Hi folks! Glad to be here and hopefully I can gain some knowledge about this issue..


Just bought a barely used 110cc atv for my kids. It says Yamazuki on the tag in front of the frame but cannot find any other name. Looks just like a pink camo Coolster. Anyway, on to the problem.


When I bought it, it started just fine. Heard it run for a few minutes and it sat for about a week before today. I bought a brand new spare battery for it just in case and charged it up. Today it initially would not start. Turned over just fine but acted like no fire or fuel. I checked the plug and it was fine. I shot a burst of carb cleaner in the cylinder and put everything back together, it started like a champ. Ran it for 15 minutes without a single issue.


Daughter killed it with the switch and tried a minute later to start it back up. It acted like the battery was low, starter was clicking and barely turning the engine over. I took it to the garage and put it on the charger.


An hour later I tried to fire it up and it acted the same way. Would only either click or barely turn the engine...like the battery was dead. Put a fresh battery on it and the same thing happened. Took the starter off and it engaged just like it should but noted it was VERY hot. I pulled the generator cover off to see if the flywheel would turn and it would BARELY turn with my hand. After working with it, it would get to a point where it would turn like it should (with some compression feel to it) and then it would get back to the point where it got hard as heck. I put a socket and ratchet to it and worked it until it was spinning like normal.


Put everything back together and starter is sometimes turning the motor over and sometimes it just clicks and/or barely turns it over. I did work with it enough to get it started again (with another shot of carb cleaner) and it ran flawlessly for another 15 min. But once killing it, it seems like the heat is almost making the engine seize somewhat and it will not turn over again.


Does this sound like the starter since it engages just fine when I pull it off? And trying to turn the crankshaft by hand is sometimes easy and sometimes difficult... it sounds like something is happening internally when it heats up. The oil level is fine and I am at a loss..

 

2 stroke or 4 stroke? Did you drain and re-fill the gear box with new gear oil? Same thing with motor (4 stroke), drain and fill with motor oil.

Also, you might be running real lean on that carb.

 

It is a four stroke.

I have not changed any fluids whatsoever. Checked engine oil only and its fine. ATV had maybe an hour of run time when I bought it. Any ideas what I can try next? How would the carb being too lean make this situation happen? Thanks for your help!

 

There should be two screws on your carb. One for idle and one for a/f. Verify a/f by counting clockwise how many turns till it stops. I run mine at about 3 to 3-1/2 turns out. Report back on how many your's is at now.

Some carbs can be adjusted by sound of the engine as well. Mid way between engine stumbling.

All this is assuming you have no air leaks too, which will cause a lean running motor. Verify air leaks with carb cleaner and spraying around rubber intake pieces while running. It will stumble if it sucks in the carb cleaner.

 

Thanks for the info... I am just wondering why a lean running motor would cause it to lock up slightly? Like if it is running lean would it cause the flywheel/crankshaft to not turn easily as it should?
When I can get the starter to turn the motor over and it fires up, it runs perfect. No hesitation or stumbling at all. It's just getting the starter to turn the flywheel enough to crank isn't happening..

 

Lean runs hot. Sounds like it's overheating. Also, does this have a coolant reservoir? If so, water pump may be faulty.

 

No coolant reservoir. Looks to be air cooled. I also can only find one screw on the carb drivers side and that one adjusts idle. There is a brass screw on the other side that is on the bottom of the bowl. Looks to be a drain possibly?

I just took the flywheel cover off, manipulated it into turning freely again. A shot of carb cleaner in the cylinder and she's been running strong again for the past ten minutes. I'm baffled by what's causing the engine to not turn over on its own after running it for a while...

But also appears to not be getting fuel initially since I have to prime with choke cleaner. There is a manual choke on the handle bar but it seems to not be functional.

 

Change Oil ASAP.