turkhuntr

Member
Sep 8, 2005
8
0
Hello. Purchased a 1991 Kawasaki KX80 for my son. Top end
was just rebuilt with a high performance weisco piston. Mechanic told me to run 40:1 fuel mixture. My son rides this guy pretty hard, but it is fouling plugs like crazy. (oil fouled)
This is my first experience with a dirt bike and not sure what to do. The mechanic said we should not be fouling plugs if we mix the oil/fuel correctly, mix it well, and warm the engine before taking off. Any help would be appreciated!

Thanks!
Turkhuntr
 

FruDaddy

Member
Aug 21, 2005
2,854
0
You might try dropping 1 size on the main jet. Also, think about changing the heat range on the plug. Is there oil dripping out of the end of the pipe as well?
 

turkhuntr

Member
Sep 8, 2005
8
0
Yes, we are dripping oil at the point where the exhaust enters the silencer, at least that's where it appears.

Also, just jumped to a hotter plug and no difference.
 

bikepilot

Member
Nov 12, 2004
804
0
Your jetting is way off and/or the right side crank seal is bad allowing the engine to burn transmission oil. Unless its smoking a huge amount or your loosing noticeable amounts of transmission fluid I'd bet on the former being the case. If its rich, it will also be loading up and generally running rather badly. If this is the case, try leaning out whater portion of the throttle range is rich (probably mid-top or all of it). For example, if it seems basically ok at really low throttle openings but rich once you get going try dropping the needle one notch and install a one size smaller main jet. Continue to go leaner till it cleans up.

Where are you located? If in noVA I can help you out.
 

turkhuntr

Member
Sep 8, 2005
8
0
Pilot, this is my first bike ever and a newbie. Located near Altoona, PA. About installing main jets'. How do I know what size to get, are the current ones marked ?
Also, never had one of these carbs apart. Is there instructions on the web of how to take apart? I'm fairly handy and not afraid to do myself, just never did one. The carb on the '91 KX80 is a KEIHIN. Not sure if this is the stock carb that came with the bike, but supposedly the carb was rebuilt when the topend was redone. Thanks PILOT!!!!!!

P.S. Also, if the top end was just rebuilt, how long does it
take to "break in" and how do you know when it's broke in?

thanks again!
 

FruDaddy

Member
Aug 21, 2005
2,854
0
I know you asked pilot, but I'll answer part of it. Our 65 was running rich, fouling plugs, and dripping oil out of the pipe. We also run 40:1 ratio. I went down one factory size (which is 2 Mikuni sizes) on the main jet and the problem seems to be fixed. The stock jet was a 190, I installed a 180. I am not really familiar with Keihin carbs, but the principles are the same. To change the main jet, you ned to remove the carb, you might be able to get away with leaving the throttle cable attached. Remove the 4 screws on the bottom of the carb. These are often extremely difficult, using a properly fitted screwdriver and applying a generous amount of pressure to the screwdriver will help. The bowl should then come off, if it doesn't, tap the sides of it with the blunt end of the screwdriver to break it loose, NEVER PRY it off. The main jet should be locate at the center. It will have either a hex shape head or a round head with a slot cut in it, either way, it will have a hole throught it and the size will be stamped on it.
If it is being riddin at WOT most of the time, you probably don't need to worry about the needle. There are detailed instructions on the net, you just have to search around.
 

Jasle

Sponsoring Member
Nov 27, 2001
1,358
0
yes it sounds like you are running very rich. the spooge is a key indicator of running too rich. you might spend some time at www.ericgorr.com in the two stroke section and read up on carb tuning. The kehin will probably have a jet size around 200. You will want a size smaller than what you currently have. if you have a 200 you probably want to go to 195 or 190...if you ahve 220 then 215 or 210. There are sizes in between but they are not that much different and harder to find. you can find the sizes in increments of 5 pretty easily at any motorcycle shop.

also...I'd suggest finding another mechanic. Your guy doesn't know his arse from his head if he tells you you should not foul plugs if your oil/gas mixture is right. he should have known right away that you were Rich. IMO anyway. If you run 32:1 or 40:1 or even 16:1 doesn't matter one bit as long as you have the proper jetting and plug heat range. There are some good topics throughout this site about jetting. do a search and read up.
 

bikepilot

Member
Nov 12, 2004
804
0
On most bike carbs there is a 17mm (sometimes 14mm) plug on the botom of the float bowl, to get to it you can usually loosen the two clamps on each end of the carb (#2 phillips typicaly), rotate the carb so that the top is pointing away from you and the bottom towards you. (this saves you the trouble of removeing the carb). Remove the 17mm plug and you will see a 6mm brass thing. Use a 6mm socket and unscrew it, this is your main jet. There will be numbers on it, probably between 118 and 138. Once you know what size you have you can buy one smaller. Typically they run in even numbers.

to adjust the needle jet, unscrew the top portion of the carb (again, you should be able to leave the carb in place and twist it in its boots), slide the throttle slide out of the carb as you pull the top portion of the carb off (throttle cable will still be atached). Be carefull of the needle protruding from the bottom of the slide. Now you need to take the needle out of the slide so you can move the clip that secures it to a higher notch (which will lower the needle, blocking more fuel under partial throttle). Put it back together, making sure to get the slide in facing the right way (backwards and it will only close half way, making for an interesting ride to say the least IIRC).

Let me know if you need a more detailed explaination. I have a 1991 KX80BW in my trailer now I can go look at, take pix etc. It was mine many years ago, then became my sister's and now I am storing it for her. I've spent many evenings working on it, but not in the last 6 years or so. Our current jetting specs will not be of much use to you as the motor is heavily modified.

For the top end...They do not take long to be broken in, 30minutes of running at the most. There is no real way to tell its broken in, but trust me, if its been running for 30+ minutes its broken in. All breaking in really is, is the mating of the piston rings to the cylinder wall and prior to being broken in they create more friction and leak more than they will once broken in. The only real thing to watch for while breaking in a 2-stroke dirt bike is that you have plenty of oil in the fuel and don't get the bike too hot (as it can overheat more easily while breaking in). Typically its advised that you not operate the motor at high rpm/high load while breaking in, but as your still a novice you don't have to worry abou it very much as you are not likely to be very hard on the motor anyway.

A KEIHIN 26mm carb is stock on that bike and works very well in my experence and it is unlikely that anyone has swaped it out for something other than stock (keihin is a carb company, they make all sorts of carbs). The only real advantage to swaping out carbs is a marginal gain in peak hp with a 28mm carb. However, these seem to hurt the low end and make jetting more tempermental (newer KX85/100's like my wife's 03 have 28mm keihin's and while they are not bad, I'm not sure it is an improvement over the 26mm carb).

Altoona PA is a great riding area, I spent a couple days there on a club ride last spring:)
 

turkhuntr

Member
Sep 8, 2005
8
0
Thanks pilot. Just before I was going to tackle my first carb
disassemble, we tried something that another bike mechanic told me when I was picking up another spark plug,,,(at a different bike shop).....
He told me to try a different oil and mix it at 32:1. I was running 40:1 as I was instructed. It seems the fouling dissappeared and after my son rode for a couple of days, the plug was "tan colored" like the pics I found on the internet showed it should look like. However, I'm still getting the oil from the silencer dripping onto the swingarm. I've read your suggestions and as soon as my son lets me have an evening or two, I'm going to remove the jet and try a smaller size like you suggest. I appreciate you taking the time to respond with such detail....Thanks again and I'll let you know how I make out. Happy riding!
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
Also make sure you run the highest grade fuel avialable. The better the fuel the more completely it burns.
 
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