Big Problem. Hit 7,000 RPMs and then steadily drops? Fuel delivery problem?

[HotDogLXA]

Hey guys,

I took my bike, 1980 GS550L, out on the highway tonight and encountered a heck of a problem. When I got it into 6th gear on the highway the bike would rev to 5-6000 rpm then steadily drop off to the point i had to pull off onto the break down lane and start again from 1st gear. It happened everytime I got into 5th or 6th gear. Is this a fuel delivery problem or something else? Should I just bring it to a bike mechanic? When I pulled on the throttle it just seemed to buck and not respond and slowly drop down in rpms.

Thanks alot.

[HotDogLXA]

Also, the bike is topping out at like 60-65 mph. Could it not be running on all cylinders, they are all hot to the touch.

[plucky]

Eeek

Sounds just like when I run out of gas. Maybe your intank filter is plugging up? Has anybody been messing with your carb jets? Way too big or small would cause it to run bad and drop rpms, but not usually die and have to pull over. :-)

[KEITH KRAUSE]

Your problem description suggests a fuel problem.
Any chance the tank is near reserve? Your '80 model has that poor designed petcock with no reserve but I'm just asking in case you have a different petcock with on/reserve/prime positions.
Next easy check is to check the fuel and vacuum lines for any kinking.
Next easy thing to check is the gas cap venting. If clogged, the bike will act as you say.
Next would be any clogged aftermarket fuel filter?
Next would be to check/clean out the petcock.
If none of the above, you may have clogged screens above the float needle valve(s) or sticking float(s) or a clog in the main fuel passage to the float bowls.
You may also need to clean the jets, etc, if the carbs have been sitting or it's been awhile since they were serviced.