Speaking of which, turning up the mixture screws from 3/4 turn out to 1 1/2 to 1 3/4 seems to have helped with the part throttle stumble. Extreme part throttle lean out, Holley HP Greetings. I can get 20" hg at idle, steady gauge with no fluctuation. Very few enthusiasts truly appreciate just how much a functioning vacuum advance helps drivability. It happens at pretty much any speed, but only at really light throttle. It's not a stumble/surge that appens at that point and then goes away (like a bog), but constant and does not go away. Power system not operating. Adjust throttle linkage to obtain wide open throttle in carburetor. I am experiencing a BIG cruise (part-throttle) surge/stumbling - at approx. 351 4V Cleveland (351C) in a 1965 Mustang (Yes, that is right) with a lumpy roller cam and single plane Edelbrock intake with a Holley 4777-5 double pumper 650 carburetor. PISTON TYPE – Check power piston for free up and down movement. Discussion in 'The Hokey Ass Message Board' started by Mr. Sinister, May 6, 2011. 1/4-throttle. Carburetor throttle valve (s) not going wide open. C-4 automatic transmission with stock lock up converter (I know, it will be going away soon! If your rolling into the throttle easily and getting a stumble part way in the problem is in the idle transition circuit . I have an issue I have been hoping to resolve through searching and lurking, but to no avail. Although Holley employees will take part in answering questions from time to time, your questions may or may not be answered by Holley personnel. Lots of folks lately with Holley issues. This will add timing at part throttle under light acceleration and will often cover up a part-throttle stumble. That could be from how rich I have been turning up the idle mixture trying to test different things out to cure the part throttle miss. (Check by pushing accelerator pedal to floor). Add 2 jet sizes in the primaries in the winter and it should do just fine. Hey folks, I've been having a light throttle stumble issue on my Holley Street Avenger 670. Thus, Holley can not guarantee an answer or timing on an answer. ). When I give a very light throttle input, with on take off or while cruising, I have a lean spot (verifyed with an O2 meter) hich is causign the car to stutter for a second or too. Ok, so I am tuning my holley and making good strides. How-to adjust the accelerator pump on Holley carburetors to avoid stumbling and hesitation upon acceleration. I am trying to tune out a hesitation in the off idle part throttle range. Stumble when punching throttle. I believe the Holley HP 750 to have an inherent problem of leaning out severely at part throttle tip in as the vacuum decreases, but not before PVcomes in. I have one fairly large problem with the Holley 670. Bad part is these hot plugs are turning black too. The switch to winter formulation gas can make a borderline mix go a bit lean. Replace with a new filter element. With the car idling you can spray carb and choke cleaner around where the carb seats on the intake and vacuum hoses etc. On a Holley carburetor, this is usually the nipple located on passenger side of the primary metering block. Light throttle stumble, Holley carb. Your cruise surge can be because your jetting is borderline too lean. One issue I am havingis with a part throttle input / crusie. First check for any vacuum leaks anywhere near the carb or elsewhere. i think i'll try a few different things with the tuning before i buy any parts, just to see where i can get it. Electric choke works great, after the choke comes off and the car idles at 800 rpm glass smooth. Page 3 of 3 < Prev 1 2 3. Unfortunately, my engine only requires light throttle to keep the car up to speed, so it can get annoying. ... thanks for all the input guys. Dirty or plugged fuel filter(s). Holley carbs run on the idle circuit up to about 2000 RPM at light throttle. The carb I am using is a NOS Holley 9834-1 Here is what happens: Car starts fine hot or cold.