kx80 carb issue


7 replies to this topic
  • 96xr200driven

Posted July 10, 2006 - 10:20 PM

#1

I just got a 1987 kx80 to work on and I have a problem with understanding the carb. I was talking with a guy at a motorcycle store who seemed pretty knowledgible and he insisted that every carb has at least two adjustments...the idle screw and the fuel/air screw. I have an idle screw on my kx80 but i have no other adjustment screws on it. It smokes pretty bad and i think it's because i need to make it burn leaner...but i have no adjustment screw to do this. I've already taken the whole thing apart and put it back together and cleaned it, but there are no other adjustment screws. Does anyone know how to adjust it? Sorry i don't have pictures, but i can't figure out how to post them. Any help would be greatly appreciated. almost forgot, I looked at my friends 1995 kx80 today and his had both screws.

also, i was wondering if i could take the reeds and carb off of any newer models to put on it. does anyone know what years would fit, if any?


Thanks

  • Jack G

Posted July 11, 2006 - 05:54 AM

#2

The idle speed adjustment is up on the slide portion at its base and the idle adjustment is down on the body of the carb. IIRC it's at the rear, but might be at the front, don't remember. I have a larger Mikuni on my KX80 along with a lot of mods.

Anyway, you cannot adjust jetting with a screw. There are five jetting circuits in the carb, the idle mixture (adjustable by screw), the pilot (off idle to maybe 1/4 throttle), the needle jet and needle taper (up to about 1/2 throttle), and the main jet. Also, the slide cutaway has an effect off idle. The needle jet you normally only change needles and that's really fine tuning that I never mess with. You're two most important "adjustments" are the pilot jet and main jet. Pull the float bowl off and turn the carb upside down and the main jet is staring you in the face. It's the big jet in the center, hex shaped, and will unscrew. There is a number on that jet that signifies its size. Bigger the number the richer the jet. This is the most important jet, the one that if you get it too lean, it will seize your engine.

The pilot jet is just in front of the main recessed down into a hole and it takes a small flat blade screw driver to get it out. It also has a number like the main. It affects the bike's low speed jetting off idle until the transition to the main.

You can also raise or lower the needle clip which changes the point at which the throttle climbs through the needle jet and onto the main. That's a fine tuning sort of adjustment. The thing you wanna do is get it running fairly clean off idle with proper pilot, then take "plug cuts" and read the plug (an art form best learned from someone who's done it a lot) and adjust your main jetting accordingly. Main jetting changes drastically with altitude, temperature, and humidity (IOW air density) and GP road racers will have either an air density meter or a temp/humidity meter with a graph for the track's altitude to use (made out of meticulous note taking) for getting in the right jetting range. The main jet is everything here.

You can also determine proper jetting by installing an exhaust gas temperature gauge. But, none of this is too problematic for a motocrosser as it is not tuned to the level that a GP road racer like the RS125 Honda or TZ125 Yamaha are and you're not on the main so much in the dirt, anyway. But, I have seized a KX80 before (okay, it's a motard running slicks and I road race it) when I went down to no problem raceway in Louisiana which is like, below sea level. They can stick if the main jetting is enough lean.

For all this carb tuning work, you should probably find a guy that's willing to help you 'cause a lot of it takes experience and understanding you probably don't have. It's all just part of life with a racing two stroke, though, and is probably a dying art since two strokes are a dying breed.

Oh, an edit, but some carbs like the Keihin flat slide CR on my XR150 (Frank Nye motor) flat tracker don't have idle circuits. You must blip the trottle to keep the thing running. These are racing carbs and race engines don't idle.

  • kx_rider53

Posted July 11, 2006 - 07:01 AM

#3

Here are too links for anything you need to adjust on the carb;
http://www.allthings...ead.php?t=13608
http://pingertalk.co...hread.php?t=528

  • Polar_Bus

Posted July 11, 2006 - 08:24 AM

#4

I just got a 1987 kx80 to work on and I have a problem with understanding the carb. I was talking with a guy at a motorcycle store who seemed pretty knowledgible and he insisted that every carb has at least two adjustments...the idle screw and the fuel/air screw. I have an idle screw on my kx80 but i have no other adjustment screws on it. It smokes pretty bad and i think it's because i need to make it burn leaner...but i have no adjustment screw to do this. I've already taken the whole thing apart and put it back together and cleaned it, but there are no other adjustment screws. Does anyone know how to adjust it? Sorry i don't have pictures, but i can't figure out how to post them. Any help would be greatly appreciated. almost forgot, I looked at my friends 1995 kx80 today and his had both screws.

also, i was wondering if i could take the reeds and carb off of any newer models to put on it. does anyone know what years would fit, if any?


Thanks


I did some quick reasearch, and you are right, your KX80 only has one external screw adjustment. That screw in the side of the carb adjusts your idle. Go here, then find your 1987 KX, and choose carburator for a diagram:

http://www.kawasaki....ID=2&intParts=1


As for your smoke, it's happening from either too rich of an oil ratio (like 32:1). I always recommend 42 to 50:1 for the average play bike. The second reason you might have excessive smoke, is you are in need of a new piston and rings. Low compression from a worn out top end will cause a bike to smoke, be hard to start, and have poor power. Put in a fresh piston and rings, and trust me, you will ba amazed at the new power your bike will have.
Rich

  • 96xr200driven

Posted July 11, 2006 - 05:17 PM

#5

ok. thanks for the jetting info guys, but ill probably have to wait with that until I find out where my fuel/air adjustment is. I just don't understand how it could not be there...maybe the adjustment is in the carb? I'm pretty sure my top end is good because it feels like it has a lot of compression. There's a 91 kx80 carb on ebay right now...does anyone know if that will fit on an 87?

Thanks for the help so far ,keep it comin

  • Polar_Bus

Posted July 12, 2006 - 03:48 AM

#6

My guess is the air/fuel is metered just by your pilot jet. Even if you did have an external air/fuel screw, adjusting that screw will not stop your bike from smoking. The sole purpose of the air/fuel screw is idle quality, and "off idle" throttle response. After 1/4 throttle, the air fuel screw has almost no effect on engine behavior.

  • 96xr200driven

Posted July 23, 2006 - 08:49 AM

#7

is there anyone who knows what carbs will fit on an 87 kx80 because I bought a new wiseco piston and rings and want to put a newer/better carb on it after the rebuild. Will all kx80 carbs fit? even newer ones? and what about kx100's?

  • 96xr200driven

Posted July 26, 2006 - 11:55 AM

#8

anyone? any help would be greatly appreciated.

Thanks guys





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