Problems Vxmax 600 XT -96 Engine

D

Diversion

Member
Joined
Mar 3, 2009
Messages
69
Age
54
Location
sweden
It has run for 2100 miles and the pistons were changed at 1200, not because any fault but just as a precaution.

When I came home after a ride the idle suddenly went up, not enough to engage the clutch but still. I thought it had to do with the TORS so i fiddled a bit with the throttle and it went down to normal.

The next day the sled was suddenly without power. It starts immediately every time but it is like it's only a third of an engine. When given throttle it increases rpm much more slowly than normal and it is almost like it's four-stroking in some rpm ranges.

I have spark on both cylinders but the plugs look a bit on the oily side. I also checked the clutch and everything seems to be ok, i ran it with the track in the air and it is still the same. I removed the belt and turned the secondary and the track moves very easily so i don't think it is clutch related or some bearing. The engine itself also turns over as it should when i rotate it by hand.

I might add that It has never been ridden hard or in high temp so a piston seizure doesn't look likely either. Could it be an electrical problem related to the ECU?
 
Try putting a fresh set of spark plugs in it to if it cures the sluggishness. The carburetors may need to be cleaned.
 
Take the gold tops off of the carbs to see if the set screw that is used to sync them has fallen out.
 
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Pull the plugs and hold your thumb over the hole while pulling the starter rope, compression should push air past your finger off the spark plug hole. sounds like maybe you lost one piston.
 
My first thought is she leaned out a little causing the spike in RPM at idle (possible set screw loose - very common).

This could have taken out a piston unfortunetly.
 
The compression seems fine. I can't say it's the same on both cylinders without a gauge but it feels close. I can't imagine a slight difference would cause this behaviour. I could get a quite good look at the pistons when removing the spark plugs and it looks fine as far as I can tell. Does anybody know if the fuel system has these solenoid controlled valves that the 600 DX has?
 
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You can't really get a "good" look at the piston through the plug holes. You think you can because you can see a lot of piston but if there's a chunk missing on the edge you can totally miss it unless you pull the head.

Get a gauge and do a compression test. Then pull the carbs and pipe, plug the holes, and do a pressure test (pressurize the crank case to 6-10 psi (don't exceed 10), close it off and watch the pressure - it shouldn't drop more than .5-1 psi in 10 minutes, if at all - I can usually get them to not drop at all). If you fail the compression test pull the head and have a look. If you fail the pressure test start spraying the motor with soapy water looking for your leak. If you have a bad seal it could cause the motor to lean out and have some of the symptoms you describe. Long term it would lunch a motor.
 
A better way to do a visual inspection is to pop the pipe(s) and look into the cylinder so you can see the skirts (this will only show the exhaust side but may give you and idea. The pressure test is the best sure fire way to know if you have a leak just make sure you not leaking out of the exhaust/intake.
 
It was a lever on the carb coming loose so only one cylinder got fed when giving throttle. It's now fixed. I am glad it was nothing more serious and expensive.
 
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