2 Stoke power problem (no one knows the problem) PLEASE HELP

[neilus123]

Hi Peoples

I have been riding a little Kawasaki KH100 for over 2 years with a problem that no one knows the answer to. I have tried other forums but nothing has worked so I trying one last time.

The bike starts first kick every time, will tick over lovely all day long and is as reliable as they come. The bikes engine sounds great no nasty noises.

Now the problem once you get to 7000 revs it has no more power it still revs to 9000 but just has no guts and can only get 45 to 50mph. I have just built another bike with the same engine and this goes like stink in comparison. It seems and feels like the problem bike has no powerband.

The bike has been re bored, up jetted, exhaust de coked, carb cleaned and new plug. I have changed the points and condenser to another used unit, changed the ignition coil.

Its seems to me that since I tried the other bike that its the powerband area it just doesn't have one that's where my problem lies.

Any ideas peoples

[Tango]

Welcome to TMBF mate......pop over to the Newbies section and say hi to the guys......

To your problem......does it have a reed valve......and if it does, is it sealing correctly.......

[neilus123]

Will go and introduce myself mate thanks and no its a rotary valve system

[Tango]

Is the carb float set correctly......could it be starving of fuel at higher revs?

What's the compression like too?

[neilus123]

Have had it rebored so assuming compression is ok and don't have any starting issues so think compression should be ok. Havent got a compression tester and don't know what it should be but will look into it. As for float again seems ok but not sure what it should be set to. Will try removing the carb on the quicker engine and see if that runs better. What effect does moving the needle height have.

[Tango]

Needle height can affect the higher rev running.......if the needle is too low it won't go onto main jet as soon.....so it'll starve the engine of fuel. Have you inspected the rotary valve?

What colour is the plug?

[neilus123]

Havent stripped it down because its so dam reliable I would trust it to start anytime anywhere, plug colour is somewhere between the perfect rusty brown and black but not oily. Although it does seem to be running rich as it smokes like hell on start up when cold and its seems to use more 2 stroke then I can remember other bikes of mine using.

[Tango]

Maybe the oil pump is overdoing it.......any adjustment on it?

[neilus123]

don't think there is its autolube but don't think to much oil would give them symtoms

[Tango]

No.....probably not......too much oil could possibly foul the plug though......

[neilus123]

Thinking maybe a broken piston ring. Had one on my lambretta that was broken but still in one piece. Gave it very little power top end not that it has much anyway lol

[Tango]

It's got the correct plug in it?

The RD350 I had yonks back used to run out of top end puff when the plugs needed changing......I know you said that the plug was changed......but if it's the wrong one it could cause top end probs......just throwing ideas out mate.....

[Tango]

Yes.....broken or sticking ring could cause probs.....but you'd see that with a compression check.....

[neilus123]

will have to get a compression tester and yes the plug is the correct type have even tried the iridium plug

[Tango]

Air filter is ok? and it's running a standard exhaust?

[neilus123]

tried standard, no air filter and now with k and n but no difference. Has been up jetted. Standard exhaust de coked with caustic soda and run with baffles removed with no difference.

[Tango]

Hmmmm.....maybe some of the other guys may have more ideas......

[neilus123]

ok mate thanks will change carb tomorrow and maybe exhaust system from other bike and see what happens thanks for your help

[Tango]

No probs mate.....

[Fozzie]

Crank case seals in the bottom end

When they fail they can do one of a few things, cause the bike to cough mid-way up the rev range and then operate normally if forced, or they can just sap power off the top end if they only partially go.

Without them the bottom end isn't as pressurised as it should be so when the piston comes down on it's downward stroke which compresses fuel and oil together and fires it up a port, if you have a pressure leak in the bottom end it will work ok at lower RPM's as the pressure isn't pushing passed the seal, but at high rpm's it will cause the seal to break and you will have a loss of power.

[Dav3y]

Exhaust ?

[Grumpy Old Git]

Crank case seals in the bottom end

When they fail they can do one of a few things, cause the bike to cough mid-way up the rev range and then operate normally if forced, or they can just sap power off the top end if they only partially go.

Without them the bottom end isn't as pressurised as it should be so when the piston comes down on it's downward stroke which compresses fuel and oil together and fires it up a port, if you have a pressure leak in the bottom end it will work ok at lower RPM's as the pressure isn't pushing passed the seal, but at high rpm's it will cause the seal to break and you will have a loss of power.

 

Had the same with an early 2-stroke. Replaced all bottom end seals and gasket. Problem solved!