Backfiring & leaking oil

[Mrjorp]

I have a kawasaki kh100, it's a two stroke.

Once it gets to half the revs it will start to backire(I think), By that I mean it makes popping noises and blows out a cloud of blue smoke, and half blows the baffler out the back of the exhaust pipe.

When it pops there is a loss of power and the bike almost dies.

If I ride the bike for about ten minutes, the exhaust becomes loose as the bolts are forced out of the manifold on the cylinder.

Finally, oil gets spat out of the exhaust port (down the pipe and round the edge of it, onto the outside of engine)

I have replaced the oil seal on the right side of the crankcase.

Could there be too much pressure inside the cylinder?, so it is sucking oil from the engine case, and forcing the exhaust off, please help. Thanks

[Big B]

if it's a two stroke - there is no oil in the crankcase. is it oil injected or do you pre-mix the oil in the gas tank?

[BuzZz]

Big B is right, your bike has no oil in the engine crankcase, only the tranny. And those crankseals are critically important to the engine performance and survival. They don't keep oil in the motor, they keep air out, and if they leak the carburation will be melt-your-motor-lean due to the extra air bypassing the carb and not picking up fuel to make the mixture correct.

But it sounds more like your bike is rich, not lean. Hard to say from the info so far. How hot does it run? Rich will run cool, lean will run hot.

I think your bike uses a piston port intake (I am not sure and far too lazy to look it up myself) and if the piston skirt is cracked/broke, that alters the intake timing of that style engine, and not for the better. If it is reed valved, then broken reeds can mess with the engine, but normally that makes hard/impossible starting and poor lowspeed performance. That's guess #1.

Guess #2 is simple carb jetting being way off. Like the main jet fell out or the needle broke or wore down greatly.

What about the injection oil? Do you ever fill the oil tank or do you run pre-mix? However it's done, that bike needs 2-stroke oil in the fuel somehow.

[Mrjorp]

There is not supposed to be oil in the crankcase and the seal is for keeping the oil out however there is a lot of oil in the crankcase.

My bike has an oil pump and mixes the fuel and oil just after the carb (which is internal) using the venturi effect.

I rarely have to fill up the two stroke oil, but it is in a separate tank to the petrol. I wasn't too bothered about not having to fill up the oil very often because there is a lot in the cylinder anyway.

The cylinder does use ports not reed valves. And there is a small bit of the piston skirt missing on the side of the piston next to the exhaust port.

Thanks for your help so far, any more info would be great.

P.S I've just looked at the spark plug and piston: The spark plug is a dark brown colour, blacker on the edge next to the exhaust port (I think this means it is running fairly close to it's optimum). However When I looked at the piston it was coated in Black carbon deposits and was quite oil free on top, yet the sides are coated in oil.

The Black carbon is in a rounded triangle shape from the centre of the piston to the exhaust port and is slightly bigger on the right side, there are carbon lines from each of the intake ports joining to the main carbon deposits.

I understand that looking at the colour, texture and positioning of any deposits can tell a lot about an engine. I hope this info helps.