crack in the expansion chamber

[schmanman]

I am curious, can a large crack in a 2-stroke's expansion chamber cause the bike to rev uncontrollably? I am going to re-weld it in a little while, but I have done some experiments, and I suspect this is the culprit.
the bike started first kick this wednesday, and ran perfect. the bike has a rev-limiter (thank god) so the motor didn't blow)

and where can I get a new cylinder and piston for a
1976 kawasaki ke-175?
I found some scratches on my piston when I looked through my exhaust port.the scoring does not look new, And I cannot hear any noises, and it turns over and starts great.
well, now that the expansion chamber is cracked, it takes a little pull on the throttle to start it. or at least it did this morning.

I got the bike for free, It has good compression, so I'm not sure how long the scratches have been there.

what is involved in replacing a top end? I am extremely mechanically inclined.

is it very difficult?

 

[just_a_rider]

I'm not sure on that one, I've had cracks before and noticed no dif but thats not to say it wouldn't make a difference.

 

[schmanman]

this is a big a** crack (no pun intended), not a small pinhole leak or crack. it is all the way around a bracket, the crack on three sides, each being 2 inches long at least.
I am 99% sure this is the problem, because the carb is 100% fine and in good running condition, and there are no air leaks in the cases or seals.

and, why else would they put the expansion chamber on there? it makes a big difference, try taking the pipe off your 2-stroke and firing it up, and see the difference. that is, if It will even fire.

the scratches are not at the bottom of the cylinder, then there's a little tiny patch that starts and stops 1 1/2 inches from the bottom, and then there's more unharmed metal above that.

anyway,....
it's a rotary valve 2-stroke if that makes any difference. I am searching as we speak, but where can I get a new cylinder, and piston?I may just get it bored once or twice over if required.

oh, nevermind, the engine is the same as the kd 175, and the F-7 maby the kx. not sure on that one.

 

[76GMC1500]

Air leaks on the intake side and lean jetting cause a 2-stroke to rev uncontrollably.

 

[schmanman]

hmm, I'll check the air intake side, and that would lead to lean jetting because it would lean out the air:fuel mix.
the jetting is fine, It ran perfect and started first kick last Wednesday.

oh, wait! the engine, since it's a rotary two stroke, the carb is attached directly to the engine, it makes no difference!


ok, here is my engine.
the green circle is around the air intake from the air box, through the case, to the carb. I'll take some pics today of the carb. (it's under the left side cover).

 

[schmanman]

ok, update:
the bike runs and starts as good as before with the hole plugged. now to weld it.

I'm still interested in replacing the rings, piston, and cylinder jug.
I cant seem to find a wiseco part for my cylinder, it is a 1976 ke-175.
same engine as the 1975 model.
the engine is also the same in the F7 and the kd. not sure about the kx.

 

[ZOMBIE666]

a crack in the exhaust, no matter how large would not cause your bike to rev to the moon. like 76GMC1500 said, a lean condition is most lkely the caulprit. just a thought, have you made sure you have gas? i remember my first bike, a 72 dt100, would rev like a mofo if it ran out of gas or the float stuck closed(lean condition)

 

[schmanman]

maby a float is stuck closed. the carb's a munuki (spelling?) carb.

where would the floats be?

would you like some pictures?

oh, I figured out what was happening. I feel prettttty stupid now. :whoa:

the throttle was sticking a little bit.

I loosened it up.