KX500 38mm Mikuni Jetting Question

[Kawadougie]

I have a 2003 KX500 with an EFM automatic clutch. :) I rode the Fools Gold Enduro here in Northern California last weekend and did great but I found I had some problems with consistant idling speed which is a problem with my auto clutch. It's set to disengage just before idle speed is reached which allows me to chug up hills in difficult conditions. I've just bought a new 38mm Mikuni roundslide carburetor (old school) to try out and would appreciate any jetting info anyone might have. I think the older KX500's used to come with them. I'm currently using the stock 39mm Kehin PWK and have spent a fortune in brass jetting it. :ahhh:

Thanks,

Kawadougie

2003 KX-500 Folsom, California - EFM Auto Clutch, porting and head work by Eric Gorr, V-Force reed block, Moose Spacer, FMF Gnarly pipe, plastic tank by Clarke, suspension by NorCal Racetech :blah:

 

[Kawadougie]

Help!

 

[reknelb]

what did the carb come off of?
I have a manual for the kx500 that ranges from '83 and up. Problem is, the jetting specs for the '83 , '84, '87 are all different but, they list those years as all using vm38ss mikuni's. They used a 40mm vm mikuni in '85+'86

 

[nephron]

What kind of problems are you having with the 39? That's a great carb for the KX500, IMO. Maybe it's something specific to your situation?

 

[91kx]

I read somewhere that racetech used to use a R1370N needle on the standard carb and that mostly cleaned it up but I haven't tried it yet.

 

[Rider 007]

I've had KX500's since 1989. My current one is a 97 model.

From my experience the first thing you need to do is get the head modified so it will run properly (it eliminates the raspiness and rough running at low rpm).

I had Eric port mine to be electric (along with the head mod) and have a RAD valve in it. It has the stock 39mm PWK and if you can find a cleaner running KX500... buy it.

Here's the brass for my locale:
Main - 168
Pilot - 55
Needle - R1370N

Adjust clip position and air screw as needed.

You would be amazed at how good this engine is compared to stock.

Hope it helps.

:ride:

 

[Kawadougie]

I'm running the same main jet but a 42 pilot. I'm still using the stock needle. I've already had Eric modify my head and porting for increased bottom end. I also have a V-Force reed block and a Moose intake spacer. It runs fine most of the time. The 38mm carb is brand new. I actually found the jetting specs I need for the 38mm Mikuni at http://www.buykawasaki.com/ and looked under the parts diagrams for a 1987 KX-500. I'll let you know how it all works out.

 

[bruiserkx500]

What altitude are you flying at ? Mine runs great at 4200ft. Gorman , Ca . 39pwk 158 main 55 pilot 3rd position on needle ! Nice light brown spark plug ! 32:1 H1R synthetic oil ! Good luck !

 

[bruiserkx500]

Been riding and tuning dirt bikes for over forty years ! CZ ! Maico ! KTM ! Suzuki ! Honda ! Kawasaki ! Yamaha ! Just a few ! Loved them all !

 

[87KX500RIDER]

What about a vm40ss does anyone know the proper jetting for that carb. Its on my 87 kx500 but everything seems the same between my vm38ss and the vm40ss except for the floats... Replies appreciated