Seller Scammed Me On This Rare 2-Stroke Dirt Bike (First Ride)

Several previous commenters have touched on the likely issue(s). The bore is way oversize from stock. The port edges originally are chamfered to prevent catching the ring. Likely when it was bored (or honed, see below) the chamfer was eliminated and not recreated. Also ports can only get so wide before the ring falls into them no matter what you do - that's why at a certain point an exhaust bridge is implemented. The ports in this cylinder have likely widened due to the degree of overbore, making the chamfer situation worse. It is likely the cylinder is out of round and may also have straightness issues, especially if most of the oversize was created with a hone rather than boring bar. The amount of material a hone removes is affected by the amount of cylinder wall it contacts - so the bore will grow in areas of the cylinder that have a lot of port area, and thus less wall area, hurting straightness even if it is still round. I've not seen this wear the rings funny, but it sure will place an upper bound on compression and therefore power. It is also possible the power valve is contacting the ring, but I think you'd have ugly scars on the piston if that was the case. Overall you've been pretty lucky to this point in not evaluating cylinder straightness and the crosshatch and roughness your honing technique produces. I'd recommend picking up a dial-bore gage so you can measure precisely and slowing your drill way down when you hone to achieve a more optimal crosshatch angle. It's also non-trivial to create the proper roughness with a hand hone, even a Sunnen portable one, much less brake-cylinder hone types. Luck only goes so far. You can also get a better feel for roundness and straightness with a telescoping gage and appropriately-sized outside micrometer, but you can probably pick up a used dial-bore gage of adequate quality about as cheaply as a good set of snap gages and outside micrometers. Dial-bore gauge is the way to go, it's much quicker and more precise. This all comes from a guy with a lot of 2-stroke engine building experience, including a lot of cylinder measuring and honing.

At this stage your patience is the stuff legends are made. Well done

I would put my money on the fact that when you honed the cylinder you didn't chamfer the ports when you hone a cylinder you're essentially making the edge of the port sharp you need to take a Dremel and round that edge so that when the ring slides by it's not like a razor going past the ring all the time it's a nice smooth transition that's I would say 95% sure that's what caused it these older bikes are a little less forgiving if everything's not right they'll start breaking down quick

Bore gauge to check roundness in cylinder and check power valve for any signs of contact. The only things I can think of.

Go back and look at the sequence where you drained some fuel into the clear container. There appears to be no mix in the gas.

I have a 1982 Yz250, its been in the garage for several years because i cannot find parts for it. 82's were one year only and didn't share many parts with the 83s or 81s. Good job Joe your patience paid off.

"look how big that gap is" ..... I've said that once or twice in my life. LOL

I know you want to keep the cost down, but I noticed it on a couple of videos now Normally if you change to a new sprocket you should do the front and back and a new chain. Now you run a worn and stretched chain on the new back sprocket which will ruin the new sprocket a lot faster. But again I understand you want the cost down.❤

This the junkyard special Yamaha you can see these everywhere with so much potential

@ 3:55 You are suppose to use a pin, that is put in that little fork at the end, and into a matching hole in the cylinder casting,--to hold that power valve actuator in place while you tighten the nut. Since you did not do that, the power valve is not "clocked" correctly. I thought you knew what you were doing?,---for all of us to see. lol

Dude, you are an experienced bike mechanic! Why are you making rookie mistakes. Clean the darn brakes before replacing. ALWAYS check the cylinder bore roundness, especially when you can't trust the seller! You're letting me down, I love the channel.

With your skills and knowledge you need to develop a ten point system to evaluate every new purchase. If the seller won't allow the inspection, just assume there scammers

My man. You need to start and measure the bores. Get you a good mic and inside snap gauge to get a pretty good reading. And if you can afford it get a dial bore gauge with the mic. Once set to the dimension you need. You can use it to determine out of round , taper in the bore.

Badass bike man! I've been watching you for years now youve taught me so much and I now have my own small business at 16!

I would inspect the power valve for contact abrasion from ring. Also, you might check cylinder squareness with a good straight edge.

Bore could be out of round and you may need to chamfer the ports! Definitely invest in a bore gage!

I think it is the edges of the ports cutting the ring.

Every time i watch a video of Joes. I learn so much. Even though he thought he knew what the problem was. He still went down the checklist checking possible but unlikely causes and ultimately narrows it down to only being a couple possible culprits. Joes never to cocky to assume he knows the problem.

Many people today have no moral compass and therefore are liars, cheats and thieves NOT scammers (too nice a word). Do NOT trust what people say, instead, CHECK OUT THE CAR, TRUCK, MOTORCYCLE, ATV etc. BEFORE BUYING!!! The old adage of BUYER BEWARE is paramount in today's world. GREAT CHANNEL!!!! (My take on what's wrong......bad metallurgy in the ring, Chinese junk?)

If cylinder is over bored... Yes stock pv will be an issue. You need to check cylinder for egg shaped