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post #1 of 15 (permalink) Old 04-17-2019, 09:30 PM Thread Starter
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Polaris Indy 440 No Muffler

Hello. I recently cut out my baffle on my single piece exhaust on my 92 440. I left the convergent cone on the pipe alone and welded the same outlet pipe back that came out the bottom back onto the rear cone. The outlet pipe is the same diameter as the outlet of the expansion pipe. From what I know, outlet pipes have little effect on the performance, heat, fuel consumption, and a/f ratio of a two stroke. If anyone knows different please let me know. I planned on water crossing this in the summer so I was going to jet down from 290 (stock with 38mm carbs) to a 250 for running in 70-90 degrees. But I want to make sure that I'm not going to be any leaner now without the baffle. Is 250 too lean either way? How about pilot jets for summer? Sorry lots of questions. Any help or advice would be great. Thanks, Erik.
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Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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post #2 of 15 (permalink) Old 04-18-2019, 06:15 AM
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I am going to assume XCR as only they are the only 440's that came with 38mm carbs. Also stock main jets for the XCR was 270's for 1992 not 290's. I would also go with a colder plug possibly.
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post #3 of 15 (permalink) Old 04-18-2019, 06:34 AM
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Welcome!
That is going to be Harsh!
I have Moded several stock exhausts, never completely removed the can though!
Go down one main size and one slot on the needle and see what you have!
Keep an eye on the plugs and piston wash!
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post #4 of 15 (permalink) Old 04-18-2019, 10:06 AM
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Personally I don't see a reason for this at all as I have seen several people run across water on sleds like he wants to do with a full exhaust on them and never a problem.
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post #5 of 15 (permalink) Old 04-18-2019, 10:29 AM Thread Starter
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The sled is actually a regular Indy 440 I just put the XCR carbs on. From the jetting chart I have, the stock jet is 290 for -20 to +10. And its 260 for 40+ degrees. So a 280 or 270 would be all I have to go down? I already have the needle dropped one notch. I have noticed that sometimes if it's warmer than freezing out the sled sometimes gets really boggy if you let it try to take off from an idle after running it for more than 10 minutes. And will maybe only rev to 5000 no matter the throttle position and just crawls around. One time I tried to start at the waters edge and it just slowly drove right into the pond LOL. Once it's up in the rpms it doesn't bog as long as you don't stop. Once it cools down it's fine again. Is this a pilot jet size problem? Thanks, Erik

P.S. There was no reason for doing this other than to just try it and be annoying. It's only going to be used on private land and racetracks.

Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled

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post #6 of 15 (permalink) Old 04-19-2019, 08:37 PM Thread Starter
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Anyone? This bog is a bit annoying and would like to run this thing tomorrow. I’ll drop mains to 280 and try that for sure but I’m not sure that’s going to help with my problem.

Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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post #7 of 15 (permalink) Old 04-20-2019, 07:30 AM
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Before you drop the pilot jets try the air screw?
But what you are saying sounds like the mains and the needle?
What do the plugs and piston wash look like?
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post #8 of 15 (permalink) Old 04-20-2019, 07:45 AM Thread Starter
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Plugs have been coming out really rich. The air screws are at like 2-2.5 turns right now and don’t seem to effect much. I have 280 and 250 mains on the bench right now. I think I’ll try the 280s and see but I’m not sure that will be lean enough. The needle is dropped one clip so far. I’ll see if I can check wash and then find what I really need to change. I was also thinking maybe venting carbs to airbox? I heard that leans it up by about 3 sizes.

Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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post #9 of 15 (permalink) Old 04-20-2019, 02:55 PM
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Well if you go 250 only run short full throttle pulls till you know where you are!
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post #10 of 15 (permalink) Old 04-22-2019, 09:55 PM Thread Starter
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Took it out with 280 mains with needle lowered one clip and airbox plate/shelf drilled with some more holes yesterday. Seemed to do a lot better than last time even thought it was 80* out instead of 40* like last time. Would still lose power and bog once it got hot but this time you could recover from it by playing with throttle a bit. I just put 260s in today and am thinking that will be spot on for 80*. Thanks guys.

Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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post #11 of 15 (permalink) Old 04-23-2019, 09:58 AM
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PICS!
Have someone get a Video on the water for us!
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post #12 of 15 (permalink) Old 04-23-2019, 10:33 AM Thread Starter
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Here are some pics. The first one was from this weekend. Not sure how I can post video on here?
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Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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post #13 of 15 (permalink) Old 04-25-2019, 09:46 AM
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Outlet from the convergent cone does have an impact on the performance, but as long as you have the same diameter and length you should then have the same back pressure and be OK. Raising back pressure (by reducing diameter and/or increasing length) will increase heat and raise high rpm power. But raising heat enough melts stuff you don't want to melt (pistons). If you care to learn some basics of pipe design, a book by Alexander Graham Bell titled "Performance Tuning in Theory and Practice: Two Strokes" that, although an old book, can give some very good insight. If you're really interested, I may have a file of the book on my computer I could email to you.
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post #14 of 15 (permalink) Old 04-26-2019, 06:32 AM
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Nice pics!
So many riders are scared to death of open water, for good reason.
I hope this will help them understand the physics of a snowmobile and its true abilities!
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post #15 of 15 (permalink) Old 05-06-2019, 09:47 AM Thread Starter
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Thanks wildcat. I do have that book (or at least some of it) saved on my phone and that’s where I got most of my info. I came here cause I just wanted to confirm since there’s lots of racers that usually don’t run silencers.

Polaris XLT - SLP pipes, SLP billet heads, clutched, Racepak Avenger III EGT, RSI bars, Cobra windshield, Fox front clickers, Pro-X rear suspension, 192 stud track, RMK seat and tank, plastic skis, painted hood and vents

1999 Arctic Cat Z440 Sno Pro- guest sled
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