Expansion Chamber

I purchased a pocketbike expansion chamber on Ebay. It was under $20. with shipping, and with some 3/4" copper, copper fittings, shelf bracket, some bending and shaping this is what I came up with. It still needs to be painted. It is very loud, but sounds great, and I hope to repack the silencer with fiberglass. I havent had a chance to take it out as it was late when I finished. Here are a few pictures and I will post performance later...

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Man - that's a huge long run pre chamber - could be good for low end torque.

Good work!!

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You are right Pablo the low end is incredible, still get about the same top end but it seems to have more. I think I am going to go up a jet size, and adjust needle. I already had good low end torque cause im running a 50t rear sprocket, but the bike takes off out of the hole, then sputters around 15mph then at about 18 kicks back in thru 23mph.

Have you ported the manifolds? Most importantly do the exhaust port, flange and gasket all match perfectly?

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Yep all done, I replied to you on the other thread. Stepping all over the guy thread lol.....

The reason it is sputtering is because your pipe has been altered from how it was designed. The distance from the exhaust port to the beginning of the expansion chamber is a very critical dimension. If this distance is changed the pipe will not work properly. I am sure it works better than the stock pipe but unless tuned correctly it will not offer the performance advantage that it should. These engines have a powerband in the 4 to 6 thousand rpm range. To properly tune a scooter/pocket bike pipe for one of these engines, the recommended distance from exhaust port to the start of the expansion chamber is about 12 inches. This can be altered plus or minus an inch or so to correctly tune it to your gearing and riding style. The attached photo illustrates how to measure your header length.

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Your pipe looks good. I guess I will have to live with it then. I dont see away to shorten the header length. I am very happy with the performance overall, so much better than stock. Thanks for the info Ghost.

P.S. Im sure your asked alot, but how much longer till the kits are ready?

We will be shipping in July!!

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You rarely have to "live with it", my rendering suggests that it is possible. You may need to get a 45 deg fitting to bend the silencer but shouldn't be too hard.

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do you get more power from the tuned pipe? and is it much louder than stock or just a little? I like to draw attention but not that much!

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