This melt down just might have me stumped..

[Dartman]

i would up the torque on the girdle studs to 40 ft lbs
use an msd enhancer just to get a slightly better timing curve-more retard up top
make sure no less than .005 piston to wall for dual cooling with cast piston
.006 with forged pistons
try lowering the popoff 3-4 lbs with spring or next size needle valve=overall richer jetting

edit: after rereading-go to a 2.0 n&s

 

[Dartman]

manifold/headpipe size needs to be at least 47.5-48mm minimum
try using a little less water to the stinger to lower backpressure

 

[Roseand]

i would up the torque on the girdle studs to 40 ft lbs
use an msd enhancer just to get a slightly better timing curve-more retard up top
make sure no less than .005 piston to wall for dual cooling with cast piston
.006 with forged pistons
try lowering the popoff 3-4 lbs with spring or next size needle valve=overall richer jetting

40 seems pretty high. A couple builders I've talked to say 30-34 is good. I don't have the funds for an enhancer and if I did I'd go for an atp HX3 instead.
Honestly right now I just want to know what the hell happened so I know what to do next time. I want to know the exact cause but so far the tear down hasnt said much..

 

[Roseand]

manifold/headpipe size needs to be at least 47.5-48mm minimum
try using a little less water to the stinger to lower backpressure

Headpipe is bored to 49mm and I'm running a flow control valve, etc.

 

[Dartman]

jet the stinger down after the flow valve-use a 2.5 old needle valve stuck in the hose
all it does is control the opening time-not much for flow when open

 

[Roseand]

jet the stinger down after the flow valve-use a 2.5 old needle valve stuck in the hose
all it does is control the opening time-not much for flow when open

Yeaaaah I know. I did that last year and I didn't notice much of a difference. That has nothing to do with what happened to my motor tho...

 

[jo5hi3]

Check your crank and seals. I once heard of the rear collar, that the seals ride against, spinning and causing it to not seal. Roasted the rear cylinder a few times cause of it. It will pressure check fine if this is your issue.

 

[Roseand]

Check your crank and seals. I once heard of the rear collar, that the seals ride against, spinning and causing it to not seal. Roasted the rear cylinder a few times cause of it. It will pressure check fine if this is your issue.

Sounds more likely then other circumstances, however I feel like it would not run properly and be hard to tune if this was the case of a severe air leak. Like I said, there weren't really any tell tale signs before it went :l

 

[jo5hi3]

Sounds more likely then other circumstances, however I feel like it would not run properly and be hard to tune if this was the case of a severe air leak. Like I said, there weren't really any tell tale signs before it went :l

5 or 10 gallons of fuel is not really a super long time. It also may of just happened within the last few minutes before it seized. But its just another idea to throw in the pot.

 

[alberta guy]

The piston ring coulda seized running 45 to 1 on break in. Causing the scoring on the piston and cylinder wall. Most recommend 32 to one. Any two stroke motor land or water that I have broken in is a 25 to 1 for two tanks.

 

[Roseand]

The piston ring coulda seized running 45 to 1 on break in. Causing the scoring on the piston and cylinder wall. Most recommend 32 to one. Any two stroke motor land or water that I have broken in is a 25 to 1 for two tanks.

It wasn't a break in. Was already broken in from last season. Front cylinder is absolutely perfect.

 

[holeshot]

It does look lean on one cylinder. But how many of us make an extended run on the pipe at 1/2 to 3/4 throttle and then read plugs? Not many im sure. It can be a dangerzone as has been mentioned before in this thread. Also port timings were mentioned. His port timings are stock. Exhaust port is mild at 64% of bore. There is one thing that wasnt mentioned that could cause a lean condition on one cylinder on a single carb set up and thats reeds. Im not saying your reeds and reed tension are the culprit im simply adding to the thread.
Repair it, reassemble it. Leak down test it. Check squish and cranking compression. Lower pop off or go to a larger pilot jet to richen up the fuel at 1/2 to 3/4 throttle. Make sure the main jet is large enough that the ski goes too rich and wont rev when the high screw is opened more than 2.5 turns. Inspect reeds for damage or lifting, replace them if they are well used.
Many good responses in this thread and good advise that can be put to good use.

 

[Roseand]

It does look lean on one cylinder. But how many of us make an extended run on the pipe at 1/2 to 3/4 throttle and then read plugs? Not many im sure. It can be a dangerzone as has been mentioned before in this thread. Also port timings were mentioned. His port timings are stock. Exhaust port is mild at 64% of bore. There is one thing that wasnt mentioned that could cause a lean condition on one cylinder on a single carb set up and thats reeds. Im not saying your reeds and reed tension are the culprit im simply adding to the thread.
Repair it, reassemble it. Leak down test it. Check squish and cranking compression. Lower pop off or go to a larger pilot jet to richen up the fuel at 1/2 to 3/4 throttle. Make sure the main jet is large enough that the ski goes too rich and wont rev when the high screw is opened more than 2.5 turns. Inspect reeds for damage or lifting, replace them if they are well used.
Many good responses in this thread and good advise that can be put to good use.

Thanks for the insight!
Is it possible there was a sudden catastrophic one time random issue that messed up that one cylinder and the other was perfectly fine? Reeds are brand new carbon tech low tension ones.
I will do all the above you mentioned for sure.

 

[holeshot]

Honestly no one knows 100% what went wrong and you may never know. But there has been superb advise given in this thread that can help avoid the same issue raring its ugly head. jetting, pop off or needle and seat size, timing curve, fuel, squish and compression, reeds, air leaks, ect ect.
without a doubt it was too lean and or detonating. And as far as detonation is concerned this is one of the symptoms of detonation so i would check squish clearance. I know you mixed a small percentage of race gas but that doesnt mean it was enough octane for the conditions either.

 

[Roseand]

Honestly no one knows 100% what went wrong and you may never know. But there has been superb advise given in this thread that can help avoid the same issue raring its ugly head. jetting, pop off or needle and seat size, timing curve, fuel, squish and compression, reeds, air leaks, ect ect.
without a doubt it was too lean and or detonating. And as far as detonation is concerned this is one of the symptoms of detonation so i would check squish clearance. I know you mixed a small percentage of race gas but that doesnt mean it was enough octane for the conditions either.

I should mention the picture on the left is messed up and looks like deto. But it's actually in perfect shape but has some dust from the loctite that was on the head and a combination of antisieze on my hands and a wierd glare from my phone. I'll take a better picture tomorrow but the rear piston head is absolutely perfect. That picture just looks hella wierd.

Edit: I looked on my phone and it's just a reflection off of the casting marks the top a piston has. It was oily so it emphasized it. Hard to explain kinda but it's in perfect shape.

 

[holeshot]

I just want to be clear in saying that this failure can be one of the signs of detonation. There doesnt have to be any abnormal patterns or powders on the piston crown.

 

[Roseand]

And the rear piston experiences more of a load and would show deto first.. Awesome info guys! I really appreciate it. Just gotta clean up the aluminum transfer and give it a hone and I should be game for a new piston and rings. No scoring from what I felt so far.

Is muriatic acid on a q tip the way to go for removing aluminum deposits?

And what could I soak my assembled cases in to make sure the bearings are free of any aluminum/metal dust?

 

[Harbor]

You know @amitchell was having a sorta similar issue @15 seconds of 3/4 to wide open, he also had one cylinder leaner than the other but It was a dual carb 38 set up. You might review that thread.

For me 3/4 throttle is the same as wide open, I notice no speed increase beyond 3/4 so 15 seconds is too long. After you get her fixed you might limit your throttle more

My skis been driving me crazy too, Electrical issue effecting the Cdi. Sucks some times. Hope you get to the bottom of it

http://www.x-h2o.com/index.php?threads/dual-38-fuel-delivery-problem.150494/

 

[550headache]

I just built a motor and used a ada head and girdled studs. they say 25 foot lbs. you guys are at 35-40. why so high? I'm a little worried now! also. do you re-torque when hot or cold?

hope ya get it figured Roseand. muriatic acid work wonders for removing aluminum. be careful and safe with it!

 

[BruceSki]

You know @amitchell was having a sorta similar issue @15 seconds of 3/4 to wide open, he also had one cylinder leaner than the other but It was a dual carb 38 set up. You might review that thread.

For me 3/4 throttle is the same as wide open, I notice no speed increase beyond 3/4 so 15 seconds is too long. After you get her fixed you might limit your throttle more

My skis been driving me crazy too, Electrical issue effecting the Cdi. Sucks some times. Hope you get to the bottom of it

http://www.x-h2o.com/index.php?threads/dual-38-fuel-delivery-problem.150494/

If 3/4 and full throttle is the same you aren't jetted correctly.

38's usually have a lean spot that's hard to tune out at 2/3-3/4 throttle. Cruising around for 10 minutes there is no good and a quick way to blow your motor.

As for roseand's issue: A single 44 should be easier to tune but my guess is needle and seat is too small or popoff is too high and you were running lean at that 2/3-3/4 mark you feel is "safer" to not blow your engine. You probably would have been safer at WOT with that 150 main in there than the cruising speed.