A Success Story

So today I finally found time to take off my muffler and took a dremel to the manifold to make the opening bigger. I put the muffler back on and couldn't believe what happened! I am now able to cruise at 25 mph with 3/4 throttle where as before I was at about 18-20 mph. I got up to 30 mph and the SOB was still pulling like crazy! The engine sounded like it was going to explode from high RPMs so I backed off (w/ a 44t sprocket)! I can't believe the performance I got from such a simple and quick mod. I am wondering what else I can do to my engine to increase performance even more. This is the only mod I have made other than improving the chain idler. I have a 67 cc Power King and plan on getting a Champion plug and new wire tomorrow. What else can I do? Should I port the intake manifold too? I am thinking about getting a 40t rear sprocket so I can cruise at 30+ without blowing my motor up. I appreciate your input!

spark plug wire is a good idea.
40 tooth, more power to ya.

what about a new air filter? that whould icrease speed, and also a new gas jet.

glad to hear everythings going great!!

sounds interesting, can you post a pic of the exhaust port after dremel?....

Try the same on the intake side.

Sure, I have another bike that I will also port out the exhaust so I will take before and after pics of the exhaust and intake.

It may take me a few days though...

After the advice I got here on the forum about the intake manifold leaking I tested mine with starting fluid and found that the gasket was leaking. So while I had it apart I ported the intake and the exhaust manifolds. It made the engine louder and gave me a very smooth idel. More tork at the bottom end, but it hits a wall at 17 to 21mph, like it has a rev limitor on it. But given enough time and stright away it will pick up again at about 22 mpg and run right up to 28 mph. My question is, why the dead spot? I like what the porting has done for the low end, and I can live without the high end because I don't let it rev that high most of the time anyway, but it is strange to me that it hits that point where if it were a four cycle I would say the valves were floating.

My guess is your fuel mixture.

Here are some before and after on the stock exhaust before I added the tuned pipe. First is stock exhaust and gasket. Second is stock exhaust. Third is exhaust port. Fourth is new gasket. Fifth is new exhaust manifold. So I start by creating a new exhaust gasket using the exhaust port as a template. Then I use the new gasket as a template for the exhaust manifold. Then repeat for the intake side.

Nice and easy!

These area pretty much standard steps to get any performance out of the engine. Intake matching does help as well.

T-Dav - it's probably the mixture and the stock pipe and lousy spark plug.