Hiya folks- first post here. Got a stumper.. I have a '96 FXSTSB 80 Cu in. with a Mikuni carb, Pingel petcock and one of those glass-walled inline fuel filters. Lately, when I get on the bike and ride, I can see the fuel level in the filter drop, to be replaced by air. This happens at random intervals and occasionally gets so low the bike will stall which is hella dangerous in traffic. There appears to be no rhyme or reason to it, the filter will be full of fuel and then 3 seconds later nearly empty...then it will fill back up in the space of several seconds as I watch. The fuel levels will vary wildly back and forth over the space of a minute or so. Sometimes when it gets low it will fill back up if I goose the accelerator, and when it runs dry if I pull over and park the bike it will fill back up again after a few minutes. Shaking the lines and filter does nothing. There are no apparent leaks in the fuel delivery system, everything looks tight and it wont leak if I store it overnight with the petcock open. Nothing seems to help, I can run 30 miles with the filter full of fuel and then it will drain abruptly and stall out. Again, nothing is leaking but somehow air is getting into the line. It does not seem to matter how full my tanks are or what the road conditions are.

In order to troubleshoot I have done the following: Replaced the fuel lines from petcock to filter and filter to carbs. Checked all fuel line clamps for tightness. Checked the tank crossover fuel line for crimps and obstructions (ran a pipe cleaner thru it), checked the secondary tank vent line for obstructions by disconnecting it and blowing through it. Removed the petcock, cleaned the mesh strainer and ran water through it to clear any sediment or debris out of the petcock body. Made sure the inline filter was clean of sediment.


I can't imagine the carb is leaking air backwards thru the line, the filter is 6" below the level of the tanks and carb, and air doesn't flow downwards..and you'd figure if the carb seals were bad it would leak at the carb body. My local fix it shop is out of ideas... any thoughts?

 

Could be the petcoc o-ring that seals the valve?

 

I just got off the phone with Pingel, the tech there said if the petcock seals were bad it would leak fuel, not just air. He had no clue why my bike is exhibiting these symptoms and had never heard of such a thing either. He was nice enough to offer to rebuild the petcock (apparently Pingel will rebuild one for $15 with new seals, which is a great deal considering a new one is $110 range!) but could think of no way that a bad seal would cause that up and down of fuel flow. He did suggest replacing it with the OEM shutoff to see if that would help troubleshoot, which was a great idea but now I need to find my $%^@ original valve....after 10 years...wish me luck!

 

More than likely, it the gas cap not venting properly. Next time you see it happening, loosen the gascap, if fuel instantly fills the fuel filter, you've found your answer! I had this happen on a couple of different bikes over my 40 yrs riding. Newer bike vent thru a one way valve on front of the tank, but yours will have check valve/flap that releases built up pressure in the tank, causing a vaccuum, stopping fuel flow. FWIW Fastrider124

 

Good call.

 

Good thought! I hadn't thought to try that, figuring the problem was somewhere down below... now that I think on it, that makes perfect sense and I'm gonna give it a try as soon as the weather clears up a bit. Sure would beat hell out of swapping out the petcock. Will let you know how it works out. THANKS MUCH!

 

Well, that didnt work. I just ran her 45 miles and when the filter showed low on fuel I unscrewed *Both* tank caps. It did not refill, and then sputtered and died on me a few miles later, WITH gas in the fuel filter. Restarted it, rant it another 10 miles, died again. Weird.

Any other suggestions?

 

OK so ya get air intrusion somewhere. When I have a piece of equipment that is sucking air in the fuel line I will apply air to the tank and where ever it is drawing air it will now leak fuel identifieng the leak. Never done this to a bike but you would have to pinch the line to the carb and use no more than 30 lb of pressure. Not sure if I even recommend this but if it were me I'd prolly give it a try. Hope someone comes up with a better solution or test.

 

Since removing the gas cap didn't instantly fill the line, we have to assume the vent system is working.
As strange as it seems, I think its time to send out your petcock for a rebuild, or disassemble it yourself to check for a plugged up port within. Does it do the same thing regardless of position, ON or RESERVE? Over ten years and the gas quality, it could be shellaced up enough to cause a restricted port, I suppose.
If you decide to try to pressurize the tank, please don't use any more than 3-5lbs of air. Can't think of anything else right now that might help. Fastrider124

 

I know at one time, S&S stongly suggested, that those in-line filters, should not be installed, or better yet, removed.
We do not even carry those in stock any more.
Scott