How far can you jet down from the stock jets on a MXZ600. I have heard that you can jet down two sizes and still be ok. Should I go down one or two sizes, or should I leave it stock?
I always run premium fuel so fuel quality is not a problem, and I run Amsoil as well.
When I check my plugs, sometimes they look tanned sometimes they look a little black!

With most doo's,dropping two sizes from stock is fairly safe as they tend to be a little fat from the factory.Just no
prolonged WOT runs on very cold days ;)

id !!! on two but one shouldnt be a problem! drop it 1 run it like 1000 feet on new plugs and check them, run it back 1000 do the same that will show if you can drop it again.

What I did with mine is I dropped down only one size on the mains but I pulled out that little washer under the needle. That made a nice difference. Still just a tad fat but that should be my insurance on a cold day. Made a big difference in my fuel economy getting rid of that washer. One of the guys I've ridin with did this last year to his 02 MX 6 and had the same results.

Are you talking about the washer that goes between the main jets and the carb? On my 98 mxz 670 I have what looks to be a washer with little holes in it that is held in place by the main jets.

Best way is to jet down until a hole is burned in the top of the piston.
Then jet up 1 for warm days a 2 for cold days.
Some sleds can go as much as 6 sizes down before this happens.

I second mikadoo, it is the best way. No burn, no pain...no gain..

the little washer is probably the on needle under the c-clip you may be able to go to the next grove higher, the cup on the main jet is there to keep fuel supplied to the mains. :) Synthetic oils won't help if you go too lean they come off the parts that get the hottest. Fuel milage is usually made in the low to mid-range but watch for part throttle leanness, I stuck my 670 at 1/2 throttle with a load of bad gas, brown in the mid-range also for plug color

C`mon guy`s.. the post should of been about readin top`s and plugs...uncle meltie is a comin, dont mess with stock stuff unless you want to take a risk and force yourself to learn more and take the responsibility for it, winging it I can say drop one jet... but the next person will say 2 or 4....

Thanks for the info, I think I will try one size and see how the plugs look. I am not looking to burn down an engine, just looking for small gains here and there!

Originally posted by zeng62@Dec 16 2002, 11:55 PM
the little washer is probably the on needle under the c-clip you may be able to go to the next grove higher,
Thats the washer I tossed out. You can not move the e-clip on mine since there is only one groove. After doing this and dropping my jet size down one I checked plugs and piston wash. Both indicate the sled is still rich.