I've been having problems with getting an air bubble built up in the fuel line as it makes the loop up over the rear axle. Now I know that "ideally" the fuel line should travel in a constant slight downhill from the tank up to the mechanical fuel pump in front, but due to the large Z (actually more of a U) in the frame that was done to get the car to sit low, the fuel line now has to make a big loop UP and OVER the rear axle. The problem is that after the car sits for an extended period, a pocket of air will form in that loop and keep the carb from getting fuel. Once I take an airhose and pressurize the tank while someone cranks the motor, it forces the fuel up through the loop and it starts right up. Originally, I liked the idea of just having a simple mechanical fuel pump up front, but now I'm thinking I need to go with an electric pump out back to force the fuel up over the hump. Anyone else experience this? What was your solution? Thoughts?
Very strange.The fuel lines on all the late models run up over the rear axle,along the floor. The fuel in the float bowl should be enough to run the motor for several seconds. By that time,the mechanical pump should be able to supply enough fuel to keep the motor running. Any chance you can raise the fuel tank? Have you tried a new fuel pump?
Or try a bigger fuel line, or an electric pump to prime with. Right back by the tank, get a pulse pump and shut it off after you're fired up. Don't need an expensive pump your only using it to prime the mechanical. But your problem sounds like a bad fuel pump. Flatheads have the pump clear up on top of the motor and don't have any problems. You could always park facing down hill.
Sounds like you need an electrical pump for back there, to force it thru the bend and keep fuel flowing to your motor.
[ QUOTE ] But your problem sounds like a bad fuel pump. [/ QUOTE ] When I first put it together and got it on the road, I had a nice Holly high volume pump (mechanical) and really had problems with getting fuel. I went back and re-ran the whole line - new filters, etc. STILL had problems. Swapped in a cheep auto parts store pump and it seemed to fix the problem and started great for many miles - even after it sat a while. But now that the car has sat for over a month (doing some body mods) all the fuel has disappeared from the floats down and the pump is dry. I have a glass filter right before the carb, so I can see for sure that there is no gas going to the carb (gas tank is full). I know as soon as I pressurize the tank it will fire, but what a pain. Guess I'll have to add an electric pump right after the tank.
Of course it's possible. I have a compression fitting from the pump to the copper line heading to the carb....I suspect it may be part of the problem - I think the copper line vibrates around and loosens up the compression fitting. I'd like to redo that settup anyway - no copper - no glass filter. I'll try that first.
Sounds to me like you more than likely have an air leak. Not allowing the high volume pump to work completely. I would definetly run a small electric pump at or around the fuel tank, but the line may just be the whole problem. I had a similar experience that was resolved with an electric pump.
Cleatus, How do you know you are getting a air bubble in the hump? Are you running clear tubing? I only say this because your remedy can also remedy other situations, In fact I really think your problem is your pump is losin its prime, you should vacume test your fuel line from your carb back and see were the leak is, or maybe you just need a new pump, I have never taken a pump apart but I imagine it should have a check valve in it or something. other wise based on gravity since a the carb on the engine is higher than your gas tank, fuel would be sucked out of your carb bowl and back into your tank.. Which is what i think is happening in your case. or I may be talking out my ass...
funny five people basicly said the same thing i did in the time it took me to type that, I wanted to come off all smart and shit, like I knew what the f*ck I was talking about
Oh yeah American copper Bad for fuel lines, can crack and cause air leaks I guess english copper is different, they can use copper in there fuel lines
is the tank vented? what i mean is,when you open the gas cap after driving a while,do you hear any air "whoosh" into the tank?
If you show us some pics of the body mods you're doing to your sled, that might also help us figure out what it is
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