Hi all, I’m trying to troubleshoot my flathead mechanical fuel pump, wondered who knows what. What happens is after driving for a while (distance/time varies randomly) the engine burbles and eventually dies, as though I ran out of gas. I can go out, pull the sediment bowl and clean the filter, reassemble, and it starts and runs fine until it happens again. There’s never anything substantial in the bowl, and the screen is never clogged, just small particulates, and not many at that - 1-3 maybe. Anyone have any ideas? I installed an electric fuel pump to bypass the issue and the engine runs great. Definitely in the fuel pump itself. I’ve run a stock rebuilt (by me) fuel pump, and also a brand new Offy pump from speedway. Both have the same problem. Thoughts? Thanks, Mike Sent from my iPhone using The H.A.M.B. mobile app
Bump for the weekend crowd. Also note the gas cap is vented, the fuel tank is new (and clean) and the fuel line to the pump is a new aluminum 3/8 line.
Install a by-pass line after the pump which runs back to the tank. A small amount of flow back to the tank will allow the fuel going to the pump to stay cool. Also, check the routing of the fuel line to make sure it is not picking up heat from the exhaust pipes.
Back in the 60s I had a flathead in a 29 roadster and it acted as you describe. I recall that I had trouble with the pump rod wearing down on my motor. An old mechanic looked at the pump rod and then reached in his pocket and pulled out a dime. He put that on top of the rod and put every thing back together. It ran great again. The rod wore down, but cam was good.
Bill may be correct, back in the day an old boy showed me how to measure the pump rod and gas weld the end to bring it back to correct length.
It doesn't seem to be related to engine temp, as the problem has occurred hot or cold. Hadn't thought of this... and I'll have to look at the routing near exhaust. I think it's far enough away, but will verify. Hadn't thought about this one at all! I did pull the mechanical pump(s) and put in electric, and the problem mostly went away, so that points to this right here. Thanks!
Another good idea is to install a small, low pressure electric pump in the line before the mechanical pump with it's own fuse and switch. Two purposes for this; First it will eliminate a vaporlock problem on a hot day and second, you can use it to fill the carbs after extended storage so the battery, starter and mechanical pump don't have to work so hard. Then of course, there is the day when the mechanical pump quits at the worst possible moment and all you need to do is flip the switch.
So I did actually install an electric fuel pump while sitting outside a NAPA in Indiana... I didn't route it before the mechanical pump, but rather around it. Still have similar problems, though definitely not as frequently. Yup, 100% open. It's actually the fuel neck that vents on my system, and I've verified multiple times that it's clear and working. I wish it were the problem!
Update on this for those interested - I picked up a carb spacer because I suspected I might be getting some vapor lock in the carb itself, as I could get it to run/limp it home using the choke after it started sputtering. Long and short is I think it's fixed! Won't really know until I can drive it around some more, but I've put about an hour on it of around-town driving and no hiccups. Sometimes it's the simple things. And ethanol....
It's a new coil, and works most of the time, so I don't think the coil is the culprit in this one. Could be though, and if it happens again, I'll swap it out for another.
Someone brought this up in another thread I was researching. Definitely looking into it if it reappears.
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