fuel mixture screw

[Jeff Khoury]

As I alluded to in my last email, carburetor tuning is an art. I have developed this procedure and have used it on three bikes: My '09 KLR My '92 Seca II My friends V-star 1100 This may not be the "by the book way" of doing it, but I get really good results from this. The instructions that come with a DynoJet kit will get you CLOSE. You will still have to do some tuning to get it right. If you have driveability problems, give this a try. I'm not a mechanic, but I'm an enthusiast who's played a lot with carb tuning. Primer: Pilot and (and starter, if equipped) jets affect ONLY the idle and transition from idle to needle. The mixture screw affects ONLY this circuit. 1. Adjust the size of the main first. The main jet in most CV slide carburetors feeds the needle as well, so changing the main will most likely require adjusting the needle. You can do this by sound/feel if you have a good ear for it, or try the spark plug color trick. Set the needle mid-range to adjust the size of the main. To do this: find a nice, deserted stretch of road at your operating altitude of choice. Warm up the bike to operating temperature. Don't worry about hesitations or bad behaviour at anything other than full throttle right now. Take the bike out on the road and run it out to full throttle, let it run for 15-20 seconds, then simultaneously pull in the clutch and hit the kill switch. Coast to the side of the road. Pull a spark plug and examine its color. You're looking for a nice gray. White = too lean, darker = too rich. Another indicator is rough running at full throttle, indicating a rich condition. Change the mains until you get the desired full-throttle performance. Next, adjust the needle up until you get mid-range hesitations when the bike is hot, after leaving it idle for a bit until the fan kicks in, then drop it a notch. This gives you the richest setting without incomplete atomization. Put it all back together and warm the bike up again. Adjust the idle to its highest point that does not drift down when you blip the throttle. When you blip the throttle, it should return to idle quickly, not slowly glide down. Once you've done this, adjust the idle mixture screw until you have it set where you have the highest idle. Then back off the idle thumbscrew to desired hot idle rpm (blip the throttle a few times to ensure it stays where you want it). Bear in mind that when the bike is cold it will idle at a lower rpm than when it's hot. This may take some massaging. Your bike should now cold start easier, pop less on deceleration and have more go-fast. Synchronization of multi-carb engines is out of scope of this email. Thoughts and counterpoints welcome. -Jeff Khoury Astatic Solutions, LLC. [Non-text portions of this message have been removed]

[Rick McCauley]

What I have learned from trying to squeeze more power out of many of the bikes I have owned, is that the smoothest, hiccup free carburetion usually comes right from the factory. There are of course exceptions, thanks to the EPA. If you make modifications you can get more top end power, but it will cost you in the low and midrange. My best example was my 78 KZ1000. I rode it bone stock, and it was quite impressive. Of course I immediately purchased K&N filters, and a Vance & Hines header. With a lot of trial and error, and guideance from a Kawasaki mechanic friend of mine, we got the jetting as good as possible without tons of money and a dyno. The plug readings were all good, and the top end rush was impressive, but I lost that impressive midrange, and the bike had a mild surge at highway speeds. Not bad, but I could feel it at certain times. I think mid-range is more fun than having to wring the engines neck to get the best the engine has to offer. I think the majority of riders want the top end hit. I guess I am getting old. I like midrange grunt. Rick (swamp dweller) A17

--- On Fri, 5/1/09, Jeff Khoury wrote: From: Jeff Khoury Subject: Re: [DSN_KLR650] fuel mixture screw To: ramachm12@... Cc: "dsn klr650" dsn_klr650@yahoogroups.com> Date: Friday, May 1, 2009, 10:59 AM Just as a primer to those messing with jetting, here are the results of my learnin' based on spending a lot of time tuning my old Seca II. I learned this the hard way, and it's even harder because you have to do everything x4. These are some general tuning tips I've learned by trial-and-error. * Any time you do anything to increase flow of air or exhaust, you need to richen everything. The opposite is true of restriction. -From idle to 1/8 throttle or so: Pilot (Idle mixture) screw -from 1/8 to about 2/3 throttle: needle -2/3 and up: mains These areas overlap, but this is a good rule-of-thumb *watch out for altitude. If you tune at sea level, then go up a few thousand feet, behaviour could be different. *If you get popping on deceleration (with throttle closed) most likely you are too lean, but you could also have an exhaust leak or air injection problem if your bike is so equipped. This could also be an indication that your pilot jets are becoming clogged if you have made no adjustments, especially if the bike has sat for a while. *If the bike runs well cold, then develops a hesitation when it warms up, you're too rich. *If it runs well warm, but is cold-blooded and you have to choke the crap out of it, you're too lean. *If you install a needle with an aggressive taper, like the KLX needle, and you have stock exhaust, you may have to go DOWN a jet size or two. *if it hesitates coming off idle when warm, lean up the pilot circuit a hair. *If it does the same at 1/4 throttle or so, lower the needle a notch. *If you rejet and actually lose top end, but gain accelleration, the main is probably too rich. (you'll hear a distinct change in tone if you're too rich. ) All of these changes affect the others, so unless you're an expert, you'll have to keep tweaking until you hit that magical driveability balance... where it's smooth throughout the whole range. Remember. In carburetors, RPM is not important... it is about throttle position. I'll add more as I think of them. -Jeff Khoury ----- Original Message ----- From: "Rick McCauley" To: "dsn klr650" Sent: Friday, May 1, 2009 8:39:28 AM GMT -08:00 US/Canada Pacific Subject: Re: [DSN_KLR650] fuel mixture screw The KLR is lean to start with. I am assuming that it is not a good idea to remove the snorkel unless you make other mods, like raising the needle. Correct? Rick (swamp dweller) A17 --- On Fri, 5/1/09, Jeff Khoury < jeff@astatic. net > wrote: From: Jeff Khoury < jeff@astatic. net > Subject: Re: [DSN_KLR650] fuel mixture screw To: corybaby@sbcglobal. net Cc: "DSN KLR650" < DSN_KLR650@yahoogro ups.com > Date: Friday, May 1, 2009, 10:30 AM I have an '09, so it should be identical. I have gotten good results with the following: I have the stock exhaust, and have removed the snorkel from the airbox. I drilled the slide and adjusted the pilot (idle mixture screws) per instructions from the DynoJet kit, you can get a pdf from their website. I then placed a shim (#4 brass washer) under the needle clip to richen the midrange a bit. Throttle response is improved as well as cold start and idle. YMMV. I don't know about increased horespower, but it feels "snappier" Some people install the needle out of a KLX to make it more agressive. -Jeff Khoury ----- Original Message ----- From: corybaby@sbcglobal. net To: "DSN KLR650" Sent: Friday, May 1, 2009 6:44:55 AM GMT -08:00 US/Canada Pacific Subject: [DSN_KLR650] fuel mixture screw So ive done alot of research on techniques for richening up the 08 klr, some say to turn the mix screw (bottom of carb behind plug)all the way in and then out 3/4 turn....some say turn it out 2 1/2 - 3-1/2 turns out...which is it? 2 1/2 was stock on my bike.......which way is richer and leaner thanks in advance 08 klr e2 pipe ,grommet from airbox removed,(marknet) no other engine mods cory [Non-text portions of this message have been removed] [Non-text portions of this message have been removed] [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]