2007 600 rmk help!! no power in bottom end

[DUSTINSPELLMAN]

posting in this area as well

hey guys
im posting this for a buddy...
we have been trying everything to get this thing to get proper fuel milage and not to bogg in the lower rpm range. fuel mileage is terrrible, i get double with my 09dragon 800.

-we have tried every possible jet, needle setting. we have it jetted to the best we can.
-the machine has a slp intake with a mbrp can with around 3800miles
-we checked the reed valves and they seem to be ok.
-idling it leaves huge black spots in the snow and like i say in the bottom it boggs then once around 5500-6000 rmp she cleans up and takes off..

his sled did once over heat last year which scares me that he might need to rebuild his motor
could it possibly be a electical problem or a motor problem
any help would be great...im stumped

 

[Fallen]

maybe start with checking the compression. I seen some cheap compression testing kits at crappy tire. If the compression is still good i would assume it's a air/fuel ratio problem if it's running rich and leaving black spots in the snow.

 

[xc_rider08]

While lurking as a guest Rob1334 saw this post, and wanted me to copy and paste this for him:

“The 07 RMK 600 has been known for the problem that you described. I ran into this same problem as well as many other owners of these last year carb setups. When setup these sleds run strong and hard, but the factory missed the setup on the stock jetting.

The problem that you described is a rich idle circuit, a very common problem that can be easily solved. At idle it is rich enough to load up and cause problems with acceleration, as well as “black spots” left from the exhaust.

The fix is simple, a smaller pilot jet. Stock in the Mikuni 38 is a 50, which should have been a 45 or even a 40 from factory. This cleans up the idle circuit tremendously, no more “black spots”, and fuel consumption is improved. I have heard of others going to a bigger pilot air jet, but on mine I went to a 45 pilot jet and did not need any more adjustments.

Since I can’t post on here, email me at bob1334@hotmail.com and will help ya with any other tuning you might have questions on.”

 

[DUSTINSPELLMAN]

i should have checked that pilot jet out
thx for the help
ill email u if i need more info
thx a million

 

[mxz sledhead]

If the machine has Reeds that would be the place i,ll be looking

 

[DUSTINSPELLMAN]

already checked reed valves and they are fine
still going to try changing the pilot in a week or so when we bring his sled out of storage

 

[Modman]

I would check compression as well, like Fallen said, just to be sure.

 

[DUSTINSPELLMAN]

yah were going to double check the compression to be on the safe side

 

[xc_rider08]

It has nothing to do with compression, if it was low on compression it would run like a dog top end too, the black spot is from a rich mixture at idle.

Its simple, idle jet is too high which is giving you too much gas at idle.. drop size down like rob1334 says and it should go away


Here is a link for you and some diagrams

Mikuni TM carburetor drawings