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I got a issue that has got me stumped . Take sled out do a couple WOT Pulls then it starts dropping the mag cylinder some times it comes back sometimes you could run 600 ft and it stays running on one cylinder if I stop and let it idle it will usually kick in and go a couple hundred feet and then drop again . I determined it was mag side when I held it WOT and it lost power I ran it for about 600 feet hit kill switch and took out plugs pto golden tan. mag side black as black can be I don't know if it's a fuel issue or electric issue I cleaned carbs and put new plug wires and boots on all to no good , I'm stumped . No check engine lights I had it on buds and cleared all the old codes ran it for a bit hooked it back up and buds detected nothing .. Any suggestions would be appreciated.. It's almost like its losing spark on mag side but I don't know what to go after next . It comes and goes i may get 5 good 600 ft passes. And then it will drop you may be half way down track or sometimes it spits from a take off.. Sometimes it will drop and come right back in .
This is a 06 rev800 ho ptek

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Discussion Starter · #2 ·
Well I guess I am truly stumped. I checked DPM Solenoid it checked good, power valves are good I tried plug wires on opposite cylinders. My mag cylinder just cuts out on top end .

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Discussion Starter · #8 ·
Checked that, readjusted cable when I cleaned the carbs . I'm just lost as Easter egg on this one .. I'm assuming it's a fuel issue but I'm not positive .. I've been through everything except reeds but my boots are good and when I put motor together they looked good . I just can't figure out what would cause one cylinder to cut out on the big end .

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Checked that, readjusted cable when I cleaned the carbs . I'm just lost as Easter egg on this one .. I'm assuming it's a fuel issue but I'm not positive .. I've been through everything except reeds but my boots are good and when I put motor together they looked good . I just can't figure out what would cause one cylinder to cut out on the big end .

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Maybe a piece of crap under one of the plungers??

Well I was gona suggest the float bowl o-rings but that would be more noticeable at lower rpm. Maybe look at the raves again and reeds I guess.

Please let us know when you figure it out!
 

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Discussion Starter · #11 ·
If I had a issue with DPM solenoid or power valve solenoid or TPS or even fuel pump or stator. would these parts if bad most likely affect both cylinders and not just one. Like I said earlier pto is burning great. I'm gonna pull carbs back off tomorrow for one more inspection then on to reeds. I'm tending to agree with you guys its most likely a carburetor problem .. I think I may be over thinking things..

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Possible it's sucking gas through the fuel pump impulse line? Fuel pump is ran off the mag side. TPS, RAVE or DPM problem should affect both problems equally. A black plug sounds like an overly rich condition, a loss of spark should show a wet plug, the fact that it's black says that combustion is still happening.
 

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Possible it's sucking gas through the fuel pump impulse line? Fuel pump is ran off the mag side. TPS, RAVE or DPM problem should affect both problems equally. A black plug sounds like an overly rich condition, a loss of spark should show a wet plug, the fact that it's black says that combustion is still happening.
I was thinking the same thing on the bold. Very easy to make false assumptions on which cylinder is going out with plug colour. This is where EGTs are a fantastic tool to eliminate the guess work.
 

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Discussion Starter · #17 ·
Well I was going to put it on trailer till I got more time to mess with it next week . Fired it up took it down road and it ran perfect so I got on my gear and went for a ride got about 8 miles and it started doing it again . But for 8 miles it ran with out a hiccup. Now I'm kinda of thinking electrical issue ???? What PITA...

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Well I was going to put it on trailer till I got more time to mess with it next week . Fired it up took it down road and it ran perfect so I got on my gear and went for a ride got about 8 miles and it started doing it again . But for 8 miles it ran with out a hiccup. Now I'm kinda of thinking electrical issue ???? What PITA...

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Take a compression tester with you and when it starts acting up shut it down and test the compression before it gets a chance to cool off any. I had almost the same symptoms about 5 years ago on my 600 summit, ran good for 10-15 mins or so then would drop a cylinder I would stop let it sit for a little while then the same thing would happen again and again. I tested the compression after letting it sit for only 5 mins or so and both tested around 120 ( high mileage motor so seemed good enough to me) so I tried new plug wires, ignition coil, thought it was electrical but that didn't fix it. Then I thought it might be fuel related so I went through the carbs, tried a different fuel pump, reeds and it still did it so I took it for a ride close to my house and when it started acting up I drove it back and into the garage and tested the compression as quickly as I could the PTO still showed around 120 and the MAG only showed 65! I let it cool off for 5 minutes or so and tried the mag again and it was back up to 120 again! I took off the head and on the MAG side a small chunk of the piston had broken off bounced around on top of the piston and went out the exhaust port denting the top of the piston and the head and scratched the cylinder but ring was still intact so it still had decent compression when cold.

That's pretty much the worst case scenario, hopefully your's is something else!

here's some pictures I dug up.

IMG_8720.jpg


IMG_8716.jpg


IMG_8721.jpg
 

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Discussion Starter · #20 ·
Well took compression on hot motor had throttle wide open and got about 130-5 on each cylinder .. Just for piece of mind i took head off everything looks good except domes on pto side are oily and gummed up and mag side is clean as new no oil or carbon Just shiny aluminum.

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