Hate to say it, need jetting advice!

[Van Epps]

03 Mountain Cat 900. Ride 3-6k elevations. New mods to motor include porting, head cut 13:5.1, pods w/socks, SLP single and can. V force. Running non ethanol 92 w/3 gallons 112.

Have 360 mains in with power jets turned 2.5 turns out. Each turn = 2.5 main sizes so it should equate to 420 mains. Stock pilots.

Are 420 mains safe for this motor / elevation as a starting point or should I richen up? What would you recommend as a safe starting point?

Thanks

 

[maddogwfo]

My 2003 Mod 900

I ran the same elevation as you with a SLP single pipe, Boyseen Rad Valves, bored carbs, SLP porting and mod airbox, I was running 450/460 mains and never had a issue, sled ran strong, a good 3/8 inch wash on the pistons, I no I was running bigger jets than most but it worked and no burn downs, better to be safe, never fouled a plug either, MADDOGWFO

 

[Arctic Thunder]

410-420's should be good above 5000'.

Just keep an eye on it. At least you can pull plugs easily and check your wash and plugs compared to the M series.

Thunder

 

[kidrman]

I am running 13.6:1 on an 800 with no porting and only run one gallon of 110 per tank. Seems like alot of race gas for the comp.

 

[Van Epps]

Artic Thunder,

410-420 above 5k... is this with airbox or pods? I understand pods require a increase in mains of 3-4 sizes.

 

[CATSLEDMAN1]

jet'n

usually making air box mods or pods or open carbs effects mid range jetting more than top end.

keep an eye on your wash as suggested. most of these motors go down with lean midrange jettting. going way big on mains does help the lean mid range.
this winter a friend aquired a highly modded big bore KKAT that had been problemmatic for the disgusted former owner.

First we went from 360 mains to 500 mains so we could sort of safely start gingerly riding it and test jetting. went from anemic low mid range to an animal with a flat top end. Keep in mind as you get into the 400 and above Mikuni main jet range, one jet size means very little as your percentage of increased gas flow is very small, sometimes 3 or 4 jet sizes is necessary to detect any real running difference.

when done it runs a set of sanded down needles from a 2009 xp and 430 mains, so really we had to go way way fatter in the mid and not really that much more gas on top end. perfect............not yet, ok narrow wash, not yeat dead clean wash so still some mid lean spots, work in progress , reallly smartly glides past my lightly modded M8 on a hill.

I have never been able to run the stock cat KK needles and not have mid range lean issues.