I just did a tune up on my 71 LS-5 with new repo wires ac plugs I set the points ect.. It runs real good.. except when you are going down the road it has a real slight surge. oh I also put in a new fuel filter. now this car has been siting up for a few years. do you think I should go through the carb? I called my chevrolet dealer for a good AC Delco rebuild kit an they no longer have them. who would make the best after market kit for a Qjet carb?
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Re: tune up
Not unusual for a '71, which is an emission controlled engine, and cruise mixtures were lean. The ignition timing map is also retarded throughout most of the operating range relative to the antecedent L-36, which had no exhaust emission controls in 49-state trim.
Long periods of inactivity can cause deposit buildup from old or evaporated fuel in some of the small passages that are part of the idle/off idle system, which can cause leaness at cruise, particularly at lower speeds.
You might try a bottle of Techron in the next tank of fuel as it may remove some gum or varnish deposits. If not, you can overhaul the carb, and be sure all internal passages are thoroughly cleaned, but the slight cruise surge may not go away because it could be a "designed in feature" due to emission control requirements. GM has pretty much abandoned supplying service parts for older components, but there are plenty aftermarket zip kits being as how GM must have built at least 30 million Quadrajets. I expect what NAPA offers is as good as anything out there.
A size or two increase in main jets and remapping the ignition advance will probably solve the problem if it persists after a carb overhaul.
Duke
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