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Discussion Starter · #1 ·
I am bewildered, this will be long but I am going to try to include everything. my 91 FXRS, is completely stock and runs great until it doesn't. It runs well at low speed ( under 50 mph) but when I get on the highway it accelerates normaly up to 75 mph and then runs out of gas. I pull in the clutch, keep it running and pull over. after a short time it's fine so I ride around , go back to the highway and it does it again, everytime. I bought this bike last fall, it has 42,000 and had belonged to a woman and she had changed virtually nothing. the gaskets were leaking and it had a bad front motor mount. I took it to my indi shop that has a very well trained mechanic with a lot of FXR/EVO experience. He removed the heads and jugs, Said it looked like it was leaking air at the intake manifold, I had the heads and jugs powder coated, he the put in new rings, lapped the valves, reassembled everything and it ran great, until you get on the highway. He then rebuilt the carb, changed the fuel petcock. replaced the fuel line, and it run great, until I got on the hiway. I thought it might be the gas cap not venting so when it stalled I loosened the gas cap. no joy. after I restarted it I left the cap loose and rode a 5 mile circle and pulled back on the highway same thing. Has anyone had this experience? I need to get this sorted out, I love riding this old bike. So hopefully someone here can provide so insight.
Thank you all in advance.


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I'd double check fuel flow out of petcock and carburetor fuel valve as well as float for leaks and height setting.
 

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It's them whore whips on your handlebar grips. LOL
Maybe there's some sediment in the bottom of the tank and petcock. Also wonder if it could be electrical, ignition get's hot and you lose a cylinder until it cools some. Had that happen years ago with a Crane HI 4.
 

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Two good ideas there, and I lean towards clogged gas filter or petcock screen. Get rid of the second filter (if there) if petcock screen is where it should be.
 

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Is the fuel line from the petcock to the carb touching a cylinder or a head? Is it mount up to the frame between the heads? Is it hanging down between the cylinders and resting on the engine case? If it is touching any of these you are probably having a vapor lock issue. The fuel line should be mounted up between the heads to the frame.
 

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Petcock screen could be plugged partially up. Saw one that was installed with the wrapping still on it. Or, some 91's had a tank vent system on them. The little valves in the line go bad. And if its a vented cap tank, it could have a non vented cap on it.

Now since the carb was worked on, there is also the issue of float drop. It may not open enough to feed the carb at speed. And just for shits and giggles, make sure the slide moves freely.
 

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Discussion Starter · #8 ·
The mechanic started off thinking it was electrical and I was thinking not enough fuel. Now we both think it is a fuel issue. I was thinking blocked vent but now I think the carb is screwed up,, maybe. it is something that is predictable though. The bike is 30 years old, 42K but not beat up. I don't believe it is sucking air anywhere. It comes back very quickly when you stop and idle, I don't know if an overheated electrical component would cool off tha quickly.

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Discussion Starter · #9 ·
If there is a Vacuum operated petcock still there, then you found the problem.
I have changed the petcock, even though it had a newish one one there, and I ordered a new one but it is not here yet. How can you tell if it is vacuum operated?

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1989 Honda 350 quad: Bought new, ran it 20+ years with the petcock in the 'Run' position.
Had to switch to 'Reserve' on a hunting trip. Wouldn't run. A quart of rusty water in the bottom of the tank.
Run my bikes and quads with the petcock in 'Reserve' all the time now. No problems.
 

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Is the fuel line from the petcock to the carb touching a cylinder or a head? Is it mount up to the frame between the heads? Is it hanging down between the cylinders and resting on the engine case? If it is touching any of these you are probably having a vapor lock issue. The fuel line should be mounted up between the heads to the frame.
Whhhhaaaaaaaaat?! Who is this? springer? I must be mis-reading the date on this post.
 
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Discussion Starter · #14 ·
I dont have a vacuum operated petcock but the fuel hose is not tied to the frame, I don't suspect vapor lock because I thought it is associated with warm weather and we haven't had that here yet it has been cool when I have been riding, usually 50° 60°
The tank has been off and drained of any leftover crap during the ring job. The mechanic jetted the carb a little richer when he was working on it but that didn't seem to help. It almost seems like I am circling back to an ignition issue. I could get a new one and if that doesn't help at least it will be there when I do find out what the oroblem is.
Also it seems to run ok in a lower gear at higher rpm than in 5th gear at hiway speed.

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I dont have a vacuum operated petcock but the fuel hose is not tied to the frame, I don't suspect vapor lock because I thought it is associated with warm weather and we haven't had that here yet it has been cool when I have been riding, usually 50° 60°
The tank has been off and drained of any leftover crap during the ring job. The mechanic jetted the carb a little richer when he was working on it but that didn't seem to help. It almost seems like I am circling back to an ignition issue. I could get a new one and if that doesn't help at least it will be there when I do find out what the oroblem is.
Also it seems to run ok in a lower gear at higher rpm than in 5th gear at hiway speed.

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Take a picture of your fuel line between the cylinders and post it.

I'm not saying it is vapor lock but I wouldn't rule it out just yet. Vapor lock has nothing to do with the weather. Vapor lock is when the fuel line is heated up, usually from being in contact with something very hot like the heads or cylinders. I've seen many many times where people run a fuel line and it rests up against the cylinder or goes all the way to the V in the cases. Once it heats up the fuel vaporizes at that hot spot and barely trickles by if you are lucky. Under greater loads, like in 5th gear when it demands more fuel you can run the bowl dry. When you stop and check it out, the fuel trickles by and fill the bowl. It's a viscous circle. This is very common when people add an inline fuel filter. They usually rest it directly between the cylinders and being metal or glass they heat up even more.

Again, I'm not saying it's your problem but I'd make sure it definitely isn't the problem. The fuel line should be inches away from heads and cylinders. That's why the factory ties them up high. On older bikes they are almost always hanging down.
 

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Discussion Starter · #17 ·
couple photos of gas valve and hose., there is a ribbed cover over the gas line, and there is a crack in the elbow leading to the float bowl. the slide moves freely and the accelerator pump is working pretty good.


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couple photos of gas valve and hose., there is a ribbed cover over the gas line, and there is a crack in the elbow leading to the float bowl. the slide moves freely and the accelerator pump is working pretty good.


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Whoever you had do that carb for you, you need to find someone else. That fuel nipple is getting ready to give you a bad day. Not sure I would trust that hose either, looks pretty old. And after being soaked in fuel, then drying out repeatedly, they with start shedding particles internally.

That fuel valve looks original. No Vacuum.
 

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Discussion Starter · #20 ·
the petcock was replaced because the one on at the time came out the bottom and it was changed to one that exited out the side to route better. This was an experiment and a used petcock was all that was available at the time. I agree the carb work is not up to standards. I have been looking for another guy but I guess carb guys have just about all died of old age. I like to keep things original as possible, if possible.

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