Rough Idle, Help!
04-13-2015, 06:51 PM
#21
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Today I pulled the valve cover and changed the leaky gasket, painted it while I had it off, replaced the PCV valve, the PCV intake elbow, and the hose and grommet. Running a little smoother than it was. I played around with the idle adjustment screw on the carb, and it really didn't seem to respond much either way. I'm thinking about a carb rebuild kit now. I did try to twist the carb like you guys mentioned and it seemed to be securely mounted.
04-13-2015, 09:57 PM
#22
Idle mixture adjustment screw (been awhile) - you want to turn it in till the motor gets rough(er), then out till the same thing happens, then halfway in between.
On the old v8's we would turn it all the way in (gently, you never want to crank it all the way in hard and damage the seat)till it stops, then turn it 3 1/2 full turns out to get it idling then adjust from there.
If you already have it idling, just turn it in till the engine starts to buck, out till it does the same, then find a happy medium.
No point adjusting the idle mixture much until you have good plugs and wires etc, the timing set right, and a good tight vacuum system.
If the motor runs good at rpm and accelerates smoothly, you don't need a rebuild.
Carburetor is pretty simple inside and unless it's full of shellac or the floats are screwed up (as in they don't float) or the seats have crap in them a carb kit won't change much. Most of those things cause it to flood out.
One problem with old carbs that can give you idle problems is if the shaft that holds the butterfly valves (throttle plates) has worn the bushings (or metal) in the carb itself where they go through it, you can get a vacuum leak there which makes it impossible to get a good idle.
You can gob grease on there (to seal them temporarily) and fire it up to test if that changes the idle.
On the old v8's we would turn it all the way in (gently, you never want to crank it all the way in hard and damage the seat)till it stops, then turn it 3 1/2 full turns out to get it idling then adjust from there.
If you already have it idling, just turn it in till the engine starts to buck, out till it does the same, then find a happy medium.
No point adjusting the idle mixture much until you have good plugs and wires etc, the timing set right, and a good tight vacuum system.
If the motor runs good at rpm and accelerates smoothly, you don't need a rebuild.
Carburetor is pretty simple inside and unless it's full of shellac or the floats are screwed up (as in they don't float) or the seats have crap in them a carb kit won't change much. Most of those things cause it to flood out.
One problem with old carbs that can give you idle problems is if the shaft that holds the butterfly valves (throttle plates) has worn the bushings (or metal) in the carb itself where they go through it, you can get a vacuum leak there which makes it impossible to get a good idle.
You can gob grease on there (to seal them temporarily) and fire it up to test if that changes the idle.