The Stovebolt Site Forums The Shop Area Engine Shop Will not run without being choked

I have a 1950 3800 series Chev with an engine from a 1966 chev in it. The new engine is a 250 and was rebuilt years ago (12) as well as the carb. It has never un without being choked. I just bought a new rebuilt Rochester monojet and put it place and the thruck runs exactly the same. I have done all the usual thing to check for vacuum leaks and I don't believe I have any. The fuel pump pressure was 6 I believe. The vacuum is running at a steady 18 until I give it some gas and then it drops but comes right back. I have removed the fuel filter in the carb body and replaced it with an inline filter. The fuel lines are all brand new. Can anyone help me? I have been working on this truck since 93 and never driven it. Would really like to some day.

Did You take the vac reading using the choke? Having the choke on will give a false vac reading less air thru the carb but pulling gas into the cly. Try and take the vac. when there is no choke on ,if the engine will not run than it has to be a vac. leak some where ,it's a pain to put new gaskets on but You can check both the intake and the head surfaces when it's apart.

Pete

First off are thre points & timing set right? If it doesn't have vacuum leaks it might be the float level is too low. I would take the top off the carb & check the float level & metering rod adjustment. You could raise the float level about 2/32. Try screwing the idle jet out about 1 turn.
A better discription of the symptoms would help, like does it idle without the choke? That carb was not standard on a 66 engine, but it should work good but needing a little tayloring. Most reman carbs are not right. You might think about sending it to a carb specialist like Carbking.

Pete, I had the head off last spring and had it checked for cracks and level surfaces and at the same time , I had the manifold checked and everything checked out OK. I did the Vac test with the choke on as it will not run unless choked. All new gaskets since the original rebuild and then again when I pulled the head and manifold off to have them checked.

Wrenchbender, The points are right and is the timing. The carb is new as I figured I screwed up the original when I rebuilt it but even with the new carb the truck runs exactly the same. I sort of figured it must not be a carb problem now since the way it acted was exactly the same with either carb. I have just had the top of the carb off and I changed the float level a bit, and now it will run without being choked for a couple of minutes then just die out. I gave it some throttle and as the accelerator pump kicks in it would run but then just die out.

Now we are getting down to a fuel delivery problem. That model has the fuel line on the bottom of the tank. The cutoff valve could be clogged up or the flex hose swollen. You might try running a hose to the inlet on the pump & putting it down in a can of gas. Run it that way & see if it works. Just because a fuel pump has good pressure it still can be defective. This gasahol we get in the gas now can eat up an old fuel pump.

Since both carbs run the same problem I would think it's a vac leak.

Pete

This past spring, I got under the beast and disconnected the line at the tank. Gas flowed freely all over me! Today I made an adjustment in the float setting. I am sure it is not correct since I don't know what it should be and this float doesn't look like any of the ones I played with in the 60's. Anyway, It idles now without being choked but went I tried to drive out of the garage it had nothing. I had to struggle to keep it running. The vacuum is running at about 16 now when I test it at idle with the choke off.

Pete, Almost every person I have ever spoken to about this problem says the same thing.
"Vacuum Leak" I have tried all the usual tricks and cannot find any leaks.

Could there be a hairline crack in the intake manifold?One thing you can try is take a rag and stuff it into the tailpipe,take another rag and take you're blow off tool for you're compressor put it in the carb with only about 2 to 5 psi.then while blowing in the air feel around for an air leak I use a punk ,one of those things that you use to keep bugs away or just use a cig.you'll see the smoke move when and if there is a leak.

When you're done don't forget to remove the rag from the tailpipe.
Pete

I had a similar issue with 'Tater when I 1st got her running. As it turned out the carb that was on it was for a MUCH smaller engine. The venturi & jetting was totaly wrong for the volume of air the engine needed so it simply wasn't pulling enough fuel & would only run choked. Beautiful idle, but once I got it out on the road it gasped, stumbled, & died in a loud grotesque military manner. It was sad, really. BUT! With some help from the wonderful folks here on the bolt I mananged to track down a factory correct carb and she's run like a champ ever since.
So yeah, my point, I have a point! I'd look up the specs for your engine, see what carb is supposed to be on there, and work from there.

If you have a solid idle now, to verify your manifold leakage you can use carb cleaner spray. Just spray short shots at all the suspect points & if there's a leak it will draw it in and the engine will stumble. Super simple way to find manifold leaks, MY preference anyway.

If it idles smooth with 16 in. of vacuum I don't think it's a vacuum leak. Do a fuel pump volumn check. Disconnect the line from the carb & put a cup under it. Start the engine . It should fill the cup in 20-30 seconds. What about the filter inside the fuel inlet fitting? If you give me the carb # I can get the specks on it tomorrow. Usually the float level is 1/4 in below the top of the bowl to the top of the float. With the throttle closed push down on the metering rod holder. It should be 2to 3/32. from the top of the bowl.The metering rod spring should be on top of the holder. Some oddball aftermarket needle seats have a tiny screen in them. I just had one of those throw me recently.

Pete, Early on in this project I had the radiator re-cored and then I just left it sit in the garage. I live in the country and we have lot's of mice etc. around. Well the buggers made quite a nest in my new radiator. After having overheat problems along with the carb problems I was a bit dismayed. I took the radiator in and had it cleaned out. The shop that did it said it was the worst they had ever seen. Well, I have heard that statement a few times in my life but they did get it cleaned out. Now I have read that a blocked exhaust might cause the problems I am having. Sin ce the truck has just been sittin g for years I began to think that maybe they had made a nest in my muffler since I never plugged that. I pulled the muffler and it is clean as a whistle. Scratch that idea. Unrelated, All my newly upholstered seats are now missing all their new stuffing and it has been relocated to my camping trailer silverware drawer.

Wrenchbender, Someone down the line told me to dump the filter in the carb body and replace it with an in-line filter so that's what I have now. This afternoon, I was tinkering with her ("her" for a good reason) and I looked at the filter and it was empty. I thought "what next?" and I was really upset till I realized it was out of gas! Off to the gas station.