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I found a set of Fast twin pipes for my 96 Summit 670. I am currently running 330/310 jets, and ride at 8000' - 10000'. Will I need to jet up a couple of sizes with these pipes? It still has stock airbox and HAC hooked up. Thanks in advance Mike
 

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I found a set of Fast twin pipes for my 96 Summit 670. I am currently running 330/310 jets, and ride at 8000' - 10000'. Will I need to jet up a couple of sizes with these pipes? It still has stock airbox and HAC hooked up. Thanks in advance Mike[/b]
If those pipes are the models with resonators on the pipes as well as having a muffler, the kit came with a special rotary valve disk (167 degree) and pod filters. You could substitute a Rotax 501 R/V but as mr670 said you will need to jet for your altitude and temperature and check the jet needles. The best models to correct any part throttle lean spots are the 224-AA-3. The sea level jetting for that kit recommended mains for -20 F was PTO 310 MAG 290 and -40F was PTO 330 and MAG 310.
 

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Thanks that will get me started as I have a jetting spreadsheet that should get me close. I found these pipes at a great price and decided to do a little hot roddin when I rebuild my spare motor. I'll have something to do if theres still no snow when I get stateside in 2 weeks. If there is snow my hot roddin project will have to wait until spring. Thanks Mike
 

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You will have to reclutch too. It will probably be way way off. I can't emphasize how much pipes change your power band. Say goodbye to your low-end torque, you'd better be looking at about a 5000RPM engagement. If you don't reclutch, it will probably be unridable especially in powder. I can say this from personal experience owning and tuning 2 different piped twins, a 600 and a 700. I was given this warning, I didn't fully understand, and it became a long hard road figuring out how to properly tune for pipes that will eat up a good chunk of your season.

The pipe-maker may/should have a clutching chart on file that will tell you how to set it up for your altitude. That is the quickest and best way to tune, only a dyno test is better. If not, good luck you'll need it. Pipes are very much an engine modification on a 2-stroke and you can't just leave the clutch the way it was before. The OEM clutching chart can be thrown out the window, it no longer applies. Also you have to run premium fuel if you don't already. *If* you can get it set up just right you will enjoy the boost.
 
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