2003 Viper Cylinder issue?

M

munisean

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Munising, MI
I have a 2003 Viper Mountain with Bender triple pipes. The sled has around 5k on it. The motor was went through about 500 miles ago. All new seals and new rings.

Last weekend I all of a sudden was loseing a cylinder. At low rpm the cylinder closest to the clutch was running cooler. (egt guages) About 250 degrees compared to the other being at least 500 degrees at idle. At high rpm I could get the cylinder to come alive. But never running at equal temp to the other cylinders. The plug would foul out completely after a while and the cylinder will not come back. I pulled the carbs and went through them.
I did a compression test. The suspect cylinder is around 90. The 2 others were equal around 110. I read some where that a carb dumping to much gas can cause wash out in the cylinder and cause the lower compression. This is why I cleaned the carbs.

It was like a switch was flicked and the the problem was there. It did not get worse over time or any thing.

Do you think some thing happened to the piston or rings in this cylinder?
What would you do? I was considering just buying a new piton and rings for one cylinder. Get a top end gasket kit, and be out in the plains by the weekend. Would you replace all 3 sets of rings while you were in the motor?

I am trying to order every thing I will need with out being there to take the motor apart and diagnose to then order and wait for parts.

Also, Could a power valve or coil not working properly cause this? I dont think it would change compression but thought it would not hurt to ask.

Thanks in advance for any info you can provide.
 

are u sure the piston or cylinder is damage ??? if not check the reed they are maybe broke ....better take off the head and check
 
like mod said, i would pull the reed block in that cyl. first and check it. Also, the pto cylinder will be lower then the center and mag because of the larger chamber in the viper head.
 
After some research I learned that the pto cyl compression is lower. I wound up getting a new craftsman compression tester and retested. 120 120 and pto 110.
Inspected reeds. - perfect
Cleaned carbs - just because.
I did pull the head and all looks perfect.

I found a thread in this forum from 2005 that some one talked about a pto cyl dropping issue.
http://www.totallyamaha.net/forums/showthread.php?t=48975&highlight=viper+coil+test
After reading that thread I inspected all of the wiring under my hood. I have every thing wrapped pretty good with metal hvac tape. Found no obvious issues.
I then removed the coil and tested based on recommendations in the thread link posted above.
I used the following thread for testing specs.
http://www.totallyamaha.net/forums/showthread.php?t=11501&highlight=viper+coil+test
The stupid spark plug cap!!!!!!! It is reading about 40k instead of the 5k it is supposed to. The coil checks out with in spec.
Going to pick up a new cap this week and start putting this thing back together over the next couple of weeks. I started this thread last spring. I put this one off for as long as I could.

Thanks to TY for being such a great source of info!
 
I had the same problem chasing a high RPM issue. Sled would go to 8,500 and then drop after a couple of seconds to 7k. Went thru everything including replacing the entire primary clutch. I finally tested the Ohms in the spark plug caps. One of them was reading 5.8k instead of 5. Now it holds 8,500 RPM.

Go figure.
 
Any one know if the plug caps off of a 98 srx 700 will work on the viper? It is not the same part #. Wondering if any one has done this with success.
 
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