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Need help, swapped to Holley carb, engine hesitates a little off idle

Hey gang,

Here's the sitchi-ation. 1975 Chevy truck, 350 engine, TH350 trans. I swapped the carb, intake manifold and cam. Carburetor is a Holley

4160 (600 CFM vacuum secondaries), intake is a Weiand 8004 and cam is an SSI with advertised figures of 250 deg intake duration/0.245" lift and 260 deg exhaust/.265" lift. The carburetor is just as it came out of the box except I adjusted the primary idle speed screw and float level. Accelerator pump cam is set to the "early" position (biggest shot early in accel travel). Choke is locked open and ignition timing is at 8 degrees BTDC running 87 octane gasoline. Stock 882 heads and exhaust manifolds.

The engine starts and runs fine, BUT, when I gun the throttle off idle the engine has a bit of a hesitation. Once it overcomes the hesitation she pulls strong to about 5,000 RPM. (I don't really want to rev it higher.)

Any suggestions as to where I should begin looking for the source of the hesitation? I don't know how to tell if the accel pump squirter isn't pumping enough/too much fuel.

Reply to
Miki Kanazawa
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Call your cam companies tech support line and get their opinions on modifying your distributor's advance curve. It is probably not giving you enough advance early on if your still using the stock distributor.

And next time you do this, keep in mind that you don't just go out and buy cams and intakes and such off the shelf. If your going to performance out an engine you need to do it as a whole package, and look at the entire engine, not just a piece here and a piece there. If just dropping an intake manifold and cam into an engine were to give you an extra 100 horsies, don't you think the auto manufacturers would have done it?

Ted

Reply to
Ted Mittelstaedt

Sounds like the cam isn't much over stock & I've never seen a Holley that didn't give too little a squirt from the accel pump. Look in the top while snapping the throttle (engine OFF) & make sure your getting a nice stream from both sides. If so, try a few more degrees of timing (12 or 14), as long as it doesn't ping This advance will probably fix you. Good luck.

Reply to
PA-ter

Thanks for the info. I upped the base ignition timing from 8 BTDC to

12 BTDC and it alllllmost cured the off-idle hesitation. Amazing that you can type a few keystrokes and someone thousands of miles away gets to work on their vehicle eh?

Went to a smog station during a slow time of day and goosed the throttle on their smog analyzer. The tech said it looks like a bigger accel squirt would be helpful.

I said ok. :-)

I have a spare 4160 with a stock .025" accel squirter. I guess I will open it .001" at a time until I get a clean snap from the throttle at idle. "Holley Carburetors, Manifolds & Fuel Injection" (HP Books) says once a clean snap can be had at idle, go .002" larger.

Reply to
Miki Kanazawa

||> Sounds like the cam isn't much over stock & I've never seen a Holley ||> that didn't give too little a squirt from the accel pump. || ||Thanks for the info. I upped the base ignition timing from 8 BTDC to ||12 BTDC and it alllllmost cured the off-idle hesitation. Amazing that ||you can type a few keystrokes and someone thousands of miles away gets ||to work on their vehicle eh? || ||Went to a smog station during a slow time of day and goosed the ||throttle on their smog analyzer. The tech said it looks like a bigger ||accel squirt would be helpful. || ||I said ok. :-) || ||I have a spare 4160 with a stock .025" accel squirter. I guess I will ||open it .001" at a time until I get a clean snap from the throttle at ||idle. "Holley Carburetors, Manifolds & Fuel Injection" (HP Books) ||says once a clean snap can be had at idle, go .002" larger.

Rex in Fort Worth

Reply to
Rex B

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