Quick question for a friend of mine

[Racerjoey1]

My buddy just bought a 1991 KDX 250. The bike is in really good shape and runs strong but it has a massive Turbine Core spark arrestor on it. We have a few questions about the bike.

1) Is the motor any different besides a flywheel weight and tuning from the KX250 of the same year?

2) Would a silencer for a KX250 fit, or could it be modified easily to fit?

3) Is the KIPS as notorious for having issues on the 250 as the 200?


Thanks for the help,

Joey

 

[dirt bike dave]

1) The motor is based on the '88 KX250. It thinke the '89 KX is very similar; not sure about the '90 and '91. The cylinder porting is very different. The carb jetting is different. Pipes are different. You can use the thin head gaskets from a '88 KX250 to raise compression and get even more low end power, and it will still run fine on pump premium fuel.

2) Not sure about a KX250 silencer, but an aftermarket silencer/apark arrestor from the '89 - '93 KDX200 can be modified to fit. That's what I ran on mine.

3) Not as much, but the stock jetting is WAY too rich (even worse than the 200). To avoid powervalve problems and to to help the bike run better, the stock main, pilot, needel and slide should be leaned out.



Basically, the bike was not well set up by Kawasaki, but with some attention to detail (mainly the forks and the jetting) it can be made to work quite well and is reilable with good low end power. After much effort with setup, I really preferred mine to any 200 I've ridden.

Look for posts by blackduc748 ( I think that is his name). He has a KDX250 home page where he summarized many of the set up things my friend and I developed for our KDX250s back in the day, as well as things from many other posters.

 

[Racerjoey1]

Thank you very much for the help. I forgot one thing though. Here is a little more info on the bike:

He is running Castor 927 at 32:1 with 93 octane fuel. The bike will not idle. It sounds like it is idling a little high, but it will not stay running unless you give it a little throttle every few seconds. The motor runs strong, we are just wondering how we can adjust the carb to make it idle.


Also, we dont think the clutch is fully disengaging. When you are in neutral with the clutch in and kick it down into first, the bike pulls forward a little and will stall the motor unless you give it gas, but you can rev the motor with the clutch in gear and it will not move. He just bought the bike Friday night and it runs great except for those few minor issues.


Thank you all in advance for the help,

Joey

 

[Tom68]

My KDX250sr is fussy about gear oil, lighter grades work better. Don't know what Castor 927 is but I do know castor base oils smell good but gum up engines. Idle problem could be a number of things start with the obvious like carby and work your way towards the expensive stuff like crankcase seals.

 

[dirt bike dave]

I agree on the lighter grade gear oil workign better for the KDX250 clutch/gear box.

I usually used 10w40 motor oil. If he has a heavier weight gear oil in there, that could be part of the trouble. On one trip, I had 90w gear oil in the box, and left the bike outside on a cold night. It took a few miles of first gear warming up before I could shift. With lighter weight oil, I never had that trouble.

For pre-mix, I had good success with Maxima Super M at 40:1. The Super M reportedly is a good oil for a trail bike. Some of the 'race' oils might not burn completely in a low rpm, cool running (rich) trail bike.

As for the idle, mine would idle very well, but I had the jetting sorted out. Mine had a slide with 1 mm more cutaway installed when I bought it. (if you find blackduc748's KDX250 page, some good jetting recommendats will be in there).

His idle problem is probably due to the overly rich stock jetting. Get the bike warmed up, and try turning the airscrew out. This is the little brass screw on the lower left side of the carb, just above the float bowl. If it has the stock pilot and slide, you might need to turn the airscrew out 3 turns or so (after that much, it does not make much if any difference) to lean it up some.

The stock carb slide is known to not have enought cut-away. Replacing the slide with 1 mm more cutaway is expensive, but would help lean the bike out at idle. It is possible to scribe a line 1mm up from the bottom of the slide and grind up to the line, but most people will not go through the trouble.

There is an idle speed adjustment on the side of the carb (left side, can't remember the exacnt location). I think it has a little spring on it.

BTW, he can safely run a hotter plug than Kawasaki recommends. I used a BR7ES safely for years. If he has stock jetting and a stock plug heat range, it could really be loading up at idle.

 

[glad2ride]

Check the clutch basket for grooves worn into it, not allowing the plates to slide properly.