The Stovebolt Site Forums The Shop Area Engine Shop problem with the fuel system

first off i know i have asked this in a previous post, but still have not been able to find the problem. my 55, 235 engine seems to vapour lock in the fuel system and I can't find out why. Confirmed, no fuel in the carb. Have change the fuel pump to a glass bowl type, relined the tank, changed the lines and it still is doing the same thing about half an hour of runnning and it will do it, no fuel in the carb. There seems to be pressure in the line at carb. Any one have any ideas? Have a one barrel carb that I got from napa.

forgot to say, one mechanic told me to vent the top of the tank, which I did and it still did it. With the new fuel pump in place, the last time we took it out, there was no fuel in the pump it self. Had to play around till i got fuel back in the pump, totally stumped to what is causing it. two different pumps, same results.

Check for a hole or crack in the fuel line at vthe top of the tank or in the pickup tube in the tank. It could be sucking air.

You don't say what vehicle you have. Generically speaking I would proceed as follows:
1: Pull the line from the pump to the carb at the carb and turn the engine over. Are you getting gas? If so it's could be the needle valve in the carb sticking closed. If not work backward to the line between the pump & carb.
2: Pull the line & blow through it. Is it plugged? If not work backward to the pump.
3: Pull the pump and manually work the lever with your fingers over the intake & output ports. Is it pulling a vacuum at the intake port and creating pressure at the outlet? If so work backward to the fuel line leading into the pump from the tank. If not the pump is bad.
4: Pull the line between the tank & pump. Blow through it. Is it clear? If so work back to the connection between the tank & line. My 38 had a petcock there that was plugged.

If you are clear to this point it about has to be something in the tank that's restricting flow. Good luck.

Don't know what you're working with.
I know that on the old Rochesters there was an additional filter, a mesh screen inside the carb body itself, where the fuel line screws in. Remove the fuel line, then twist out the filter and check it for crap.
Couldn't hurt to blow some air through all the carb passages while you're at it.
I hope this is of some help.

f63,

I have seen internal filter elements in four barrels but have never seen one in an old single barrel Rochester. Maybe I haven't looked close enough.

Stuart

well the truck is a 46 chevy, but the engine is a 55 235. i have taken the carb apart and nothing seems to be plugged. all the fuel lines have been replaced trying to remedey the problem all the way from the tank to the carb, and still same problem. the fuel pump is brand new, and doing the same as old pump, which, not sure what else to look at. unless it is right at the tape at the tank, just have to keep looking until i can fighure out what is putting air in the fuel line

shmkr,

The contents of the fuel bowl in the carburetor won't allow the engine to run for 1/2 a hour if there were a fuel supply problem. To cause the problem you describe, the fuel flow would have to be experiencing a intermittent blockage. Any broken or partially plugged line would be static...it wouldn't allow the rig to run for 1/2 an hour then shut it down, it would happen consistently and much sooner than that.

Have you made sure the floats are nicely centered in float chamber and that they aren't hanging up and shutting off the flow. You have replaced all the components from carburetor to tank including the fuel pump and still have the exact same problem.

I am guessing your tank has a bottom tap and maybe a small neoprene flex line from tank to hard line. That flex line can become soft and sometimes collapse, cutting off the fuel flow.

A mechanical fuel pump has the ability to pump air as well as fuel. The air exits the bowl vent in the carburetor. Even with some air present, there should be fuel too. I think the key here is how long the rig runs before it fails.

Stuart

If you have fuel pressure at the carb and an empty float bowl there are only the float level and needle valve to play with. If you have rubber line at the carb you can put one of those clear inline fuel filters at the carb this will give you a good idea of how much fuel is getting to that point. Look at the level when it is first running and then when it crashes. If the level is about the same in both cases you have a carb problem. The gas can't get to the float bowl. The float or the needle valve are sticking shut or trash. If the level is not about the same move the filter to the suction side of the pump. If the level is different here you have a blockage before that point. If it is about the same I would look at the pump. You could run rubber temporary lines just for the test. I guess there could be a pump problem that would cause the suction side fuel level to be different but this has worked for me.

Stuart,
I guess its the Rochester 'B' they put on those 230s. Anyway, yeah, that weird plug thing they stuck inside the carb body. I've never had a problem with mine, but watched a guy tear his hair out over a few days working on an old Caterpillar. Finally found out there's a similiar filter in his deisel pump, and it was clogged.
Speaking of deisel pumps, shmkr, my tractor was acting similiar to your truck last month. Run five minutes, quit. Run an hour, quit. Run fifteen .... All the diagnostic stuff I did indicated no problems. Changed the filters, it acted the same. Brought the injectors and the pump to the shop that rebuilt them last year - everything checked out. Stuck in the middle of the field, again, I said: This is rediculous. I tore the entire fuel system apart right there in the field, cleaned everything, extra clean, changed filters, again, bled and rebled the lines, used fresh deisel, and ... started right up and haven't had a problem since. I know this isn't the hard, concrete advice you seek, but that's the way these problems go away sometimes. Take it apart, put it back together.
Also, I like Neilroy's see through filter idea. I run those on both my trucks. Don't know why - I just like to keep an eye on things.