Double Pumper issues
 

Hi all,

I have a 1972 vintage 700cfm double pumper on an LS5 El Camino. Runs well enough to have broken in the cam, but won't idle well unless I partially open the choke. If I take the choke off completely, it needs around 16 degrees of timing to idle (no vacuum advance). One other note: the idle speed seems to be inconsistent, and when I let off the throttle it takes a while to settle back to idle speed.


I have the mixture screw set to 1.5 turns, and just rebuilt this thing with one of Eric's basic kits. I assume this is user error on my part, but wondering if the symptoms point to something familiar.

Thanks!
Tony

Re: Double Pumper issues
 

check your advance wieghts in the dizzy..may be hanging up/sticky and causing a slow return to idle

Re: Double Pumper issues
 

Throttle stuck a little? Internal fuel leak or vacuum leak?

Re: Double Pumper issues
 

Tony;

Do the mixture screws have any effect at all? Try turning them out another 1/2 to 1 turn each and see if the issue improves. If so, it's running lean, and there can be any number of causes for that:

Did you check the metering block and throttle body mating surfaces for warp? If the metering block surfaces are too far off, the block won't seal properly and can exhibit the issues you're having. Same thing goes for the throttle body surface, esp. at the front & rear of the main body where the curb idle and transfer slot discharge passages seal to the throttle body.

Did you examine the idle feed restrictors for damage, corrosion or previous modifications? If they're blocked off by corrosion (common problem that conventional carb cleaner won't touch) it will idle lean.

If you can't get a handle on it, shoot me a PM or give me a call and I'll help you get it sorted out.