I have some problems with my ’98 XCR 440. Last year I used it bone stock, only rejetted to MJ 340. I used R8 helix and silver/blue sec. spring (stock) and S53R weights and almond/gold spring (also stock), drive belt OEM -67. It ran pretty good, more top end than most ’98 ZR 440 SnoPro’s. I could even reach almost 110 mph @ 8500-8600 rpm on the speedo in absolutely ideal conditions, 100 mph in most every condition. It usually revved at 8300 rpm.
By the end of last season it started to behave funny. I slowly lost my top end, and my back-shift decreased. I thought it was due to the warm weather, causing my soft -67 belt to stick to the clutches, since this was at the very last days of the season. But when I used it this year I had the same problem in cold weather, decreasing rpm’s when approaching 60 mph, dropping to approx. 7400. By then it refuses to go above 80-85 mph. Terrible back-shift.
I’ve tried a lot of things, changing to a harder -66 CVT belt improved my backshift and raised my rpm’s a bit, but still no top end. I’ve changed my primary spring to a brand new, which took care of some of the problem and raised my engagement a couple of hundred rpm’s. I’ve tried new weights (a bunch of them). With 10MBs I have a snappy engine, but it overrevs to 8700 rpm. So far it seems like 10M works OK, but my backshift could be a lot better, the engine has rubber band feeling and I have a 300-400 drop in the rpm’s in midrange. Now I can reach at least 95 mph at good conditions, @ 8300 rpm.
I suspected a power loss, but I’ve dynoed it to approx. 97 hp. which is I believe is OK. What has happened with my trusty XC racer?
Instead of trying to fix the problem with calibration changes, I would concentrate on finding what changed that is causing a good working set-up to not work any more. How many miles do you have on this sled? It sounds like you’re convinced that the engine is in proper condition based on your dyno verification, but I’m not so sure. 97 HP sounds way too high for that engine, I’d expect more like high 80s, low 90s. I wouldn’t be surprised if you need a new set of pistons and rings. Remember, this is a little 440 being squeezed for about all she’s got, and what you’re describing sounds about right for loss of compression. Anything over 1000 miles and I’d be very suspicious.
Once you have eliminated the engine power for sure, then you would need to concentrate on the drive train. All the way from the drive clutch to the track and suspension. Have the clutches been cleaned and serviced? Bushings OK? Any binding? Belt deflection, ride height, side clearance all OK? Button condition? Are the clutches shifting out as far as they used to? Driveline bearing condition? I’m not convinced your engine is making full power. If it is, then one of these basic components is likely the cause of your woes.