Stumble

[Aron Gleason]

I've been fighting a stumble forever, at cruise at any speed I can stab the throttle and it has a huge stumble then it will pickup after about 5 seconds. Looking at the afr gauge when this happens it will spike up to 17. Is it possible the cause could be how the msd Distributor is setup? It's the mechanical advance distributor with the black bushing, 1 light silver spring and 1 light blue spring. Ps. This is literally driving me crazy.

 

[Don67Satellite]

Assuming you have a carb, maybe you need to increase tension on the secondary air flap.

 

[Aron Gleason]

It's a 950 double pump carburetor

 

[Don67Satellite]

I run an AVS2, and had stumble issues like you describe. I adjusted the air flap over the secondaries to open slower and the stumble went away.

 

[Photon440]

You used to have only a three second stumble ( Follow up to carburetor stumble ) so what was changed that made it get worse?

 

[Geoff 2]

Get rid of the POS 950 DP & install a TQ or Edel 800 AVS2.
No more stumble.

 

[pnora]

Lock the distributor and set the timing at 36. Then drive it. If the stumble is gone it was in your ignition set up. If the stumble is still there it could be an carb. issue.

 

[hunt2elk]

Have you experimented with different accelerator pump cams and squirters?

 

[68-500]

Yep you need more fuel when your opening the secondaries. I bet if you roll into it no stumble? Auto or manual transmission? Rule of thumb has been vacuum secondaries on automatic, manual secondaries on manual trans.

 

[WileERobby]

What the heck do you have, that you need a 950 DP ????

 

[PurpleBeeper]

in general, it is going lean….so you need more squirt from your accelerator pump(s)

 

[R413]

Dominic Thumper was your man, what happened?

are BOTH accelerator pumps giving fuel?

 

[Aron Gleason]

Have you experimented with different accelerator pump cams and squirters?

Yes. I've tried the blue cams with 31 squirters up to 37 and even 42 squirters. No change.

 

[Aron Gleason]

Dominic Thumper was your man, what happened?

are BOTH accelerator pumps giving fuel?

He's still my go to carb guy. Just wondering what I might be overlooking, carb issue or distributor.

 

[Aron Gleason]

You used to have only a three second stumble ( Follow up to carburetor stumble ) so what was changed that made it get worse?

I don't really know. When I'm cruising along and give it some throttle I can see my afr's go up into the 15's. But if I stab it from a light in 1st gear, it goes like a rocket. No stumble.

 

[Aron Gleason]

Yep you need more fuel when your opening the secondaries. I bet if you roll into it no stumble? Auto or manual transmission? Rule of thumb has been vacuum secondaries on automatic, manual secondaries on manual trans.

Full manual valve body.

 

[Aron Gleason]

in general, it is going lean….so you need more squirt from your accelerator pump(s)

I have the pink cams on the primary and secondary with 37 squirters.

 

[Aron Gleason]

Yep you need more fuel when your opening the secondaries. I bet if you roll into it no stumble? Auto or manual transmission? Rule of thumb has been vacuum secondaries on automatic, manual secondaries on manual trans.

Yep. No stumble rolling into it. Just when I stab the throttle quickly

 

[R413]

now we are getting somewhere.

When you stab the throttle:
what is the engine RPM?
what gear is the trans in?
What rear end gear Ratio?
how tall are the rear tires?

But if I stab it from a light in 1st gear, it goes like a rocket. No stumble.

 

[Aron Gleason]

now we are getting somewhere.

When you stab the throttle:
what is the engine RPM?
what gear is the trans in?
What rear end gear Ratio?
how tall are the rear tires?

Anywhere from 2000 rpms on up.
It happens in 2nd and 3rd gear
4.57
28 inch tall tire