1964 330V8, replaced the intake with an Edelbrock unit and at the same time installed a Holley 570 Street Avenger (manual choke). The car was running with a slight hesitation off idle before with the factory quiet single 2 1/4" exhaust. I have recently replaced the exhaust with the Flowmaster American Thunder dual 2.5" system and now my off idle hesitation is a flat out stumble (near stall). It doesn't matter if the car is stopped or whether I'm rolling 40mph.... any accelleration off-idle almost stalls the car out.

So how would I fix this? Do you think it's a carb problem, or ignition problem? Ignition is a chineesium HEI through Autozone plug wires into cheap autolite plugs.

Once I pump through and wake up the engine it comes alive- but it seems to have no kick in the seat throttle response as I'm always having to feather the throttle to keep the car from stalling out.

Thanks folx.

 

Check for vacuum leaks and verify the accelerator pump shot is good.

 

Ok, yeah I should have stated that already.... sprayed starter fluid all around the intake/carb and no increase in throttle. Also took off the cleaner cover and revved it several times.... you can see the fuel being pumped in on the front 2 barrels.

I also forgot to mention that it does this under load. When in Park or Neutral it revs fine off-idle.... I only get the stumble/stall when in drive.

 

Best advice I got...check the secondaries

https://classicoldsmobile.com/forums...-problems.html

 

My 64 88 does exactly the same thing. Because of this issue I am planning on a carb rebuild and replace the fuel pump (fuel pump is bad..had to add an electric pump late this past summer just to get some enjoyment before putting her away for the winter)
If i get to cruising speed @ 40/45 the engine just dies...a second or two off the pedal and then the engine regroups. Pain in the *** 'cause I could not take it on highway.

 

With the engine off, check the gap from the accelerator linkage to the accelerator pump actuating arm - there's supposed to be .050 gap - and it's adjustable.
If that's off, could account for a stumble.
Also check your initial timing, and make sure your vacuum advance is working!

 

Great suggestion on the .050 gap. I checked my 88 manual and then checked my linkage.
Bottom line I have issues with the pump ( planned to replace when I rebuild carb) .
I'm confident with a new pump,a rebuilt carb and a very detailed inspection of accelarator linkage and a the typical timing my hesitation should stop.
Great ideas...
Thanks

 

I would disconnect the vacuume advance and drive the car. It may be advancing the timing at an idle. Any accelertion would cause a momentary retarding of the timing. It's just one thing to eliminate and it won't cost a penny.

 

Just make sure you plug the live hole the advance hose comes off of!
Major vacuum leaks cause a kinds of crap!
If there's no difference when you pull that line, you've a bad vacuum advance can, which is more common than most woud think!
After all, it's rubber, too!!

 

Problem solved.... oddly enough.

I read somewhere online that you cannot use the old solid core plugs after changing from points to HEI. I bought some new plugs Sunday and installed them. She idles and drives completely different.... like a whole new car! Hesitation/stumble is about 98% gone.