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Discussion Starter · #1 ·
Need some help guys!!! I have an 06 600 switchback with about 4000 miles on it. It starts all the time on one pull, runs great except I believe that it runs rich at low speed...also is a real gas hog. Anyway, last week I was out riding in the evening and I ran it up to about 50-60 mph for about 1.5 miles and I could see some glowing under the hood. Stopped and popped the hood and saw that the can was red hot. It went back to normal color while idleing and I drove it home slowly...still ran good. My first thought that it was lean...which I find hard to believe but I couldn't think of too much else that would turn the can red hot, first time it ever happened. I took the carbs off and dropped them off at my dealer and told him to check them over after I explained my problem to him. When I stopped back later he told me that they were adjusted correctly and he found nothing he would change. My plugs were brownish in color although they seemed to also have fuel wettness on them. I still felt that the problem was in the carbs so I ordered a brand new pair. Prior to the new ones arriving, we had planned on a 150 mile day trip so I took off the next morning, went about 5 miles and the sled started to miss. I turned around, took the sled back to my garage and grabbed my 700 XC and took my trip. The next day my new carbs arrived and I installed them. The sled runs exactly the same, misses and backfires, starts hard and basically undriveable. Now I suspect an electrical issue...off to the dealer and explain it to the service tech...he suspects not an electrical problem but a bad cylinder/piston ring problem. A compression test back in my garage comes back at 80#s per cylinder...I suspect that even with 4000 miles I should still have somewhere in the neighborhood of 120#s per cylinder. So I pop the head and the pistons look great, cylinders look fine although I haven't pulled the clyinders so I certainly may have bad rings. Before I spend 400 bucks on pistons, rings and gaskets I thought I would ask for some more ideas out there. Any other thoughts on what may make low comprssion other than what I explained? It now is a chore to start. I'm afraid if I rebuild the top end and it still runs terrible I'll go out and buy a Ski-Doo!!!

Any input would be greatly appreciated.

Thanks,

Rob :)


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Did a compression test get performed? Pop the cylinders, you have the heads off. A.couple of more base gaskets. Should be able to analyze complete top end
 

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When you did your compression test were you holding the throttle wide open? Did you continue to pull it over until the needle stopped rising?

The pipe glowing red is usually a sign of unburnt fuel in the pipe/can that is burning inside the pipe. Sounds like the pipe had some unburnt fuel in it.

Unburnt fuel could be caused by overly rich jetting or it could be that the timing is off causing the fuel to make it out the exhaust port. Timing could be off due to a bad key on the flywheel, or maybe even a TPS sensor. I'd defiantly check out the TPS and wiring harness to make sure it is working properly.

it sounds like most people are running 410 main jets, needle in the #3 position, fuel screws at 1.5 turns out, and 45 pilot jets in the carbs.
 

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Discussion Starter · #5 ·
Thanks for the input so far...I still feel that the problem is still electrical but the low compression really baffles me.

:)
 

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Nothing wrong with the original carbs so why would you go and order new ones that made it worse?
Here is what you need to jet to: 40 pilot jets, make sure the pilot air jets are .9 or 1.0, drop the needles to #2 from top, 400 mains if you don't ride below 0*F.
And yes, with 80psi compression it is time for at least new rings, but I'd go full pistons and rings. Unless you had a faulty compression tester. And it must be done on a warm engine.
 

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Discussion Starter · #7 ·
myvertxcape said:
Nothing wrong with the original carbs so why would you go and order new ones that made it worse?
Here is what you need to jet to: 40 pilot jets, make sure the pilot air jets are .9 or 1.0, drop the needles to #2 from top, 400 mains if you don't ride below 0*F.
And yes, with 80psi compression it is time for at least new rings, but I'd go full pistons and rings. Unless you had a faulty compression tester. And it must be done on a warm engine.
Never thought the carbs were right, always seemed to run rich, thought something else might be going on with them that I couldn't locate so the new carbs were for me a good investment just out of piece of mind. I installed 390's in the original set of carbs and running #2 on the needle. I did this last year near the end of the season and it still seemed to run rich at low speed...great at anything above 5200 rpm. I am installing new pistons, rings and gaskets on Monday so we'll see what happens then. I still suspect an electrical problem but the new slugs should help the compression. Keeping my fingers crossed.
 

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Run that compression tester on the XC again to be sure that it's not really the tester, it might save you a lot of time and expense. (like buying a set of carbs that got you nothing)
 
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