Great spark... No Start...???

I have an 80cc motor running well for the first 45 miles. I am still in the break in period, and while out riding, the engine just died. I discovered that my spark plug boot disconnected from the spark plug and while trying to reconnect it, I broke the little metal U part, so the boot would not stay on the plug. After pedaling home and visiting my local scooter store, I purchased another boot. The weekend had past and today, after attaching everything, it would not start. I am getting a great spark, but cannot get the engine to start. I though it may be flooded since I left the fuel line cut-off switch open over the weekend. I removed the carburetor and excess fuel. After reattaching, still does not want to start. I removed the kill switch completely, still no start. I am at a loss. 2 strokes are not supposed to be hard to work on, but I am baffled at this one. I know I am getting a great spark because I have removed the plug and from the cylinder and while cranking the pedals with the clutch engaged, it sparks nice and bright. Any thoughts?

I have tried to start it repeatedly with no luck. I tickled it for 3 seconds, and tried to start it at half choke (multiple start attempts)… no start. I tried to start it at 1/4 choke (multiple start attempts)… no start. I tried to start it at full choke (multiple start attempts)… no start. I tried to start it at open choke (multiple start attempts)… no start. I know I am getting fuel and spark, and compression (by removing the spark plug and holding my finger/thumb over the plug hole and cranking the pedal with the clutch engaged). It used to crank right up, but now seems like it is bogged down. When trying to start it, it sounds as if the kill switch is being pressed while starting, but I have disconnected the kill switch. I only have blue to blue and black to black hooked up. When trying to start it, if I give it gas, it sounds as if more air is getting to the engine, but still does not start. I am using 16:1 gas/2-cycle oil mix. It seems rich, and I would have already diluted it but it ran quite well before with the same fuel (literally). I removed the cylinder head to make sure the piston was moving, and it still had full range of motion. This is becoming extremely frustrating. I have worked on small (and large) engines before and until today, have never had a newer engine like this fail to start.

I am still at a loss.

I have almost done a complete tear down and rebuild with the exception of the piston and clutch. I changed out the spark plug, gapped to .045, showed an even better spark and still no start. I thought it may be my gas, so I emptied the tank, cleared the line, opened the float compartment on the carburetor, and emptied that, made sure nothing was clogging the pinhole and put new gas (87 octane) and mixed it 24:1. I filled up the carburetor, choked it, and still no start. I removed the exhaust (blew through it and everything), and without replacing it, tried to start it and still no start (multiple times). I removed the magneto and inspected it. Put it back and reconnected my wires, (black to black - blue to blue - removed the kill switch), still no start. I tightened the bolts holding the cylinder head and reinstalled the head, still no start. I am so frustrated I want to throw this f&$%#@! motor through a window. The only thing I can figure is that it is not getting gas, but even pouring some gas through the spark plug hole and screwing back the spark plug, I still cannot get it to start. I am totally baffled. Other than placing my finger over the spark plug hole, how can I check for compression? It should have great compression since the engine has less than 50 miles on it. Other than replacing the piston and piston ring, what else have I left out?

Well, I think I figured it out. I had tried everything listed and still no luck. Thank you for all your help! A piece of the cylinder apparently flaked off and rubbed on the piston and piston rings. It must have gotten hot and pushed the piston ring flush with the piston, then “fused” it to the piston. Looks like a bad break-in, but I didn’t think I was too hard on it. Anyway, I am going to order a new cylinder, piston, and piston rings and baby the engine. I stayed at half-throttle and only occasionally brought it close to full-throttle for a few seconds. I have broken in many engines, but this is the first one that gave me any problems. I am hoping it was just a defective cylinder. We’ll see.

Here is a photo of the piston: http://pack127.net/images/piston.jpg

I just put everything back together (yes with the bad piston - I'm getting a new cyclinder, piston, and rings), but I filed down the damaged rings and piston with 1200 grit wet sandpaper. As soon as I popped the clutch...vroom, she fired right up. Now all I have to do is wait for my new parts and break it in nice and easy...again. I am hoping I just got a bad assembly since it looked like a piece of metal was rubbing the cylinder. SWEET...it works!

I agree with you completely. I just wanted to make sure that was the problem (the piston & rings). I have already taken the cylinder and piston apart and am awaiting the arrival of my new parts.

Bikeguy Joe, Large Filipino, svc, fenderhole, Norman, hill climber, & POPS, thanks for all of help and suggestions.

My son now wants a motor for his bike. I told him if he buys it I will show him how to install it, but he has to do the work. He is thrilled. I know I would have been if I were 13 or 14 and had a motor on my bike. Good luck to you all and keep motorin'!