The Stovebolt Site Forums The Shop Area Engine Shop 235 Only Runs with Choke

My 235 will only run when I have the choke about half way out. Thinking it might be an air leak I sprayed starter fluid arounfd the intake manifold and the carb base but did not notice any increase in RPM.

The carb is a Rochester B

Any ideas of something else I can check?

Spray a little of that quick start between the top & bottom of the carb, all the way around. Those bodies warp, and pull air past the upper gasket.

buckaroo01,

I think you either have a vacuum leak or a plugged passage in your carburetor.

Your detective work with the starting fluid should have revealed a leak had their been one...good work.

Sometimes water can plug an idle port in the carburetor. If you can remove the air cleaner, start the truck and bring it quickly to full throttle, then cover the carburetor completely with the palm of your hand.

Leave the throttle all the way open and leave your hand on the air horn, tightly, until the engine dies.

This procedure will usually clear any blocked passages.

This is a quick easy procedure..give it try and see what develops.


Stuart

Sounds like the old classic "dirt in the main jet" to me.

I may have missed, but I did not see if it had been running or if this is a problem after it had been sitting a while, could be that the old mystery goo has got in the carburetor too or various other things, ....

The problem has been present since I've gotten it running. I purchased a rebuilt carb and the vacuum advance is new and new vacuum lines.

buckaroo01,

Are you indicating that the same exact symptoms exist BEFORE and AFTER installing a rebuilt carburetor!

Have you timed the engine.


Stuart

Sorry, the problem started after I installed the rebuilt carb. The engine was rebuilt and I put on the rebuilt carb and that's when I discovered the problem.

buckaroo01,

So the problem came with the carburetor. Would it be possible to return the carburetor as defective and get another one.

I don't know if a float setting that was way low would cause this problem. Have you adjusted the idle screw to the approximate 1 1/2 turns out.

If you get the engine off the idle circuit..bring it up to mid RPM, will it run without the choke on.

This is a toughie, as Spock would have said, "something doesn't compute".

Stuart

Sounds similar to a problem I had with my 58, 235 with a Rochester B. In my case, I could start the engine with no problems, but once I pushed the choke all the way in it would misfire with an occasional backfire, under load. It would run fine if I left the choke partially out. I played and tinkered with the carb to no avail. Then I checked the timing. It was the timing. I still need to replace the vacuum advance, but the timing is currently set so that I have no problems during my normal driving. I suppose if I were operating under a real heavy load, it would still misfire given the vacuum advance is inoperative.

The carb idle screw is about 1 1/2 turns out. I will check and make sure the timing is correct as someone else set the timing for me.

I think atomark has probably hit the nail on the head. sounds like trash/water in the main jet. Do the power flush thing (hand over the carb while running at high rpm) If it clears up invest in some fuel treatment to mix with the water that may be in your tank. Dont freek out when the carb. sucks you hand like a vacuum cleaner on you cheek.

I repeat, dirt in the main jet! Four screws and the top of a "B" is off look at the main jet probaly has a bit of trash from the fuel tank, you did clean the tank before running gas to a rebuilt motor and new carb didn't you? :rolleyes:

I just whent through this with my 261 I thought it was a vacume leak also. Turned out the timing was retarded.

Obsa, yes I cleaned the tank and replaced all the fuel lines and fuel pump. I'll try the power flush and if that doesn't work I'll check check the main jet for dirt.

If all else fails maybe I'll replace the Rochester with a Carter. If I replace it with a Carter does anyone know if I have to modify the linkage?

buckaroo01,

These rigs ran with Rochesters for a bazillion years. I would leave it on and concentrate on your current problem. As HevyHauler mentioned, timing is important. Have you checked your friends work yet!

You mention you cleaned the fuel tank and replaced all the lines. Has this truck ever run since you've done all these things to it.

Stuart

Atomarc,

I've had the truck running, but the issue with the choke has been present since I got the truck running. I've not had an opportunity to check my friends work yet ... been to busy at work to even see straight.

I'm not saying that it couldn't be a problem with the carb; I'm just saying that it could also be the timing. I spent a lot of time on the carb because I was certain that it had to be a carb problem, afterall it was somewhat cured by leaving the choke partially out. Ignition and carb problems can have very similar symptoms, so don't count out a problem with the ignition system is all I'm saying.

It is a matter of fact that mechanics/technicians condem, adjust or replace the carb "TOO SOON". A carburetor can only function correctly (or be fine tuned) when the:
1. The engine mechanical condition is sound.(correct steady vacuum)
2. The ignition system is adjusted and operating correctly (synchronized with the mechanical timing components).
Always troubleshoot in the correct sequence.
Mechanical
Electrical
Fuel
With the choke partially engaged it indicates that the engine air fuel mix is "over lean" and the choke position is compensating by restricting air or enrichening bringing the mix closer to correct (15:1). The lean condition may be caused by:
Air being drawn into the cylinders at leaks anywhere from the intake manifold, gaskets,or carb, or fittings, hoses, accessories.
Lack of fuel being delivered by the carburetor idle/low speed circuit.
At idle the throttle valve is almost completely closed allowing fuel metering at the idle / low speed fuel ports. If these are clogged, closing the choke valve with cause fuel to flow throw the main jet at idle.
I would suggest:
Measure the ammount of vacuum at idle at the intake mainfold using a gauge. (18-21 HG) steady reading should be observed.
Unsteady wandering needle, or low pulsing indicates leaks.Check all gasket areas and fittings, hoses and any accessory that operates off of intake manifold vacuum.
Ensure the ignition system is tuned and timed.
(proper timing will result in a optimum vacuum reading).
Ensure carburetor passages and jets are clear and clean.(to be done right, dis-assemble and inspect)Carb cleaner followed by low pressure air usually clears anything.

just read your carb issue.
you probably have it fixed by now.
I had the same problem and fixed it by grinding the
intake manifold rings a tiny bit to help the intake fit against the gasket and head completely.
good luck
Jimmy

I was reading your carb issue and notice you had a new vacuum advance. I ordered one from classic chevy and they sent me one but it isn't an exact replacement. The original off of my 235 has an angled bracket to avoid hold down bolt interference and the new one is just straight. WHere did you get your new one and is it correct for the 235 or did you have to modify it.
Thanks
Craig