The Stovebolt Site Forums The Shop Area Engine Shop Carb needs choke to run

I have a 235 c.i. with a rochester single barrel carb. The problem I'm having is that to keep the engine running I have to have the choke almost fully closed. I sprayed WD-40 around the base and insulator plate and did not get an increase in RPM so I guess I don't have a vacuum leak. I started with the needle valve turned out 1 1/2 turns.

Does anyone have any ideas to help me get this running correctly? I'm at wits end !!!

It sounds like you've got a main jet clogged, or a very low float level. Be sure you're getting enough gas to the carb by running a fuel pump capacity check. Disconnect the fuel line, run a line to a container, and crank the engine, or run it at an idle if possible. You should get at least a pint in 30 seconds at idle speed. If there's enough volume, the problem is internal in the carb.
Jerry

I'll check the output of the fuel pump this next weekend. Is there a way to check if the main fuel jet is OK or do you just replace it?

If you've gotten to the point of a carb teardown, might as well rebuild it. The main jet usually cleans up OK, but you might have to run a pipe cleaner or something similar through it to get all the crud out. Resist the urge to use a drill bit on the jet! Also, after a good long soak in dip-type carb cleaner, wash all the parts thoroughly in HOT water to neutralize the cleaner, and put a lot of compressed air through all the drilled passages. Carb cleaner just softens the gunk, the air does the actual cleaning. Don't soak any plastic or rubber parts you're planning to re-use. My carburetion instructor a lot of years ago used to say "Put 50 gallons of air through every hole!" Spray-type cleaners are just about worthless, other than for cosmetic cleanup of the parts. Reassemble and adjust, using the specifications in the kit, and it will probably run OK.
Jerry

if the above suggestions don't do the trick, it sounds to me like the idle circuit of the carb is closed and not working. when you close the choke , you are drawing fuel from another circuit to keep it running. either the mixture screw is turned in too far, or the idle circuit is clogged. check to see that the mixture screw is at least 1 1/2 turns out from being bottomed out for an initial adjustment. if it won't run with this adjustment, the carb might need to be thoroughly cleaned. i have not had good luck spraying wd40 around carbs. it tends to leave a film that is great for rust prevention, but it will stick small metal parts that are meant to move freely. good luck

Still sounds like a vacuum leak to me. Did this just start all at once? Did you check the other vacuum lines? Windshield wipers, distributor advance, etc.? No need to tear into a good carb. without first checking all other vacuum sources.

trappers chevy is right. a vacuum test is in order before opening up the carb.

Not that I have money to burn, but I've tried rebuilding Carb's in the past and I can take one that's barely running and by the time I'm finished it hasn't got a chance.
The last time around I got a rebuilt from a national auto parts chain for $79.00 with a life time warranty. Connect 2 bolts, 1 fuel line, 1 linkage and 1 choke cable and we were driving again.

This problem has been this way since I put a rebuilt carb on. What is the best way to check for a vacuum leak? I replaced the vacuum line from the distributor and I have a plug in the hole for the windshield wipers. I appreciate any help.

Oh, your going to get me in trouble this time.

Here's an old Diesel Mech's way... so be CAREFUL.

The Carb's opposite the Distr. & Spark plugs, so when the engine is COLD and running take a can a starting fuild and lightly blast around the base of the Carb. and intake. If the engine speeds up.. you fould it.

Be D&^%%^D Careful.

If the problem started right after installing a rebuilt carb; do you have the old carb which you can reinstall to see if the problem goes away?

If the engine runs on one, but not the other; you have the answer.

If you no longer have the other, then the suggestions concerning vacuum leak checking are good.

A good rule of thumb (in the absense of other knowledge) is (1) compression test; (2) check for vacuum leaks; (3) check the ignition system; (4) check the fuel delivery system; (5) check the carburetor.

In your case, if the engine ran fairly well prior to changing to this carb, I would probably suspect the carb is defective.

Jon.

starting fluid is very dangerous! You can acheive the same results while being some what safer by useing a propane tourch (unlite). If there is a vacuum leak the propane will increase the idle. I recomend getting some rubber vacuum hose and slipping it over the end of your propane tourch then taking the other end and passing it around the intake and base of the carb.

Good luck

Thanks for all the posts. I don't have the old carb and the engine has been rebuilt since when I got the truck nothing worked. The fuel pump and vacuum advance and lines are all new.

Does anyone know if there is a gasket needed on both sides of the insulator plate or only between the carb and insulator plate?

I'd reccomend a gasket on both sides. Also, be sure the gaskets you're using seal completely. if there's any leak at all at the carb base, it will cause the symptoms you're getting. NO gasket sealer, please!
Jerry

If the engine has not run well since the rebuild, it is possible the carb is not the problem.

Start with a compression test (even if the cylinder head is new!).

Next would be hook the engine up to a diagnostic oscilloscope to look at the ignition.

If neither of these tests turn up anything unusual, would then look at the valve timimg, and valve lash adjustment.

An engine needs compression, fuel, and spark; all delivered at the correct time, and the engine runs. The trick is to determine which item is giving the problem. Of these, the carburetor (even a Rochester B) is the least likely to cause problems.

Jon.

I appreciate all the great information. Looks like I've got my work cut out for me. I hope I live long enough toget the old beast running and out on the road !!!!!!!!!!!!!!!!

can you kill the motor by putting your hand over the mouth of the carb while it idles? If you can't you've got a vacuum leak...either external (or more likely) internal to the carb. That's there I'd start.

I can kill the engine by placing my hand over the mouth of the carb. I have it choked almost closed to get it to idle. If I open the choke I need to give it more gas to keep it running. When I have the choke almost closed the throttle raises the rpm and it works well, no hesitation when giving it more throttle.