93 pw50 won't start cold

[rick]

I have a 93 pw50 that wont start cold unless I put my finger over the carb opening. When it does start it will try to stall unless I operate the throttle until it warms up. Once it is warm it will idle good and runs fine.I have gone through the carb and used gauged pins to clean the passages. I checked the choke operation and can see the brass plug pull up past the enrichment circuit. It didn't come with the stock air cleaner and has a foam aftermarket air cleaner. I checked the compression and it is 85 psi. I have been given different ideas as to why it won't start.
1. must have stock air filter box to cause enough airflow restriction to pull fuel through enrichment circuit.
2. low compression not allowing enough vacuum on intake stroke to pull fuel in.
3. reed valves leaking not allowing enough vacuum.

Any help would be greatly appreciated, my son is anxious to ride.

Rick

[quadracer]

When cold the rings are cold. when hot they will seal tight to the cylinder. You have very low compression though. check the piston make sure the intake side is still intact like it should be. if so replace the rings and your go to go. if piston is bad just slap in a new piston and rings and your good. very simple job, reeds don't effect cold starting.

[rick]

Thanks for the information, I'll have to take it apart and see what I find. I was looking for some confirmation on my diagnosis before I took it apart.

[rick]

Took it apart today and found some cylinder scoring on the exhaust side, measured cylinder bore and piston. Found the cylinder to be egg shaped near the exhaust port and measured ring end gap at .090( which is supposed to be .006 to .014). Looks like a top end rebuild is in order.

Rick

[rick]

Replaced piston with a wiseco .020 over and had the cylinder bored. Compression is now 130 psi. Runs good and starts on first kick.

[quadracer]

Glad everything come out easy and clean.