Bought a secondhand Yamaha SR150 (my second one in 12 years) in June last year. It is in really good condition compared to my last one, but from week one has had this nagging problem: after a brief ride, it loses power. It starts fine in the morning and goes pretty well the whole 2 km route to the breakfast shop. I always only stop for about a minute or two and then I am on my way to work. When I start again the bike has very little power even with the throttle wide open. It has made me late for work on a number of occasions and can be quite dangerous crossing a busy intersection when you find you don’t have enough power to do it quickly enough.
It kept on fouling up spark plugs and the mechanic put in a new one for me on at least two occasions. He also replaced the fuel line from the carburetor to the fuel tank. Still the problem persisted. He sprayed some stuff in the carburetor to clean it out. That didn’t work. He adjusted the idling and still nothing. Then he replaced some electrical component which he said wasnt working as it should. That didn’t work so in desperation I asked him to replace another electrical component (slightly more expensive) which I had previously had trouble with on my older bike. It was when he was replacing this that he discovered that the timing was out! He said that the bike had obviously been stripped before and that whoever had put it back together again hadn’t set the timing and it was out buy one whole notch!
I knew that timing has to be set on cars on a regular basis but I had no idea that it was something that needed to be checked on motorbikes. I feel rather dumb that I didn’t think about it first. However, I did some online searching and it seems that it is, indeed,set at the factory and not normally something that needs to be adjusted again. I guess it was just because my bike had been put together incorrectly.
The power problem has been completely solved. The bike is a pleasure to ride. Another unexpected benefit is that it is cheaper on gas, too. I used to get about 165 km to the tank, but since the fix I have gone 225 km on a full tank and I still haven’t switched to the reserve tank, yet. An extra 60 km per tank is going to be a huge saving when you work it out over the year. (I fill my tank up every 7 - 10 days).
Anyway, just wanted to document this on the remote chance someone else might have this problem.