Motorcycle Repair: 1991 kawasaki ex500 loses power, 1991 kawasaki ex500, vapour lock


Question
I have a 1991 kawasaki ex500 and recently it started losing power then dying all together while on the freeway at about 70mph. After pulling over it would start right back up. What could be causing this?

Answer
Check the routing of the fuel line from the gas tank to the carbs. It's possible the heat from extended high speed riding is causing a vapour lock that is starving the engine of fuel. When you pull over and let the bike cool off a bit the fuel will condense in the line and the bike will start again.

The problem could also be in the ignition system; high heat from the motor might be causing the ignition pickup plate or coils to open circuit and kill the ignition system. Letting the bike cool down will make it function again. This type of problem will gradually get worse until the ignition system is completely inoperative.

Make sure the fuel tap and filter screen are clean, as this can restrict fuel flow to the carbs to the point where they do not get enough fuel to run the motor at high speed.

One last thing to check is the venting of the fuel cap - next time this problem occurs, pull over and open the gas cap. If you hear a whooshing sound, then the vent in the cap is plugged and you need a new one.