300xs dropping cyl intermittently

[Revolution141]

Hi guys
Since my rebuild last year I have had a few issues,
1st I'd had a long term problem with engine loosing power when at or very close to wot. Fixed this with a new tps.
Ran great for a while then started getting a gradual breakdown in power, very sporadic, I pulled all my plugs and found no.6 looked like it hadn't been firing, switched coil packs and it came good.
put about another 10 hrs on it and a few months ago at a race (ski racing) I had been running all day fine then went out to start another race and I couldn't pull skier out! Got him up by whip starting then about 3km later I felt the engine pick up power again. Had no problems then for the rest of that day.
2 weeks ago went to another race and same thing happened only this time it took longer to pick up again and then had it re occur in final race. It actually started fine in final but then dropped power for about 10km before picking up again.
i pulled all plugs again at home but this time they all look similar (no.6 and 4 may be slightly wetter than the rest). However I noticed that most the plugs don't have that real bright white spot on the electrode like normal.

Its definitely only dropping out on the one cylinder when it occurs, loose about 1000rpm and feels gutless. Was going to try loom to coil packs in case it's a dodgy wire in the loom.
worst thing is it can take quite a few hrs running sometimes for it to happen so not like I can chuck something on and know in 5min if its that.

any thoughts? I'm 99.9% sure it's an electrical issue, not fuel or air related.

[strokerdean]

On my 07 300xs I have had 2 coil wire harneses replaced. The wires would break inside the insulation and loose contact (intermitent) due to vibration. The tech tried changing coils, checked everything possible and finally after about 4 trips to the shop found the problem by using a continuity (ohm meter) tester by moving/bending the wires around and watching the tester readings change. The last one was replaced last year, the new harness came with bolt on clamps to hold the wires in place that the original and first replacement didn't have.

[Revolution141]

We're you seeing similar thing to me with one cyl dropping out intermittently? I'm thinking this is my issue as I have changed everything else. My father in law just got a new 250 pro Xs and his loom has heaps more clamps also to support the loom.

[strokerdean]

I would be runnning and drop a cylinder just like loosing a coil. Thought we had it fixed, idled out of the no wake area after launching and would drop a cylinder. We ended up splicing about 6 wires that had vibrated and broke until the new harness arived. Again we used a continuity tester to check the wires and had to wiggle and bend the wires. Not sure my problem is the same as yours but it is possible. Hope this helps, good luck.

[Liza2]

Been riding sportbike since 07. MSF course, track days, enjoy my GSXR 750 immensely--for about 2hrs. as I get older, the pains cramps and of hunching over hit me sooner.

[mlb75]

I've got a very similar issue that actually brought me back to this forum to research. For me I've only noticed it while I'm running it at WOT. It's like I'll be runnign along fine and then feel a noticeable drop in power on one of the motors (can't tell which at the moment) and then at a random time shortly thereafter I'll feel a kick in the butt and the boat takes off again and the power is back. VERY FRUSTRATING Also very strange the port motor drinks about 25% more fuel than the STRBD. I had this same issue with loss of power before and could never figure it out but it went away for awhile then came back at a poker run this weekend. All the gauges read perfect other than a drop in RPM when I lose power but that's to be expected. Any thoughts other than coil wires? The motors are almost out of warranty and want to get this fixed before they run out.

[DonG]

I had a similar issue with my 300xs's and it turns out it was the crank sensor. It would run ok at lower speeds but run like crap on top end almost seems like it was running out of fuel, surging at WOT. Replaced crank sensor and runs great now. Hope this helps.

[mlb75]

Thanks I'll order one for both motors just to be safe...

[mlb75]

It definitely feels like a surge it's crazy the way it'll go out and come back in...

[28SkaterCa.]

Hi guys
Since my rebuild last year I have had a few issues,
1st I'd had a long term problem with engine loosing power when at or very close to wot. Fixed this with a new tps.
Ran great for a while then started getting a gradual breakdown in power, very sporadic, I pulled all my plugs and found no.6 looked like it hadn't been firing, switched coil packs and it came good.
put about another 10 hrs on it and a few months ago at a race (ski racing) I had been running all day fine then went out to start another race and I couldn't pull skier out! Got him up by whip starting then about 3km later I felt the engine pick up power again. Had no problems then for the rest of that day.
2 weeks ago went to another race and same thing happened only this time it took longer to pick up again and then had it re occur in final race. It actually started fine in final but then dropped power for about 10km before picking up again.
i pulled all plugs again at home but this time they all look similar (no.6 and 4 may be slightly wetter than the rest). However I noticed that most the plugs don't have that real bright white spot on the electrode like normal.

Its definitely only dropping out on the one cylinder when it occurs, loose about 1000rpm and feels gutless. Was going to try loom to coil packs in case it's a dodgy wire in the loom.
worst thing is it can take quite a few hrs running sometimes for it to happen so not like I can chuck something on and know in 5min if its that.

any thoughts? I'm 99.9% sure it's an electrical issue, not fuel or air related.

Any Luck?, Just posted new Thread with a similar issues. Thanks

[AlaskaStreamin]

I had a loose ground bolts that the three coil grounds per side shared 300 PM. The weaker coil in that bank would cut in and out. Very frustrating,.... till I rested my hand on the ring connector leaning over the motor and felt it move. 1/4 turn and it was tight. No more problems!!!

[Devold]

I had the same problem with my 250 Racing XS.
The problem was that the coil wiring would brake inside the insulation.