Rough Idle

[55 Fargo]

Hi all, my engine seems to idle a bit rough, now that I have the idle speed adjusted a little lower, to where it should be around 550 rpm.

I have tried to adjust the idle mixture, doesn't seem to do much, to correct this.

It idles smooth when cold and the fast idle is in position.

When the engine is warm, I have bit of an idle lope, puff-puff, but there is no hairy cam in this engine.

Perhaps a burnt valve, or a valve that does not seat well, or is sticking.

I isn't so bad that I cannot drive the car, or it stalls, but it is on the roughr side at an idle.

Acceleration is fine, no missing or anything.

Any ideas????

[greg g]

Hook up a vacuum gauge and report its readings, single carb should be steady at about 20 inches at idle of maifold pressure.

also put some oil or wd 40 or such at the intake manifold to block meeting areas. If it smoothes out you have a vacuum leak throught he intake gasket.

[Tom Skinner]

Greg is right. afterwards check your plugs and see if they have a lot of carbon on them.

Take it for a long highway ride say 30 miles at say 55 -60 mph.

That should blow out the crap in there and settle her down to a nice quiet

idle.

Tom

[Andydodge]

Also check the actual vaccum line for the wipers and the wire inside the dissy that goes to the points, they sometimes break

[Don Coatney]

Fred;

For your own piece of mind (and ours as well) you would be best off to completely disassemble your engine and do a complete rebuild. Then you will know that all the internals on your engine are fresh and you will be able to correctly adjust your idle. Until you do so your worn engine will most likely have a rough idle.

[greg g]

With a fluid drive and semi automatic, the idle speed is critical to proper operation. Idle smoothness would be secondary. When you replaced the intake and exhaust manifolds, did you re snug the nuts after a few heat cycles/ Heating and cooling caused them to move a bit, that movement may have caused a slight air leak, leaning the mixture to the adjacent cylinders.

[55 Fargo]

Hi Greg and Norm, yes I do not have a fluid drive, so I could increase the idle speed a bit, it's not bad, just slightly rough at 550 rpm, not a huge deal.

I just thought maybe I was overlooking something.

Greg I did re-tighten the manifold bolts after a few heat cycles, and a few of them were loose.

Don C, you are no doubt right, a complete engine overhaul would result in a smoother better running engine.

I do plan on rebuilding either a 265 or a 251 engine that I also own, someday, but not soon.The 218 longblock will have to do for now.

Yesterday it was close to 80 here, my engine temp ran at 180 or so, on the highway, with a 160 t/stat, I know she will no doubt run hotter when its 90 plus degrees outside, but I can live with this for now, just won't be pushing it during the hottest part of any day.

The engine is actually doing pretty good, considering it's not rebuilt and 57 yo..............Fred