Switchback Assault Clutching - HCS Snowmobile Forums

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Old 01-05-2020, 02:09 PM   #1 (permalink)
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Default Switchback Assault Clutching

Hi guys, long time reader but this is my first post as I bought my first sled early this winter. Picked up a 2011 SBA with 4300 miles. Top-end was rebuilt with a BMP "Fix-IT" kit and has the 1.352" track. It has been running strong (always starts first or second pull) only it seems to rev only until 7700rpm. I know peak power is made at higher rpm and the general rule is to shoot for about 8200-8250rpm. I am running at sea level (0-1000ft) The guy gave me two sets of clutch weights, 10-66 and 10-68. The 10-68 are currently installed, and with those, it revs to about 7700rpm at the highest. If I'm riding at sea level do you thing putting in the 10-66s will solve my problem? What are the stock weights? Any advice would be greatly appreciated, just trying to help my sled run as best as possible and I know you guys have the knowledge to help me make that happen, Thanks in advance!
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Old 01-05-2020, 03:34 PM   #2 (permalink)
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10-66 was stock in mine. It revved to 8250-8300. I'd try those first.

Also new springs in the clutches if unsure of age
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Old 01-05-2020, 04:31 PM   #3 (permalink)
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10-66 is stock. switch the 68s out to 66 and you should be hitting the 8050-8100 you need. and yes, new springs do wonders.
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Old 01-06-2020, 07:42 AM   #4 (permalink)
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Condition of belt? Clean valves? Rollers in primary clutch? Not going to gain 500 rpm with stock 66gram weights. Something else is going on.

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Old 01-06-2020, 10:28 AM   #5 (permalink)
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It's possible some parts are worn in the primary clutch too. Could be a lot of things. My XC would only rev to 7600 when I first got it, it was a combo of worn rollers and pins, clutch weight bushings, weak springs, etc. Rebuilt the primary clutch and it came alive.

But as said above, a new belt, fresh springs in both clutches, a delrin washer in secondary, clean valves, check belt and chain tension, and make sure clutch is in good condition. Also, TPS could need adjusting. The joys of a snowmobiler, lol. That is a fun machine though and worth getting to run tip top

If your primary spring is weak, or broken? A new one with the 66's could fix it up too. It's common for those springs to break, and would cause low rpm.
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