gs1000e running odd

[brucegoetz]

I have a 1979 GS1000e that has had an engine rebuild and currently has a vance and hines 4 into 1, it also has 750 carbs which have been redone also. my problem is the bike will run good for about 19 miles then it acts like it is running out of gas, when the bike sits for awhile it is good again, I thought it might be a vaccum problem but ruled that out with trial and error, so I dont believe that is my problem, i was wondering if 750 carbs could be my problem but am not sure, since they are so simaliar to the 1000, if any one has any ideas please let me know, I have put new plugs in and they are fine not running lean or rich. Also I have put a new petcock on the bike so I dont think it is a fuel delivery problem either, if any one has had any simialar problems and or have any ideas please let me know, thanks

 

[tkent02]

Just a WAG, gas cap vent clogged???

Just a WAG, gas cap vent clogged???

seems like it might take about 19 miles to suck just enough gas out so that the gas won't flow. Try cracking the cap. Just a WAG.

 

[Kaiser Sosei]

Kink in the fuel line? i had that happen once, I had put the tank back on and didn't notice the line was getting kinked. I didn't get 19 miles though.

 

[flyingace]

Maybe the vacuum diaphragm in the petcock is marginal, and can go for so long before it loses ground. Try running on prime and see if it goes > 19 miles.

 

[Jethro]

Is there a fuel filter installed on the bike? Do you have the correct 5/16" fuel line installed?

 

[KEITH KRAUSE]

Could be any of the suggestions above. You say you've ruled out any vacuum issues. What did you try? How about venting? Also, are the two floatbowl vent lines clear and not kinked?
If not venting or vacuum related (easiest to check first),then I'd suspect the float valves have dirt or ? clogging their seats. Makes sense and even one carb clogging will cause your problem. If it really is a fuel flow problem, the bowl(s) could be running too low because of a partial clog. Then, after sitting several minutes, the fuel still in the line and carb passages could have time to drain into the bowls and it would help temporarily. Most clogs effect things before 19 miles though.
If you have good finger dexterity you can remove just the bowls and take out the float pins/floats and check/clean the valves and their seats and the passage to the seat. Turn the petcock to prime and help flush any debris through. Use some rags for spilling and to catch the small valves if you drop them. Keep each valve with its own seat. It's a little tricky to keep the valve up inside its seat and install the float and pin though.
If you have a fuel level gauge, that would be easier. After the problem begins, immediately place the bike on the centerstand and hook it up and check the levels. Depending on how fast you are, you may have time to check only one at a time, since the fuel will be draining into the effected bowl(s) as you work.
Another thing you can do to check levels is drain the fuel from each bowl by removing the bowl drain screw. If you do it quick enough, you may see one or more fuel amounts significantly less from the others. If you find one for example has less fuel than the others, I would do the cleaning/check I decribed earlier to that carb and re-test. If dirt is found in one, it's probably a good idea to check them all though.
When exactly does it feel like it's running out of gas? After you try to idle after 19 miles or does it happen as you're cruising along?