Exhaust Won't run With Exhaust Pipe On!?


New Member
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8:26 AM
May 26, 2008
I have a 70cc 2 stroke that was recently installed. The engine would always start and the throttle would rev the engine but there was no acceleration at all. We have been trying and trying to figure out why and ended up taking the exhaust pipe off...then the bike took off! It runs great with the pipe off, but after putting it back on, nothing again! any ideas?
I started with a 20:1 ratio and when that wasnt working tried a 30:1, which still didnt work until the pipe came off. It ran with that, then we put 20:1 back in and it still ran, so I dont think thats the problem. There are no visible blockages because there are so many solid parts inside the pipe you cant really tell anyways. My boyfriend says the whole pipe is just a blockage...can you harm the engine by riding w/out the pipe? My dad has a welder, is it possble to change the shape or anything without destroying anything?
It is definitely harmful to run your engine without the pipe! A two stroke engine operates primarily on the backpressure the exhaust creates. I suggest you take the pipe apart before you weld anything and such. Depending on the type of exhaust you have there should be 1 or 2 screws near the bottom of pipe. When you unscrew these the bottom of the pipe should drop out along with a small in diameter pipe (this is the baffle). Make sure the baffle and the exhaust housing are clear. Shine a laser pointer or flash light straight down the baffle pipe, the beam should come out the end clear and undistorted if its clear.

Blow into the pipe- should go right through without restriction....if you feel like keeping your mouth off the pipe, try compressed air or even a garden hose provided you make sure and dry it out before bolting it back up.
As far as the bottom of the pipe is concerned...it will not just "drop out" as described above. The screws secure a metal cap with tip that is wedge quite tightly inside the diameter of the muffler. If you need to remove this cap do so with the understanding that you will need to pry and pull it off with pliers and may deform it slightly. My efforts worked, and the worst you can do is just scratch the chrome paint off the pipe.
Have you checked for a blockage in the exhaust pipe?

Yes, your exhaust is restricted. Carbon deposits or oil gummed up inside is resricting exhaust flow. Cars also will run doggy/sluggish or not at all if the catalytic converter is plugged. I think it's the same principle here. It may seem like a dumb question, but did you make your own exhaust gasket and forget to cut out the hole?:D
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