I just got an ATC 110 for my kid. It runs really well for it's age. The previous owner said he replaced one of the crankcase halves because the old one had a leak in it. He honed out the cylinder and put on new rings. It has pretty good compression. I've noticed after about 20 minutes of riding if you take the dipstick out, a rush of air blows out. I don't remember this happening on my old ones I had as a kid. I also noticed that if you have the dipstick loose in the hole, it will pop up when you pull the starter rope. Normally I would think it is blowing by the piston and putting pressure into the crank case, but the compression is pretty good. Is there any way to remedy this problem? And what is causing it?

 

I would check the breather hose out of the crankcase. My guess is that it's blocked. Increase in preasure is a normal thing as the engine heats up and maybe a slight bit of blow by. This is allowed for by the breather. I think it must be blocked.

Gary

 

I thought of that and I just can't seem to find it. I have 2 engines laying around and I still can't see where there is one.

 

I can't help ya with that one sorry. I have an 85 250es. The tube is right there and ya can't miss it. I'm sure someone on the list will be able to tell ya.

Good luck

Gary