Weber 40mm DCOE Conversion

[Alexrobic604]

This carb does not start well cold or warm and does not idle well, I just built this engine with this weber conversion. The carb I bought some time ago on ebay from Pierce Manifolds it's a 40 mm dcoe weber copy. Since day one this carb has not run right, I've had it to my mechanic and we chanded the idle jets, main jets, choke tubes and emulsion tubes. I'm at the end of my rope with this carb and I'm ready to go to the original carter carb but I will have to find one first. If anyone has had first hand experience with this set up and could shed some light on this situation I would be very great full. My engine spec's 63 145 ci with 64 turbo, isky cam, roller rockers engine is balanced.

Thanks,

[Alexrobic604]

PS floats have be adjusted.

[thewolfe]

I have a progressive 40DCOE on my car and it runs real good once warmed up. These carbs do not have a choke so cold starts can be a challenge. When the temps outside are around 50 or above it has no problem starting. I do use the 'cold start device' with a choke cable that runs underneath the dash though. This richens the mix and I find pretty much mandatory when I'm starting cold.

What chokes are you running and what are your jetting/air corrector/emulsion tubes? Webers have a lot of different parts and almost infinite tuning so if you're not in the ballpark it isn't going to run well. Alexrobic604's comment about floats is also true. Float level and fuel pressure are critical in getting it to run right as well. You only want 2-3 psi fuel pressure just like the yh.

[855r]

I have a Weber 40DCOE on my car too I had a steep learning curve to get mine to run correctly. In this thread viewtopic.php?f=55&t=9629&p=65434#p65434 it has some tuning and other information that got me pointed in the right direction. I did not make satisfying progress though until I got an A/F ratio gauge.

Until I knew exactly what was going on in my exhaust from idle to full throttle I was really just guessing and throwing parts at the carb hoping to make a difference. Those little weber parts add up quick too$$$$ We have almost the same engine, I have a performance cam in mine ect. Tonight I can pull my top cover off and make a list of what I have in mine right now and you can compare to what your currently running. My car is still a bit rough when cold but runs good when warm. The cold rough issue I feel has more to do with fuel condensing in the intake when cold. My carb will be nearly ice cold for awhile until enough heat migrates to it. Even after running down the freeway my engine can be at temp, and the carb is cool to the touch. I post up my carb specs later tonight when I'm home from work.

[Alexrobic604]

I'm running the following parts.
main jet 155
pump jet 40
emulsion tube 215
main venturi choke tube 28mm

Thanks for all your help.

[Alexrobic604]

Correction:
emulsion tube is F11
pump exhaust jet is 215

[cnicol]

Wouldn't it be expected that the Weber would run poorly when cold? The Webers I had didn't have a regular "choke", only a "cold enrichment" lever, which was not effective. Does your Weber have a choke system?

[Alexrobic604]

This weber has the cold enrichment lever, hot warm, cold makes no difference at all just idles poorly and very hard to start.

[thewolfe]

You say you just built the engine. Are you sure there is not some other issue you might possibly have besides the carb?

[855r]

Ok I got my spec's. Keep this in mind these carbs normally feed one cylinder per throttle bore. So a 4cyl MG for example would have two DCOE's. We have one carb supplying fuel/air to 6 cylinders.

Acell pump jet 1.00
Idle Jet 50F8
Emulsion Jet F16
Air Corrector 220
Main Jet 145.............Edit 145 is not correct mine is much, much larger!!!! See post below.
Choke tube's 34
Mixture screws are two full turns out
Fuel Pressure set to 2psi on cheap regulator

Our set ups are pretty different. Look at the picture I attached to this post. Many circuits overlap each other when coming into play. Accelerator pump jets of course supply shot a of fuel when the gas is pressed to prevent a stumble or lean miss fire, but in these carbs they continue to flow fuel by venturi effect. That may explain why I have a smaller main jet and a larger accel pump jet than you(remember we're feeding 6cylinders). Your car may be running rich on the top end giving you poor performance and running lean bottom end giving you poor performance there too.

I think your leaving potential on the table by running #28 choke tubes and with the size of your main jet may be adding to an overly rich mixture by limiting air flow. Also keep in mind that smaller choke tubes will increase the velocity of the air through the carb and cause a stronger suction on the fuel flowing components but not move a higher volume of air.

[Alexrobic604]

Thanks for all your help, my mechanic had me change the choke tube to 28mm also he change main emulsion tubes and idle jets. I will talk to him tomorrow and see what he has to say. This is a great start in the right direction. Thanks Alex

[Alexrobic604]

You say you just built the engine. Are you sure there is not some other issue you might possibly have besides the carb?

Yes anything is possible I've checked the ignition system plugs and also checked for vacuum leaks.

[cnicol]

28mm x 2 seems pretty small. My Weber car was 34 x 6. I'll have to dig out my Weber book and see what's recommended for your application. Would it be safe to estimate 10 pounds of boost on top of your 145 cubic inches??

[Alexrobic604]

28mm x 2 seems pretty small. My Weber car was 34 x 6. I'll have to dig out my Weber book and see what's recommended for your application. Would it be safe to estimate 10 pounds of boost on top of your 145 cubic inches??

If you could dig up that information that would be great. I originally had 34mm, my mechanic suggested trying the 28mm to draw more vacuum.

[miniman82]

You have a turbo, a strong signal on the mains will be the least of your worries. Respectfully if you don't have a wideband, there's no way you can possibly know if your tuning is going in the right direction or not. Add to that the complexity of it being a new build, and Occams Razor quickly bites you in your hind quarters chasing problems that don't exist. You need to eliminate variables one at a time, till you pin down the source of the trouble. So put a wideband in the car and see what the mixtures are doing, my guess is you're pig rich and drowning in fuel.

[855r]

Alexrobic604, I gave you bad info up above by mistake. 145 main jet is way too small I'm sorry I don't know what I was thinking. Yes I have a 145's in my car but it totally slipped my mind that I drilled them out. I found this out(remembered) because I upped my boost and was tuning for it and started looking at my jets and said how can a 180 be smaller than my 145. Then it dawned on me I drilled them out, yes that's 1.95mm remember we are fueling for six cylinders. I'll PM you to let you know my mistake.