The Stovebolt Site Forums The Shop Area Engine Shop 216 Rough Idle

Purchased 53 3100,it been in restoration for 7 yrs and he gave up.now its my turn,engine rebilt about 6 yrs,I put new points,plugs,cond,cap,rotor
vac advance,a rebilt Holley-Weber carb.Starts good run good on high RPM but Idles Rough.Took comp test,5 cyl at 125 lbs one at 120 lbs,any one have any Ideas?

That is real good compression. You probably have a vacuum leak. Check around the manifold gaskets. Make shure the secondary throttle plate is closeing tight. Check point gap & for bent dist. shaft or worn bushings. Possible a valve clearance too tight.

Wow, all that on a 216, what a deal. Mr.G, your list doesn't say plug wires, but I'll bet you actually replaced them.

I would doubt the five pound difference would be detectable, and although I have never even seen one, the rebuilt carb would be my first suspect.

If you can verify no vacuum leaks anywhere, and the idle smooths out as the RPM's are brought up slightly, it would sound like a idle circuit problem in the carburetor.

I would make sure the wires are indeed new. You could let it idle rough for a couple of minutes, shut it off a take a peek at the plugs..you might find a surprise.

If it is smooth under a load, say lugging it up a hill, the ignition might be ruled out.

A "idle only" problem usually screams vacuum leak or idle circuit problems. Keep searching!

Stuart

Thanks,I have adj. valves 1st on a cold engine and @ and 3 time on a hot engine,new plug wires,new intake gaskets,????????

Maybe the fellow you brought the truck from.Put a mild cam in it.check for vacuum leaks.cracked hoses to wipers,dist.Firing order.timming

Mr. Giant,

Did you get the truck in this condition. Did you do all the work or did the previous owner. Have you ever heard the truck run perfectly...this problem has developed over time??


Stuart

The engine was rebilt and put in the frame,cab installed,and never started,I purchased truck and this is the first it ran in 7 yrs.Now it is only cab and frame,Iwant to have it running good before I go on.

Mr. Giant,

There are lots of good ideas in this thread. If you have done all the tune up stuff correctly and it sure sounds like you have, I think I would concentrate on the carburetor.

I am not familiar with your carburetor, but it must have a idle circuit that is separate from the mid to high speed system.

If it is ONLY a "at idle" problem, as soon as the carburetor is off the idle the engine should immediately smooth out.

Don't forget to look at motor mounts as you indicate the engine is sort of just sitting there. If the engine isn't mounted properly it might tend to hop around and make you think it isn't running right.

Sometimes you can use a aerosol can of Berryman or brake clean to find a vacuum leak. Remember to look at the plugs...they can give you good clues! Don't give up, it's only a 216.

Stuart

Had a similar problem and could not find it until I decided to change the steel vacuum line between the carb and the distributor. There was a small crack in the flared end of the steel line which I could not see until I took the fitting off. Give it a look, won't hurt.

The Weber carb is a two Barrel w/ progresive linkage,I am going to see if the throttle plate on the second barrel is closed at idle,if it is I going to do the brake clean test,Stuart thank for the help along with everone else,What a great site THANKS I post what I find.

While you're looking for vacuum leaks,spray around the throttle shaft. The last 3 carbs I've had problems like this with,it was vacuum leaks around worn throttle shafts. Maybe I'm just gun-shy...
Speed

Low float level?

THANKS Guys,Found Leak on Intake manifold,Put new gasket on,now I have exhaust leak,Took it apart installed new gasket,intake Leak back,took it back apart,insall new gasket intake leak fixed,EXHAUST Leak BACK !. Time to walk away and try another day.

sounds like the manifolds are warped or the head.check them with a metal square.You may have to get them planed down at a machine shop.Use proper torque pattern also

Today i got back to my intake, had a friend hold intake and exst manifold , much easer wilt help.New gasket on no leaks 216 runs great,

Thank every-one for your help.

Don

glad you got it fixed and thanks for the feed-back..Fred