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Running problems with 03 XC 800

N

Nothwoods

New Member
Messages
4
Age
50
Location
NH
Country
USA
Years Snowmobiling
38
Snowmobile
ZR800
Hello, I’m looking for advice on a 2003 XC800 that won’t go over 70 mph. It’s got 1800 miles, bone stock, with carbs. For the most part it runs pretty well, and has decent low speed power although maybe not what an 800 should. I’ve cleaned the carbs and rebuilt both clutches with stock tuning. If the throttle sensor is plugged in it coughs and backfires and stalls, but the sensor tests fine and I’ve adjusted it to spec so it reads 4 volts at WOT. Runs fine with the sensor unplugged. I’ve run it with the throttle monitor unplugged and no change, and I’ve tried the different key settings for premium fuel with no change. Flat out on the lake it was only pulling about 68-6900 rpm. I found a bulletin for an updated CDI, and I got hold of one and now it pulls about 7000-7100 rpm. I’m not trying to turn it into a rocket, just would like to have it running properly. Mostly I’d like to know if anyone has any info about the problem with the throttle position sensor. Thanks for any help!
 
Have you cleaned and inspected the power valves?

On the TPS sensor, I'd be willing to bet the temp sensor in the head is bad. That is the other major input to the CDI box, they usually fail full cold.
 
Yup I cleaned the power valves, and I checked them by running it on the stand and sticking a rod through the hole in the covers, they open and close fine. I did put a new temp sensor on too because I suspected it had failed but I think the old one was fine anyway. The sled seems prone to overheating if it’s run slow on a warmer day, but I’m wondering if it’s an ignition timing problem from the tps not being plugged in.
 
Today I did a bunch of circuit checks on the stator, ect sensor, ignition switch, tps sensor, coil and plug wires, all seems good to me. It’s a weird one for sure.
 
How about the thermostat? Possibly sticking and its running too hot?

Also I read there was supposedly jetting changes as part of that CDI remap, are you running the revised recommendations?
 
THermostat is new, but the problem with the tps sensor is when it's cold, if anything it gets better once it's warmed up. They want you to put 450 mains in for that bulletin, if memory serves it had 460's in it when I cleaned the carbs, but I'm sure that's not my tps issue. At this point I'm thinking it's got to be the sensor but I really can't find any faults or glitches in it. I know the guys at our local Cat/Polaris dealer really well, I'll have them take a peak and report back on here if I get it figured out.
 
Are you checking the TPS with a digital meter? You need to check the sweep with an old analog meter, the digital doesn't refresh fast enough to catch faults sometimes. Much easier to see the needle twitching on an old analog meter.
I wouldn't totally rule out carbs, my buddy had a 01 600 that did something very similiar. I'm trying to remember what the factory fix was, something in the low speed pilot circuiting of the carb.
 
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