Motorcycle Repair: Stalling Problem, radiator cap, summer temps

Question
Hi Mark,

I have a 1985 Yamaha Maxim 700 that loses power and wants to stall when it gets hot.   This ususally happens when sitting through several stoplights in town during summer temps.  I changed coolant, and even pulled out thermostat thinking that it would help.  It didn't.  The fan does kick on but doesn't seem to cool quick enough to help.  It starts to sputter, kind of like a miss, I can watch the tachometer dip and if you don't give it some gas it will eventually stall.  You have to give it a lot more gas just to get going from a stop or you'll bog and stall. When you start riding again and it cools back down runs fine again.   Appreciate any advice you can give.  Thanks, John

Answer
Hi John,

Sorry for the delay in replying. I've worked alot of overtime this week.

I suspect the cooling system has air in the system.

The cooling system is designed to be air-free. Anytime the system is opened other than the radiator cap, air must be purged from the system.

Air in the cooling system lowers the boiling temperature of the coolant.

The MityVac company manufactures a tool called the AirEvac tool. This tool is designed to purge air from the system. See the tool online- type the name in the address bar.

Respectfully,
Mark Shively