Viper bog and intermittent spark on pto cylinder

A

Alweld1652

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Dec 25, 2013
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I worked on my viper adding a rear cooler last weekend and noticed a slight bog midrange when testing it out after installing the rear cooler. I pulled the carbs and went through them twice over the weekend with the bog not getting better or worse. Monday I sent my carbs off to a buddy to go through them at his shop and run them through his tank. After getting the carbs back and going through and double checking the power valves where adjusted and working I went for a ride and still had the bog I pulled the plugs with both the middle and mag side both tan and the PTO side had little to no color. Pulled the plugs to check spark whick looked strong on all cylinders. At a idle and low rpms it feels like it is running on all 3 and wide open I am right around 8900 which is what it has turned since I bought it last spring. If I am easy on the throttle it will run up to 8000 and fall flat like it does when the tors kicks in. I ran across a post on here with a similar issue and it ended up being the throttle cable was to tight and making it drop the PTO cylinder. Which after checking my cable and loosening it and taking it for a ride on the river I thought I had found my problem. It ran perfect like when I picked it up last spring.

A group of us loaded up and headed 3.5hrs north to ride for the day yesterday and as soon as my triple hit the trail it quit firing on the PTO side unless at idle or wide open. I tried unplugging the tors while on the trail yesterday to see if it made a difference which after a ride up and down the trail I thought I was back in businesses. But as always as soon as I took off again back to running on 2.

During the week while trying to trouble shoot I had checked the ohms on the plug boot and it was right at 5k but swapped it out just in case. I am out of ideas on what to do next and getting beyond my knowledge of sleds. Anyone with similar issues in the past or any ideas on where to look next? We have another trip planned for this coming weekend and I can't be that guy again with a sick sled.
 

possible things:

1.) rust on flywheel magnet
2.) bad pto coil connection on harness at coil rack
3.) wire for pto coil chaffed/broken
 
I am going to start checking out the wiring this afternoon. While I am at it what are the known rub thru spots I plan on addressing it before it becomes a problem. Under motor, handlebars, and by the cdi? Are there other places that are common?
 
Alweld1652 said:
I am going to start checking out the wiring this afternoon. While I am at it what are the known rub thru spots I plan on addressing it before it becomes a problem. Under motor, handlebars, and by the cdi? Are there other places that are common?
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You mentioned all the known areas but those won't typically take out just one cylinder.

While you have the flywheel off checking for rust it would be a good time to remove the harness under the engine to inspect/repair/protect.

I would start with Mr. Viper's last two suggestions - being they're the easiest to inspect.
 
IMG_20150305_154434_559.jpgWiring on the coil rack looked great. From the looks of the wiring harness the previous owner already pulled it and ran a rubber sleeve around it under the motor and up by the thermostat. He had mentioned the headache he had on another sled with a rub through. Pulled the recoil and the flywheel was pretty rusty. I cleaned up the outside. Should I find a puller to check the inside?
 

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sand the magnets on outside of flywheel and then spray it with like wd40 or kroil, also check the pick up coil thats mounted right there at the flywheel make sure its clean. then try the sled. Inside of flywheel has stainless liner so it doesnt rust,no need to pull it off.

if the crank was out of phase it wouldnt run on a cylinder then not, and they backfire and vibrate, thats not your issue, the rusty flywheel looks like its the problem if the wiring is all good, recheck engine operation and report back.
 
You said you unplugged the tors switch. Did you connect the 2 wires on harness side together?
Nevermind, after rereading your post, it sounds like you did. It seems like everytime you mess around that area of the tors wiring, it works for a while. Maybe something is rubbing through or bad connection in that area.
 
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I pulled all of that apart yesterday and checked over a the wires and found no nicks or rub throughs.
 
I checked out the pickup coil like you mentioned and cleaned it. Started it up and still not hitting on the PTO cylinder. With it running it is spitting fuel out of the PTO carb into the air box. When I shut it down there is white smoke flowing out of the same carb. I have video of it but no idea how to post it.
 
At this point I have no idea. It has good spark but every time I run it there is not any color on the plug or very little. It seems to be running on all 3 at a idle and it still hits 8900rpm every time I have rode it this year but it will only get to 8900 if I hit it hard from down low in rpms. If I am cruising at 6-7000 and accelerate it will hit 8000 and stay there.
 
Alweld1652 said:
I checked out the pickup coil like you mentioned and cleaned it. Started it up and still not hitting on the PTO cylinder. With it running it is spitting fuel out of the PTO carb into the air box. When I shut it down there is white smoke flowing out of the same carb. I have video of it but no idea how to post it.
Click to expand...

if its doing this then there is some kind of problem going on in that cylinder, I would first pull the carbs and check the pto one real well, pull the bowl off and check all jets,check float level in it, and pull the top screen out and check it, youll see there is an o-ring that goes on the needle/seat that may be bad.

if all that is good then pull the reed block out of that cylinder, check reeds to see they are not chipped off and are sealing to block. While you are there, look in at the piston skirt and see if its still on the piston, I have seen them come off before and still have good compression and the skirt is broken off the bottom.
 
Wow, glad you finally found it and that's one messed up reed. I'd just replace all of them while you're in there.
 
I replaced all of the reeds with boyesen reeds. I had chipped reeds on both the other cylinders but nowhere near as bad as the cylinder I was having trouble with. Went through the carbs and got it running last night. Everything seems to be back to normal. Once it warmed up the idle would hang when coming to a stop. I know I have ran across this on here before. Am I right on that you adjust the air screw to get rid of the hang idle? Any other time it idles around 1700-1800. I checked the plugs after idling awhile with good color and also after a few pulls across the yard which looked good to.
 
How many turns out are you on the fuel screws now? I would start with lowering the idle since you don't have to pull the carbs to try it. Don't forget to adjust throttle free play after.
 
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