A confusing fuel problem

[murf]

I recently started a thread " baffled about baffles " in this column. Now that I'm pretty sure that fuel contamination is not the problem, I have a question. The bike will run well after cold/warm start until I ride 3-5 miles at hwy speeds. better than 50% of the time if I fill with fuel the problem will go away for a short or not so short time. What could filling the tank do. I would have bet that trash in fuel was the issue, but it isn't. Fuel is clean from tank to float bowl. ?

 

[VMGR252Nav]

I am by no means an expert but I did have a similar sounding problem with my lawn tractor, just not at highway speeds . Turned out that the gas cap was not allowing air into the tank as gas was being used and it created a vacuum. Not sure how the bike tank is vented but if no air is getting in to displace the gas going out I would imagine similar symptoms.

Apologize if completely off the mark but will throw it out there anyway...

 

[BUBBIE]

I am by no means an expert but I did have a similar sounding problem with my lawn tractor, just not at highway speeds . Turned out that the gas cap was not allowing air into the tank as gas was being used and it created a vacuum. Not sure how the bike tank is vented but if no air is getting in to displace the gas going out I would imagine similar symptoms.

Apologize if completely off the mark but will throw it out there anyway...

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bseal182

You are probably "right on" with this thinking... Good Call ..

The simple way murf Just Re-Stated the problem, this is PROBABLY the answer... I think it has been suggested before in the other thread IF NOT murf,,, ?Have you tried to leave the gas cover Loose enough to get air around the cap.??? IF you Have tried this it May be the vacuum line loosing vacuum and shutting off the fuel...or as suggested before ALSO the valve on the tank IF it is Vacuum controlled, might be bad...

signed....BUBBIE

 

[Breeze3at]

I recently started a thread " baffled about baffles " in this column. Now that I'm pretty sure that fuel contamination is not the problem, I have a question. The bike will run well after cold/warm start until I ride 3-5 miles at hwy speeds. better than 50% of the time if I fill with fuel the problem will go away for a short or not so short time. What could filling the tank do. I would have bet that trash in fuel was the issue, but it isn't. Fuel is clean from tank to float bowl. ?

Filling the tank = higher level. Your petcock has a micro screen surrounding the pickup tube. Maybe the screen is clogged, and a higher fuel level allows more surface area for fuel to seep in?

 

[Jack Klarich]

Agree with Breeze and Bubbie, I would add how is your fuel line routed? Not getting hot and causing vapor lock? We saw this on many Shovel motors years ago running the fuel line between the cylinders:s

 

[glider]

I'm going with the gas cap not venting too. Try loosening the cap when it acts up again and see if that cures it.

 

[HDDon]

I am trying to remember if your model FXR has a vent line at the top front of the gas tank. If it does this can become pinched and you will have the problem you speak of. Cracking the gas cap a little will tell you if venting is the problem. The screen on the petcock could also be the problem, it clogs from the bottom up so the top of the screen is allowing enough gas when you fill up. If you still have the vacuum operated petcock these can give you the problem your experiencing.

 

[murf]

OK, first the fuel line is run between thr jugs below the tank, but has been that way since I bought it and the problem is recent. ? How would be the best routing. ?
Second, I pulled the tank and drained it, drained the fuel through a rag and got no contamination. Petcock was clean with nothing inside micro screen and blew through it with nothing coming out. Fuel was clean all the way to the float bowl. I haven't tried the loose gas cap theory, and this could be the problem. I will try the loose cap tomorrow and report. Thanks very much to this forum for concerned responses intended to help fellow bikers. Proud to be here. God Bless.

 

[Breeze3at]

Due to petcock and carb. inlet positions, you don't have any choice on fuel line routing. IF it is a vapor lock (and I doubt it is), crumpling tin foil around the line between the cylinders can alleviate boiling the gas.

 

[glider]

I recently started a thread " baffled about baffles " in this column. Now that I'm pretty sure that fuel contamination is not the problem, I have a question. The bike will run well after cold/warm start until I ride 3-5 miles at hwy speeds. better than 50% of the time if I fill with fuel the problem will go away for a short or not so short time. What could filling the tank do. I would have bet that trash in fuel was the issue, but it isn't. Fuel is clean from tank to float bowl. ?

The early FXR's had a main breaker problem that would kill the engine when it was hot. Possibly filling the tank gives the breaker time to cool off. Try replacing the breaker with a new one. They're cheap to buy and observe the polarity of the terminals (gold and silver) and wires on them so you don't install it backwards.

The trick here is to test the breaker with a test light on both terminals when this condition occurs to validate the condition if it is open or closed.