1980 NC50 engine won't turnover
 

There is a spark, i double checked. there is fuel getting to the carb... When I turn it over and release all you hear is the piston move up and down, its like there is no attempt at combustion..... the piston cycles up and down until all of the energy stored up in the crank is expended..... Any tips? where should I look? I have played with the choke and thats not helping... Any ideas?

Thanks

A bike requires three essential things to run:

1) Fuel
2) Spark
3) Compression

You verified the presence of spark and fuel. The next step is to determine if you have proper compression. You need to attach a "compression tester" to your engine and get the EXACT PSI of compression you have. An NC50 needs 90 to 120 psi. You CANNOT use FEEL to determine amount of compression, you MUST USE a compression tester.

you can get a compression tester at the auto parts store for like $30 or ask around maybe some you know has one. You can find a lot of youtube vids and articles on how to do this.

Thanks guys, I squirted gas into the engine intake, started right up. Cleanedu p the carb with carb cleaner and its back to perfection. Next question is a little more technical.

Below is a link to a diagram that i found that will help explain my point:

http://www.bikebandit.com/houseofmot...3605#sch406583

The final drive gear, part #9, and the driven sprocket are rubbing against each other. Whats actually rubbing is the chain attached to the driven sprocket moving forwards towards the back of the final gear, causing rubbing. I made sure that the washer, bearing, and the second washer were on the sprocket gear but it still makes the grinding noise. The sprocket gear is still sliding forward into the final drive gear...

Any idea whats going on?