I'm wondering if you can help me out. I bought a 2012 linhai 150cc second hand. I know that there has been a lot of work done on it just based on what I can see.( Keep in mind I know a little bit about ATVs but no expert at all). And it doesn't have reverse. I'm just wondering if anyone knows if this model had reverse from the beginning? Also, it seems like after it's been running for a while, it likes to run on its own. I did adjust the idle on the carburetor, and it did help it but I'm wondering if the carburetor needs to be cleaned. Or am I just as well to get a new carburetor. If you guys can help me out would be greatly appreciated.
I also have to note, that it doesn't have a have a shifter to shift to reverse, but looks there is a hole where the shifter would be
So it just goes forward no backwards.

 

Engines tend to rev higher as they warm up. Carburettor equipped cars often had a lever or cam on the choke, which increased idle speed when on choke. Best you can do, is set the idle speed slow enough to avoid the clutch bringing in the drive, when the engine engine is warm. If this leads to it stalling at idle when the engine is cold, so be it.

I don't know the model at all. Most cheap Chinese bikes use a motorcycle engine, which doesn't have reverse. Some fit reverse in the rear axle. Some convert the engine's gearbox to include a reverse. Some just leave them forward gears only. Pics of the "hole where the shifter would be" may help.