Need help to fix my little guys bike Yamaha Pw-50

My poor little guy only had 2 rides in when I presume he blew out the top end of his pw-50. I don't know for sure that this is what happened, but it would appear that way. We were riding in some extreme clay/mud and the bike was working hard. Kept stalling, and then the kick start seized up. I managed to break it free, and start the bike, only for that to happen again! Now I can barely start it, it sounds bad, and has hardly any power. (not ridable) Anyone know of any do -it yourself videos out there on the net? The dealer quoted me $80 per hour plus tax and parts! yikes! His bike is a 1999. Many thanks!!! I would love to get him back out riding!:thumbsup:

before you do anything, clean it as much as you can....clean clean clean! then pull the plug and see if there is any telltale signs on the plug. there is really nothing to the top of one of those. there is nothing to pop out and go boing! just pull the pipe, carb, and the head/jug bolts......lift the head/jug off and should see your problem. if it is chewed up, first try muratic acid for removing the aluminum left by the piston. post some pics of the piston and perhaps we can figure out why it stuck. could be a variety of reasons

Thanks guys, I'll give it a shot. What signs am I looking for on the plug? I hear sometimes the oil mixing gets faulty causing a seize- I was told to just pre mix myself instead of using the oil resevoir. I am far from that right now! I'll start taking it apart, and let y'all know what i discover!Thanks!

usually an oil related seizeure is easy to spot due to galling on the sides of the piston. the whole area that contacts the bore gets beat up.

What you are describing could be as simple as a piston seizure or a blown crank. What kind of injector oil were you running?

PW's cylinders are borable. They are really easy to work on. Pull the pipe & carb and the 4 head bolts and the head & cylinder will slide off.

Thanks for the info- I actually pulled it apart yesterday. The plug looked good. As for the cylinder it had some abrasion scratches on the bottom, and the botttom of the piston did as well. Now what? I could have the cylinder bored out, but I would also need to change the piston correct?Or possibly get new rings? How would I know if i have a blown crank? I pushed the kickstart down slow while it was open, and the piston moved freely out..I'm debating taking it in- but geeze at $80 an hour! If I get it bored out- does the dealerships have the machinery to do that, or would i go to a machine shop? Sorry guys- again, this is all so new to me!Thanks!

Oh yeah- the oil was right from the Yamaha dealership "s2" i believe

The whole cylinder kit from pwsonly is $175. New cylinder, piston, gaskets and head.

Inspect the crank and make sure it's ok.

Yes, you can bore it and buy an bigger piston and maybe save a few bucks but that is a alot of hassle for the $175 it would take to bolt on new stuff.

The main issue here is figuring out what happened so it doesn't happen again. some pics would help.

Most MC shops offer boring.....either in house or they send it out......there is more than just the bore thats needed and a typical machine shop does not chanfer ports.

1st get a factory repair manual as you will need it. With the manual and basic tools & knowledge you should be able to do the top end reb and it will tell you how to check the crank.

Take the cylinder to the local shop and have them take a quick look at it. They should be able to tell you for free if it needs to be bored or just a hone and what size the bore is now.

For a 6 pack of brew you should be able to get a mechanic to come into the parking lot and check the crank for you.

While you are there have parts quote you on a new piston, rings, piston bearing, piston pin, 2 circlips, head & base gaskets.

usually an oil related seizeure is easy to spot due to galling on the sides of the piston. the whole area that contacts the bore gets beat up.

hi ive got a pw50 yamaha i

took my carb apart and wen i put it back to gether the pin has got jammed in the carb carnt get it out can u tell me how to pull it out

Scotty,start another thread. There will be someone to help you.


Mike,how did you mix the gas and oil?

How to fix my kick start on a yamaha pw 50 it doesnt connect when I push it down wat do I need to do thanks

Mike, Yamalube 2-s is the correct oil for that bike. (I'm assuming that's what you meant.)

There can often be a problem with the injectors on those bikes, especially in off-throttle situations (going downhill?) when the engine is hot. Throttle off = no oil. I would definitely look into switching over to premix. It's not hard to mix the gas and your kid's engine will be more reliable.

PS- the crank should turn over freely by hand when you remove the cylinder from the cases. You can have a little side-to-side motion in the crank assembly, but absolutely no up-down when the engine is at top dead or bottom dead center.

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