kevins750 Posted November 3, 2013 Report Share Posted November 3, 2013 My 74 620 idles around 850 but when I shift into gear (F or R) doesn't matter the idle drops well below the 650(recommended).What adjustment on the carb is needed...I have looked EVERYWHERE for this info including my repair manual...thanks Quote Link to comment
ggzilla Posted November 3, 2013 Report Share Posted November 3, 2013 Adjust the carburetor like others ex. Ford, Chevy Adjustments won't fix that problem, however. There is something wrong so it needs repair. Clean the plugs maybe, or replace a cracked vacuum hose. Or maybe it needs new points (every 12 months) or the timing set. Quote Link to comment
kevins750 Posted November 3, 2013 Author Report Share Posted November 3, 2013 well I though auto carbs had something different to compensate for that..it has new plugs and hoses..points look nice and flat.... Quote Link to comment
datzenmike Posted November 3, 2013 Report Share Posted November 3, 2013 Idle mixture may be off. The mixture screw is the large one on the far right with the spring coiled around it. With timing and valve lash checked and set on a warm motor idling in neutral... turn the screw inwards until idle deteriorates. Turn out until idle deteriorates. Select a point about half way between these two points. The idle may improve and increase. If it does, turn it down with the other idle speed screw just to the left of the rust stain in the picture below. Repeat the in and out adjustment looking for an improved, smoother strong idle. If idle increases turn down and repeat until it cannot be improved. If this fails to bring the idle up in gear just turn the idle speed screw in slightly. A good strong idle requires a good strong intake vacuum. So... Check your valve lash clearance. Check your ignition timing. Check all vacuum hoses including your vacuum brake booster for cracks and leaks. Is the carb bolted down tightly? Manifold bolts snug? Quote Link to comment
kevins750 Posted November 3, 2013 Author Report Share Posted November 3, 2013 manifold vacuum is near 20 at idle.. Quote Link to comment
datzenmike Posted November 3, 2013 Report Share Posted November 3, 2013 20s good. Quote Link to comment
kevins750 Posted November 3, 2013 Author Report Share Posted November 3, 2013 What is the difference between and auto carb and manual? there are separate part numbers...Maybe I am saying this wrong.....I have good strong IDLE when I am in neutral but when I shift into gear with my foot on the brake then my idle dips below the 650 rpms that are stated in the tune up guide lines.... Quote Link to comment
ggzilla Posted November 3, 2013 Report Share Posted November 3, 2013 The difference is in tuning for emissions. You can swap them and it will work fine. Quote Link to comment
datzenmike Posted November 3, 2013 Report Share Posted November 3, 2013 Perhaps your brake booster is leaking? Try in gear with the hand brake on or against a curb so you don't have to use the brake. Quote Link to comment
kevins750 Posted November 3, 2013 Author Report Share Posted November 3, 2013 Perhaps your brake booster is leaking? Try in gear with the hand brake on or against a curb so you don't have to use the brake. I will try that,,,,sounds good...vacuum is around 15 when brakes are applied and truck shakes pretty bad..anyway thanks for all the suggestions... Quote Link to comment
ggzilla Posted November 3, 2013 Report Share Posted November 3, 2013 Vacuum should not drop when brakes are applied. Fix that problem. Quote Link to comment
kevins750 Posted November 3, 2013 Author Report Share Posted November 3, 2013 I will check it out in the morning Quote Link to comment
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