cant keep a mag side piston in my fathers 900 cat

[Mainer]

my father has a 2003 mountain cat 900 and we have been through 4 mag side pistons in 1700 miles. plugs come out on the gray side and the rings are stuck. lately the problem has been worse. last 2 rides he has smoked a piston. the sled is all stock and has the low alt. box installed when delivered. we ride from 0-3000. the PTO side likes a 450 main and and the mag needs a 470-480 which is not right. we have checked for air leaks and come up empty handed. the carbs have been run through and nothing stands out as wrong. the carb boot and reed are good. seems airbox seems to be working fine. it seems like it does it at lower speeds with little load so we dropped the needle clips down one step. we have tried to fix the problem and tried to get by the problem but noting is working.

anyone ever see something like this? any ideas on the fix. have talked to a few guys who had this problem and just gave up insisting their motors were lemons. as of now we cant come up with anything except a new piston and fatten it up until the plugs look good but i know this isnt right. we shouldnt have to stagger the jet sizes this far between the 2 sides.

 

[M Turbo]

Mag side is the lean side. 0 - 3000 ft you should be able to run 370 -380 mains. I ran into this problem before and it was the main fuel line from the tank, pinched between the steering post and air box.The fuel line has to come up over the mag boot between air box and carb. Get rid of the soft yellow fuel line. Take a look at those things.

 

[stripe]

myn did that lost 2 pistons in 100 mi it was a air leak behind the clutch once you git a new top end and its ready to go tack off the clutch and be Shir to put your air box on or stay clear of the carbs start it up and spray starting fluid all around the case if it revs up you have an air leak hope this helps good luck

 

[Quazi]

Same problem on my old 580 ext brand new kept blowing pistons (mag side) was a defective crank seal (mag side) small dent in it so it was sucking air.leaning it out took it to a dealer they pressure tested it heard the leak.No more problems after that.after they put a seal in it.

 

[chazzer]

You have to jet your mag side fat!!! For sure!!!

This happend on my old cat. What the problem was the needles, not the jetting.

Check to see if your needles are in the right position. If im not mistaken the needle should be raised for richness. So the c-clip should be on the second from the bottom notch (pointy end). So the c-clip is 4 down from the top notch (blunt end) this is the same thing. there should be 5 notches in the needle. So if your in the middle, raise the needle, drop the clip. Confused???

These 900 have a really lean mid range. Even in stock form. A good practice is to work the throttle. Never hold it at 7000rpm at half throttle for 30 seconds at a time. It may sound stupid but it's good to do.

Hope this helps!!!

Chaz

 

[Snoboner]

Crank seal...

 

[Lt Rascal]

Crank seal...

I will second this one.

 

[diggerdown]

Sucking air somewhere. Sounds like you went through everything on the carbs. Down that low, did you drop the pilots to 45's and set your air and fuel screws? I would put in zr needles too. Still sounds like a air leak but the other stuff will add safety once you find the main problem.

 

[doors4u]

My vote for crank seal as well. This is one of the weak links of this motor.

 

[CATillak]

i fifth the crank seal, went thru almost 2 motors, its tried the second time but i was EGT'd up hahaha. replace em, and probly the bearings to, which are rediculously expensive. itll be bout 300 to 350

 

[SylvanLaker]

Your crank could be out of phase. Affecting timing on that cylinder,,,, Boom.. Also check your air pulse line for your fuel pump. make sure no leaks.. Crank seal. Dirt in the Carbs..

 

[Mainer]

thanks for the suggestions. the pilot jets are labeled 130. this is the only number we could find on them??? anyon know? the seals seem to be ok because we have already done the starting fluid test. will check the air pulse line but im thinking the crank could be out of phase. what are some things that could cause the crank to be out??

 

[Quazi]

You can't test crank seal on the mag side with starting fluid...one dealer put 3 pistons in mine,did it again.got fed up took it to another dealer they pluged all the holes and put air to it. sounds like mag side seal to me. just my 2 cents

 

[Ill Named]

I had a 900 king cat that lost four pistons in 650 miles on the pto side. I finally had enough and sold the piece of chit, but then I bumped into the owner of the cat dealership here and I asked him how my sled was holding up now and he told me that the guy burned it down 2 more times since I sold it to him. Then he tells me that he figured it out though, as it turned out, one of the holes beneath where one of the jets screws into in the pto carb wasn't drilled out and was blocked off and it came like this from the factory. I was some kind of pissed let me tell ya. So there you go, something to think about.

 

[Mainer]

hmm so u say you cant test the mag side crank seal? i sprayed starting fluid in gap where the recoil mounts. this wouldnt do it??? is there another way to test without a good dealer because we dont have one! ours shut down. a friend talked to a dealer out west where he used to live and the dealer said he had seen where the crank was bad, gas goes in and hits the scorching hot bearing and vaporizes causing the mag side to lean out. sound good to anyone?

 

[diggerdown]

hmm so u say you cant test the mag side crank seal? i sprayed starting fluid in gap where the recoil mounts. this wouldnt do it??? is there another way to test without a good dealer because we dont have one! ours shut down. a friend talked to a dealer out west where he used to live and the dealer said he had seen where the crank was bad, gas goes in and hits the scorching hot bearing and vaporizes causing the mag side to lean out. sound good to anyone?

I'd like to know the name of that dealer, so I never take anything to him! BS

 

[MOB]

Being this far into it with the kind of questions still unanswered, if it were me I'd verify/check crank phase; split the cases regardless of crank phase answer; and do a bottom up inspection/rebuild. No sense dickin with it, just take the motor questions/wonderment off the table. Also check reeds/carb boots/carbs/fuel supply to check stuff feeding the motor - including TPS...

I understand the need to ID the specific problem for sanity...but I'd balance that with potential cost of a bunch of riding time ... my .02.

 

[Mainer]

pulling the motor today. cases will be split. if crank is out of phase would you have it rebuilt or would you just pay the 1100 for a new one?

 

[MOB]

would avoid the $1100 method...can't remember if you get a core for the crank or not...but I remember being around the $700 mark rather than the $1100 + tax dealer path.

FWIW...I believe 800 cranks are same stroke...http://www.snowest.com/forum/showthread.php?t=52335