Hesitation at lower RPMs

Posted By: wtucker

Hesitation at lower RPMs - 11/14/11 07:59 PM

At WOT from 2600 +/- RPMs there is no stumble or hesitation, but anything before that at WOT it will stumble for a second before taking off. Do you think the stumble is fuel related at lower RPMs? Timing?

Posted By: bboogieart

Re: Hesitation at lower RPMs - 11/14/11 08:08 PM

Sounds like maybe the accelerator pump might not be working or giving too small a shot. This happens just when you floor it? Take off the air cleaner and give the throttle a blip and you should see a good squirt of gas.

Posted By: wtucker

Re: Hesitation at lower RPMs - 11/14/11 08:13 PM

I replace the original 30 with a 50cc, which helped. Could initial fuel pressure be to low? At idle its about 5.5, not sure what it goes to an WOT

Posted By: RapidRobert

Re: Hesitation at lower RPMs - 11/14/11 08:19 PM

What eng/carb/recent mods/always done it/cold and hot? So at part throttle it will hesitate for a sec then take off OK accelerating OK moderately at part throttle? CHeck float level/acell pump squirt tip in/duration. Ideally would be to tape a vac gauge to the windshield/run it to manifold vac & take it out & note the highest in hg it hesitates at after confirming the float/squirt is good. May need richer pri jets or "cruise" step (eddy) or a higher # PV and a vac leak would do it but for now assuming it is a lean tuning prob

Posted By: Mr.Yuck

Re: Hesitation at lower RPMs - 11/14/11 08:58 PM

need a bigger pump shot or some more timing.

Posted By: wtucker

Re: Hesitation at lower RPMs - 11/15/11 07:59 PM

Eng 440 .30 over, street dominator, 850 Mighty Demon, 452 ported and milled .10, 238/244 huges Hyd cam, 2500 converter, 4.10 gears. It's been doing it for a while. I've changed to a bigger squirter 31 (I think), increased the primary jets 2 sizes. I tried changing to heavier and lighter springs in the dizzy. I'll try and give it more initial timing (currently about 12) and see what happens.

Posted By: Pntastar69

Re: Hesitation at lower RPMs - 11/15/11 08:45 PM

Adjust the acc pump. I had the same issue w/a 670 Holley at low rpm until I got in the throttle. It needed just a squirt to eliminate the hesitation.

Posted By: BSB67

Re: Hesitation at lower RPMs - 11/16/11 12:12 AM

If it has a slight stumble or hesitation under light or part throttle acceleration at lower rpm, there could be something amiss in the idle/transition circuit of the carb as well.

Posted By: Todd

Re: Hesitation at lower RPMs - 11/16/11 01:11 AM

Had the same problem and went through the carb numerous times with jets accelerator pump shot adjustments with no change. Bumped the timing up to 18 initial and all in by 2200 and all the hesitation was gone.

Posted By: joedust451

Re: Hesitation at lower RPMs - 11/16/11 03:23 AM

Quote:

Had the same problem and went through the carb numerous times with jets accelerator pump shot adjustments with no change. Bumped the timing up to 18 initial and all in by 2200 and all the hesitation was gone.

I agree, more int. timing & most likely a faster curve, Vacuum is too low at 5.5 with a cam that size, low int. timing will do that.

Posted By: MoparsnMissiles

Re: Hesitation at lower RPMs - 11/16/11 03:29 AM

Quote:

Quote:

Had the same problem and went through the carb numerous times with jets accelerator pump shot adjustments with no change. Bumped the timing up to 18 initial and all in by 2200 and all the hesitation was gone.

I agree, more int. timing & most likely a faster curve, Vacuum is too low at 5.5 with a cam that size, low int. timing will do that.

Same here, bump the timing up a few degrees. World of difference.