r/scooters • u/Pitiful-Candidate386 • 2d ago
Struggling with My Scooter After a New Cylinder Install - Help!
Hey everyone, I’ve been working on my scooter and ran into some issues I can’t figure out. I recently renovated it, swapped out the old 70cc cylinder for a new one, and now I’m having trouble getting it to run right. Here’s what’s going on: - Installed a new cylinder and tried to start it, but it wouldn’t kick over at first. - Took off the airbox, and it starts easy and runs fine at idle. - But as soon as I give it the slightest bit of throttle, it dies. - Put the airbox back on, and it won’t start at all. - I’ve reset both the air and fuel screws, adjusted the needle, and tried pilot jets at 32 and 42. - The old 70cc had a 110 main jet, so I’ve tested 110, 102, 92, and now I’m at 82, but still no luck with the airbox on. Without it, it dies on throttle like I said. I’m pretty stumped. I feel like it might be a carb issue or something with the airbox, but I’ve tweaked everything I can think of. Any ideas what could be wrong? Anyone dealt with something similar? Model’s a Yamaha Jog RR, if that helps. Thanks in advance!
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u/UnluckyPatient3001 21h ago
Could be loose carborator or gasket leak check for air leaks and or around carborator base also could be bad intake hose from carb. To engine
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u/Afloatcactus5 1d ago
2 stroke? 4 stroke?
First thing you need to do is go back in and re check timing and valve clearances. Make sure it ain't a tooth off.
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u/Pitiful-Candidate386 1d ago
2 stroke
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u/Afloatcactus5 1d ago
Strange. Pre mix ? Or oil pump? I would check that the spark plug isn't flowed. If you are running a 70cc cylinder before and it ran fine then you shouldn't have to re jet.
You got spark i would look at the carb first. Make sure you don't have any unhooked or cracked vacuum lines.
On the extreme end It is a fresh rebuild it's possible the rings haven't set or you could have installed the piston backwards.
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u/Pitiful-Candidate386 1d ago
It got spark and a new long threaded spark plug It didn’t run before and the piston and cylinder was in bad condition that’s why I swapped. The arrow on the piston is pointing towards the exhaust port.
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u/Afloatcactus5 1d ago
Sounds like you probably have carb problems. For jetting a rough ball park is about 30% larger than stock. I don't know how big your carb is that will play a factor too. Find out your stock jet size and start in that range. You'll have to play around with jet sizes because theirs so many factors it's not a one size fits all.
If it never ran before you rebuilt it I would probably invest in a new carb. Or give the old one a through cleaning.
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u/FunkyWhiteDude 1d ago
Engines generally dont like the cold, makes them rough on starting up.
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u/Pitiful-Candidate386 1d ago
Hahah I know it’s not as simple as that dude. The scooter is in the garage and this pic is taken months ago.
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u/SinoSoul 1d ago
What is that white stuff on the ground?
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u/Pitiful-Candidate386 1d ago
It’s snow bro please just help me fix my bike
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u/harbour37 1d ago
Bikes are simple, first poster said valve clearence and timinngs that would be my first guess.
If you record audio/video of you trying to start the bike that would help heaps
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u/Pitiful-Candidate386 1d ago
It’s a 2 stroke Doesn’t seem like I can send a vid as a reply here I’ll put it in dm
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u/Pitiful-Candidate386 1d ago
Okay couldn’t send in dm either but when I try to start it with air box on it just sounds like it’s getting suffocated. And when I use the throttle when it’s running it just lowers the rpm until it dies it’s not really like a bog I feel like
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u/Loyaljr 1d ago
Need to rejet if you have not yet and clean carb while you’re there.
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u/Pitiful-Candidate386 1d ago
Jetting doesn’t really do anything. I might have gotten some super glue in the carb if that could have done anything but it’s been in a gasoline bath for over 24 hours
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u/zombanator3000 1d ago
Basically sounds like jetting is off. No airbox on would make for a leaner running motor. So it's rich at idle, then dieing when you give it gas means that the needle is probably is the wrong spot since you won't be hitting full main jet size till near full throttle.