VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 40 With 52 engine.

My buddies engine will not run without the choke pulled out about a quarter if an inch which closes the choke about 1/4. Has a new valve job. We have swapped out the carb, distributor, fuel pump. and manifolds. Checked valve clearance and for vacuum leaks and exhaust restriction. Pulled front cover to check gear train timing. Probably some more things, but nothing has solved the choke problem. Any ideas?

gasket between the manifold and carb base improperly installed.

We have talked about the carb mounting gasket several times. Plus the carb and replacement carbs have been on and off at least 4 times.

So is this an old post revisited or a new post about a new problem?

It seems this was previously discussed, then a 2nd valve job was performed by a machine shop, previous owner also did a valve job ...... I think.

I originally posted on ChevyTalk. Posted here to get some new eyes on it. There is something wrong with it, but we cannot seem to find the problem after changeing and checking all suggestions.

When I said "We have talked about the carb mounting gasket several times", I meant my buddy and I have talked about it.

Did you do the solvent leak test of the entire intake system including carburetor mounting and not find a leak? What is the engine vacuum at idle with choke partly pulled out? Is it steady? Will the engine run at higher speeds with the choke pushed in?

Keith,

I'm over the hill from you on St. Helena Rd. in Sonoma County. It would be nice to know some local Chevy guys who actually take their antiques out and run them. Mine is a home restored '36 pickup that was driven from Southern California to the 1976 National Meet in Colorado Springs and surprised all the trailer queens.

I try to take my 48 out once a week up to Yountville and back to exercise her. This Friday tomorrow night, @ 5 pm there will be a bunch of cars down at the Oxbow on First street. Also the Main Street car show is Saturday August 16th, over 400 cars. Don't know where Saint Helena Rd is in Sonoma.

Did not do the solvent leak test, but change out the intake manifold with a different one and not change. I stopped over today and did the vacuum test. It showed 10" of vacuum with the choke pulled out and the needle was steady. Gage indicates late valve timeing. We checked the timing marks on the cam and crank gear and they are correct. Still have to have the choke out at higher rpm. He is very discuraged as we have been chasing this for some time.

Keith, Have you advanced the timing to see the difference?
It almost HAS to be a vacuum issue now. With the valves being redone, hopefully in a correct manner now, it all points to lean mixture, meaning vacuum leak.

I like unlit, but an opened propane torch being fanned around the intake manifold to cylinder head and at base of carb to intake. Vacuum reading is low, should not be very difficult tto find. When the RPM goes up, with propane, you have found the leak.

Could the exhaust be partially plugged? I've seen rodents fill an exhaust system...

A good point.

If the exhaust is obstructed it will give off a hissing or whistling noise under full throttle. At idle it will be normal.

This is a '40 Chevy with a '52 engine in it? Does it have the vacuum shifter?

So, was this about a '40 with a '52 engine in it, and did you ever figure out the problem?

It does have the vacuum shift. We isolated it. We have not figured out the problem. He has a 60 235 out of a truck and is going to swap it out. We have tried everything suggested here and on ChevyTalk with no luck.

Based on the basic design of the engine, seemingly, the diagnostics to isolate the problem should direct you to the culprit.

I know you guys have given this issue your best shot, just hate to see that engine win in the battle of "you ain't goin to fix me".

I am grasping at straws. Thinking that you need to start at the basics and verify the cam/piston timing by another method. Possibly the cam was not ground properly or is the wrong cam or keyway is cut wrong or timing gear(s) are not marked or keyed correctly.

Can you install a dial indicator on the #1 exhaust valve rocker and profile it? Start with #1 piston at TDC measured by a probe in the cylinder. Does it match the flywheel mark? Record lift at several points as you rotate the crankshaft two complete turns. Compare with engine cam specifications. If that all checks out then move to something else (don't have a clue what that might be???).

Check the vacuum line to the vacuum advance and also check that you have the correct distributor and vacuum advance for the year engine. Also about the carb is it the right one for the year engine? Did you do a compression test (wet cylinder and dry cylinder) I am thinking two or three problems:
(1) vacuum leak from below the choke plate valve to the cylinder head.
(2) wrong camshaft grind or bad cam.

(3) carb has a vacuum passage blocked, or wrong throttle body that won't allow proper fuel thru the jets. What carb do you have? model BV, Model BC or model B (indicated would be a model B with a manual choke)

Is he using the 216 intake manifold on the 235?
How about taking the carburetor off your '48 and putting it on his car just to see if the problem is the carburetor?

I agree with you. I had 3 bad carbs in a row on my 48. 2 were rebuilt units from ct40 and the orig. Installed a used low top Rochester on it and was perfect for over 5 years.

Jim.

I hate to give up on it also. Thought for sure the valve job would fix it, but didn't. He talked to Patrick at Patrick's and he said cut your losses and change out to a 235. Will be a little while yet we check out the 235 he picked up, plus still recovering from the earthquake last Sunday.