Expansion Chamber

misteright1_99

misteright1_99

New Member
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!!(^)
 
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.
 
misteright1_99 said:
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.
Click to expand...

Have you ported the manifolds? Most importantly do the exhaust port, flange and gasket all match perfectly?
 
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?
 
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!
 
Tuned pipes are the easiest and most inexpensive way to improve the performance of a 2 stroke motor. They are typically louder but can be made quiet by improving the silencer.
 
Ghost0 said:
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.
Click to expand...


Your the man. I hadn't put that much thought into it. Now its time to think about it... Thanks Ghost.
 
Hey GhostO,You talked me into a tuned pipe.the one I ordered looks to be the same one you have.any problem with pedal crank clearance and what are you using for a kick stand,Thanks,Ron
 
I'm not GhostO but after I put a tuned pipe on mine had kickstand problems. So I drilled a hole in a short piece of angle iron and bolted it to my back axle. Then I drilled the other side of the angle and mounted the kick stand to it. So the kickstand is basically mounted the rear axle. It really makes the bike sit on the stand better...............
 
I am using a rear mounted kickstand as Ilikeabikea suggests, but mine was made for it. I didn't have to modify it. You can get them from most of the bike shops. If you have any questions on mounting the pipe just PM me and I can walk you through it. It is pretty simple.

I didn't have any pedal clearance issues but it does get close.
 
I never had a kick stand so no worries....

My pedal was very close to my silencer, but with my magic bracket, no worries.....
 
Yes a magic piece of Al sheet bent at a magical angle with three magic holes drilled in it. Top hole too low, bottom hole too high - middle hole just right!! :D

938d1213062125-messing-my-bike-new-pipe-ac-p1010132.jpg
 
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Pablo, it appears to me that one is not to high nor is another to low. It is a "universal" magic bracket.:D........................................
 
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