Light load surging - Team Camaro Tech
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post #1 of 5 (permalink) Old Sep 8th, 05, 09:51 PM Thread Starter
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Michael Faucher
Join Date: Oct 2004
Location: Vale, NC
Posts: 226
Light load surging

got a question, looking for thoughts and ideas....72 - 350 2 bbl, driving down the road foot on gas just enough to mantain speed (any speed 35 - 60) you can feel but mostly hear a slight surge (fish bite) in the engine. heres some specs Complete rebuild, new reman carb, new dual exhaust, everything tuned to stock specs. Idle is perfect, off idle is great only issue is under light to virtually no load.

Just looking for some ideas of where you would look....fuel, ignition, vacuum, ect. The self proclaimed experts that come around offer advice from puting bigger jets in carb (due to the non-stock dual exhaust) to retard timming 4 deg or advance 4 deg.......We are open to all thoughts, fire away........

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post #2 of 5 (permalink) Old Sep 8th, 05, 10:11 PM
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Location: san jose ca usa
Posts: 503
Re: Light load surging

90% of the time when you have a light load cruise surge it is from an over lean condition. Try giving the idle mixture screws a 1/4 turn more out to slightly richen it up, at light load low throttle postion your still in the transfer slots so fattening the idle a little bit will have a noticable effect on the cruise mixture.

If fattening the mixture has little or no effect then take a look at the vacuum advance can, lots of early smog era cars had low intial timing and low mechanical timing to help with emissions and they would make up for the retarded timing by adding alot of vacuum adv. For $10 or so dollars you can pick up a crane adjustable advance can from most autoparts stores and fine tune your vacuum advance.

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74 Trans Am, 400, th400, 2.73 posi.
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post #3 of 5 (permalink) Old Sep 9th, 05, 07:14 AM
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Join Date: Oct 2004
Location: Canada
Posts: 558
Re: Light load surging

I agree on trying the 1/4 turn out on the screws. Not sure if you have HEI or not, but on my 69 I chased down the same problem (fish bite). It ended up being the resistor wire was still being used. I checked it many times and got 12v with the key in the run position and engine not running. Apparently volts drop with engine running, which I recently found out. I changed out the wire and problem went away.


'69 355-3.73 Moser-Truetrac-TKO-600-Hotchkis-DSE-QA1 coilovers-Baer brakes-17"Budnik's-Speedtech control arms
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post #4 of 5 (permalink) Old Sep 9th, 05, 08:30 AM
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Join Date: Feb 2001
Location: Concord Cal. USA
Posts: 2,664
Re: Light load surging

Like was said normally too much vacuum advance if everywhere else it runs fine. If it's converted to an HEI they have an awful lot of vac advance in them you might try a limiter.
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post #5 of 5 (permalink) Old Sep 9th, 05, 09:04 AM
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Join Date: Dec 2000
Location: Frederick Maryland
Posts: 91
Re: Light load surging

Hmmm, I would look at to much timming at normal speed. I had the same problem, the mechanical advance and vacuum were doing each other at lower speed and it caused a surge. So, I own a Sun distributor machine and just worked on the problem until I had what I needed.

It's worth a look at that as a source of the problem.

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