need some help!

[mattymac]

trying to get a buddies 03 900 going. sled has about 3K miles and has been one of the best 900's ive ever seen!

beginning of last year i put on new clutches, bearings, gears chain, pistons and so forth... sled ran 100% spot on amazing!

one long weekend at the end of last year my buddy was riding in over the hood powder for about 4 days. the last day the sled started to act up, it had a problem revving out all the way but still ran, just wouldnt hit full rpm.

he took the sled home and it dried out all week in his garage, rode it the rest of the year and never acted up agin. so at this point it was safe to say something got wet!

first ride out this year, went about 20 miles, sled was spot on yet agin until he went through a small ditch and when the sled jolted (he didnt wreck or anything just went through it like normal) it started to act up agin just like the prior year except that it wasnt over the hood powder by any means!

If you are on and off the throttle sometimes it tachs out like nothing is wrong and runs fine, other times it maybe pulls up to 7,000 or so, egt's arent outta the ordinary and definatly acts up more with underhood heat.

its definatly electrical, the mag side cyl has intermitten spark (mainly seems @ low rpm) verified using my local dealers ignition tester. I have put in a new stator, and wiring harness, swaped coil, and cdi with no change whatsoever.

It acts to me like the powervalves dont open thus the low rpm @ WOT and just the way the motor runs/acts, the problem is every once in a while while idleing the sled will miss on the mag cyl. which leads me away from the servo motor not opening up the powervalves as far as the way it acts when its idleing

I dont wanna just keep throwin parts at this thing, but it has myself along with a few others are starting to scratch our heads!

TIA!

 

[diggerdown]

It is basically impossible to lose spark on just the mag side if it is a new coil and stator. If the stator is weak you can lose spark on one side, if the coil has a crack in the jump wire internally you can lose on one side, a bad plug wire or cap will do it, and of course a bad plug. There is no other way that I know of to lose spark on only one side

 

[mattymac]

first thing I thought was obviously coil, but its rare that they go out (at least that ive seen) but what else would lose individual spark between cyls right?

like I said, it has myself along with a few other people that to say the least know their way around these 900's. I think the problem is a bit deeper. Ive done all the basics since thats always where I start, even switching plugs/plug wires didnt change the mag side losing or having erratic spark???

Im thinking the problem still lies within the APV system like some kinda short in the servo motor that for whatever reason is drawing power in the form of a short in the mag cyl. but why only the mag cyl???

I dont wanna just throw parts at this sled, I wanna figure out the cause of the problem. I aint gunna give up!

thanks yet agin!!!!!!

 

[mattymac]

messed with it agin today,

slight heat soak seems to make the problem present, like hood open running on the trailer no load running for about 2-3 minutes.

sled is definetly hitting on one cyl intermittenly

what I did find out is the servomotor will not cycle when its hitting on one cyl but does when the sled seems to be hitting fine on two

when we first fire the sled up when warm it idles fine for about 20-30 seconds then all by itself the problem appears, shut off sled, refire it and it does the same thing??? didnt do it 100% of the time but majority if its warm, (like 15 outta 20 times or so)

lights, hand warmers and racepack work fine durring this whole time

swapped out the APV rectifier, and regulator, harness under the seat, main chassis harness, unplugged hood harness, stator, and swapped CDI and coil/plug wires/caps

I didnt swap out the servo motor, when it runs good its cycling the cables/valves

I havent swapped out the chassis voltage reg, nor tested the TPS

all grounds are good (cdi/recoil chassis to motor)

unhooked key and throttle kill switch

motor is sound, good compression runs and sounds perfect untill it drops spark on one cyl

I dont know what else to check???? any other ideas????

 

[mattymac]

swapped out the coil agin and this seemed to remedy the problem, but also put in a new servo motor and another stator. I think that it was a combination of things but around the shop it seems to be running good now, gunna take it to the snow this weekend and see!