Motorcycle Repair: 1980 Kaw 100 2 stroke, internal combustion engines, engine seals

Question
I am trying to restor a Kaw 100 2 stroke.  I was able to get it running, and it ran good for a day... All of a sudden, the engine had a very high rev which I could not control.. I turned the key off, and the engine continued to run.. I hit the engine off button next, and the engine continued to run.. Before the motor blew, I reached down and covered the carb with my hand and that stopped the motor.. Ihave checked the key and engine off button several times and they work correctly..That is there is no spark to the plug... I have checked the carb, and the barrel is not sticking in the up position.. It is down where it shoud be...So each time that I start the motor again it will run fine for a minute or so, and then goes into a high rev.. Each time the key and the off switch do not work...I have only been able to shut it off using my hand over the carb...I have checked the carb barrel each time and it is down in the idel position... I have telephoned a local mechanic and he felt that the engine seals were shot and this is what causes the continuing engine run on.. But it doesn't explain to me why the spark will not shut off with the key or the engine off button.. Any advice you could give me Chris would be a help.. I would hate to have the engine rebuilt with new seals and gaskets for nothing...I am looking forward to your reply, and thanks again..AL

Answer
Hi Al.
 Perhaps I am just a bit jaded by mechanics who just want you to bring in your bike so that they can do nothing and charge you for it, but it sounds like this guy knows almost nothing about actual mechanical theory as it applies to internal combustion engines.

 Here's what you need to do.  You will need the repair manual.

1)  Doublecheck the idle speed set screw.  It could be set too high.

2)  Check the throttle cable to make sure that it is properly lubed and moving freely and check the choke cable to see if it is moving correctly as well.

3)  Remove and completely clean (maybe even rebuild if necessary) the carbs.

4)  Reseal the fuel tank and replace the fuel lines.

5)  Check the entire ignition system, from power to every switch to the coils.  Look for any power leads that are crossing the ignition system and energizing it.  There is a hot short in there somewhere and that is why the bike won't shut off.  You may be better off ordering a new wiring harness, just to be safe.

Many mechanics are very honest and most are as competant as a parts changer can be, but very few actually look to find the simplest and cheapest solution for the bike's problem.  Fewer still are actually are allowed to properly analyze the problem for the customer, thus you get a lot of improper or "quicky" diagnoses that do not work.

 In the end you may need to have the engine rebuilt, but first fix the other problems, then see if the rebuild is really needed.

Good luck.
FALCON