03 viper PTO cylinder dead?

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pitviper

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First sled for me, 2003 viper with 4500 mi. Had carbs cleaned before the first ride. Went out on three trips each one about 50 miles. Sled ran awesome. Last trip out got caught in a bad storm and rode about 40 miles at real low speed on a lake, went to load up on trailer and didn't realize my buddy had my parking brake on. Obviously took me a minute to realize it was on. Anyway, loaded it onto trailer got home and fired it back up. It backfired and didn't want idle right. I realized the PTO cylinder wasn't getting up to temp. Checked compression and all three cylinder read 123,124 and 125psi. PTO plug was black and wet and the other two were just black.
I did the MR VIPER crank check with marks on the clutch. I measured between my marks around the clutch and got 9", 9", and 8". Does this sound right? The crank gets out of phase that easily? If it is now what?
:o|
 
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Plug got so dirty it stopped firing. Sleds load up at low speed or idling for long periods of time. Yamaha sleds are jetted rich from the factory for safety. While you shouldn't sit there idling all day long, don't let it warm up for too long either. Get it off the choke as soon as it will stay running, and don't go blipping the throttle to keep it running. You can give it a bump of half choke if it needs to save it. These are all tips to prevent fouled plugs.
 
No, all 3 measurements should be the same, same thing as all 3 pistons should be at TDC exactly 120deg apart, or 1/3 of a crank revolution per cyl.
9", 9", 8" isn't 1/3, 1/3, 1/3
Also, stock Vipers had lower compression on PTO cyl, should be roughly 10% less than other 2 cyls.
May want to recheck? I wish you best of luck, hope it's not out of phase.
 
after reading the problem I have a couple questions:

1.) after you put a new spark plug in, it still wont run on the pto cylinder,is this only at idle?

2.) with the rear end up on a jackstand will the sled rev up and run, is it backfiring thru the exhaust?

if it wont run, put on a glove and pop off the spark plug boot while its running on the pto cylinder and just barely place it over the tip of the plug, can you hear the arcing of the spark to the plug? did it pick up the sparkplug/ run on the cylinder bringing up the rpm when you did this?
 
mrviper700 said:
after reading the problem I have a couple questions:

1.) after you put a new spark plug in, it still wont run on the pto cylinder,is this only at idle?

2.) with the rear end up on a jackstand will the sled rev up and run, is it backfiring thru the exhaust?

if it wont run, put on a glove and pop off the spark plug boot while its running on the pto cylinder and just barely place it over the tip of the plug, can you hear the arcing of the spark to the plug? did it pick up the sparkplug/ run on the cylinder bringing up the rpm when you did this?
Click to expand...

1.) new plug in, didn't run on the pto cylinder only at idle. I was afraid to do any further damage.

2.) it backfired pretty good through the exhaust two or three times when revved slightly, sitting on the ground. I started pulling things apart and found the gasket from the y pipe to midpipe was cracked pretty bad and blowing out a lot of oil/fuel. When I pulled the pipe off it just fell into 2 pieces. I have to get a new gasket and then I will try to get it running up on jackstand.
I truly appreciate your help with this.
 
Put new exhaust gasket on, put three new plugs in and took belt off. Started on 5th pull like usual. Immediately motor started winding out with half choke on. Started toggling the choke between half and off and got the idle to drop to around 4100. Did this for a couple of minutes and idle finally dropped to about 3000. It was starting to warm up so I revved it up a couple times. Seemed to wanna run but seemed to pop intermittently but no backfiring. Let off throttle and it started to climb on its own to about 6000! I hit the kill switch and turned key off and it kept screaming. After about 3-4 seconds it died. Any ideas?
 
did you turn the idle screw back when it was running poor and forgot to turn it back out?
 
Could be bad gas or rotten fuel filter clogging carbs. Double check the idle screw. Before you do anything, recheck the crank phase.
 
Re-checked the crank phase. Seems like a lot of room for error, but i can come up with 8.5", 8.5", and 8.5". PTO plug looks like it never fired. I put a spark plug in-line tester between plug and wire. Spark pattern appeared the same on all three cylinders.
 
The dwell of the piston will make it hard to find exact tdc, repeatedly anyway . If you have a dial indicator you could measure the stroke of the piston when it hits .010 btdc put a mark on the clutch and again when it hits .010 ptdc then measure 1/2 way between the two marks and you should have tdc .
 
Have you checked the reeds? I know a bad back fire can destroy them and do all sorts of weird things.
 
Unfortunately I do not have a dial indicator.
Am I paranoid about the crank? Would it go out of phase that quickly? It was running perfect until the parking brake instance.
I have to wait till the weekend to take the carbs off. Thanks for the help so far.
 
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