91 KDX250D1 Carb Questions.

[madmax80]

Bought a 1991 KDX250 D1 a couple months ago. New crank, rod, piston, rings, bearings, seals, and sleeve done by previous owner(friend). Stock pipe and repacked silencer. Airbox snorkel still intact. B8ES Plug. 91 Octane w/MC1@32:1. Riding elevation is sea level to 5000 ft.

Having problems getting it to idle at a consistent RPM. Have to adjust idle speed every time I start it, sometimes it idles too high, other times won't idle at all. Read here that pilot jet may be blocked. I would like to take carb off and clean, adjust float bowl and re-jet. (Engine bogs from idle to approx. 1/4 throttle).

Questions:
1. What parts should I have on-hand before taking carb apart? Seals, O-rings, Jets or whatever else?

2. What are the stock jets and air screw settings?

3. What size jets and settings should I be using for my 0-5000 ft riding elevation?

Any other tips or helpful info would be greatly appreciated. (I only get a blank page about 90% of the time when doing a search).

Thanks everyone.

 

[Joburble]

I'd be looking for an air leak.

If you want to check the jets:
Pull the carb apart, clean it out, put it back together, parts only if needed. You may need a new float bowl gasket though.

Why are you using 91 octane?

 

[madmax80]

Thanks for the reply.

It's a '91 KDX250D1. I read quite a few posts that everybody was using the highest octane they could get, so I figured I would do the same. I don't have an owners manual but I assume they recommend 87.

 

[Joburble]

Yea, sorry about the confusion regarding your type of bike, the heading was not displayed when I posted the reply and it added to my confusion.

Regarding the fuel, I guess it's a country thing, here in NZ our lowest fuel is 91octane (our highest is 98), so I assumed wrongly that you were using the cheapest stuff.

 

[reepicheep]

My experience so far (1995, ported 225 big bore with weisco piston, FMF gnarly expansion chamber, stock silencer, snorkel out but airbox cover on, 800 feet elevation) has been that vast majority of the jetting advice I have seen has been way rich.

I was down to a 152 as my main jet, and at about 35 degrees out, it *still* has a little rich bog at WOT. I have an FMF silencer on the way, which I am hoping will lean it out just a little.

But anyway, all the "standard jetting" guides I have seen were leading me down a road of running rich.

 

[Matt90GT]

A kdx200/220 is WAY different than the 250s of 91-94

The jetting is way off on the bikes from the factory. This is what you need to do to get it running right (and yes you need to do it all):

-Remove the airbox snorkle from the lid
-aftermarket pipe and silencer
-install 1989 KX250 thin headgasket (.26 vs .46 in thickness)
- install aftermarket reeds (Vforce II recommended)

and the biggie:

-Rejet the carb -- Jetting: 38/158 , R1367H needle 3rd clip from top, #6 slide
*yes you need the slide, and the needle. yes they are expensive *
Run 40-50:1 with good quality synthetic and it will rip


run a NGK Iridium IX plug (BR9EIX)

 

[reepicheep]

Wow. Thats a huge set of variables. How on earth did you manage to track them all down and tune them? Do uou have a 4 gas dyno in the garage, and a LOT of time on your hands? :ride:

 

[sr5bidder]

I would agree with joburble look for an air leak (left crank seal, intake bootand carb cap) and also try to clean the carb... while your at it check the throttle cable adjustment and make sure the slide is able to botom out with the idle speed screw turn out all the way

 

[dirt bike dave]

A kdx200/220 is WAY different than the 250s of 91-94

The jetting is way off on the bikes from the factory. This is what you need to do to get it running right (and yes you need to do it all):

-Remove the airbox snorkle from the lid
-aftermarket pipe and silencer
-install 1989 KX250 thin headgasket (.26 vs .46 in thickness)
- install aftermarket reeds (Vforce II recommended)

and the biggie:

-Rejet the carb -- Jetting: 38/158 , R1367H needle 3rd clip from top, #6 slide
*yes you need the slide, and the needle. yes they are expensive *
Run 40-50:1 with good quality synthetic and it will rip


run a NGK Iridium IX plug (BR9EIX)

That's the jetting and general set up I used on my '91 KDX250. If much of your riding is at 4,000 feet or above, you can go with a 155 main.

Pump premium, 91 octane fuel.

And FWIW, I used a BR8ES or BR7ES plug for woods riding with no ill effects.

The stock jetting on these bikes is horrible (as are the valving and springs in the forks, but that's another thread). With some attention to jetting, forks and a few other minor things, the bike can be vastly improved over stock. When set up right, it makes a nice, reliable, affordable trail bike with good low end power.

BTW, it has a very heavy flyweel stock, and a big tank, too (mine and my buddies measured 3.6 gallons; Kawi says 3.2 or 3.3).

 

[madmax80]

Thanks for the suggestions.
I do a lot of deep water crossings so I was hoping to keep my snorkle but will ditch it if I absolutely have too. Any concerns with no snorkle and deep water?
I will be getting a pipe and silencer within a couple months hopefully.
Just had to redo the head gasket because it never got re-tourqed after the first couple heat cycles and I put the stock one back in so I will probably stay with that for now.

Any suggestions on where to purchase VForce II reeds?

Can jets, needle, slide be bought aftermarket or are they Kawasaki only?

Is there any kind of carb rebuild kit available aftermarket, ie: gaskets, float needle valve or whatever else or is this Kawasaki as well?

How do I tell if the slide is bottoming out after turning idle adjustment/enriching circuit all the way out? Just crank throttle and release and I will be able to tell?

Thanks for all the help, sorry for so many questions. First dirtbike since my 84 XL125.

I do have 90 Kx 250 front end on the KDX though :)

 

[Matt90GT]

unless you submerge the bike up to the base of the seat, the snorkle will not do you any good.

It is common knowledge that the KDX250s and RMx250s were detuned and enduro'd out bikes of their KX/RM250s. So the factory corked up the exhaust and added a S/A, detuned the motor with a thicker headgasket to lower compression, then added intake snorkle and messed the jetted up something horrible.

So basically you are restoring the bike back to the KX250 it was based on. And guess what, it rips!

 

[sr5bidder]

Can jets, needle, slide be bought aftermarket or are they Kawasaki only?

Is there any kind of carb rebuild kit available aftermarket, ie: gaskets, float needle valve or whatever else or is this Kawasaki as well?

How do I tell if the slide is bottoming out after turning idle adjustment/enriching circuit all the way out? Just crank throttle and release and I will be able to tell?

:)

after turning the idle adjustment screw out, yes all you have to do is lokk in the filter side of the carb and snap the throttle a few times.

you may be able to send your carb off to rb designs and have the slide modified, I really don't know about the 250

http://www.sudco.com/ will be able to hook you up with parts for the carb