Sorry to bring this to my fellow Yama-heads, but I trust your knowledge and input! 2000 zr 440 sno-pro( I use to race sno-x) I've melted-down the exhaust side of the piston 3 times! After the 1st time,I installed 2 new wiesco's and upper gaskets, and drained the gas. 50 miles later, melt-down. This time I split the case, put in new outer seals, put in the good-used cat piston,drained the gas. Took it out yesterday 75 miles,yep, melt down!! 
Jetting is the same in both carbs,I've cleaned them both times!!
HELLLLLLPPP!!
What causes the front side to melt -down?
I'll be checking the carb-boots more closely, I know there are some cracks when you bend them , but they don't seem to deep!
Jetting is the same in both carbs,I've cleaned them both times!!HELLLLLLPPP!!
What causes the front side to melt -down?
I'll be checking the carb-boots more closely, I know there are some cracks when you bend them , but they don't seem to deep!
ModMMax
New member
IMO, an exhaust port melt down is a clear sign that the sled is jetted too lean. The plugs must be white.
Make sure your exhaust gasket is good. You can draw air back in too I've been told. Take the carbs to a dealer and ask the to completely dismantle them and soak them. Maxdlx
I didn't check the plugs until it was to late!ModMMax said:
But the good cylinders plug looked perfect, brown, the bad one actually looked a touch darker but i don't know if it would have darkened during melt-down!
Srxspec
Your #1 performance shop!
Exhaust side melting is lean. When it melted down tell us the scenario. Long wide open pull and then it melted down on the decel or riding in the midrange? Gotta tell us what speeds you're running to get a feel for which area in the carbs to adjust.
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Just trail riding, a few short distant(150-200 ft) hole shots. Its not an instant melt down, its burning the front edge down unil you start losing compression. Jetting is the same in both carbs, but the same cylinder(pto) is having the problem. The only jetting issue I believe I have is I'm running 17.5 pilots and I believe 22.5s were stock. It does high-idle when riding,takes maybe 30 seconds to come down(or a quick flip of the Choke)
Thanks for any help, Dave
Thanks for any help, Dave
skidooboy
New member
air leak, seals, gasket or carb boots. ski
yamyrider
Active member
what is the best sealant to use on the exhaust gasket on the Yamy.
I have installed pipes and notcied that there is nothing on the metal gasket.
Should I use anything to seal. I dont want a melt down like this for an air leak.
I have installed pipes and notcied that there is nothing on the metal gasket.
Should I use anything to seal. I dont want a melt down like this for an air leak.
the high idle should have been a clue to tune with
My thoughts are simply you have the low speed circuit too lean, its most likely burning down(doing the damage) after you come off of wide open. Are the needles in the stock posistion? the pilot alone does contribute to fuel flow thru the entire range of the carb until the main jet takes control at wide open. Remember the circuits all overlap each other and contribute to each other. A small pilot jet will cause you to go way lean when you let off the gas to go into a corner or something, the needle comes back abruptly to the nozzle and main jet and the pilot picks up the slack, so if its lean, theres nothing to cushion the engine and it starves for fuel for a few seconds everytime you are on and off the gas, and this is how I believe you are in your current situation
My thoughts are simply you have the low speed circuit too lean, its most likely burning down(doing the damage) after you come off of wide open. Are the needles in the stock posistion? the pilot alone does contribute to fuel flow thru the entire range of the carb until the main jet takes control at wide open. Remember the circuits all overlap each other and contribute to each other. A small pilot jet will cause you to go way lean when you let off the gas to go into a corner or something, the needle comes back abruptly to the nozzle and main jet and the pilot picks up the slack, so if its lean, theres nothing to cushion the engine and it starves for fuel for a few seconds everytime you are on and off the gas, and this is how I believe you are in your current situation
I can see what your saying,but why the same cylinder in such a short period of time(50-75 miles) 3 times in a row? Both jets seem to be clean, are there any ports (air or fuel) the would plug up and cause a similar situation?
ModMMax
New member
The high idle thing has my attention, especially when you say that a flip of the choke brings things back to normal. Tells me the idle circuit is lean. If the jetting is close to factory I would be suspicious of a vacuum leak. While it is running at idle, try going over every possible gasket and joint with a sqeeze bottle of water. If its vacuum leaking you will know it when the water is sucked in. Mrviper is sooo right about the relationship between fuel circuits. In fact he is probably right about the cause of your problem. If you establish that it is not getting excessive air on the trouble cylinder then go through the jetting process. Mains first, then runs at at 1000 rpm reductions to set the needles. Once happy with both mains and needles, set the idles jets by wicking the throttle off idle. Use your mit to reduce the area of the air intake. If you can get it to come to life with less air you need bigger pilots. If it won't clean up, the pilots are already too rich. Hope this helps you. I'd like to know how this turns out. Keep us posted.
woolyviper
New member
Check the flange and the gasket for the pipe where it contacts the Y pipe - My sons ZR was burned through at this point and the gasket was bad and same thing - also replace the exhaust springs the engine pulses will actually push the pipe away from the Y pipe -
whhops
well I missed the part where you said it was the same cylinder each time. So whens the last time you checked to see if the needles were in the correct spot?
How about the crank seal on the pto side, does it lower the rpms of the idle if you spray starting fluid on the crank seal when at idle?, next do it to the carb boot/reed area? I know you said its replaced but if a crank snout is out of round some, it can still suck air.
check this and post, can most certainly find this problem if you do this in steps of elimination.
A while ago I had a 94 thundercat here for repair and it was blown up again in about 50 miles, the cause was a rubber vacum cap rotted and fell off the back of the case, for some reason cat decided that the engine needed 2 ports for the pulse line to the pump, yet they only used 1 of them to the pumps, cat used a 2 cent vac cap on the other, to say the least, it had a serious vac leak. Check and see if you spray the starting fluid while idling if it lowers the rpm any somehwere on the case etc. I dont know off top of my head about the sno pro 440 engine and pulse ports, kinda the wrong brand if ya know what I mean...lol
well I missed the part where you said it was the same cylinder each time. So whens the last time you checked to see if the needles were in the correct spot?
How about the crank seal on the pto side, does it lower the rpms of the idle if you spray starting fluid on the crank seal when at idle?, next do it to the carb boot/reed area? I know you said its replaced but if a crank snout is out of round some, it can still suck air.
check this and post, can most certainly find this problem if you do this in steps of elimination.
A while ago I had a 94 thundercat here for repair and it was blown up again in about 50 miles, the cause was a rubber vacum cap rotted and fell off the back of the case, for some reason cat decided that the engine needed 2 ports for the pulse line to the pump, yet they only used 1 of them to the pumps, cat used a 2 cent vac cap on the other, to say the least, it had a serious vac leak. Check and see if you spray the starting fluid while idling if it lowers the rpm any somehwere on the case etc. I dont know off top of my head about the sno pro 440 engine and pulse ports, kinda the wrong brand if ya know what I mean...lol
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Thanks for the info, now i have to buck-up on some cash for another piston and rings before i can try these options. I knew I could get some good info from the BEST snowmobile site on the www!!! 
PS Anyone know where I can get a good deal on
Cat Parts?
PS Anyone know where I can get a good deal on
Cat Parts?srxbully
New member
i can tell you your problem my man...the problem is it is a arctic crap..& to solve it is to buy a yammi
ModMMax
New member
I never met an engine I didn't like.
Any time you want to race your SRX against my Arctic-crap on a sno-cross track, give me a call!srxbully said:
82 ss 440
83 V-Max
87 Phazer
96 V-Max XT
97 ZR 440 (my first race sled)
98 SRX
00 ZR sno-pro(my second)
04 Viper S
I ve had my share of Yamahas , but they do have their limitations!!
Mod, Thanks for the help, now its a matter of time and $$$$$$ModMMax said:
Brad
New member
- Joined
- May 23, 2003
- Messages
- 403
if it's the same one every time you might have a crank problem had the same problem on a srv once.is it you pto side cylinder,if so your crank seal is sucking some air crank out of index just my 2 cents
yamyrider
Active member
Hey Snow-XR let us know what you find.
Great learning material for some of us. Does not matter what machine it is this kind of problem can happen if you have an air leak and leaning out somehow.
Great learning material for some of us. Does not matter what machine it is this kind of problem can happen if you have an air leak and leaning out somehow.