oil leak into air box - Chinese generic

[galen52657]

Hi all,

I am a new member. I am working on my son's 50cc two stoke Chinese scooter. Seems the two-stroke oil is leaking from the oil tank, through the pump, into the carb and down into the airbox. About every month we have to clean oil out of the airbox and clean the filter element which is saturated with two-stroke oil. Otherwise, the bike won't start when it's cold and the plug looks a little sooty. After we clean the filter it runs like a champ. Anybody else had this issue?

[harrywr2]

On 4 strokes the problem usually works out to be oil finding it's way to the airbox thru the crankcase vent hose. If the hose is kinked or the crankcase oil is over filled oil ends up blowing into the airbox.

[90GTVert]

Well, I don't think it's gonna be a crankcase vent hose. On a 2 stroke the crankcase is pressurized with an air/fuel mixture that is compressed and sent into the cylinder for combustion. Relieving that pressure would not be good, so they don't have and sort of crankcase ventilation.

I don't use oil injection on any two strokes, I always premix, so I've never had that specific trouble. It's not really leaking from the tank to the pump to the carb, that's the path it should be taking if your oil injection is functioning properly. At least you know you're getting oil, that's a good thing.

If your air filter element is truly "saturated" then I would venture to guess you have way too much oil being injected and maybe the oil pump needs to be adjusted if possible for your model and the reed valves should be inspected. If it's a bit oily, it may be normal. I premix and my filters will get a little oily over time. 2 strokes are not exactly efficient. The reed valves can allow a mixture to be pushed backwards when the piston is traveling upwards instead of only when the piston is traveling down to draw in mixture. That's the only thing that seems logical to me.

[galen52657]

The oil filter is saturated and there is about a cup of oil laying in the filter box when you open it up. I think gravity is simply pushing it through. The oil tank is higher than the pump and the carb/airbox. The tank holds over two quarts of oil, so that is a lot of head pressure. The oil pump is actuated by a cable from the throttle. I already backed it off a little. If the oil pump won't shut off the oil supply completely when the bike is not running, the oil simply seeps all the way through the system and when the bike is leaned over on it's side stand, the oil will flow into the filter box.

[90GTVert]

Wow. Have you unhooked the oil supply line to see if it really is just seeping out? Don't drive it that way, buy let it sit overnight on some cardboard or something. If it's just running out it may be a faulty pump. My reservoir was higher than my oil pump and I don't remember oil just running out. It's been awhile though. You could always try relocating the oil reservoir at least temporarily.

[Rebel]

Galen,

Welcome to the forum. 90GTVert is our resident 2 stroke authority, then jmkjr72 is also up on the 2 strokes. I'd listen to what they have to say on the topic.