Rough Idle

[JohnnyC5]

= rough idle. Spray vacuum pump oil on the manifold gasket seams -- not carb cleaner. It stops up leaks for a few minutes and smoothes the idle before the oil gets sucked in and burned. Rough idle, imho, is rarely a vacuum leak in the manifold and carb mount. Whoever mentioned refreshing the vacuum lines is right -- but sometimes it's one bad plug wire. Little bit of arc-over through the cable insulation, little bit of miss. You can usually see the spot at night when lights are out.

I just did plugs and plug wires you think i might take em out and check em. is it possible to have bad wires out of the box. ill look for the vacume pump oil at auto zone and give it a shot. Throttle pivot sleeve bearing, where is that located and how do i check it. I am 100 percent sure on changing the carb i think camoit is going to come down and give me a hand (if i am lucky ) when i do it, get rid of the vacume line and remove that problem from the situation.

[manorchurch]

I just did plugs and plug wires you think i might take em out and check em. is it possible to have bad wires out of the box. ill look for the vacume pump oil at auto zone and give it a shot. Throttle pivot sleeve bearing, where is that located and how do i check it. I am 100 percent sure on changing the carb i think camoit is going to come down and give me a hand (if i am lucky ) when i do it, get rid of the vacume line and remove that problem from the situation.

Okay, it's probably not the wires. I had one once that would idle perfectly, then start to miss at about 2800RPM. Drove me crazy tracing through fuel delivery system, and finally found the #3 plug wire was breaking down internally at higher RPM. Camoit is right about the EGR ... something I don't think of because I spritz the EGR when I change oil.

The carb throttle plate pivots inside a sleeve bearing that's part of how it mounts inside the carb throat. An old carb can have some degree of wear in that bearing, and a little bit of outside air gets piped in, causing a little "boop" as the idle circuit unbalances every few seconds. It's annoying, but harmless - the sort of thing that finally convinces you to buy the Weber. Or go MFI :-)

I have heard that old-age failures in the jet valve assemblies can cause enough in-the-cylinder mixture irregularities to make a miss. Solution: non-MCA head. Don't go for that "put a bolt in the jet-valve hole" treatment. I still think it makes hot spots that are worse than the disease.