Board index Flathead Power-Technical Questions, Answers, and Suggestions Pans fuel problem

fuel problem

Post Wed Aug 28, 2013 5:07 pm

Posts: 903
Location: Hill City, Ks. USA

I've got a 63 Panhead that acts like it's running out of gas. Fresh engine rebuild, went through the Linkert M74B, new isolation block, new rubber ducky float and new float valve and seat. Float is set as recommended. Steel line running from gas tank through original fuel screen. Two priming kicks, key on, and it starts every time. Engine sounds good. When we get down the road about 8 miles it starts missing , some backfiring through the carb, and just generally acts like it's running out of gas. If we pull over and give it a minute, it takes off and runs OK for a few miles and does it again. When we first fired it up and ran it the first 75 miles it didn't do it. I cleaned the fuel screen, checked for gas flow, took the carb off and looked for obstructions and re-checked float level. checked for intake leaks. It only does it when the engine is warmed up. Any ideas? Thanks!

Post Wed Aug 28, 2013 5:50 pm

Posts: 2717
Location: Los Angeles, CA
Restricted flow thru fuel valve/line or plugged vent in gas cap.

Post Wed Aug 28, 2013 6:03 pm

Posts: 159
Backfiring is mostly associated to ignition. Try another condensor or coil.

Post Fri Aug 30, 2013 2:08 pm

Posts: 903
Location: Hill City, Ks. USA

Chris , I checked both of those. The line flows freely even when hot. I had a new gas cap and we swapped it out with no change.
Wilko, another tech suggested a faulty condenser . I swapped it out this morning with no change. He also suggested I replace the coil. I have another 6v coil in stock and will try swapping it out this afternoon ans we'll see what that does.

Post Sun Sep 08, 2013 9:18 pm

Posts: 903
Location: Hill City, Ks. USA

I finally got some time to work on it after the holiday. We replaced the condenser, again, the coil, and the plug wires. I checked and reset the points also. There was no change in how the bike runs. It was suggested that it could be a valve problem. One fellow said his pan was doing the same thing and it turned out to be weak valve springs. I'd rather exhaust all other possibilities before I go to pulling the heads off again.

Post Mon Sep 09, 2013 5:57 am

Posts: 1688
Location: Interlaken, NY USA

Might be a sticking valve, especially if it's backfiring through the carb. easy to check if it's a valve problem. When the problem strikes again, immediately pull off, and try kicking it over, to check that both cylinders have compression. You'll feel it if one valve is stuck open enough to cause it to misfire. If you still have the hydraulic lifters, I suppose one of those could pump up and cause the problem, don't know 'cause I don't run them. It's possible that one valve got fitted a little tight and is now sticking. Anyway, it's one explanation that could fit the facts.

Post Fri Sep 13, 2013 5:43 pm

Posts: 118
If the steel gas line runs too close to the front cylinder head as they often do it can vapor lock . try running a hose to check.

Post Tue Oct 22, 2013 4:01 pm

Posts: 903
Location: Hill City, Ks. USA

Well, Chris Haynes is the winner of this lottery. It's been sitting a lot because the customer was out on a job and I needed to work on other stuff that generated revenue. What we finally found was that there was a narrowing of the line at one of the bends. When I took the line loose it would flow gas pretty well. The guy that built the biked didn't coat the tanks and there was some rust in them. A bit of rust would back up on this bend and as you went down the road more and more would collect and eventually close off the gas flow. It would finally get to the point that you had no power in the high gears.. We ran a wire through the line and found the build-up. We switched to rubber lines and it ran fine. We did switch back to the steel line, but if that happens again we'll be switching it to rubber permanently.. Thanks for all your help.

Return to Pans