Fuel pump racing, no gas

[madhouse]

Blueskies,
I filled the tank up to about 1/2 way into the filler tube this afternoon and then checked the threaded seal where the steel line connects to the tank (at the top of the tank). I couldn't detect any leakage, I checked again after a short mile drive- and still didn't detect any leakage. It did seem that thread exposure on the male side of that connection (part of the gas tank) was quite substantial - maybe 1/2 - 3/4 inch of threads exposed. I did check the gas line attachment for tightness - and it was snug. I didn't really want to disassemble and reassemble - but perhaps that is worth a try. would you put Teflon tape on that joint?

thanks for the advice,
Rob

 

[madhouse]

I'm also trying to be more observant of conditions when the clacking sound starts. I used to think it was heat related (engine getting close to 190, outside temp over 80) - but i'm seeing it at temps below that as well. Although heat still can be the cause - maybe I put a remote thermometer on the carb bowls? Also I am trying to determine if the clacking starts when the gas level reaches a certain level. Today I noticed it at about 3/4 tank (40miles). Perhaps that can help diagnose if there is a leak in my feed tube inside the tank that is reached at a certain level of tank. I will keep experimenting.

 

[John Turney]

.... would you put Teflon tape on that joint?

thanks for the advice,
Rob

The usual white Teflon tape isn't suitable for gasoline or oil. There is one that is, the one I have is pink, but you need a fuel resistant sealer.

 

[tahoe healey]

Have you tried driving with out the gas cap on?

 

[blueskies]

You probably would not see whether there is a suction leak on that tank fitting unless the tank if full or even over full. If the tank is not full, the pump can draw air there without any fuel leaking out. I did not see the leak until I completely filled the tank.

On my BN4 tank fitting, the fitting is a compression fitting. In other words, the fitting slides on the pipe and tape on the threads will not help seal it. If it is not pushing the compression fitting tightly together, it will still leak. In my case, the fitting was tight, and it still would not seal completely. I could have replaced the pipe from the tank to the fuel pump, but the tank also possibly would have needed a new fitting installed. And those fittings are not a common thread and nearly impossible to obtain; I looked for these in the past. So I looked for an easier fix.

So, instead, I wrapped black rubber sealing tape around the fitting and pipe above the tank, one inch wide tape, the kind that seals to itself and the surface that it is applied to. It sticks to most anything and also stretches a lot as one wraps it around the fitting, adding to the effectiveness of the seal. I have had great luck with that tape for otherwise impossible to seal and difficult to replace fittings, including on heavy equipment. Years later on an excavator fuel system, for example, and no leaks.

 

[DerekJ]

As Tahoe Healey suggests, drive without the gas cap, this will at least answer the question whether a vacuum is being created in the tank due the cap not venting properly. As mentioned, I had exactly this problem which would affect the fuel pump when the fuel reduced to a certain level and the vacuum created affected the operation of the pump resulting in loud clacking.

 

[madhouse]

Blueskies, sorry for not replying sooner, but I wanted to get some good test drives in. I really think the rubber sealing tape around the fitting at the gas tank worked! I used 'flex seal'. I have done some 30min drives in 90 degree weather and the only time the pump got loud was in a fast turn (gas sloshing, i'm sure) - but soon after the loud ticking subsided.

I did try driving with the gas cap off (once I got down to a half tank) before the flex seal solution - and I didn't sense any improvement. But thanks, Tahoe Healey for the idea.