Carb Help, Accelerator Pump Jets at Idle Options

[mtc911]

Had my carbs off - as engine and trans was out for some rust repair.

Threw some new seals in there (rebuild kit)

Trying to tune…can’t get them set up right….finally noticed one side i have the accelerator pump jets “spitting” fuel even at idle. Obviously this is throwing things off. Other side is not doing it…just the one side.

Jets are clean…can hear the ball in there. All new seals and i cant cause any change in idle with the carb cleaner test spraying around the seals.

Have done a ton of research but i dont see any “adjustment” anywhere for the accelerator pump…if i push up on it during idle (from below the carb) I can stop the flow but as soon as i release pressure on that little arm that actuates the pump with my finger they will start “spitting” again and idle will increase.

Have loosened / adjusted and retightened the rod and it sees to be opening and closing the flap thing “butterflies” just fine…its good and tight.

Anyone have any ideas what might be out of whack?

Weber IDF 40 Dual Carbs

Thanks

[Superhawk996]

Take a very close look at the way the butterfly is mating to the throttle bore when in the fully closed position. At idle position there should be very little to no vacuum signal coming around the throttle plate butterfly. The butterfly should only be sitting above the small hole for the idle mixture screw. If you shine a flash light into one end of the carb, you should see a very small (about 0.001" or maybe 0.0015") ring of light around the throttle plate. This gap is only small enough to prevent metal to metal contact and wear of the throttle body bore as the brass buterfly plate opens & closes. The gap should be about the same between both throttle bores with the air bypass being used to correct for bore to bore varaince in airflow through this tiny gap.

Since you say it stops when pushing the the butterfly closed, I think you're getting vacuum bleed around the butterfly either due to misadjusted butterfly (throttle plate shafts can get twisted, or butterfly plate potentially damagged or worn to the point that it has too much clearnace to the throttle body and is allowing vacuum to bleed around the butterfly at idle.

Can't say for sure but its a hunch if you feel you have the other obvious bases covered.

At this point many Weber and Dellorto carbs are also 40 years old. I'm currently rebuilding a set of Dellorto's and had to replace the butterfly throttle plates due to wear and what looked like someone trying to "tweak" them long ago with vicegrips. (IMG:style_emoticons/default/headbang.gif)

[Shivers]

Take a very close look at the way the butterfly is mating to the throttle bore. At idle position there should be very little to no vacuum signal coming around the throttle plate butterfly. The butterfly should only be sitting above the small hole for the idle mixture screw.

Since you say it stops when pushing the the butterfly closed, I think you're getting vacuum bleed around the butterfly either due to misadjusted butterfly or butterfly plate potentially worn to the point that it has too much clearnace to the throttle body and is allowing vacuum to bleed around the butterfly at idle.

Can't say for sure but its a hunch if you feel you have the other obvious bases covered.

If this is indeed the case, and it is possible, I have heard of wrenches pulling the carbs apart and when putting them back together, the butter fly's were installed wrong. And it was causing this type of problem.

[Superhawk996]

If this is indeed the case, and it is possible, I have heard of wrenches pulling the carbs apart and when putting them back together, the butter fly's were installed wrong. And it was causing this type of problem.

Good point, the thottle plates do have a top side & a bottom side with a slight angularity to the edge of the throttle plate. Good rationality check is to look at the screws that hold the throttle plate to the throttle shaft. Witness marks from someone screwing with them with a screwdriver is a bad sign.