Old Yamaha scooter rebuild

So I got a free mower today and offered to fix up the woman's old scooter to be nice. It has sat since 1981, at that time is ran and was licensed for the street. I'm still looking up info on them, but I think this thing is a 4-stroke, which is not common I don't think. Anyway, here's some pics and I'll take pics as I work on it. Not a full restore or anything, just clean it up and get it running.

Didn't take long for Wiki to find it. Yamaha QT50 Yamahopper. 50cc 2-stroke, supposedly has a 6V battery and alternator on there somewhere.

i think arild has one of these check his youtube sight out

nice find man!! i got the same bike! its not a 2 stroke so defenetly do not put straight gas in! There fun bikes! The oil Tank is under the seat. I painted mine black. Check my youtube site!

Like I said, it isn't mine. I may have to ask a few questions before it's all said and done. I went back to the garage and did some more tinkering.Brakes are good, or good enough. The throttle sticks, battery reads 1.5V, the gas tank is dry and rusty, and I forgot to check the oil. I'm afraid to try and start it without cleaning the oil pump. This thing was parked in running shape, in 1981!!! The battery is as old as I am, haha. I plan to clean the carb, oil pump, and pull the exhaust to get a better look at the cylinder. How hard should the kick start be to turn over? I put almost all 230 lbs of me on it but didn't kick down.

Sweet. I had the identical bike.
I loved mine i used to beat the crap out of it very tuff!
It's a oil injected system, the yamalube goes under the seat in the little black cap.
I'm sorry to this day i sold mine.

Well this project ended before it even got started. Took some stuff apart only to find the piston seized to the cylinder. I haven't talked to the owner yet, but I'm betting it will cost more to fix than a new chinese cheapo. Cast iron piston and sleeve, not good being left to sit for 30 years.

I didnt bother cleaning my oil pump cause i didnt think i could trust it so i just pre mix the gas like a chainsaw and poor it straight into the gas tank already mixed. Been running like that for years and nothing has gone wrong! There great reliabe bikes and id never sell mine lol i love that thing.

I looked up the parts needed and was surprised to even find them all. Total would be around $450 not counting the carb and maybe the oil pump. I think I know what the owner will say about that. It's a shame, looked like a fun little bike.

id say since it sat for 30 years, they probably wont mind it doesnt run. Id say someone ran straight gas or let the oil tank go to low last time it was ridden.

Id try soaking the combustion chamber with PB blaster for a couple days - then maybe pull the head and knock the piston with the wooden handle of a hammer to see if itll break loose.

2 cycles will have reeds in the carb- you'd want to be careful with that.

I watched a youtube video on these engines to get a better idea and they actually have thin sheetmetal reed valves on a plate under the carb. The guy in the vid replaced it with a cut up new type plastic valve. Do you think the cylinder would be usable after soaking and if the piston came free? If I could get the rod off the crank I could use electrolysis to remove all the rust and it would all come apart. I wonder if there would be come way of putting a 4hp briggs on there, haha.

This project may be back on again. $450 is crazy money to spend on this but I found a kit on ebay today for $120 shipped.
http://cgi.ebay.com/ebaymotors/YAMAHA-QT50-SET-KIT-CYLINDER-PISTON-GASKET-YAMAHOPPER-_W0QQcmdZViewItemQQhashZitem3f0901acfaQQitemZ270734044410QQptZMotorcyclesQ5fPartsQ5fAccessories
It should be ok with that kit and a carb rebuild. Just to be sure I'll disassemble the engine, clean the carb and oil pump all before ordering. I hope the connecting rod is still good.

Arild, your videos make me want to get the YT60 kit and PW50 rear gears. I have to remind myself that this isn't my bike, the owner was pleased with the original speed.

I use PB blaster all the time with the junkers i drag home - i spray the crap out of the combustion chamber , let it soak then turn the crank. Worked when i nearly seized a 11Hp briggs i have.

Good thing about PB is it burns nicely in the combustion chamber.

Heck id get a $99 6.5 HP greyhound motor from harbor freight and stick it on there 1st.

Yup, the HF cheapy honda clones is what I was thinking, about $80 with a 20% coupon. But it's not my call, the owner was ready to buy that ebay kit yesterday. I told her to hold off till I completely take the thing apart, make sure no other high dollar items would be needed. Only thing I'm worried about is the rod and crank along with their bearings. If they all look good, I'll probably proceed with the rebuild. I think I'll bump it to 60cc anyway, just for good measure, haha.

Added pics of the teardown. I have to get my new MTD running and out of the way to make room to work on the Yamachopper.

Finally got the piston and cylinder off. It took a lot of hammer work. After some more penetrating oil sprayed down into the crankcase the crank now spins over freely. Once I check out the carb and oil pump I should have a good idea on what parts will be needed. I'm pretty sure the owner is going to have me rebuild it, should be a fun journey.

Any updates?

Unfortunately no. The owner bought the wrong parts and is now battling cancer. So I'm not going to bother her with something this trivial. There will be plenty of time to fix it once she recovers, and she will. I have cleaned the carb and put it back on. Other that that, it's sitting on top that rubbermaid table.

Holy cow lots of rust

Got some parts in and looks like I'll finally get this thing back together. I got a new piston/rings/gaskets and will use the old jug. The new piston is aluminum, old was steel, guess this won't have the rust problem. I plan to use electrolysis to take all rust off the jug and then take a hone to the cylinder. I have a question though, can I powdercoat the outside of the jug without it overheating? I've seen the rebuild kits with a new jub and it comes painted. I just don't want it overheating. I have one of those powdercoating guns from harbor freight and have used it on small parts.

Hey thanks for the info. I ended up painting the jug. I doubt it will hold up, but after the electrolysis it was surface rusting quick, needed something. I am just putting this thing back together stock for a friend, no hopping up. Next step is cleaning the rust out of the tank, but I'm in no rush, many other things going on right now.