motor dies while moving

[goboleko]

OK,  Here's the Deal,

My buddy has purchased a 1980 cb750k as a first bike and it needs some attention.  I rode it home from the seller and it was something of a dog.  It is very clean and original excepting what appears to be a goldwing exhaust that has been cobbled into position.  I suspect it was never re-jetted as there is no tourque, and very slow to accelerate.  The motor starts fine and there is no smoke or other indications of any real issues.

We are planning on purchasing a new exhaust from cycle x http://www.cyclexchange.net/Exhaust%20System%20Page.htm
Once it is in place, we plan to take it to Dreyer Honda - the local old-time Honda dealer for jetting and a carb sync.

being the anxious type, he has been putting around the neighborhood until the new exhaust arrives, but the bike has been stalling and he can't get it restarted until it cools down.  Sight unseen, I suspect some type of ignition issue or possible over-heating from the poor jeting and low RPM neighborhood rides.

Any direction you might suggest in troubleshooting would be appreciated.

I'm a decent amateur mechanic, but I'm most familiar with BMW airheads, shovelheads and the trusty KLR 650.

I'll start by evaluating the air / fuel / ignition situation, but if this sounds familiar to anyone, I would appreciate any pointers.

He's bringing it to my house tomorrow morning so please feel free to post any ideas ASAP.

thanks,

Goboleko
Indianapolis, IN

[Re-run]

Well, it may be ignition but I put my bet on the carbs. The exhaust should not have this much of an effect. I suppose it could but it really shouldnt. My guess is the carbs are much too lean and the engine is starving for fuel and overheating some. Is there a filter in the airbox?
I suppose another thing could be the airbox filter is plugged and not enough air is getting to the engine.

[TOOLS1]

Has someone replaced the main fuse with a breaker? These old bikes are known for blowing fuses. when it dies, do the lights go out?
TOOLS

[Rodgil]

You should also check the fuel tank breather (in the fuel cap). If it is blocked, it will stall the motor until the air gets in. Try loosening the cap just after it has stalled, and listen for a "hiss". This gives the same symtoms as something overheated, that takes time to cool down. That is, the motor runs for a while, then stalls, and re-starts after a while.