KDX 220 jetting problems

[Fiche]

I am looking forward to find the best start point for a good jetting, once considering the throttle response, I would say that only pilot circuit and WOT are Ok. Current is 160 main, 52 pilot, R1173L jet needle in the second from the top clip position and #5 slide valve.

Bike: KDX 220 1997 with performance pipe/expansion chamber, air box lid removed, aftermarket silencer, stock 33 carburetor and Boyesen reeds.

Riding conditions: Diverse area, riding in high load conditions(loose sand, mud and long step hills), with fluctuations in temperature greater than 10 ºC(18º F) and altitude changes dropping more than 3000 ft over the course of the day.
Air temperature: 22 - 35 ºC (71.6ºF - 95 ºF)
Altitude: 1100 a 4200 ft
Average humidity: 75%
95 octane fuel blend(75% Gasoline 25% Alcohol)
Premix ratio: 100:1(Motul 800 Oil)

 

[Fiche]

Folks, I understand jetting has been discussed hundred times before and this maybe is bothering you with the same subject, but believe me, I can not be sure. For example, I could see a good discussion about fuel blend(gasoline + alcohol), but nothing straight. I could see that I should go richer, but how much?
For those who have good experience on jetting, please help me!

 

[Domenic]

http://justkdx.dirtrider.net/ tech...carb tuning

I can't comment intelligently on your present jetting :think:

 

[Red_Chili]

For 4200 ft. you seem awfully rich already (I don't have B-reeds, do have a Gnarly Desert, and run a 140 main/42 pilot/stock needle clip one down from the top and that seems darn close for 5280 ft. I might need to put the clip in the middle, dunno, we'll see come spring). The variable that would throw me is the alcohol, that throws everything out the window. Lots of oxygen in that stuff.

I would just do the basics: play with the pilot until you idle cleanly and small throttle openings pull cleanly. Now take a plug reading WOT, mid-throttle, WRITE IT DOWN.

Then go several steps in whatever direction the plug reading tells you to, and repeat. For instance, if the plug is white and you get the dreaded buh-WAAAH, go maybe three steps richer on the main until WOT won't run all that cleanly but the BUH stops. That is your upper limit and you've 'bracketed' it. Take it a step at a time leaner until WOT runs cleanly, and the plug looks correct-ish.

Did I mention to write everything down?

Once you get WOT to run well, play with the needle and partial throttle. There's where it gets complicated unless your mid range is close, especially with the slide. I have had a scooter that I just could NOT dial in right, if it ran cleanly it also ran lean/hot in the mid range (this was a KLX300 with an early pumper carb mod). We started COMPLETELY over, a different needle jet, different needle, different main even. Got it sorted out and loved the bike, so of course I sold it. :bang:

Hope that helps somewhat - and GOOD LUCK!

 

[Fiche]

Domenic

I had read tech...carb tuning and many others prior to post here...considering this and the current running performance I decided to ask for help, once I have no experience and that the current jetting is a bad heritage. I am almost sure it is completely wrong.
If I would consider the tech tip, I think I would start with 148 main, 42 pilot and R1173L jet needle in the second from the top clip position, but I have the fuel blend issue that I can not disregard, and I have no parameters here, except a clue that I should go richer, but how much? One, two, three...sizes? I would appreciate your and other's advices, as did Red_Chili(thanks BTW)...

 

[Domenic]

IMHO You're too rich...I would drop the pilot to at least an 42..Then go do main jet tests..the alcohol blend should require a larger main and or richer needle..I'm also interested in the final results. Maybe email James Dean (jdjetting.com) and see what his thoughts are on the jetting requirements..Good luck

Domenic

 

[Rhodester]

I can't imagine what fuel blend you'd be using to require running a 160 main jet in a 33mm carb! If the majority of the blend is good ol' gasoline you'd still be rich even at below sea level and at below freezing temperatures.

 

[Domenic]

I can't imagine what fuel blend you'd be using to require running a 160 main jet in a 33mm carb! If the majority of the blend is good ol' gasoline you'd still be rich even at below sea level and at below freezing temperatures.

I meant richer than a 148..sorry :bang:

 

[Fiche]

Rhodester
I am using the best "gosoline" available in Brazil. It is a 95 octane fuel blend(75% Gasoline 25% Alcohol). All types of gas in Brazil has this amount of alcohol to increase octane at a lower price.
Anyway, I strongly believe that the guys that tried to jet my carburetor has not even a clue about jetting, and this is the reason I am trying to understand things better to to it by myself. Another point is the premix. Some people told me to use 100:1 but researching a little, I decided to try to go back to 1,5%(66,6:1).

 

[Rhodester]

I run 40:1 synthetic. I'd be reluctant to go less than 50:1.

 

[canyncarvr]

I didn't go looking for quotes from people that know this stuff to prove the point, but I think any 'blend' that is 25% alcohol is 100% garbage.

I'd never consider running 100:1 no matter what dyno-whoppin' hamsearl someone made me run.

You realize that the higher the numbers in that ratio figure, the more rich an air/fuel mixture you have, correct?

I see nothing in your post saying anything about what the situation is..what your bike is doing.

'Jet-By-Email' (closely related to an earlier released phenom, 'Jet-By-Fone') doesn't work. Someones maximus is required to be strapped to the bike to determine what the performance characteristics of the bike are in order to learn anything about what's going on.

Even so, Red_Chili lined it out well. If I read correctly, though, the questions remain after RC ( ;) ) answered them..so I'm not sure what you're after.

There is no 'real' fuel available? Once you start mixing fuels in an attempt to get something to work you have a job on your hands!

About as big a job as trying to jet a machine running on a 25% (purported) alcohol (methanol? ethanol?) mess.

Good luck, though!! :nod:

 

[Red_Chili]

AFAIK, you might end up needing a serious bump in compression just to make ponies!!! You gotta find a decent starting point where the bike begins to run sorta cleanly and go from there, changing ONE thing at a time until they lead you in an intuitive direction.

My story with the KLX is a case in point, things had to be jetted really weird to even run without being a teakettle. That itself was an indication to the tuner (on a phone no less) that we had to start over. I got lucky on the jet-by-phone scenario with that one. Often it goes badly as canyncarvr describes. Find a working main jet size and you're money; it's just incremental changes from there.

 

[Fiche]

canyncarvr
Unfortunately I am using the best fuel available in Brazil...I wish I could run betters like in US...
Yes I realize the ratio subject, NOW, and this is one of the reasons I will move to 1.5 - 2%(66.6 - 50:1).
The bike situation is this: bad throttle response from 1/4 thru 3/4, engine is like choking, spark plugs gets "fouled" easily, and I can see much oil from spark arrestor. If I insist on throttle or go suddenly to WOT, the engine stop choking and the bike "jumps" with a better sound. I hope I made myself understood...
I am not trying to 'Jet-By-Email' or phone, I am just trying to get a good starting point, then, be strapped to the bike and make it happen...
I believe the higher the number of posts I get here, the best is my chance to have a good starting point...
The alcohol is ethyl anhydrous alcohol(no water and no lead)...
Thank you for your post

 

[Red_Chili]

Let's assume your WOT (main) is close. Sounds like it's the closest of all anyway. 160, huh? Let that be the starting point.

Go back to sea-level stock pilot, needle, needle jet (if changed). Set your pilot air to 1.5 turns. What happens now? How does it run? Write it down, 1/4 throttle, 1/2 throttle, WOT behavior.

I suspect it will be a bit lean with your fuel even at your altitude if 160 mains run decent there, maybe quite a bit. If it hardly runs at all go 3-4 steps richer with the pilot, if it runs sorta ok but bogs/then hits at partial throttle then runs cleanly go 2 steps richer. What happens now? Write it down again. Keep going richer, the closer you get the smaller the jump.

Now hold it at half-throttle under some load. Does it surge? Too lean. Does it have a staccato sound and run 'dirty'? Too rich. Play with the needle clip. Write it down. Again, keep altering things one step at a time. If you are way off go way the other side of the problem (if it will hardly run it's so lean, go to where you KNOW it will be rich. You just 'bracketed' the problem and you know about where you need to end up to be right).

Now go back to WOT and fine tune the main. Review your notes. Is anything near it's limits or weird (needle clip on top or bottom and still not *quite* right, pilot air a bunch of turns out or in and still not right, that kind of thing)? These are clues, hopefully by this point things are much better.

The variable I can't speak to is the slide cutout. The needle jet should be fairly easy; compare how much richer than sea level your main is to run clean; the needle jet will be about that percentage richer +/- from stock as a starting point.

The only way to approach this is one step at a time, the hard way. Good hunting!

The good news is, you are too rich everywhere (sounds like, at least, without having a .wav file to listen to) but the main. You ain't that far off. No matter how many posts you get, we don't ride with 25% alcohol, which seems to be your complicating factor. Your most reliable guide is your ear, and the fact that at least WOT it runs not so bad on a 160 main.