Just bought my son a 98 600F3 a few weeks ago. We knew it had a running problem at higher rpm's & figured that was ok for him as it is his first real bike. We also have been charging the battery almost everyday. Today i looked at it & it wasnt charging. I put a new regulator & fixed that problem, so i decided to see about the power problem. All i know about the bike is it has a 2 brothers exhaust, & supposedly the engine was rebuilt?
What it does is, it runs strong through the lower gears, but in 5th & especially 6th gear it doesnt go much over 6k rpm. You can roll off the throttle & ease back into, but it still wont run right. The fuel pump was replaced with what looks to be a Mitsubishi fuel pump? When it starts bogging down in 6th, if i choke it some, it doesnt do anything for it, so not sure if it is a lean condition, as choking it some should help it.
Anybody have any ideas? I hate to take it to the shop & spend a fortune, as i have already spent 350.00 for a rear tire, regulator & oil & filter for the bike.

 

Is it running rich? ie: black smoke out the pipe. My thought is maybe its jetted way wrong, or even a carb problem. Any more history on the bike, when motor was built? how many miles now?

 

No black smoke out the pipe. I amthinking it is running lean. I guess i need to take it apart & see what jets are in it. Any ideas on what stock jets size are? What size should i try. A local place said about 125.00 for the complete jet kits just for parts.
The bike has 34,000 miles on it. have had it for almost a month. The kid we got it from didnt seem to know **** about it & didnt have it long.
I hate having to always fix someone elses mistakes or problems. Welcome to the world of used bikes & cars.

 

It does sound as if its running out of gas. Check the petcock to make sure its flowing fuel freely. Check the tank vent to make sure its not plugged. Choking it wont always help a lean condition if your running out of fuel. If your bike is running out of fuel, choking it isnt going to help when your throttle is applied and the engine still doesnt have the fuel it needs to accelerate.

Also, pull the fuel line going to the carbs, get a small gas can and place the fuel pump hose into it. Turn on the ignition and watch to see that it flows. the flow is not going to be high, but it should be a steady stream of gas. You might see the pulsing, but it should never stop completely. I think they are only rated at 2psi.

Also, dirty carbs will act this way as well. Plugged main jet, or even sticking floats. If your unsure of the last time the carbs were cleaned, it might be time for a cleaning. If thats too much of an undertaking, you could try to run a can of seafoam through it. It may clear it up. But in most cases, if its heavy deposits in the carbs, it will need to be pulled apart.

Once it runs like this, does it return to normal if you switch ot a lower gear? If so, how long does it take to return to normal?

Since the engine was rebuilt. It could be any number of things from timing, to carbs not being snycronized properly... any number of things.

just as a side note. My wife had an R6 with the same issue. It turned out to be a faulty coil. Its spark was hot enough at lower rpms, but once you got going on the bike, the spark was too weak to keep up and it wouldnt go any higher than around 10 grand....