KX100 Jetting Survey

[griffbones]

I am curious how other KX100 owners have their jetting set-up? I am NOT asking how to jet my son's bike since I already know how and have it running good. What I am interested in, is seeing how many jetting variations the KX100 seems to receive based on elevation, average temp ect... I found quite a vast variance with the KX85's and YZ85's from owner to owner. I am mainly interested in the 2001 - 2007 models using the PWK 28 carb. So please speak up and help me with this research.

My Current set-up for my son's KX100 engine:

1000 Ft above sea level
Average temps (spring until late fall) 60 - 85 degrees farenheight

Stock 45 pilot jet (48 jet in the winter for temps below 50 deg.)
Air screw anywhere from 1 3/8 turns out - 2 turns out (depending on temps)
Stock #NAPF needle in the 3rd clip postion down (one position leaner than stock clip position)
stock 138 main jet

[griffbones]

Come on guys, nobody?


Well since I posted this a few days ago my son's bike had a catastrophic failure! Looks like lean or lack or lube, but it was fresh fuel at 40:1 like I have always run and stock jetting with the exception of the needle being set one clip position leaner than stock, so?


Hey Lakeshore, do you have any insight as to what could have caused this?
Brand new 2007 KX100 engine with maybe 8 hours of ride time at the most. 75 degree day, going down a long straight away, my son claims he was letting off the gas periodically and not holding it wide open steady, but varying the throttle some as he went down this long 1/8+ mile straight away. Had a clean air filter, fresh fuel mixed with Amsoil Dominator at 40:1, and had been running a nice tan plug previous to this failure.
After the seizer the plug looked like this, dark gray and power coated looking instead of the nice tan color that I had been accustomed to.

[2stroke173]

sorry to here that the kx100 motor seized so soon...i'll give you my setup even though your mainly interested in the 01-07 models...

95' KX100 (does not have a power valve) Doesn't need one! Plenty fast lots of low and mid consistant power through out the powerband...

414 Ft altitude
Average temps (April until October) 62 - 82 degrees farenheight

Pilot jet #50 (stock #55) Main jet stock #122
Jet needle stock #N68U 1st clip position leanest (stock is 4th)
Air screw anywhere from 1 1/2 - 2 turns out (depending on temps)
Float level standard 19mm
Keihin PK-26 carb
38:1 mixture, 93 octane gas

i took my bike out Saturday and rode it hard for a total of 3-5 hours and it ran great...

did the cylinder get damaged?

[YurFatMom]

Originally Posted by griffbones

Come on guys, nobody?


Well since I posted this a few days ago my son's bike had a catastrophic failure! Looks like lean or lack or lube, but it was fresh fuel at 40:1 like I have always run and stock jetting with the exception of the needle being set one clip position leaner than stock, so?


Hey Lakeshore, do you have any insight as to what could have caused this?
Brand new 2007 KX100 engine with maybe 8 hours of ride time at the most. 75 degree day, going down a long straight away, my son claims he was letting off the gas periodically and not holding it wide open steady, but varying the throttle some as he went down this long 1/8+ mile straight away. Had a clean air filter, fresh fuel mixed with Amsoil Dominator at 40:1, and had been running a nice tan plug previous to this failure.
After the seizer the plug looked like this, dark gray and power coated looking instead of the nice tan color that I had been accustomed to.

It SUCKS when that happens!

To me, it looks like it might have overheated, but the sparky is not white, so I dont imagine that that was the problem. I will think on that more this afternoon.

[corvettesR1]

Hi griffbones, I have an 04 kx100 with roughly the same hours on it as yours. I have been running the stock jetting with a 32:1 ratio motul 2 stoke oil .I was thinking of going to a 40:1 but after seeing this ,I think Ill stick with the 32. Sorry about your troubles hope you get it fixed up soon with no further troubles.All I can add is that my bike always kicks right over and has been running very well for me so far.

[Sledder]

That is probably a cold seizure. Either on this run or on one just previous(it can be a bit cumulative and not always tighten up and stay that way)......it got reved out before the cylinder was sufficiently warmed up to match the expansion of the piston.

Cold seizure usually doesnt tighten up right away,but a few minutes later.
It is evedenced by tight piston marking usually starting just below the rings,....and carries it's own signature "4 corner scuff"

When drag racing high rpm snowmobile engines,we run a bit more piston to cyl wall clearance,as there is often little time between heat races for proper warm up.....even more clearance if running forged pistons (like wiseco) that have a faster expansion rate than cast ones.

...if it was a lean condition,it would have shown detonation and or burning down the front upper corner by the exhaust port side. ....or peppered the top a bit. Lean condition is also usually above the rings,or around them.....and would seldom ever scuff the intake side to any extent.

[griffbones]

Yeah the cylinder is trashed!

Funny thing is we always give the bike plenty of warm up time and I never let my son ride until the radiator is warm. I have seen cold siezures before and I do understand exactly what you are saying, but I know it wasn't a cold siezure. Actually the more I think about it, my son had trucked down that straight away for more than likely well over a 1/4 mile not an 1/8 mile. I really think that he just stayed in it hard for too long and got it way too hot. This bike is geared like a KX100 but with the short KX85 wheels, so he is really zinging the R's when he tops it out. Most of our riding is at another place with lots of tight stuff and steep uphills, so he rarley gets above 3rd gear, but this day we were out in the wide open and he was running longer distances. BTW this happened after almost an hour of riding.

[2stroke173]

Do you still have the kx85 engine that you can put back in and use for awhile? Do you think that the motor wasn't broken in good since it only had about 8 hrs on it?

[griffbones]

I did the break in myself and did it by the book according to Kawaski.

I think I may know what happened, I guy told me that by having my son run the bike up in the rpm's and then coast and to keep repeating this would starv the engine of fuel/oil. He said that the engine would still be spinning really fast when coasting, and by coasting with the throttle closed greatly reduces the amount of premix that enters the cylinder. He also told me that it would be better to stay on the gas and periodically hit the kill switch while leaving the throttle open so that the engine continues to pull pre-mix in the cylinder. Sounds like this could make some sence.

[YurFatMom]

Originally Posted by griffbones

He also told me that it would be better to stay on the gas and periodically hit the kill switch while leaving the throttle open so that the engine continues to pull pre-mix in the cylinder. Sounds like this could make some sence.

I do that any time I am on a wide open stretch. I have done many 2 mi+ runs and havent had a siezure yet. Another thing I do is pull the clutch in and give the engine alittle rev to get the plates seperated. Then you can just coast with the engine idleing, and then when you slow down, dump the clutch and accelerate and repeat.

[corvettesR1]

Thanks for posting this information. I had no idea that a longish deceleration could contribe to this condition. You can bet Ill pull in the clutch and blip the throttle when I can insted of off gas coast ./

[VISaki]

This is true for 4 strokes as well off the gas your oil pump isn't working its during acceleration that its sucking from the oil pan..but alot harder to mess up since you have oil and gas seperated. Its always good to blip the gas if your gona coast or just hold the clutch in and use your brakes.

[dmstarr]

After installing the fatty, shorty, and V-force, Ty's bike was running hot so I have dropped the clip one position (4th from top - I think that is stock). I may have to bump the pilot up one.

[griffbones]

Originally Posted by dmstarr

After installing the fatty, shorty, and V-force, Ty's bike was running hot so I have dropped the clip one position (4th from top - I think that is stock). I may have to bump the pilot up one.

Hey dave, I think I saw a couple of different jetting charts from FMF that did show bumping the KX100 pilot jet up one size to a 48 and running the stock clip position. I have run a 48 in the really cold weather, but on our basically stock engine and pipe set-up, the 45 pilot seems to work better, and I do have to lean it out when it hits 80 - 90 degrees combined with the high humidity that we sometimes have around here.

Pro Circuit used to show leaning the pilot one and leaning the clip two positons (the second from the top postion), but even in really hot weather I thought the bike seemed a little slow to respond and too soft with the clip leaned two postions.

[dmstarr]

Just did a test ride behind the house. He feels it lost a little "zip." I'm not sure that his throttle hand is that well-tuned - I guess I shouldn't have told him I made the change!

[griffbones]

Originally Posted by dmstarr

Just did a test ride behind the house. He feels it lost a little "zip." I'm not sure that his throttle hand is that well-tuned - I guess I shouldn't have told him I made the change!

Boy oh boy do I know that one too my friend.

[VISaki]

How does the sleeve look that piston looks trashed...I go 32:1 40:1 unless your racing isn't really all that good unless you use a really thick type of oil like motul I use Klotz and yet to have a problem but then again all I have is a V-Force reeds soon expansion chamber and shorty..and sprocket.

[griffbones]

Originally Posted by VISaki

How does the sleeve look that piston looks trashed...I go 32:1 40:1 unless your racing isn't really all that good unless you use a really thick type of oil like motul I use Klotz and yet to have a problem but then again all I have is a V-Force reeds soon expansion chamber and shorty..and sprocket.

Most all of this is completely irrelevant! The mix ratio didn't cause the problem and won't cause the problem with proper jetting.

BTW these cylinders don't have a sleave, they are plated, but yeah, it was trashed.

This failure was caused by repeated very high speed throttle chops, in other words a lack of lubrication due to operator error.

By throwing out statements about oil brands with out knowing what you are talking about is only creating more dis-information founded on nothing more than incorrect speculation. IMHO