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I am about to install my new 860 from RK Tek. A lot of people question Kelsey's formula for putting in smaller jets. (480 down to 460) has anyone tried this or are there any opinions out there?
RK TeK 860 Big Bore Kit
- Thread starter Trickle860
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- 860 big bore jets reeds rk tek
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I'm running his 13.5 head and I've got 450s in mine. No issues. They come jetted fat from the factory.
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Do you run a little race gas?
Two full seasons on my 860R kit. Yes follow Kelsey's suggestions, 460's are where you want to be. I am running 14:1 domes above 8000 ft. 6200 to 7200 RPM is the "hotspot" for the engine, try to avoid running in this RPM range. I run a few gallons of Av gas per tank to help eliminate detno in this RPM range. I tried some Torco Accelerator to raise the octane of 91 pump gas but I through a DET code on the trail right away so I am going back to Av gas. Other than that the engine has been stellar!
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Good gas and elevation play the biggest part. On mine i had the 14:1 head and stock pipe and can. Went down to 460 and it was to lean and tightened up.
Ran 480 mains with colder temps and 470's in the spring. Made good power and never had any more trouble. After the tighten up i ran 2 gallons of 110 with 91.
Elevation was 3500 to 6500ft.
I would still be running it but bought a used 2010 sled with 880 BMP in it already and sold my 2008 stock that i had the 860 in.
Still have the top end in drawer as wanted to run the 880 to see the difference.
Just my findings as far as jetting. Also talked with engine builder about this and it was to lean with 460's.
Ran 480 mains with colder temps and 470's in the spring. Made good power and never had any more trouble. After the tighten up i ran 2 gallons of 110 with 91.
Elevation was 3500 to 6500ft.
I would still be running it but bought a used 2010 sled with 880 BMP in it already and sold my 2008 stock that i had the 860 in.
Still have the top end in drawer as wanted to run the 880 to see the difference.
Just my findings as far as jetting. Also talked with engine builder about this and it was to lean with 460's.
You had deto at 8k with 14.1? Really? I run 14.7 and it run's great 8k and up. I tried running a few gallons of 110 didn't seem to like it up around 9,500 seemed a little rich. I don't have guages but am running 91 non ethenol fuel. Also a premix setup. But shouldn't matter. I am running 470's in my 860 runs perfect
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Yes I do. 20% 110 with 94 or 30% with 91.
When jetting down just remember that the needle is pulling through the main and if the main is smaller then it's going to get real lean at the top end of the mids as was described in a earlier post as the rpm range to avoid. Bored carbs make it worse. At one point during testing mine was so lean it ran better in the mids with the choke half on. Now with dual egt and a/f it was much easier to dial.
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Why does bored carbs make a difference
my 42.5 bored carbs done by Rich at Dynoport on the 860 and the 880 were easier to tune than stock carbs.Mains remained the same and raised the needle .030. stock pilots. Very easy and ran flawless. noticeable mid hit and top gains as well as responsiveness .
I ADD a .030" shim to stock needle and 470 mains on all XP 860's...now if your jetting down to 460 for the RKT kit and NOT adding any fuel to the mids then...well...good luck...
If my memory serves, Kelsey likes/recomends the 2007 800R needle (#3 position vs stock)...either way...add fuel to mids...BJ
If my memory serves, Kelsey likes/recomends the 2007 800R needle (#3 position vs stock)...either way...add fuel to mids...BJ
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keep in mind if you do the boyseen reeds, i was rich by a margin in the middle... 10 thou shim 07 needles, mid position 460 mains on 42.5mm carbs stock pilots worked the best in the 880 case...added a few degrees of timing and egts stay well in check
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Is everyone on this post running the RK TEK 860?
Yes I am. PM me if you have questions.
I put the high dome pistons in my 02 - 800 several years ago, and dropped from 500's to 460's like RKT recommended. The sled ran like a banshee for a day and a half and then seized up tighter than dog crap. Don't do it.
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You are correct and i had 2007 needles with .010 shim and 460 mains when it tightened up. Also Boyseen reeds.
Instructions are for 460 mains but i still think that alot has to do with fuel.
Great motors as far as i have found but as we all know people all have options.:face-icon-small-win
Forgot to mention that it was at wide open on the hill that it tightened up. Felt it just for a second and still ran the rest of the day without trouble.
When i got home i checked it and seen the results.
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So my friend and I spent 11 hours installing the new 860 today. We went to the local SkiDoo shop today and it just so happened that all the badass Skidoo guys were in there when we were. Two of them stated that they have friends who have had terrible luck with RK Tek 860's but that's a side note. Anyway we decided to go with 500 jets with one washer/spacer in the needles during the break in to keep it cool. After 150 miles I plan on trying to lean it down. One guy who knows his **** runs 530's with his Trigstad 860 and says its perfect. Anyway, as we were connecting all the various lines we discovered that my oil cable was almost completely frayed thru. I probably had two more rides before a terrible disaster could have taken place. We will have it all together and hopefully running by Wednesday. If anyone feels like giving me a call with some advice, I'd really appreciate it. 406-207-9206
If your oil cable breaks it goes full rich... No disaster
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could you be mistaken on the trygstad 860? mikuni does not make 530 mains
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Daves motors like the fuel, that jetting sounds correct. Keep in mind with the RKT kit and Kelsey's head it will require different jetting than Trygstad.
