At the start of summer my friend bought a Yamaha Aerox for £600 and it worked pretty much fine but 2 weeks after riding it, it wouldn't start. I do motor mechanics on cars and I've fixed lots of broken mopeds in the past. After it broke down he threw the air filter away and said 'It's f*cked'. I recently bought it off him for £90 and spent ages getting it started then the kick stand went through the new air box I had just bought so I asked him and he said that happened to him as well so that is why it broke down because it got all wet. I got a sports exhaust and it was running fine i got it MOTed and used it to go to work but on the way home last Tuesday it stopped getting spark or something and the engine turned off. I stopped at the side and looked at it and didnt see anything wrong with it so I kick started it about 10 times and it started up and seemed fine so I started riding down the road again and it stopped again after about 5 seconds and this time I went to kick it and it was completely seized. I got someone to tow me home and the next day took the cylinder head and everything off. I had to hit the piston with a hammer to get it to go down through the cylinder. After taking it all apart and looking at the piston and cylinder it all looked fine I've had people that have been mechanics for 40+ years and they have said they look fine. The piston was definitely seized because I could move the crankshaft back and forth a little bit but the piston wouldn't move in the cylinder. I ordered a new 70cc sport cylinder and piston. I searched everywhere and found out it could've been running lean as I didn't re-jet it when I got the exhaust so I got a box of jets 68 - 82 or something because the stock jet is meant to be 62 from what I found but when I opened the carb I found out it had a 80 jet in it already. I bought another set of jets 90 - 108 and fitted the new 70cc cylinder and put a 92 jet in because running rich doesn't cause as much heat. I also got a new drive belt after fitting it all I started it up and it started first kick but sounded like absolute sh*t. After showing people a video of the sound they all said it sounded like a truck or tractor but when I put my phone near the exhaust it sounded like a 2 stroke. I went for a test ride and was out for about 5 minutes then went to turn around and as I slowed down and turned it stopped again and It had seized once again so I got someone to tow me home again and when I got home I pushed the kick starter down and it was nice and free so it had heat seized. There is 2 nipples ontop of the cylinder and 2 on the side of the carb that had blanks over them and I have recently found out that it is for carb heating. I found a hose that would fit over and took the belt off because I thought it was the belt or clutch making it sound bad and it sounded better but still not the best it and it was very smoky. After running it for about 30 seconds my whole garage was full of smoke. I learnt at college last year that white smoke can be unburned fuel but I have got a brand new spark plug on it. What could be causing it to be heat seizing? What could be causing the sound? Is there any point spending more money on it? What could be causing the smoke? (its white smoke btw but its not coolant because it doesn't smell coolanty(sweet) it does smell a bit fuely)
It is only heat seizing because it comes free after cooling down the smoke/smell is because I put a jet too big in so it was running a bit rich after googling a bit more about it it sounds quite like ‘cold seizing’ which is where you don’t let it warm up enough then the piston expands quicker than the cylinder and makes it seize does that only happen with dirtbikes or so mopeds get it too
Did you heat cycle the engine before you took it out on the road? Did you keep the revs down and not rev the nuts off it before it is run in properly? 300 miles at 30 - 35 mph, no more.
Got it going the other day and working how it should its fine on little roads where I do alot of stop and starting but when i was on a long straight road testing how it would cope in a straight line for a long time it started choking so i pulled over i left it for about 30 seconds then started it up and it worked fine i rode it a couple minutes home and didnt see any problems
Shouldn’t be running lean the temperature light didn’t come on so I don’t think it overheated and if it was too hot it wouldn’t have been fine after 30 seconds
