Hey all,

I'm back with another set of questions. I finally got most of my new parts in (DJ kit, T handle fuel screw, uni filter), and tore down the bike to install them all last night. The needle and main jet install went fairly smoothly, the hardest part by far was removing and reinstalling the carb.


However, after reading all the comments about how these mods should make a world of difference, I was a bit underwhelmed. The bike started right up and ran well, more responsive off idle while revving in neutral. But when I went to take a spin on it, the bike didn't feel much different. Maybe slightly faster, but probably wouldn't have thought twice about it if I hadn't been looking for a difference.

My conditions:
Altitude: 8000-9000ft ASL
Temp: 50-70
Humidity: dry

The settings:
DJ 120 main
Stock pilot
Needle 3rd clip from top (one leaner than DJ recommends)
Fuel Screw 2 1/4 turns out
Uni Filter
Airbox lid removed
Slide drilled


So I'm wondering, could my jetting just be really off? Or is the air so thin up here that no basic mods will make a huge difference? I did notice more popping on decel than before, which would indicate a slightly lean pilot. However, I'm concerned about being too rich, since DJ recommends a 120 main for 6000+ feet on the 300 (which is the kit I got), and I only have the 250.

I only took a 5 minute spin on it, but the power curve just felt flat. No stuttering or surging though. I haven't had a chance to mess with air volume into the engine to see what makes it better or worse.

Any thoughts? Thanks! -Chris

 

Hey, dude, you need an exhaust system and possibly a larger (? at 8000 feet) main jet to see any noticable improvement in performance. Even then, we're only talking about 3-4 hp increase. I definately noticed a performance increase when I put the large snorkle and Pro-Circuit pipe on my bike with the appropriate jetting (not huge, but noticable...seemed to run better in general, also). I put a 128 DJ main jet in with the stock low speed jet and out a couple turns on the mixture screw. If I ever bother to take out the carb again, I'll probalby go to a 40 idle jet and run the mixture screw back in where it was originally......I would guess that your altitude would suck some of the life out of the performance gains a pipe would bring though......

 

I have a HMF pipe for sale it will make a huge difference it did with mine just being stock.

 

Chris,

You are really going to have to change the exhaust to make much of a difference (to go with your jetting changes), and even then you may still be disappointed.

The main jet is only really effective past 3/4 throttle to wide-open-throttle, your primary concern will be with airflow (lid on or off) and needle position. The needle jet (both the taper of the needle and the circlip position on the end) controls fuel mixture through the midrange from 1/4 throttle opening to 7/8ths throttle opening. Lowering the needle (circlip placement) will lean out your midrange while raising it will richen your midrange. I have no experience with the DJ kit, so you will have to experiment. I do know that after about the third time, you'll be able to pull the carb in about ten minutes. I also remember that if you decide to ride above 12,000ft I had more success with using a 115 main (118 is stock), Kawi part # 92063-1118. My bike, when stock, would not run above 8000ft. I think I was using the stock pilot jet although I may have gone smaller, and for 8000-9000ft, I think I was using a 120 (keihin) main. The recommended 40 (Keihin) pilot and 128 (Keihin) main are for those riders lucky enough to be near sea level. I had my bike jetted for sea level while I was in Oregon and It was definitely a different bike! If you could get an assortment of jets and some time on a dyno, that would be the way to go.

It took quite a few trys for me to get it. Sorry I can't give you the exact configuration, that was three years and many mods ago...Good luck!

 

Well for the jetting to have an effect...you need an aftermarket or opened up pipe ..... will that make the difference you expect..probably not, but improve it will.


Did you buy the right bike for your needs?

 

You're too rich. The bike comes stock with a 118 if I remember right. 10% smaller than that for your altitude if otherwise stock. You went up on the needle just by switching to the DJ, it has a much more aggressive taper than the stocker. Probably too rich there also. The air filter change is probably negligible as to anything, certainly with a stock exhaust.

 

Thanks for the quick responses everyone!

To respond to some of the posts:

- Yes, I definitely need an exhaust, or at least a slip on. But, that will have to wait until I can replenish my dirt bike funds (thanks for the offer buff36).

- I think I bought the right bike for my needs (as a beginner), but would like it to run as well as possible and have a decent throttle response.

Warski- Thanks for the detailed response. Glad to hear you eventually got it figured out! How stock was your bike when you were dealing with those altitudes?

Bake- I was thinking that with the airbox lid removed and an aftermarket filter, there is a lot more air flowing through than with the stock setup, so I could get away with letting more fuel in.

Also, a ride update: I'm actually thinking the main jet is decent, while the needle is off. I took it out for a cruise and really tried to get a feel for all throttle positions and RPM ranges. It pulled well at WOT in the upper RPM range (>7k). It also had decent throttle response/pull down low. However, when hammering on it in the middle rpm range, it felt flat and slightly boggy. Had kind of a burble sound to it. I also realize that jetting is more a factor of throttle position than RPM's, but I'm sometimes having trouble completely distinguishing the two while riding (still very new to this sport!). I'm going to try messing with the needle position, and if that doesn't work, go back to the stock main jet and keep the DJ needle.

 

good luck! keep us posted!

 

So I have another ride update:

I removed the carb again (much easier the second time!) and raised the needle one clip to try and eliminate the mid range flatness I felt. The end result: an improvement. Definitely a more responsive mid range, and a fairly strong pull from bottom to top. Only one small issue remains: when I’m at 4-5krpm in a taller gear, it still doesn’t really want to move. I’m not sure if this is due to gearing and (lack of) aerodynamics, or if my jetting is still slightly off. Additionally, I’m still considering going back to stock on the main jet, because as I rode to around 12k feet yesterday the bike definitely felt boggy. I’m not sure if I should jet it leaner to make it run well up high, or just deal with the high elevation issues to get more power on more standard rides.

 

A few points to remember.
1)This bike with the stock carb doesn't really have instantaneous throttle response to begin with.
2) A 250cc four stroke with only about 18 hp and almost 300lbs ready to ride ain't really going to pull that hard from a taller gear at 4/5 K any way. Downshift, also you might want to look into a 13 tooth counter shaft sprocket.
3) At 12K feet asl any motorcycle is going to make considerably less power.
4) CV carbs aren't quite as sensitive to elevation changes as "regular carbs"
5) I seriously doubt aerodynamics has much to do with it, unless you want to break the 250cc four stroke world record at Bonneville.
You might be over thinking this a bit. If I remember correctly (and I don't quite frequently) I think the rule of thumb is with a stock bike for each 2000/3000 ft you go up drop the main 1 step and raise the clip one notch adjust the idle screw. Now bear in mind this is from memory sitting here f&*^ing off at work. There is sure to be some jetting vs elevation charts and information somewhere on the net.Those basic rules will get you into the ball park, but to get it really get it right you have to experiment. Change one thing at a time then test and remember temperature and humidity are also factors. Remember if you jet for 12Kft it's may run dangerously lean at lower elevations. Unless you want to rejet for every ride you take your not going to achieve a perfect fuel air mixture any way, especially if the ride includes major elevation changes. Good luck.