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High Performance Bicycle Engine Tips and Motorized Race Bicycles We all want our bicycle engines to push our bikes faster. Get exclusive engine modification tips and suggestions from us. Also check out some of our racing members builds

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  #1  
Old 05-10-2016, 07:41 PM
Keef B Keef B is offline
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Default Tuning your expansion chamber and Carburetor

I'm trying to understand how to get the most performance out of these engines..

Can anyone explain what it means when people say the following:


KX-65 expansion chamber exhaust pipe that has been tuned for high RPMs,Keihin carb that has been re-jetted for this engine (& pipe), (this was a post I saw on craigslist for a bike)

How do I know what jet size 65,70, etc etc to use in regards to what expansion pipe I have. Also does this have anything to do with how you port the cylinder jug meaning the size and shape in regards to the pipe on the exhaust side?? Also what about the intake side does that have anything to do in regards to how to you tune the carb and what pipe you choose.. Basically what's, when, where, why how's of this.


I apologize if this question was posted before I apologize.

Thanks fellas

as always ride safe PEACE..

Last edited by Keef B; 05-10-2016 at 07:50 PM.
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  #2  
Old 05-10-2016, 08:03 PM
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Greg58 Greg58 is offline
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Default Re: Tuning your expansion chamber and Carburetor

There's a lot to tuning to a expansion chamber, the shorter the head pipe is from the flange till it flares into the chamber the higher the rpm range is before you hit the power band or it starts producing felt power. Different lengths from flange to the cone at the stinger will change the power band.
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Old 05-10-2016, 08:13 PM
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Greg58 Greg58 is offline
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Default Re: Tuning your expansion chamber and Carburetor

In the search box near the top of the page if you type in "expansion chamber" you will find a lot of info. The link below will help explain.

https://www.google.com/url?q=http://...cJC93M2JtiQwdA
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Last edited by Greg58; 05-10-2016 at 08:16 PM.
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Old 05-11-2016, 10:17 AM
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Venice Motor Bikes Venice Motor Bikes is offline
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Default Re: Tuning your expansion chamber and Carburetor

The CL ad you are talking about is mine... http://losangeles.craigslist.org/wst...568219674.html

As Greg said above, there is indeed a lot of hours that go into properly tuning a pipe & carb to work with any engine.
You have to test (& re-test) different header/ stinger lengths & carb jets until you get the best performance; (& believe it or not), the size of the sprocket also plays a big role in tuning the pipe.
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Old 05-11-2016, 10:22 AM
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Greg58 Greg58 is offline
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Default Re: Tuning your expansion chamber and Carburetor

Good looking bike Norm.
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Old 05-11-2016, 01:05 PM
KCvale KCvale is offline
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Default Re: Tuning your expansion chamber and Carburetor

'Tuning" and expansion chamber exhaust is all about wave timing.

This is how they work.
Follow the green mixed gas.



All I can offer beyond that is I never have to jet a carb in Phoenix, and with a SickBikeParts expansion chamber it's single straight copper pipe length is perfect for a 48cc engine. Cut it in half and its perfect of a 66cc.
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Old 05-11-2016, 07:56 PM
Keef B Keef B is offline
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Default Re: Tuning your expansion chamber and Carburetor

Fellas,

Thanks for clarifying things for me guys this info really helps Greg58 I will check out that link read up on this more.. But it makes sense shorter header means higher RPM's. Yes "Venice Motorbikes" that is exactly where I got it from was your CL post. I freaking love that bike I check it out everyday (Wish list bike)lol lol . What I have now is a 32 Tooth sprocket, Jakes diamond head, port cylinder jug with a long stretch expansion chamber pipe. Which I assume I would need to tune for Higher RPM's since that sprocket is small. I'm looking at getting the reed valve setup & cylinder from gas bikes.com. Right now im debating on getting a Yamaha kx85 or Honda cr 80 pipe have it modified to fit or buying the Big bertha pipe from MZMIAMI on e-bay.
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Old 05-12-2016, 09:10 PM
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Venice Motor Bikes Venice Motor Bikes is offline
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Default Re: Tuning your expansion chamber and Carburetor

Something to keep in mind... Those factory motorcycle pipes are way better than any other pipe out there, but you'll have to cut & weld it to fit your bike (& you'll also have to make a header that bolts it onto your engine).

I can do it all if you need it done.
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  #9  
Old 05-13-2016, 02:35 PM
Keef B Keef B is offline
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Default Re: Tuning your expansion chamber and Carburetor

I was thinking the same thing?? Do you have access to get those pipes?? Send me a PM with you prices on muffler modifications.
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  #10  
Old 10-24-2016, 11:20 AM
JOBAfunky JOBAfunky is offline
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Default Re: Tuning your expansion chamber and Carburetor

OK, so I just got my banana expansion chamber on my beach cruiser last night. It was tough though. I got it to where the pedal just barely scrapes it and into the 1cm window of clearance between the front tire and the crank bearings. So I don't think I'll have room for any kind of extension pipe. It's a 66cc engine with a low compression huge Puch head on it. I'm noticing an occasional loud pop when idling, and I get it to quiet down when I gently throttle. I didn't get the low end power boost I was looking for. Maybe a little in the low middle. I have a racing carb with a bunch of jets, any advice on which way I should adjust?
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