The Stovebolt Site Forums The Shop Area Engine Shop Engine runs only on choke

I recently removed distributor, carb and manifolds and repainted the engine. When I putting it back all my timing was all messed up. So I set the TDC and got the engine to fire up with Choke on - Carb is remanufactured single barrel Rochester carb by auto line. I tried my old carb and new. With either of it, trucks idles only with choke and when I give gas and turn off choke with full gas it runs but backfires little but as soon as I take off foot, trucks turns off

Any suggestions are appreciated

Ganesh

Your timing may be way off, but it sure sounds like a big vacuum leak.

Crenwelge

How do I find out out if I have vacuum leak, I have new gaskets from manifold to carb, vacuum is all tight and fit.One of my mechanic friend who works more on newer cars came over and took a look at it and he set the TDC and fired it up still truck runs fine on choke or half choke and no back fire with choke and when I remove choke and gas back fires. He says the it could be starving for fuel. He said probably carb, but my new carb and old rebuilt carb is behaving same and so he now thinks fuel pump. He thinks since engine didnot run for a year or so fuel pump can be gunked up so he say we should rebuild and try

What do you all think, my opinion was if it starves for fuel,does it back fire and run fine on choke. I still think timing issue

Need some advise from all extreme gabsters.

Ganesh

I'd say timing, maybe you got the dist back in the wrong position? maybe you got the plug wires on moved one position around? maybe the vacuum advance is bad?

Bill

It could be timing, but it sounds like a vacuum leak. You did hook up your wiper hose. I have seen that happen. Or did you possibly cross plug wires. My way of finding a vacuum leak is by putting something like Marvel Mystery oil in a pump oil can, plug the wiper fitting and squirt a little around manifold to head and manifold to carb. If it smokes white, you have found your vacuum leak. You could have a warped intake manifold that was fine until it was disturbed it. If thats the case, a machine shop can true it on a belt sander. By the way, when you timed it, did you have the distributor vacuum disconnected? If you time them with the vacuum connected, the advance may have had it retarded and you are too much advanced.

Crenwelge

My wiper vacuum is all connected but your last sentence, when I time it I had the vacuum connected, so should I disconnect and do the timing? hmmm you got me thinking, I will try to disconnect the vacuum and try

Thanks for your input, Squeeze also thinks timing I will leave the fuel part alone and mess with timing for now

Ganesh

If the timing is good,then all of the above. low float level, weak fuel pump? It's allways the elimination game. It sounds like your getting close. Good luck.

I would put $5 on a vacuum leak.....

I use a unlit propane torch and while the engine is running hold the leaking propane near ( one icnh)the intake manifold...... if the engine races you found a leak....you may need to use a piece of cardboard to shield the carb side of the engine from the fan blast..... leaks can also be underneath the manifold...... I discovered that I had installed the manifold wrong and the rings.... one anyways ..had pinched and nicked itself..... I replaced it... new gaskets all around and the problem disappeared.

One more thing..... try installing a large face cheap after market vacuum gauge near the carb for ease of adjustment..... and make sure the guage is connected to the wiper port of the intake manifold AND NOT to the vacuum line from the vacuum dizzy advance mechanism..... the vacuum advance connects to the brass fitting at the base of the carb..... if you Tee connect the gauge to that line your vacuum readings will be all screwie.....

Keep us posted of your progress.... that is how we all learn..

Bob C.

Thanks Bob, my wiper of the vacumm runs strong, today I will use vacuum gauge and test the vacuum. I never separate inake and exhaust manifold when I removed. The carb to manifold has new gasket. Only thing one exhaust port was not flush but got it surfaced in machine shop and put a new gasket and it is all flush.

Will see what is my vacuum pressure and update

Ganesh

You have a remanned carb. Check the float level.
It only runs on choke. Odds are that the plugs are now fouled. Take them out and clean them or replace them.

Check for leaks around the throttle plate shaft. The normal carb rebuild kits do not include a bushing to tighten those up. Over time, they wear out the holes as they twist back and forth, causing an air leak. You typically can't see it, but try the propane or carb cleaner trick, spraying it right up against where the shaft enters the carb body.

Ok I fixed the problem and it purrs at 500 rpm and no backfires at higher RPM

One thing was had gas pedal rod was stuck a little bit so always engine was running at higher rpms, fixed that and reset TDC, adjusted the timing with timing light not by ear. Then adjusted carb idle and air now it runs good.

Just to add note, 216 motor flywheel and bellhousing timing marks works good for 58 235 motor as I did a swap. They are all same since lot people said the timings may be different but today I set the timing with timing light and marks worked good

Sprayed carb cleaner no leakes around, put the vacuum gauage to wiper and showed in green zone in ~20 inches range.

Thanks for all the support help and you guys are awesome

Ganesh

I had the same problem. I took my carb to a good rebuilder. The power valve (?) was messed up.

Runs great now. Better gas mileage, too.

- Joe

Your problem sounds exactly like mine, I have a 50 3800 with a 1966 250 in it. I rebuilt the engine years ago and it never ran because of that problem. It kind of was put on hold for a number of years til now and I have been going at it hard. Everyone said it was a vacuum leak but that wasn't the case. With help from this web site I started with the basics and did the points , condenser, timing etc. I got it to idle finally without being choked but it still had zero power when I tried to drive it. An old timer said your carb needs to be rebuilt. ( It was a new rebuilt Rochester Monojet) I took it off, got a new carb kit and delivered it to him. Today I was all excited and put her on, fired her up and had gas pumping out everywhere. Upon inspection, he had cross threaded the fuel inlet fitting so bad that the carb is shot. He also removed some plug in the carb body and gas poured from there as well. Now I guess I need to find another carb, And back to square one. Good lick on your project and I havent read all the threads but someone may have told you this already but start with a basic tuneup and leave the carb to last. I will try to find the info that was sent to me and I will forward it along.

Just read the last post before mine and I guess you don't need my help. I will send you my truck and have you fix it for me.