Hi everyone... last fall I posted about a problem with my 89 600F. It starts fine, idles well, choke works as it should, bike runs great when cold. Problem starts at normal operating temp, where at exactly 4,000 RPM it makes a throatier sound (best way to describe it) and starts to stumble and lose power. Hold throttle steady and it won't accelerate - if I apply more throttle, it revs right up to redline with lots of power. Bike has new plugs, stock muffler with D & D header... PO put in a jet kit of unknown origin. I made an app't with local honda dealer, and the service guy on the phone says it is probably the ethanol in the modern day gasoline? Has anyone heard of this and of any ill effects from ethanol additives? What damages could this cause? I am going to have it looked at, but I assumed it was a simple needle position or float that needed tweaking as the carbs were cleaned last spring!

 

I avoid ethanol blend fuel if at all possible...my bike just doesn't run as well on it. Before you spend a bunch of money, try filling up with different fuel.

 

my bike behaves like you described, when i've been stopped at a long red light and the temp needle is approaching redline.
where does your needle sit at "normal operating temp"? mine is normaly around the 1/4 mark.

 

I rode my bike around town for a long time with the lowers off due to the "getting hot in traffic".The temp would spike at long lights. In town it would cook the inside of my legs. Out on the highway it runs great with all the plastic on.
I think this is the inspiration for many of the streetfighter conversions...that and OEM plastic is hard to find in good condition.
Tripicana, your bike and mine sound like they are about the same temp wise.

 

strange, my bike roars on the 10% ethonol fuel but im running totaly stock i think anyway, never took the carbs apart they work to good to tinker. Check the ethonol based engines quip from wiki http://en.wikipedia.org/wiki/Ethanol...-based_engines it explains the drop in power due to lower energy per unit volume but not the selective rpm isue
anyone try ethonol injection in the manifold? on cars the evaperation is so rapid that it cools the engine and boosts the power, the manifold gets ice cold. course thats on an injection system

 

Sounds like the bike has a "flat spot" at 4000 revs. It could be jetting, airfilter dirty, or something similar. Hard to tell exactly.

 

I took the bike to a Honda dealer tonight and the service manager started it and listened to it... I agree with him that at some points in the RPM range it sounds like it is running on 3 cylinders :-(
I left it there and won't know what it is up for a few days - but I put new plugs in the other day, and it runs great at some RPM and then is missing on one cylinder? I sure hope it is just a clogged carb or float problem... but now that I think about it, could it be electrical?

 

could be electrical. I think the only thing ethanol would be affecting in your case would be that it evaporated fast and now you have dirty carbs.