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Discussion Starter · #1 ·
hello all
i am new to forum.
i have a 2000 polaris rmk 500 i use to get in and out of a camp in winter, bought it new
it only has like 1600 miles
last winter it flooded badly and it took me a bit to figure out floats must have been stuck or somthing (never worked on sleds, only small 4 cycle engines) I was out in the woods at camp
I shut fuel off pulled plugs and purged it by pulling recoil about 30x
Started fine and i just kept shutting fuel off the rest of the week

Pulled carbs a week ago( finally) and replaced the O rings as the float needle and seats seemed to hold pressure when i blew on hose
started right up after, but idle was bad and it backfired a few times.
I had added oil to gas as I had replaced the oil lines to carburetor and wasn't sure how long to fill them. They eventually did fill with several attempts at running at idle
I pulled the carbs back off and cleaned the jets, but they all looked clean.
I gently seated the two mix screws to count turns ,and when i pulled one out it was blunt, the other was a fine tip like i would thought. The tip is stuck in the mixture seat and its not coming out with any air or gentle poking
I called around and every one from Vermont to Minnesota tells these carbs Mikuni(TM 38)are hard/impossible to find.Mixture needles too
I also was told adding oil may effect the leaning out?
sled ran fine before as long as i shut gas off, so i suspect it is carburetor but?
I live in MN and wonder are there other model polaris sleds have the same mikuni tm 38 ?
Could have I damaged by the backfiring at all? reeds look ok peering into the intake
As I am clueless on 2 cycle and mikuni carbs suggestions are what i am seeking here
Thanks to all who have the experience to provide suggestions馃檹
 

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Polaris only shows that VM carb as being used on the 2000, 2001, 2002 RMK 500.

Having part of the needle broken off in the passage is not good. That needs to be addressed. Maybe a strong magnet (assuming the needles are magnetic, not sure, never tested) along with a bit of percussion may dislodge the broken part.

I agree with Steve, the flooding was probably due to a bad inlet needle/seat.

You may have to contact a salvage yard to try to locate a carb body or carb assembly. Even the 600 was using the TM 40, so it may be a bit of a challenge to find one.

Good luck!
 

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Discussion Starter · #4 ·
Thank you for reply鈥檚
searching few salvage yards now
the needle on the mixture screw broke off so square and smooth I wonder if it had stress when machined
if I try to drill it I suppose the seat or fit with a new needle wouldn鈥檛 be right鈥
if I try to heat the body I suspect the gaskets will be ruined
it looks like it鈥檚 brass but I check magnetism
thanks again
 

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Discussion Starter · #6 ·
Thanks again I have located a carb rack from a Polaris 2000 XC 500 from a salvage place online
can anyone tell me if this is the same carburator as the rmk 500 I have?

any watch out tips on used stuff like this?
I suppose I鈥檒l need to disassemble etc and need gaskets
its like $200 as is鈥..
if anyone thinks I鈥檓 just chasing a disaster with this sled ,,,let me have it too
I hate to dig A money pit with it and not have something I can rely on
im going to try the tips to dislodge the needle but it seems hopeless.
still can鈥檛 believe it broke like it did, so clean and square. The needle is not magnetic
drop of superglue and stick a wire down to it maybe as another Hail Mary 馃槼..
thank you all again
 

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It should be, the jetting for the RMK is different than the XC, so use the jets (and maybe needle) from the old carb. The 500 is pretty well known for being a reliable engine, once you get the carb sorted, it should be good to go...

It's likely that if you disassemble the carb with care, you won't need to buy any gaskets. Make sure the inlet needle/seats are not sticking and look for worn parts. When I had carb sleds, I would disassemble them for cleaning every year pre-season and never had a bowl gasket fail. I did have a few sticking inlet needles that were bad and a few inlet needles that were all metal that had ridges in them, but that was about it. Most were disassemble, clean, reassemble.

It's likely that the previous owner tightened the screw too tight, which damaged the tip. That is why the book always says "lightly seated"... to prevent damage to the tip or the orifice the tip is going in. Too bad it's you that has to pay for the lesson...
 

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Discussion Starter · #8 ·
It should be, the jetting for the RMK is different than the XC, so use the jets (and maybe needle) from the old carb. The 500 is pretty well known for being a reliable engine, once you get the carb sorted, it should be good to go...

It's likely that if you disassemble the carb with care, you won't need to buy any gaskets. Make sure the inlet needle/seats are not sticking and look for worn parts. When I had carb sleds, I would disassemble them for cleaning every year pre-season and never had a bowl gasket fail. I did have a few sticking inlet needles that were bad and a few inlet needles that were all metal that had ridges in them, but that was about it. Most were disassemble, clean, reassemble.

It's likely that the previous owner tightened the screw too tight, which damaged the tip. That is why the book always says "lightly seated"... to prevent damage to the tip or the orifice the tip is going in. Too bad it's you that has to pay for the lesson...
 

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Discussion Starter · #9 ·
Yea still gnawing on an old golf ball about this
I still have all the jets etc
flooding/gas leaking from exhaust quit after I replaced the O rings on the float body so I thought I was done
I check them again nothing is really ruled out for me馃槵
sled ran fine before I pulled carbs and so I think its carbs not cdi or something weird
the busted needle on mix screw is wrong just don鈥檛 know if that would make backfire/poor throttle response . hopefully backfire didn鈥檛 wreck something else? Local guy told me crank or timing could be bent or off kilter? WTF 馃槼
heading up to salvage yard this weekend to look
thank you all & have a great thanksgiving !
 

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Because snowmobile crankshafts have roller bearings, they are pressed together in parts. If you get a bad enough backfire, it can spin that part backwards compared to the rest of the crank. It doesn't happen often, but it can happen. And that can have an effect on timing on that cylinder or on the whole engine.

One way to determine if you have an issue... Put one piston at Top Dead Center. Make a mark on the primary and have a pointer that directs at the mark. Put the other piston to top dead center. Mark the primary. The two marks on the primary should be 180 degrees apart. That would be a rough estimate to see if you have an issue...

Have a Happy Thanksgiving, as well!
 

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Because snowmobile crankshafts have roller bearings, they are pressed together in parts. If you get a bad enough backfire, it can spin that part backwards compared to the rest of the crank. It doesn't happen often, but it can happen. And that can have an effect on timing on that cylinder or on the whole engine.

One way to determine if you have an issue... Put one piston at Top Dead Center. Make a mark on the primary and have a pointer that directs at the mark. Put the other piston to top dead center. Mark the primary. The two marks on the primary should be 180 degrees apart. That would be a rough estimate to see if you have an issue...

Have a Happy Thanksgiving, as well!
Ball bearing on all snowmobile cranks that I've seen.
Joey65 you might see if you can acquire a small lefthand drill bit and see if that might back out your broken off mixture screw.
 
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