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Discussion Starter #1
Last year, when drag racing buddies with my 670 HO, I noticed that from a stop, the revs climb quickly to 7600-7800rpm, then slower to 8000-8200. What revs should I be running at (on the stock tach)? I bought the sled used last season, and didn't have much riding time. I don't even know what holes the secondary spring is in.. I'll be checking on that next time I'm at the cottage. I have the TRA adjusters on 3 or 4 to get the revs to where I thought they should be.

Would not enough secondary preload (stock) cause this, allowing the clutches to shift too quick? (I forget.. is that the way it works?)

A few people on here have recommended running A-6 (~18.5lbs) or B-6 (~20lbs) in previous posts. Previous posts have said the stock position is around 15.4lbs.. what position is this?

Thanks.
 

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All tachs are a little different but just under 8000 on your tach you can shoot for. If you click down one your there. Your probably due for maintanance , get em serviced. I have a smokin set up for your sled but you will be buyin parts, pm me if your interested.
 

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Discussion Starter #3
The sled only has 3200kms.. It doesn't need maintenance. Before the season starts I'll take apart the secondary to check it out.

I am asking for recommendations as to what I can do to set it up properly.
 

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Any 670 that i have worked on pulled better if they were reving around 7800 rpm. I would turn your clickers down to an even lower number and see what happens. Do you have anyone that you can run beside to see if you are making progress or not??Ill bet that if you could find a dyno chart for your sled youd probably find after 7900 you are probably loosing at least ten horse power if not more, ski doo pipes fall off very fast once past peak. IMO
 

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Discussion Starter #5
I think that's what the numbers were.. this was last year. I thought on average Ski-Doo tachs read 200 rpm high.. now that I think about it, I think I had it adjusted so the rpms quickly climbed to ~7700, then took about 2 - 3 seconds more to finally get close to 8000. Its the slow climb at the end I was wondering about and hoping to fix. Could a low secondary preload cause this?
 

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Listen to Ballsout and do a little maint. 3200 kms is time for a new primary spring and for sure a good clutch cleaning and check. Now back to your problem. I have two HO's and have friends with them also and I have yet to see one that could pull the 53 deg start on that helix with the stock primary setup of 297 ramps,200-290 and 16.4 g. Put in a fresh spring and see where you are at. If it still loads up too much (after checking cen-cen, alignment etc.) try a straight 50 or a 50-47 if you have access to them and see how they work.
 

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Stock preload is not 15.4 as the race manual suggests it is A6. Mine works better at b6. 19 pounds on mine. I have calibrated both my tachs and dont assume they are all 200 high as some say they are. I have one that is 150 high but the other is 50 low. Mine work best just under 8000 on a calibrated tach. My standard 670's worked best at 7700 unless the base gasket and y pipe were modded.
 

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Discussion Starter #8
How do you calibrate the tach? Send it out somewhere, or can you do this yourself by sending a known signal to it and move the needle?
 

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I used a signal generator and an amplifier to produce the signal. I didnt calibrate the tach, I just know where 8000 reads on them. One was 150 high and one was 50 low.
 
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