2013 Pro RMK 800 AFR target

[Eivel]

Hi,

What would be the ideal/safe target AFR for my NA 2013 Pro Rmk 800, at sea level?

Mods:
SLP stage 2
RKT drop in kit

Cruise = ?
WOT = ?

Im currenty running 12.7, but only being able to pull aprox 7950rpm.
Would leaning it out some rise my rpm's, or should I remove some weight from my MTX's? (71g with 3+3g)

Seeing through my datalogs I hit 8200rpm for a split second, and then settling down to 7900-7950, so I hope I don't hit the revlimiter if I have remove weight..

 

[max9string]

I'm running at 0-1000 elevation usually and my set up is

71 gram MTX, 2 gram in outer hole, first hole empty

Green/Pink Drive Spring, 160/340

engages at around 4100+, spike to 8400 and drops to 8250 in medium or hardpack snow

and in heavy deep snow spikes 8300 and runs at 8150

I bought an HPS can and PAR Head probably going to try

1 gram in middle and 2 or 3 gram in outer or 2 and 2


for you I would try 1 - 3 or 2 - 2 but leaning more through 1 - 3 for a more aggressive top end shift to prevent high spike rpm

for a 5 - 10 horse gain, 77 grams seems way to heavy, at the rpm your running your probably sacrificing like 10 hp and speed =S

top performance is 8250 safe zone is lower 8450 and lower

 

[Reg2view]

I would suggest you check piston wash and plugs in conjunction with AFR at different RPMs. I've run AFR on carb two stroke rotaxes (and DPM), not a poo, but what I found what works best is to find the wash and plug you want for that motor for midrange and WFO, at least, mark the AFR when you get there, and then you can make other mods tuning to those AFRs, or consistently use AFR to monitor fuel quality, air leaks, elevation, etc. Assuming the 02 sensor is calibrated and reading well, of course. JMPE on 2s AFR. Just can't replace 2s wash. I found scary lean wash at 12.5 AFR WFO, e.g., but could safely run 14.5 midrange, but unique to that motor/pipe/can, sensor, etc. Sorry, probably not the info you'd like. Good luck.

 

[mrquick68]

good info Reg2view, and good answer. AFR only means something on that specific sled. Wash and plug color will give you a much better read, then note AFR at the correct wash. Then you can monitor AFR instead of looking in the motor (which is annoying!).

As for your 8200 spike's, when does that happen? I would venture to guess when you pop out of the snow at WOT, crossing trenches in a climb, or when you go full throttle super quickly (slight belt slip upon WOT). To test actual peak RPMs, start a climb in untracked desired snow conditions and roll into the throttle to WOT consistently over 2 seconds (or so). Then you won't spike. test wash the same way, keeping WOT for 10 seconds or so to set desired wash on piston crown.

Or do what I do, ride it stock!!!and never look back! (except for clutching and suspension )

 

[Eivel]

Thank you all for good info

I tought reading afr's would be more precise than looking at wash and plugs. More lika a rough dial-in..

I had some det-issues wich made me do some changes from last year (installed the above mods late last season).
The changes where:
- More tip weight in clutch (from 1g to 3g)
- Got a new map to the pcv, and added 2% on every changed cell over stock
- Added a bottle of octane booster to the fuel tank

I have had zero det problems so far this season. I know I shouldnt have done more than one change at a time, but my plan was to reverse them if everything was good. (like no octane booster first, lean out map second etc.)

mrquick68:
Regarding the 8200rpm spike it happend like 1,4seconds in to the wot-pull, and yes I stabbed the throttle rather than rolling in on slowly.

Unfortunatly we don't have the long nice bottomless powder hills over here to really test the sled. Our situation is more like a medium packed field, and maby a 6-7 sec wot-pull. (if we have the balls to hang on to the throttle for that long before running into the trees, lol)

 

[polarisperformance]

clutching

For clutching, try to be in the 8300-8450 RPM ... the drop in kit produce hp at higher rpm,

Hi,



Mods:
SLP stage 2
RKT drop in kit


Im currenty running 12.7, but only being able to pull aprox 7950rpm.
Would leaning it out some rise my rpm's, or should I remove some weight from my MTX's? (71g with 3+3g)

Seeing through my datalogs I hit 8200rpm for a split second, and then settling down to 7900-7950, so I hope I don't hit the revlimiter if I have remove weight..

 

[Eivel]

For clutching, try to be in the 8300-8450 RPM ... the drop in kit produce hp at higher rpm,

Yes, I'm aware of this, and thats why I wonder how I best should attack this problem: Fuel for more power (rpm) or change weight, or both!

 

[die hard poo]

12.7 at WOT is about as lean as I would go. I prefer on a naturally aspirated sled to have more of my weight located at the heel. At sea level, I run on my wife's 13 for clutching:
SLP Blue/Pink Primary Spring
SLP MTX 71g weights with 2g at heel and empty at tip
Stock Sec. Spring with derlin and stock helix.
Carslile XS809 Belt
With her riding it (120lbs) eth. mode
With me riding it (200lbs) non eth. mode
I would try running 3g at the heel and nothing at the tip. If you over-rev on hard pack use the eth. mode for trail and then when you get to the deep, switch to non eth. mode. This will give you peak rpm when you are in the heavy load. If you are still over revving in the deep, try adding a gram to the tip.
Hope this helps

 

[theultrarider]

I would suggest you check piston wash and plugs in conjunction with AFR at different RPMs. I've run AFR on carb two stroke rotaxes (and DPM), not a poo, but what I found what works best is to find the wash and plug you want for that motor for midrange and WFO, at least, mark the AFR when you get there, and then you can make other mods tuning to those AFRs, or consistently use AFR to monitor fuel quality, air leaks, elevation, etc. Assuming the 02 sensor is calibrated and reading well, of course. JMPE on 2s AFR. Just can't replace 2s wash. I found scary lean wash at 12.5 AFR WFO, e.g., but could safely run 14.5 midrange, but unique to that motor/pipe/can, sensor, etc. Sorry, probably not the info you'd like. Good luck.

Exactly. There is nothing more precise than looking at the tops of your pistons. Onc you get them looking the way you want them, THEN look at that number on your afr and you it as your baseline. To pick a number out of the air either leaves hp on the table, or pistons in the trash can.

 

[gopher-it!]

afr

I installed afr on a 2011 bone stocker with sensor 2" away from pipe sensor. At 3000ft wot afr was 13.3 for about 500 ft then settled in at 12.8 for rest of run. My cfi 1000 makes it's power with these exact same #s. And yes, verified by plugs and wash.