2002 Yamaha R6 hot running problem...

[zone47]

I have a 02 Yamaha R6 ( last year for carbs ) and it runs great while the weather is cooler (60s-70s ) but last year and again this year when the weather got into the 90s the bike runs well for about 30 minutes and then acts like it's starving for fuel.

A few years back, I pulled the carbs loose to experiment with different jets and am wondering if I got the intake hose network put on correctly? Last night I tore it apart and noticed gasoline in that little resonance chamber that connects to the carb vent system and then to the top of the airbox. There is another network of hoses from that mess that goes nowhere!

More about the problem: The bike's idle begins dropping and it won't rev at all. I hit the choke, then it finally revs. It sounds like vapor lock or something weird like that. I insulated the fuel intake from the engine heat, checked to make sure the fuel flow was good, but still the same prob.

I wonder if the coolant hoses going to heat the fuel bowls is a bit too much on a hot day?

Any ideas or advice?

[HalfLiterBeater]

Any fuel-system-related vacuum line that's running into the airbox shouldn't be getting liquid fuel, just fuel vapors to be burned for cleaner emissions. The little 'chamber' in-line might just be a vapor separator, which would mean it's probably normal to get liquid fuel in there. The problem is if fuel is getting PAST it...fuel being drawn through this line could be pulled into the airbox and make you run rich....but choking it should've made it worse if that was the case, I would think.

Your mention of hoses that go nowhere makes me think some of yours could be mixed up. I'd get a service manual if you don't have one already, and go through all the hoses and their routing, I'm betting your problem is in the hoses, and definitely vapor lock being a possibility. Check your tank vent also...maybe blow a little compressed air through it.

Next time it wants to die or acts up, shut it down and open the fuel cap. Close it and restart the bike and see if it clears up. If it does, it's pretty much a no-brainer answer then.

[RayOSV]

If it doesn't run well without some choke, it's running really lean and starved for fuel.

Have someone who knows what to look for check all the hoses.

[zone47]

Thanks for the replies.

I did find an intake hose routing schematic on line. The only problem was that the vent hose connecting to the float bowl vents and then running into the series of connections * going nowhere * and also to the top of the air box was plugged. There is a 'T' that should be left open as a vent I guess and it was capped.

The other change I made was to bypass the carb float bowl coolant network. I also checked the fuel filter and the petcock screens, both of which were fine.

It's hard to tell without pulling the plugs to tell if this problem was an over rich condition or a lean condition. Since it started running better with full choke, my guess is somehow it began starving for fuel for whatever reason.

The bike runs so much stronger now. I took it out for a couple hours, and while it was a cooler day, I think it's going to be ok.

I almost forgot, it seems there was originally a heat shield down there between the engine block and the carbs or fuel line? I made a temporary make shift insulator from fiberglass insulation wrapped in foil. That may have been a problem too.

Again, thanks guys for your input and ideas!

[YZFHEFF]

Yah, the carbs have to be vented to atmosphere. Good job.