The Stovebolt Site Forums The Shop Area Engine Shop Will not idle with out choke

I just put a new 235 in my 1950 3100 and I cannot get it to idle or run without the choke. I sprayed WD-40 around the carb and the intake manifold looking for a vacuum leak. Did not find one, I also pulled the carb blew it out with compressed air and checked the float level. All seemed to be fine, I also disconnected the fuel pump and hooked it up to a gravity feed bottle in case the new fuel pump has too much PSI. Sometimes when it dies, I cannot get it to restart for a long time. Does anyone have any recommendations on what the issue may be or what to check?

What do you mean by "new"? Fresh rebuild, or new to you?
An unlit propane torch works better for finding vacuum leaks. Try that before you do anything else.
Where do have the timing set? You need to have the needle on the "BB" everytime the #1 cylinder fires.
It would be cool if you had someone nearby who had a known good-to-go carburetor to try if you don't find a vacuum leak, and your timing proves to be correct.

It could be as simple as a carb adjustment. Is the idle speed set correctly? Idle mixture screw adjusted?

What model carburetor?

Unless you're using a very old can of WD-40, it's no longer combustible, they took the Propane propellent out years ago. The old cans advertised it could be used as starting fluid...new cans don't say that. You might want to redo that test using an un-lit small hand held Propane touch.

Mike B

Spray carb / choke cleaner in your friend in short bursts.

Rochester Model B Hand Choked

New to me, but not long ago rebuilt.

I have tried to adjust Idle screw and idle speed, but it has not helped.

Get a carb kit and rebuild it. Blowing compressed air through it is not good enough. Dissemble, soak parts in cleaner overnight and blow air through all passages. Check and clean out out dried up fuel residue. Pay attention to the power piston - it's probably stuck. When installing on manifold, make sure vacuum port is not blocked by gasket.

Could also be ignition. A weak spark fires a rick mixture easier.

Check point points first.

When you say it won’t restart for a while after it dies, it sounds like it could also be a bad condenser or coil.

Good advise above, and avoid fuel with alcohol additives unless carb is rebuilt with alcohol resistant parts, even then I avoid it in my 59.

I just went through a similar situation with my Rochester B. I chased everything from vacuum leaks and fuel delivery, to spark and timing. Everything checked out. It would start but not idle.

If your Rochester is older, I guarantee there is gunk in there that shouldn't be. Get a rebuild kit. My power piston was completely stuck, and if you're new to these carbs (I was), you would never know the power piston is supposed to move up and down. When the power piston seizes it almost looks like it's pressed in the body of the carb. It should move freely and squirt fuel into the main body. You can hear it working correctly. Aside from the power piston there could also be several other passages gunked up. I soaked mine and cleaned thoroughly with carb cleaner. Also pay attention to the "check balls". If you take apart one of these carbs you won't even notice them fall out. There is a ton of good information on this site, and Mike's Carburetor can help with a rebuild kit.

Also, I can't speak for other people's rigs, but my truck almost always needs a quick choke to start. Even when warm. Otherwise it will crank and crank.

So, I found the vacuum leak it is where the intake manifold bolts into the engine block on my 235. There is not a visible gap but it was sucking in starter fluid on both sides. I have the metal gasket installed that you are suppose to have, and recommendations on how to proceed?

You may have a warped manifold, which would cause a vacuum leak. Remove the manifold and put a straight edge, like a carpenter's square against it and look for a gap. If the gap is less than 1/8 inch, you may solve the problem by using a Remflex gasket. This is more expensive than the stock gasket ($50 vs $10) but it is thicker, 100% graphite and crushable to an extent. It is supposed to cover a gap up to 1/8 inch. Otherwise find another manifold or have yours milled flat by a machine shop.
Kent

Do 235s have alignment rings between the head and the intake manifold (asks the guy with a GMC 6 that does use the rings)? If it is supposed to, make sure it does.

Bill, they do have the rings and they are in there.

I took my manifold to get milled flat today, I am getting a new gasket as well. My dad suggested to put some light coat of silicone around the intake port on both side of the gaskets. Thoughts? Is that a good idea?

If it isn't too late, It would be a good idea to replace the gasket between the intake and exhaust manifolds, then install the bolts and nuts back in loosely, then install the assembly back onto the block without the gasket that goes against the block.
Tighten the bolts which goes into the block snugly, then tighten the nuts and bolts which hold the intake to the exhaust manifold.
Then you can remove the intake/exhaust assembly off and have a good baseline for your machinist to do an accurate milling operation for your specific block.
While doing this procedure, you might get lucky and find that the replacement of the gasket between the intake and exhaust manifold, in addition to leaving those nuts and bolts loose until after you tighten up the bolts which go in the block will eliminate your gap issue.
Use a thin feeler gauge in several locations between the manifold and the block.

Do not use silicone "paste" - if you ever want to paint parts that might get contaminated with silicone.

My memory is failing : maybe some will post a better/safer alternative to silicone paste?

Install any gasket that gets exposed to manifold vacuum DRY- - - -no sealer whatsoever. If the flanges aren't flat enough to seal dry, there's no sealer made that will help. If they are flat, sealing them is a waste of time and effort. Ditto for carburetor flange gaskets- - - -never use sealer of any kind.
Jerry

I got it fixed, I got in intake milled down flat, got a new gasket, put exhaust silicone and fuel gasket sealer on the respective port and no more leak. I wasn't sure I should use sealer on that gasket, but several people told me they always do. Any way it is now idling correctly, thanks to everyone that helped.

We have plenty of people here who give well-intentioned, yet totally wrong advice. Most of them have never made a living fixing vehicles. Good luck!
Jerry

Concur completely.

There were many older carburetors that were assembled WITHOUT body gaskets, as the machining was good enough that sealing would occur.

Especially around anything in a carburetor, the very best sealer is ALWAYS (and I detest that word) no sealer!

Jon.