Weber accelerator pump jet

507 Views 9 Replies 5 Participants Last post by twalkerp13, 15 d ago

twalkerp13

Discussion Starter · 1 mo ago

Has anyone had trouble with the stock weber carb accelerator pump jet? I just rebuilt my carburetor and dialed in my ignition timing, idle settings, etc., and if I give it some gas, it lags a lot before revving, which I figure is an accelerator pump issue. My jet only sprays into the primary venturi, and it doesn't seem like it's enough (I just replaced the accelerator pump, so I don't think that's broken).

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RallyBob

· #2 · 1 mo ago

twalkerp13 said:
Has anyone had trouble with the stock weber carb accelerator pump jet? I just rebuilt my carburetor and dialed in my ignition timing, idle settings, etc., and if I give it some gas, it lags a lot before revving, which I figure is an accelerator pump issue. My jet only sprays into the primary venturi, and it doesn't seem like it's enough (I just replaced the accelerator pump, so I don't think that's broken).

On a synchronous-opening 38 DGAS, the accelerator pump squirts into both barrels.

But on the progressive-opening 32/36 Webers, only the primary barrel gets a shot of fuel.

That initial squirt of fuel from the accelerator should be nearly instantaneous when you hit the throttle. If not, there’s a chance the accelerator pump linkage is bent and not in contact with the plunger. It might take some tweaking to fix it.

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twalkerp13

Discussion Starter · #3 · 1 mo ago

The fuel is delivered instantaneously, so I doubt the linkage is the issue. I'm thinking I might have to upgrade to a larger jet. I unknowingly ran my engine with the ignition timing a few degrees advanced for a bit, and the engine did not lag on acceleration. The engine seemed to run fine with no timing-related issues like spark knock, etc. except for a rough idle (fortunately, the engine seems to have suffered no major damage from this). I had my carb set so that it ran much richer than I have it now, which I believe compensated for the advanced timing, since the rich mixture burns slower.

The point is, I think the advanced timing also made up for an improper fuel mixture delivered by the pump jet, which is why it seemed to accelerate fine while the timing was advanced. Thoughts?

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twalkerp13

Discussion Starter · #4 · 1 mo ago

Well, I went back an hour or two later and the issue seems to have resolved itself. The throttle response is back to normal now. These carburetors have a mind of their own, I swear.

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Young Gt Lover

· #5 · 1 mo ago

twalkerp13 said:
Well, I went back an hour or two later and the issue seems to have resolved itself. The throttle response is back to normal now. These carburetors have a mind of their own, I swear.

Maybe you cleaned out some gunk in the carb by running it. My weber 32/36 had all kinds of gunk in it.

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The Cub

· #6 · 1 mo ago

Also debris does get into your idle jets so you’re not too far off with your mind of its own comment. Be sure to have a good in line fuel filter and that the gas pours out of your gas tank cleanly.
I checked mine by waiting until the tank was low on gas, removing the hose & filling up a clear gallon size container back at the tank, there shouldn’t be any visible debris, and it should come out at a very good rate.

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twalkerp13

Discussion Starter · #7 · 16 d ago

Update-- I believe my issues with the accelerator pump had nothing to do with gunk, bad gas, etc. at all (although I do need to replace my crusty gas tank).

Another issue I've been having is engine dieseling. I noticed that fuel drips out of my accelerator pump jet when the engine has reached operating temperature, which I'm almost certain is causing my dieseling issue. I believe this also caused the problem originally addressed in this post, and I'm guessing that has something to do with fuel boil in my carburetor, but I'm not sure (I don't think it has to do with the check valves, float level, etc. since I checked these things when I rebuilt my carb recently).

Has anyone dealt with this / have any ideas as to how to fix it?

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The Cub

· #8 · 15 d ago

Dripping isn’t good. In my experience having the throttle plate or plates adjusted too far open will cause the engine to diesel. The easiest way to tell is by attaching a vacuum gauge to the vacuum ported connection on the carburetor and check for any vacuum reading at all you should have zero vacuum at idle. Also be sure that you have your ignition timing set up properly. HTH

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First opel 1981

· #9 · 15 d ago

Dieseling is caused by a lot of factors. Dripping gas usually isn't one of them but, I suppose, it could be.
I had dieseling in mine after a rebuilt motor. I ended up going to a different heat range of spark plug and it was gone.
Having said that, I do get boilover.

You really only have three reasons to have gas dripping into the carb. Either you have boilover or your float is too high or your float valve is leaking. The float valve leaking could be a bad valve connection or fuel pressure too high.

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twalkerp13

Discussion Starter · #10 · 15 d ago

I should probably give some more context on my dieseling issue. I first experienced it after I rebuilt my carb. I believe it was caused by carbon buildup since it went away after I treated my motor with seafoam.

I then noticed that I had some ignition timing issues, so I fixed that and adjusted my carb as necessary, and the dieseling issue came back. The reason why I think it is caused by fuel drip this time around is because the issue diminishes / nearly goes away entirely if I wait for the fuel drip to slow down after pumping the gas.

My idle speed screw does, however, need to be driven in quite a bit in order for my engine to idle at the recommended 900 rpm, even after properly setting the idle mixture. So, my primary throttle being open too far could be contributing to it as well.

I could try and lower my float level a bit-- when I rebuilt the carb, I noticed that the floats were initially set slightly below the specified level, so I could set them back to that point.

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