Stumble off idle -

[Gaz64]

Originally Posted by Grubby

I just spent two hours of quality time with my Cobra.

Removed carb.
1. No indication of vaccum leak
2. Transfer slots were at about .028. So I backed off the idle screw to get them to .015.
3. The clearance under the accelerator pump bolt is .015
4. Confirmed float levels. Fuel just sloshes out when the car is shaking at idle.
5. Set the idle screws at 1.5 turns out.

Then I fired it up and warmed the engine.

Adjusted idle mixture screws with my vac gauge. Best vac was about 7 at 550 rpm idle. Screws are pretty close to 1 turn out. My vac gauge is old and beat up - it may not be accurate.

I do like the idle somewhat faster. Another 150 rpm would be nice, but that would open the transfer slots further.

The stumble was immediately off idle. That has moved. Off idle is now crisp.

Now if cruising at 1500 - 3000rpm and you get into the throttle pretty hard it stumbles. Moderate or less throttle and it pulls just fine. The stumble is a single, quick loss of power then it goes. The stumble decreases as you approach 3000 rpm. It is most noticeable at 1500.

I could not see any sign of black smoke under hard throttle. Primary jetting seems to be dead on. The side pipes and spark plugs are both a deep tan.

What are your suggestions? This does not seem to be the idle circuit.

John

John,

In your point 3 above, " The clearance under the accelerator pump bolt is .015", please say you understand the .015 is NOT under the bolt as some think.
The .015 is ADDITIONAL travel of the pump lever measured at WOT. It ensures the pump diaphragm won't bottom out at WOT.

If you have ANY slack/clearance in the pump mechanism, you'll have a flatspot off idle.