Nowhere To Go

"Dear Ralph" March 10, 2006 0
Dear Ralph: I have a 1998 Arctic Cat ZRT 600 which I bought used and am now trying to figure out. When I am...

Dear Ralph:
I have a 1998 Arctic Cat ZRT 600 which I bought used and am now trying to figure out. When I am running wide open across a hard packed lake it does not seem to be going as fast as I expected, so I marked both of the clutches. What I found was that the belt had worn off all the markings on the driven clutch but had left about _” of marking on the primary. Can you give me some ideas on how to get my primary to fully shift out?  Do I need a lighter primary clutch spring and heavier weights, or should I stick with the same spring and try lighter weights to gain more RPM and HP?  I guess there is something else I should tell you; the guy I bought it from said the sled was set up to run 9200RPMs the highest I got was 8900RPMs.  Any ideas would be greatly appreciated.  Thanx, love your mag.
Gregg Hilgenberg

We often hear complaints about sleds that won’t push the belt all the way to the top of the primary after guys use a magic marker on the sheaves and inspect the sheaves after a run to see how high the belt came up. If the machine is geared properly (10% higher than it should ever run) the belt will usually never get all the way to the top. Close, but not all the way. The magic marker test isn’t really to get it all the way, but more of an indicator of how close you really are. To get the belt to the top, you would have to lower the gearing, but if you did that you would likely over rev the system on a day with even more ideal conditions; colder air, less drag, longer run, etc. If the primary closes too far, the belt can come up and out and that is a very bad deal (and dangerous if the belt flips over and the track locks up).
In your case, you state the secondary is shifting all the way out, as the belt is all the way down into the sheaves. So if you did get the primary to shift further, where is the belt going to go in the secondary? Does it even have anywhere to go? I don’t believe you have a problem with the clutches not shifting all the way out, the problem is more likely in the jetting and calibration.
A 1998 ZRT 600 is not going to run properly at 9200 RPM unless it is modified with an aftermarket exhaust system. I would want to first verify the actual operating rpm of the system, which is pretty much dependent on the exhaust more than anything else. Once you know this, then you can try to reach your target. Get the motor running properly, with the right jetting, then get the shift RPMs where they need to be. If the engine is over jetted, spending time on the clutching is almost worthless.
Conventional wisdom would indicate you need lighter flyweights to raise the RPM, but I’d first make sure the engine is running strong, verify the actual target RPM, and install a new primary spring (if the one in there has sagged, the running rpm will be reduced). This is also dependent on exhaust system temperature, as heavier flyweights (which should reduce operating rpm) will load the engine and create more pipe heat which in turn makes more power and then the rpms could go up, not down). You might want to seriously consider finding a good Cat speed shop to help you save time and effort in this situation.

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