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Doug E.
Doug E., Kawasaki Master Technician
Category: Motorcycle
Satisfied Customers: 2886
Experience:  Professional motorcycle mechanic since 1978. Vintage motorcycle restorer.
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A new question is answered every 9 seconds of the cylinders had low compression..lean

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I have a 2000 Arctic Cat ZR600 that would bog down intermittently whether under hard throttle or moderate throttle. It would seem to run out of gas as if the floats bowls were not filling up fast enough but again this was not a regular occurrence. Since then I discovered one of the cylinders had low compression only to learn it was running extremely lean and burned up the one of the pistons. I replaced the piston and rings and have throughly cleaned out both carbs. One of which was really gummed up which would explain why the camber was starved for fuel. I now have plenty of power but it still bogs down during moderate throttle. Spark plugs show correct color, not to lean or rich, and both cylinders show 95lbs of compression. I'm told the throttle/ignition monitor switch could be the problem. If true, what is the adjustment for this switch under the thumb throttle or is it best to replace?

The throttle switches are a real bother, but will save you should your throttle cable freeze and the throttle stick wide open. When these fail or are out of adjustment, the engine will cut out or miss as you open the throttle. If the engine is just doggy, there are other issues.

There are a few things to check. First off, your compression numbers are low. Check them again with the motor cold, throttle wide open and pull till the gauge stops. Repeat the test when the engine is warm. Let me know what the readings are. A new motor should be about 145 and 125 is ok, but there should be no drop when the motor is warm. A motor running at 125 that drops to 110 when warm has problems.

Did you soak both carbs with the jets removed to make sure all of the varnish is gone? You may want to do this to make sure there isn't going to be a continuing problem. You might want to replace the jets and float valves to be sure. I use Yamaha carb cleaner. You mix it with water, heat it and it boils out the varnish.

There are magnets inside of the carb slides on the VM carbs. Did you take a look to see if they have come off? If so, epoxy them back into place. On the side of each carb is a wiring plug. Take your jumper plug from the tool box (or make one) and unplug the carb. Plug the jumper into the harness side and test the sled. Repeat for the other side. If this solves the problem, the magnet is loose or the wiring sensor needs to be adjusted.

If that doesn't solve the problem, pull up the handlebar pad and plug your bypass plug into the kill switch junction on the harness side. That bypasses the kill switch and safety switch. Does that solve the problem?

Let me know what you find. If you run those tests that should narrow things down so I can get you fixed up.

Arctic Cat CatMaster
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Customer: replied 7 years ago.
Thanks Doug! Great answer a few of your questions. Carbs were not soaked but were thoroughly cleaned by hand three times. I wanted to soak but did not have tank or solvent. Floats/Jets were not replaced. I did not notice any "magnets" as you Carbs according to the manual are TM38? Also, is there an adjustment for the throttle/ignition monitor switch under the thumb throttle? Or do I need to bypass it to simply check if the switch is the problem? Also what is the factory setting for the fuel/air mixture screws? I turned them down until gently seated then backed them out to where they were at approximately 2 turns. This sled has 2000 miles on it and runs strong but with the occasional bog in performance which is corrected by cracking the throttle a little more. The replaced piston camber after three pulls reads 110lbs but did come down to approximately 95-100 after warm up. I did not sleeve the head or replace it...
That was the year they went to a TPS type sensor instead of the magnets. The TM has the sensor and the VM has the magnets. My mistake.

The throttle cable play is the only adjustment in the system. The TM carbs have no freeplay between the throttle lever and housing. The washers above and below the lever wear out and need to be replaced every year or so. The housing itself can wear out if the rider twists the throttle instead of pushing straight on it.

On the engine block by the recoil, unplug the main 4 pin connector. Does the sled run fine? That bypasses all the switches and safety switch.

Try some of the Yamaha carb cleaner next time you have to soak carbs. You can mix up what you need and put it on a hot plate. In 15 minutes the carbs are clean as new. The cleaner can be saved and used again and you can wash the carbs in water to finish the job. Although not good stuff to breath, this is a far safer product that what's sold at auto parts stores. That crap will kill you 10 different ways.

If there was some scoring on your cylinder walls, that would explain the compression drop when warm. The rings are loosing some of their seal. I still think the problem is in the safety switch.


Customer: replied 7 years ago.
Thanks for the great guidance!
Anytime. Let me know what you find.