Other Xlt1200 keeps melting pistons

[mattg1.8]

Working on a ski for my friend, it’s a 2003 Yamaha xlt1200 2 stroke. He bought it used and had a ton of corrosion in the crankscase and carbs. Got a new rack of carbs and wound up doing an sbt crank, pistons, and cylinders. We did an oil pump delete and ran 32:1 premix. Got it in the water and it ran for 20 minutes then blew a crank bearing and melted the middle cylinder. Got a new crank again, new cylinder, and new piston. Drained the tank and put fresh premix in. Got it in the water and ran great for almost 2 hours then lost compression on cylinder one and got some dimpling damage on the top of number 2 piston. Already have thousands dumped into this thing and I have no idea what’s causing this. I was leaning towards heat damage since I know it’s getting oil but with the dimpling damage I was thinking maybe an ignition timing issue. Any help is appreciated. Thanks.

 

[Roseand]

Most likely running lean or detonation. Is the motor all stock? And is this happening after running wide open for extended periods of time?

 

[kevbo]

You must tune the main circuit rich enough to reduce power for a couple of tanks. All large two strokes struggle with high combustion temps.

 

[mattg1.8]

 

[Batteryman]

Have you seen these? I have a gp800 and those carbs are a pain to get to..

 

[mattg1.8]

 

[Big Kahuna]

Wow, usually its the Rear or Front........ Not seen middle. Makes me think carb not getting enough fuel thru.

 

[mattg1.8]

Anyone know what stock jetting should be? I’m wondering if the replacement carbs I got had the wrong jets. The original carbs were corroded so badly that I couldn’t get access to the jets to check stock

 

[Myself]

That dimpling appears to be debris damage. Maybe a bit of metal leftover sitting in the exhaust manifold got sucked back into the cylinder. Everything MUST be clean to assemble one of these big bore 2 strokes and make it last. You also NEED to check the fuel pickup assembly trap door at the bottom. Just remove it if it's still there. Does it have a D-plate and chip already? Does it have upgraded PV keepers? Did you make sure all 3 cylinders were level across the top before installing the head? I've seen some shorter from SBT. You just really need to go over everything with a fine tooth comb. I also like to spray copper coat on those metal base and head gaskets to make sure nothing leaks.

 

[WFO Speedracer]

Stock jetting is part of your issue, it's way , way too lean , by running premix you have leaned it out even more., if the choke shafts have been removed it has to be rejetted see below and don't try to rejet it using the O-side specs and the stock airbox , it won't work and no one has been able to make it work..for stock airbox follow the first set of specs but to use them the cat converter has to be removed which if it hasn't been already it's part of the problem. They retain too much heat and melt things in a bad bad way .

Myself is correct those 800's and 1200's are like a Swiss watch , they will not tolerate any imprecision . He is also spot on about debris, anytime a reed valve motor pukes , you have to pull all the reeds out and clean out the debris, if you don't as soon as you fire it up it goes right back through the engine, I know it's a pain to do on these but this is what happens when you don't.

I don't use those SBT cylinders they are crap , they don't dissipate heat like the stock cylinders do , cast iron retains heat , Aluminum dissipates heat , these engines were designed with plated cylinders for a reason, they ruined them when they installed those thick cast iron liners in them., the heat dissipation is so bad that they have to use a lot of extra piston to wall clearance to keep them alive probably double what the stock clearance is and they rattle like a freight train , absolute junk IMO.

The following was copied from Bamafreeride where I store important info like this :

Bit off topic but if anyone is ever wanting STANDARD European spec carb settings they are as follows. I have given myself a headache trying to source these but I have had them confirmed from 2 x Yamaha dealers in the UK
Main Jet 135
Pilot Jet 92.5
Low speed Screw carb 1 = 1 1/4 carb 2 = 1 1/2 carb 3 = 1 5/8
High speed screw Carb 1 = 7/8 carb 2 = 3/4 carb 3 = 7/8

The european specs skis have a decat plate from factory, no exhaust temp sensor and no plastic cover over the stinger.
The are set up differently from USA Skis.

Oside Bill jetting specs

1200R Aftermarket F/A's (Flame Arrestors) chokes intact

110 Pilot jets, 1 turn out on low speed adjusters
120 main jets, 1-1/2 turn out on high speed adjusters
1.5 Needle and Seat, 95 gram spring (Dull Silver) 42-45 avg. pop-off pressure.

1200R After Market F/A's chokes removed.

110 Pilot jets, 1 turn out on low speed adjusters.
125 Main jets 1-1/4 turn out on high speed adjusters
1.5 Needle and Seat, 95 gram spring (Dull Silver) 42-45 avg. pop-off pressure

 

[mattg1.8]

Great info guys thank you all very much. I got some digging to do

 

[WFO Speedracer]

Great info guys thank you all very much. I got some digging to do

If you give me more info on exactly what has been done as far as choke plate removal and cat removal I can probably be of more help.

Running that at 32/1 was a mistake with stock jetting.

 

[Myself]

I have a couple customers that I've repaired failed SBT engines for. One of them is a pretty well modded 1300fi. I've not had problems running their sleeved cylinders at .0045-.005" clearance. Any tighter and your in trouble. Same goes for sleeved Ultra 150 cylinders, and anything Seadoo 951.

 

[WFO Speedracer]

You can run them but like I said , they don't dissipate heat well and the engines are noisy as hell .
I have heard brand new SBT engines that sounded like death from the moment you started them up , I don't fool with that crap anymore life is too damn short.

 

[Myself]

Disclaimer....I've NEVER installed an SBT engine or top end for any customer and NEVER will. I HAVE, however, repaired dozens. Many of them BARELY out of warranty.

 

[WFO Speedracer]

I will put one in if the customer buys it and deals with the core return there self but I always advise against it , all you get with them is a warranty which does not cover removal and installation. I have seen the barely out of warranty situation way too many times .

 

[kevbo]

But they’re so cheap! That’s all that matters.

 

[WFO Speedracer]

The worst SBT story I have was I put an SBT reman 657 engine a costumer's SPX , as soon as I started the ski I knew it wasn't right, I called SBT wanting another engine, it was a good customer and I was willing to eat the labor on the second installation, no dice they wouldn't do it , their answer was run it , it has a warranty, which we did , a week out of warranty the engine puked and I lost a very good customer for life .

SBT didn't care and didn't cover it, surprise , surprise , their only concern is that the engine makes it out of the warranty period, I gave them every chance to make it right.

Second story I installed a reman 4tec engine in a customers ski, on the test ride the oil pressure light came on, I checked the oil and it was low, I added more oil and got it back to the boat ramp, upon inspection I discovered the valve cover gasket was separated letting the oil escape, I replaced the damaged gasket with a new OEM one, I called SBT, were they thankful I had caught it in time and saved them a warranty claim , no they were not , instead they threatened to void my customers warranty because I had opened their engine up , when I told them my customer was a Lawyer in a national law firm they changed their tune on that one really quickly.

I think their Reman engine business peaked about ten years ago and that's why you see them going in other directions like Watercraft Superstore , buying out Hydroturf and creating 4xpro ATV, UTV axle division, they started out making CV axles for cars before they got into the reman PWC engine business.

 

[kevbo]

I wish the typical jet skier was more advanced. They would likely stick around longer and not be so cheap on maintenance.

 

[WFO Speedracer]

My customers are on about a four year turnover cycle from what I have seen over the years.