Fuel Starvation above 6000 rpm on the Iron Butt 550..

[Anonymous]

greetings oh learned collegues....
well, my dear 1978 gs550, survivor of the saddlesore 1000 and countless inexperienced attempts at mechanical improvements has developed a new problem...

Above 6000 rpm, it feels like the fuel starvation.. I checked the routing of the fuel line, and it was kinked around the clutch cable, but I straightened it out and it still exhibits the same symptom

Timing is ok.. Its the Dyna III and the advance marking checks out with the timing light..

Before I go ripping out the carbs etc.. Any thoughts? When I'm on the highway above 6000 rpm I'm a little over 1/2 throttle.. Rolling the throttle back and forth maybe an 1/16th of a turn kinda smooths it out, but it really feels like its starved or missing something above 6000..

Free advice and counsel welcomed.

With Regards
Perpelexed Tim in Northern California.

[Anonymous]

two more things... copmpression is 120+ across all cylinders and the plugs are all a lovely shade of pale...

[Anonymous]

With that fuel line, its possible that it still may be kinked. An old rubber line that has been baking on there ?? years will probably have some memory and tend to return to its previous shape. Possibly....as long as its not the braided aftermarket ones that is. I have a 77gs550 that after I initially got it, on the freeway it would bog around 90mph. I cleaned the tank out and flushed the lines as best I could along with cleaning the fuel petcock. No more bogging.... :P

Did the 550 run the 1000 pretty well? How did it perform? Must have been a blast

[KEITH KRAUSE]

If it is fuel starvation and is more noticable at higher /sustained speeds, it may be a partially clogged gas cap vent or a dirty air filter. Then I would check the vacuum line condition and test the petcock diaphragm to see if it's flowing well. The same amount of fuel should flow out in the 'on' position, as it does in the prime position. Next I would check the float bowl vent passages. I had a small piece of rubber get stuck in my #1 carb float bowl vent and it ran fine until about 65 mph. Then it would start to hesitate and it was more noticable if I was keeping the throttle steady. Dirt build-up could also do this. If it's none of these, then you need to clean out all the fuel passages/jets and check the float heights.

[Anonymous]

Thanks for the feedback. I think I'll start with the tank, petcock, then lines tonight and see if that cleans it up.

re: the 1000. per my other post "GS550 completes Iron Butt" the 550 ran just fine.. I took my Concours, and Doreen took the 550. Two weeks later she did a 1400 mile run through Vegas and Death Valley and it ran sweetly too.. a heck of a long distance bike. I think she's put about 7000 miles on it since December.

Will post results tomorrow.

Cheers, Tim

[HiSPL]

I would most definately check the fuel hose AND the vacuum hose. I had a problem once where the bike would slowly starve itself out of fuel as it heat up. The problem turned out to be the vacuum hose. It would get pliable as it warmed up and kink itself enough to shut down fuel flow :? .
Wierd problem the took a couple weeks to figure out .....

[Anonymous]

well... I guess fuel lines (like wives...) have long memories.. ;-)

I rerouted the fuel line a couple of days ago, and still had the problem.

Took it out for a ride last night and all seemed well again. I guess it took a couple of days for the kink to get out of the line and return to its round high-flow shape.

Thanks for the tips.

Cheers,
Tim