7041211 slight stumble off idle sometimes

[BLUE TA]

hi guys, sometimes when I come to a stop sign. my q-jet very slightly hesitates as I leave the stop sign. if I wait 3-4 seconds. it dosent hesitate. when I rebuilt the carb I staked the pump check ball in the well with a used ball. what do you think? thanks, BLUE TA

[Cliff Ruggles]

The accl pump is there to help cover up a lean condition with quick movements of the throttle.

If you are having issues taking off at light throttle then I'd look at tuning that part of the system.  If you have an APT carb turn the APT screw CCW about 1/8 turn or so and test drive.  Continue doing this until it richens things up enough you don't get a stumble/hesitation, or bog right off idle.

It may also help to fatten up the idle system some to put more fuel to the transfer slots.  \

I've cured issues just like you are having by opening up the DCR's a couple thousanths after not getting the results I wanted with the APT system or slightly smaller primary metering rods.

I'm also curious as to what jets and metering rods you are using (primary side), and what engine the carb (specs) it's being used on?........Cliff

[BLUE TA]

 hi cliff, thanks for the reply. it is a 7041211 with stock jets and rods 72 42 it has all your parts and new throttle bushings. the problem only appears as im leaving a stop sign. leading me to think accelerator pump. if I wait 3-4 sec. it doesn't hesitate. its a 70 gmc with a 350 crate engine. 8.0 comp edelbrock intake headers dual exhaust. the q-jet works great every where else. starts up from cold and idles at 16 in vacuum then when it warms up 18 inchs. runs great just the little stumble of idle. thanks BLUE TA

[Cliff Ruggles]

Which crate engine is it?

72 jets with 42 rods is extremely lean and not going to make the grade for what you are doing.

When you get time call the shop and we'll discuss some options and tuning changes.....Cliff

[BLUE TA]

hi cliff, I made a mistake on the jet rod size. its 74 42 hope this is a little better. the engine is the goodwrench 350. chevy hi performance did a lot of dyno tests on these engines and stock with a 4bbl headers and duals they put out 265hp 350ftlbs. nice engine. works good in my truck and runs on regular. thanks, BLUE TA

[Cliff Ruggles]

That's still pretty lean for one of those.  I'd fatten it up some and if you haven't done so remove the factory APT screw in the baseplate and install one of our external APT screws.

Good thing it's not the GM 290HP crate engine, it's a complete TURD everyplace.  Not sure what they were thinking there, but using a 350/350hp camshaft in a 350 with barely 8 to 1 compression doesn't work for chit!

I've had several of those brought up here for custom tuning and they are PATHETIC.  Not even sure how GM gets away selling them.

I contrast the 330hp crate engine with the small roller cam is a home-run everyplace.........Cliff