fuel lose at high speeds

I have an all original 85 xj700n. It runs great in city although a little lean. On the expressway or any continous use above 60 mph, the bike will stutter and eventually get to the point I will have to pull over and let the bowls fill again. I have checked the petcock, changed all rubber lines and check for bowl volume and found everything up to par. Am down to thinking the fuel lines in the carbs may be restricted. Is there a way to check or clean the fuel line passages in the carbs or am I dealing with something totally different?

 

It could be float level settings. They should be 3mm +or- 1mm down from the bottom edge of the main carb body.

Could be a glogged gas cap vent.

You might try running some seafoam threw the system also.

 

I would be curious to know if you replaced the fuel lines with the specified formulation type material. If you have your Haynes handy, the Fuel system and lubrication chapter 2 cautions the user to ensure the replacement of the synthetic fuel line with a like material. Otherwise degradation will occur and the debris of that break down will end up in the carbs.

 

Another check, did you have the tank sealed? Sometimes the people sealing the tank do not clean out the fuel spouts properly to allow enough fuel. Obviously, this constricts fuel flow to the carbs.

Rob

 

The bike is all original and a 40 mile daily driver. I replaced the fuel line with an over the counter fuel line from Discount auto. The tank has never been sealed and the petcock is flowing nicely. I had the problem before changing the fuel line and it continued after the fuel line change. I going to try to check the cap senerio on the way home tonight.

 

If you do not already (and for some time) have an in-line fuel filter installed, then I suspect that the screens above the float bowl needles are plugged. I'm amazed how much gets there even with the filter. I have Tygon clear fuel lines, so I don't get any degradation. I think that the screens are so fine that they collect the really fine particles ever-so-slowly. I clean mine at least once a year.

 

Good point Otter, I've not touched mine in a while. "Otter" take a look at them soon!!

 

Wasn't the fuel cap. Drove home last night with the cap opened and still the same problem. Looks like I am pulling carbs this weekend.

 

Still sounds like a low fuel level. Especially since it occurs going uphill. The levels could be set right as per your bench test but a sticking float would cause the same low level.

 

The only thing you should have to check during your tear-down, is to remove the bowls and the float needles and seats. The screen I was talking about sits on top of the brass seat. The screen is pressed into the top of the seat, but I have removed the seat before and the screen was stuck up inside the housing. Had to carefully remove it with a tiny pick. There is an o-ring inside the brass seat that actually makes the seal on the needle. If the needles are becoming deformed (they should be a perfectly flat-sided cone) then they should be replaced along with the seal, seat, screen and gasket. When everything is clean and back to specs, check your float bowl levels as they may need readjustment.

Good Luck!

Michael

 

I am having the same issue with high speed.

 

i posted this comment just before , also on fuel prime to make sure [a test] for fuel starvation symptoms....

then on should really look at "flow" from the tank....

 

Finally got the carbs off. Let me tell everyone now, if you don't have a fuel filter, get one.

I pulled the carbs, removed the needle valve seats and immediately knew why I was having problems. After removeing the needle seats, I had to get a pair of hemostats to remove the clumps of hair and black RTV silicone that was gumming up the works. I had a ball the size of a jaw breaker in each fuel passage to the seats. I am amazed the bike was even running. After seeing this, I started checking everything out. I found the culprit being a glob of silicone someone had greatfully squirted in my tank for me and my petcock screen had managed to vibrate loose allowing it to go strait to the carbs. I never would have known about the screens without everyones help.
Thanks