engine . That I need to tuning the carburators . Any advice how get it set up from base line at cold. Thank you

[@TheCurbCut]

Well, the first thing you're going to need to do is WARM UP the engine. Never should your carbs be tuned / synced below your standard operating temp. If your car wont turn over, consider employing use of the mechanical chokes - but do NOT compensate cold start in how you baseline your carbs. Not the way to do it. Good luck!

[@israelrosario2896]

Hi Thank you very much for for information knowledge. I will work on . We will keep you updated. Car its running to rich, what woul be the best fuel pressure? Once again thank you Curb Cut!!

[@TheCurbCut]

Israel Rosario Depending on your setup, Webers tend to run best anywhere from 3.5 to 5lbs of pressure across the carbs. Good luck!

[@renegaderieths5629]

Super helpful video. I have a couple questions if you don't mind. What fuel pump is best to run? How important is the fuel return line? My kit came with the fitting to end the fuel line at the last carb. Also where do you vent the block breather to that comes off of the back of the block? This is on an L20b with 40 DCOEs. Thank you.

[@TheCurbCut]

Regynald Rieth Hey there! Thanks for watching. I run a low-pressure Carter pump. They’re noisy, but they’re preferred by a lot of old-car guys because they do a good job of pushing thru any contaminants and don’t jam up like other units if they get some rust / sediment in them. (Obviously a few in-line window filters are always a plus here too to keep an eye on just how dirty things might be for you). As far as the return line is concerned - this can go either way on a setup like this - I don’t run a return on my car across the carbs, but Mo’s car here did. I simply have a return route back to the tank from a Holley FPR at the fenderwall. At such low FP, the constant low lbs of pressure across your carbs is not enough to be an issue for spill-over or flooding as long as pressure is controlled. That being said, anything with a lot of flow should have a return post- fuel rail. And lastly - your PCV vent can vent to atmosphere when you run triple carbs. Not a problem!

[@renegaderieths5629]

@@TheCurbCut Thanks! I was about to pull the trigger on a carter pump. Thanks for the help

[@BeastFromTheEast79]

Ok so Im running 38 Doe’s on 1.8 litre and no matter what I do, after it warms up I have spent fuel that’s igniting. Ive reset my timing multiple times and it’s good. So thoughts? Main jets to big?

[@TheCurbCut]

Based on what you're describing, there is likely an extreme richness happening somewhere. If this is happening when it warms up at idle, but you havent driven the car yet, it's likely the idle jets. Not so bad, and easily remedied. If it happens when you let off the throttle while driving - or worse, after you try to turn the car off - you might even be dieseling. In any event, you need to diagnose this problem and lean out. Also make sure that you havent damaged your seals by running excessively rich, as this would only heighten the dieseling symptoms. Good luck!

[@BeastFromTheEast79]

@@TheCurbCut Right On. I greatly appreciate the second opinion. The carbs are freshly rebuilt and as mentioned checked Timing numerous times and then adjusted everything to the best of my ability to wear the car runs great. Open up to much and more popping, so obviously more fuel, and then lessen the fuel and popping goes away and becomes intermittent with no backfire after shutting off. The carbs cam with 30 m Choke But the main jets seem huge at 140 and the Idle jets at 45. Im working on locating some jets to lower the amount of fuel running through and go from there .. Once again Thank you for letting me pick your brain and taking the time to give me your Opinion. :)

[@sylvainbonhomme1409]

Like the video, however would you have one on Weber 40 IDA? I have those on my 911S 2.2. Thanks

[@TheCurbCut]

If and when we come across a friend / customer with an IDA setup, we'd be happy to make another! Thanks for the question / suggestion!

[@user-vm4ty3hg5l]

so do you use the idle speed screw to adjust the progression?

[@bsk8306]

are the mikuni solex sidedraft simular to webers when it comes to tuning?

[@tmar31]

Great Video!!! Wondering what you think about about vacuum advance with triples on a 240z, since that affects idle speed? Do you run your Z's with triples, with or without vacuum advance?

[@TheCurbCut]

Vacuum advance isn't really a thing with triples. DCOE's like to have 32deg all-in around 2500/3000 RPM, depending on your set-up.

[@ktnameerf]

at the 17:22 or so section you mention about closing the progression hole a bit, but perhaps intentionally do not show a close up of doing that, is there a reason for that... I assume that is done in a few turns of that screw you mentioned early in the video?

[@TheCurbCut]

Couldn’t get a close-up here by virtue of the chest-mounted GoPro. But you are correct to refer to earlier in the video where this is explained. Sometimes ya miss the shot, what can I say!

[@ktnameerf]

@@TheCurbCut Oh no I've looked at my setup that I bought 30 some odd years ago when I had no clue what I was doing... was shipboard in the Navy and was a weekend shade tree mechanic w/ lacking too many needed tools.. anyway my middle carb of the triples does NOT have those progression screws... they are blocked off w/ brass covers... so should I still be able to adjust ok by doing just the other four cylinders or should I look into replacing the middle carb... thanks The Curb Cut!!!!!

[@TheCurbCut]

@@ktnameerf shoot me an email about the specifics and we can discuss a solution - [e-mail]

[@TheDatsunGuy86]

Does anybody know where there shop is? Desperate need of help with my triple dcoe40 setup nobody here on Long Island is helpful

[@TheCurbCut]

Email [e-mail]

[@jayobama9582]

Thanks very much for the video. Makes it a lot more understandable. Where do you get this particular throttle linkage from? I would like that. Mine has been custom made by an old engineer and are not even

[@josephebarnes95]

Need your help man. Triple 45s italian. Did the perfect baseline, floats were measured, perfect idle with initial 3.5 psi. Then after 5 minutes, rapid decrease to zero psi to stall. Do float levels and/or faulty valve cause a decrease in the fuel pressure?

[@DanDAman2daG]

Do I need to remove carb to find out remove choke size?

[@TheCurbCut]

Everything can be accessed / pulled from the front. Good luck.

[@AZGhost623]

What did you set the timing to

[@pablob.r.4216]

Is it the same adjustment for DCOM carbs?

[@TheCurbCut]

Proceduraly, more or less. However, I’m not familiar enough w needles, specs, etc to speak on specific adjustments off-hand here. Good luck!

[@miguelnichols]

Could help me to decide what size of idle jet are better for my setup, i have a 240z L2.4 spanish tripple webers, my idle jets are a 45F9, the idle run are good but i tick its richer in low rpms, i was put a 40f2 but with that jets the car won’t start

[@TheCurbCut]

Hey there. 40’s are definitely too lean. Typically your idle jet window for a stock 240Z are going to be around 45-55. Stay in that ballpark and dial in your tuning. Good luck.

[@miguelnichols]

@@TheCurbCut TNKZ

[@miguelnichols]

Hi, it’s me again, wish its te better main get setting for a daily drive and the other question its the better timming position por this setup?

[@sebasticbaui1073]

Okay, this is a fantastic video! I have a couple questions as a young buck of 20 years excited to have a triple carb S30 someday. That gauge you're using around the 17:50 mark to check how rich/lean the mixture is, what is it? Further, I saw you use it on one of the barrels on each carb, would you use it on all six in in this case? If not, why only on one barrel per carb, if each barrel is richened independently? Thank you!

[@1978Rolla]

AEM Air fuel Gauge

[@garagetwentynine4023]

Great video! Currently tuning new weber sidedrafts on my datsun 1200 coupe...they're both reading a ridiculously high level of 10...is that the linkage/idle adjustment shown near the end of your vid? Cheers

[@Umaku_Garage]

Mine are reading the same. I can’t drop the air flow down. Was you able to figure it out ?

[@modatgarage5657]

How did Datsuns enter your life my friend?

[@sj119808]

Such a well made and informative video, thank you. I do have a question, seems like I have the same manifold and it came with the same vacuum port on it. Do you happen to know what size thread/what thread pitch it would take for a barb fitting?

[@a1steaksauce555]

Check out the plumbing section of your local hardware store. For some reason it's common for the vacuum fittings to use NPT fittings on these manifolds.

[@chejlr]

I have 40s and they sound raspy and loud and generally don't run well. A lot of hesitation. Any advice? Ty.

[@TheCurbCut]

Always start with a deep cleaning first!

[@MrPemellquist]

why not use an AFR to see ratio @ idle?

[@TheCurbCut]

Downstream or in the trumpets? AFR downstream would tell you very little about the precision at each throttle. Gotta tune AT the carb first

[@David-ty1xz]

Whats the best way to put these 40 Webers in long storage?

[@TheCurbCut]

David Really depends on how long, but the key thing no matter what is making sure the gas is thoroughly cleaned out of the carb. Beyond that, my advice would be liberal amounts of WD40 and wrapped tight in plastic wrap. Basically want to prevent rust and/or oxidation, and the WD40 would be a good barrier in preventing both.

[@David-ty1xz]

@@TheCurbCut Thank you. I completely cleaned them out, used carb cleaner then blew most of it dry. I wrapped loosely and put in a plastic bin with desiccants. I'll lube them up, thanks.

[@Corolla_Beau]

Have you tuned SK carbs before? I’m having trouble at around 3000rpm stumbling to 4000rpm then it seems to correct a little bit. Not sure what to change from this aspect. Any help appreciated thanks!

[@TheCurbCut]

Could either be accelerator pump is too lean or your air correctors might be too large and the fuel is aerating too much in the main circuit at higher rpms. Hard to say with no knowledge of your jetting and all. Good luck!

[@user-qy1pl7kz6i]

Hey good afternoon my name is Rafael i whan to now if you open your chop every day to go i have a toyota corolla 1.6 with 2 webber 45 to tune

[@TheCurbCut]

[e-mail]

[@jellybaby7]

Is that the latest multipoint injection 💉 system?

[@thomasseyffert1095]

You are good at what you do but if i ever caught you laying tools on my car !!! Really bad advertisment for your shop!

[@ulricjansson6164]

Not so informative, not so good. Sorry.