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Stumped the mechanics

My 1950 Jeepster has a 6 cylinder 161 flathead. It was always reliable, but recently wouldn’t start. After I tried the usual tune ups and carburator rebuilds with no effect, it was hauled to a gas station. After 8 weeks of them trying everything from a new fuel pump to more carb rebuilding, I asked them to bring it back. It now starts great and will keep running while the choke is manipulated but then after a couple minutes it dies. The longer it is tried, the shorter the amount of time it will run. To keep it running, the RPMs must be high. My question, could it be the intake manifold? It seems tight, but there is a black goo on the edges of the gasket. I’m wondering if it becomes porous as the engine heats up. I would so appreciate any help! I’ve had this car since 1975 and really miss driving it.

Have you checked compression in each cylinder?

Check your fuel line from the tank to the fuel pump. You may have a hole in the line where you are sucking air. I had the same problem with my 1978 Oldsmobile Cutlass a couple of years ago. lt turned out that a section of neoprene fuel line back by the gas tank had deteriorated. Today’s fuels with ethanol are rather hard on fuel systems of the 1950s.

A vacuum leak is very likely the cause. Spray carburetor cleaner around the base of the carburetor and if there is a leak the idle will change noticeably.

Thanks for the replies! I meant to add that I checked the compression, and five cylinders were good at around 100 psi. One was low at about 80, it got better when I poured in some oil. I thought fuel too, but I have pulled the top off the carb after it died and found it full of fuel! At first I was sure the problem was no air getting into the tank, because after running fine for 5+ minutes, although only at high RPM, it would sputter and die. Then the next run would be shorter etc. I left the cap off the tank, and checked the vent in the fuel bowl. Good carb vent hole (it is huge) and no effect leaving the cap off.

Have someone who really knows carbs rebuild yours…It sounds like the whole mid-range metering circuit is plugged up…Also, do a fuel pump pressure/volume test just to rule that out…

With the compression that low I’d think about rebuilding the entire engine. I’m not saying that’s what will keep it from running. Its just that if you like it that much maybe its time to just reset the clock on all of it.

100psi is not that bad for a flathead…7 to 1 compression maybe…

With a vehicle THAT SIMPLE…it should not be able to stump any “real” mechanic…I mean this is the basics folks…Not many mysterties needing solved here. I think you need to find another set of “mechanics” If you were near me I’d have you up and running in a Jiffy…not a boast…just a fact

Blackbird

Sounds like a choke problem. Check choke operation and throttle plate operation.

How was the carburetor overhauled? Disassembled, soaked in carburetor solvent, thoroughly washed, and blown out with compressed air or was it a can or two of aerosol carb cleaner and a prayer?

Sounds like a carburetor problem or a giant air leak to me. The fact the carburetor float bowl is full of gasoline doesn’t mean much if internal passages are clogged up.

Check the carb. Look for the proper float level. Check the float itself for leaks, it may have fluid in it and therefore not “floating” correctly. As the car warms up it needs a less rich mixture and a damaged float or improperly high float level could be allowing too much gas and a too rich mixture.

Are you sure it is a fuel problem? The shorter run time as it warms up sounds like a failing coil or even a bad condenser. If you have a timing light hook it up and point it toward the driver. See if the spark dies before the engine stops turning.

The carburetor may not have been properly rebuilt. The revs are so high to keep the car running that I doubt spraying carb cleaner on it would change the engine speed. I don’t know that the carb was properly rebuilt, and the mechanics did still think it was the problem. I like the timing light idea, clever! I’ll try that then the manifold gasket then go back to the carburetor. Then I’ll see if a rebuilt one is available or go through it again myself, this time soaking the parts in carb cleaner. I had replaced the coil, having read it could be heat sensitive. Thanks again for the responses.

Mechanical choke? I would carefully remove the idle mixture adjustment screw (not the idle speed screw) and spray some Gumout into the hole. When you do this, open the throttle all the way and look for the spray going into the carburetor while spraying the Gumout. It should also be spraying a little into the fuel bowl.

When that passage is clear, clean the tip of the mixture screw, insert it and run it down carefully until it just hits bottom. Do not crank down hard on this, you want it to just touch bottom, then backout 1.5 turns. start the engine and when it warms up, adjust this screw for best idle.

Hey I was thinking about his post yesterday and I thought about everyone looking into the carb…but I wanted to mention one simple but SERIOUSLY OVERLOOKED ITEM…Aside from the basics, and my idea here is still basic…YOu have Compression, Fuel, Spark…Right? Right… Guess what else I have even found myself overlooking?..THE EXHAUST…The engine CANNOT breathe…if IT CANNOT EXHALE…

I tell you I went thru the ringer one day…just listening to what the other guys told me they had done to a vehicle…and we couldnt get her running…I went thru ALL the basics…over and over…and got so mad…because everything was in order…and then…on my last gasp…my last attempt at getting this engine running…I said…out loud…the only G^% Da^% thing I didnt look into was the exhaust!!! Me and my buddy just stared at each other after I said that…and started laughing…My buddy said no way, no way…and I said…“IM UNBOLTING THE DOWNPIPE AND I BET SHE STARTS UP AND RUNS”

Wouldnt you know it? The cat was clogged…but while we were working on the car…since it wasnt running and I never heard it run, nor had any history with the car…well…it seemed normal to just check the regular suspects…so I did…over and over…and when the engine was turning over…it gave no telltale sign of any exhaust issue…BECAUSE IT NEVER RAN FOR ME… SO after a while…and this isnt normal for me…because I usually think of these weird things…and even go so far as to sniff a tailpipe or two to see if the vehicle is flooded or not…but this time…I guess I got distracted …the beers didnt help but… It just came to me at one instant…THE EXHAUST MAN…See if it smells like fuel…DUH…like I said I have done that before…just that day/night I seemed to forget to do that…and lo and behold…that was it… SO…the basics man the basics…and the exhaust is in that group…I just missed it that day…I guess two pages got stuck together in my mind and when I turned the page I skipped one without realizing it…Happens to the best of us.

Check to see that she can breathe out the exhaust pipe…just for me… Now I am not saying that is your issue…I gues I included this snippet to remind you about the basics…and this car is nothing but…

In your instance maybe she is sucking air after it warms up and leans out…thus the need for a choke after it has warmed up? Or you have some internal passageways clogged up in the carb…does the mixture screw make any noticeable changes when you adjust it? Have you tried to WILDLY ADJUST IT to see if you get any variance? Sometimes you THINK you are making an adjustment with the screw and its passageways are clogged up internally…and you get no adjustment at all that way… I usually buy me a gallon of the carburetor Dunk stuff sold at Pep Boys and Auto Zone…it looks like a gallon paint can…you put your carb body and all small parts in the parts basket inside the gallon and leave them be for a day or two…they emerge in LIKE NEW condition… and the passageways are clean too…just blow out with air… REMEMBER DO NOT PUT ANY RUBBER PARTS IN THE SOLVENT…OR THEY GO BYE-BYE’s… Just a thought

Blackbird

Thanks again everyone for the great suggestions. I did think about the exhaust, but it seems to be blowing strong. But there could be something blocking up with heat. I wondered if the plate that diverts exhaust gas to heat the intake could have fallen off and be blocking the exhaust. I’ll find that out when I pull the manifolds. Unfortunately I am traveling off and on for a few more weeks and won’t have a chance to check all these things for a while. But I will definately post with the results! Thanks again.

By the way, the car has a REALLY old exhaust system. So maybe that is the problem. I have new pipes and a muffler from years ago when I went to the Jeepsterman in New Jersey with a pickup and got systems for this car and the one I’m restoring.

I removed the manifolds, found the intake areas of the gasket hadn’t been leaking. I blew 30 psi air down the exhaust pipe, it flowed freely. I disassembled the carburetor again, removed the jets and orifices, and soaked everything in one of those gallon cans of carburetor cleaner with a basket. I have had the can forever, but it still smells strong. The engine stills just fires some while cranking. I had tried the timing light suggestion, but it wouldn’t light even with the button taped down securely. I thought maybe there was high resistance in the ignition circuit (6V system) and jumpered to the battery but that didn’t help. I started playing with the timing. It seemed more advanced helped, but I ran out of adjustment (see attached photo). I thought maybe the timing chain was stretched, but the engine has gears! When I first got the car from the garage, it would run great at high RPM for a few seconds and then die. I thought, well the chain must be warming and stretching further so it only runs briefly! Oh well. Right now with the mark on the pully weight at the pointer, the points seem to be at the correct stage of starting to open. But as I said, more advanced seems to help. Should I try to jump a distributor drive tooth engagement to try to get back in range on the adjustment off the vacuum advance? Any other ideas? Thank you again for alll the great suggestions so far!