kyle_3600

Member
Sep 4, 2005
25
0
hi,i have a 1998 kawasaki kx80 that is bored out to a 100.I just put a new top end on it and the bike has no power ,it sounds the same in every gear and when you have the throttle turned full the bike makes a weird bogging sound i think it might be the jets i dunno please help.
 

handywork

Member
Sep 5, 2005
84
0
by the way you describe,where the 2nd half or mid to top throttle are non existant apart from a low sounding drone,it`s starving.A 20cc bump up in capacity should not only have a jet resizing,but also you would have been wise to increase the choke area(carb inside effective diameter), to speak plainly you might try increasing carb size as well as jetting.Go up 2mm with a Mikuni and rejet.FUEL^means AIR^=14:1ratio(I think)
Whats compression like? is air cleaner clogged?is fuel ok?fill with clean fuel at correct oil ratio, check these first,before you rush to buy anything,or take your bike to the wreckers and try before you buy with another Mikuni,could also try a richer mixture on main jet needle pos. and see if it makes difference with filter rubber boot and assembly disconnected and old stocking stretched over rear of carb and secured with rubber band as one short blast up the road should not hurt it when warmed up,I said one.Richen mixture by lowerring needle circlip pos. down one.Don`t go up and lean it out and risk engine damage.If it`s what I suspect,an unresticted open throat and a little more fuel should make at least a small increase in performance.If so go up 2mm and buy idle and main jetting kit.Any of your freinds ride KX125,YZ125.Ask to borrow their carb as I think it`s probably the size I`m talking about.You will only know if it works properly with the engine under load also.
I don`t really expect that the head would be the problem,but just an unrelated question.Did you do the head as well,if not,just an observation,that would put a big lip on the top.As well you have 20cc greater capacity and the squish is made for 80cc,thus raising your compression.Just curious as I`m guessing it went out around 2mm or so.It has nothing to do with your problem,as if it blew a head gasket it probably wouldn`t go at all.Just wonderring thats all.
 

motometal

LIFETIME SPONSOR
Sep 3, 2001
2,682
3
there's some good advice in the above thread but...

I'm pretty sure from 2000 on back, the KX80 and 100 both had the same carb, and the 100 ran like a raped ape. Carb size should not be your problem. Could you benefit from a larger carb, 'possibly' but this isn't why the engine won't rev out.

When experimenting with jetting, only change one thing at a time, keep an eye on the plug, and use good gas (race fuel if possible). Don't be afraid to try a leaner main jet, do a quick run through a few gears (don't go full throttle for more than a few seconds at a time) just to try it out. If you go leaner and it doesn't make it run harder, go back richer again. BUT, if it runs better with the leaner jet, this is what you need, the tricky part is determining just how lean it is safe to go.
 

kyle_3600

Member
Sep 4, 2005
25
0
hi,this is me speaking with the kx80 with the problems.I took it out in a local forest and alot of people ride there i was going around the track 6th gear and the thing had to be only going like 10mph so this guy came up to me and tightend my clutch and the thing ran totally better it had power and it went alot faster it sounds beter to but it still sounds the same in every gear and doesnt go as fast as it could.thanks bye.
 

motometal

LIFETIME SPONSOR
Sep 3, 2001
2,682
3
kyle...sounds like your clutch may be bad. Symptoms? Engine rpm doesn't change with the speed of the bike. Once it hits the powerband, especially in higher gears, it revs and just stays at one rpm regardless of ground speed. Also, if you change your oil, it may look very contaminated from the clutch slipping (black). Also, normally as the clutch starts to go bad, it will slip worse when the bike isn't yet fully warmed up. Sounds to me like it may be beyond that point though.
 

bikepilot

Member
Nov 12, 2004
804
0
I'd look into carb jetting and a slipping clutch then a stuck power valve. The size of the stock carb is fine to support a 100cc motor. The KX100 uses the exact same carb as the KX80 and runs quite well. My sister even races a KX107 that uses the stock carb and runs really well (typically holeshoots the 125cc and or womens classes).

Be sure there is some slack in the clutch cable and if it still slipps take it apart, measure the plates and springs and replace whatever is out of spec.

good luck
 

KrazyKX

Member
Sep 18, 2005
4
0
Ok, So i am having the same problem. Same bike kinda, 80 into a 100 except this one is 50 over. I went with a bigger main jet (from a 132 to a 138) not much change, went with a smaller jet and it got worse. And I adjusted the clutch and made it so i could use the thing, grabs gears fine. The bike has a new top and bottom ends and has been gone through since its retirement as a race bike. The problem i am having is from mid to high range, it feels as though the bike snaps right up to the mid range then bogs out. Idles fine. if anyone can help with maybe some new info thats not on this post it would be greatly appreciated. Thx.
 

bikepilot

Member
Nov 12, 2004
804
0
Oh, just looked back, this is a 98' we are talking about so no power valve to worry about.

Its a long shot, but you might check the ignition timeing. Take the ignition cover off. The stator plate mounting screws go through slotted holes allowing you to rotate the stator plate. There are 3 marks indicating stock (middle) advanced and retarded settings. Turning the stator plate the opposite direction of engine rotating advances the timeing.

krazykx, first figure out if the trouble is with the running of the engine or the clutch slipping. Does the rear wheel speed increase with engine speed, or does it sorta lag behind? Does the engine rev out cleanly or is it loaded up and blubbery sounding with lots of smoke?

good luck
 

KrazyKX

Member
Sep 18, 2005
4
0
The rear wheel increases speed with the motor, if i grab gears i can get hauling a$$(generally speaking). In 6th gear with the motor just puttering along (about 3000 rpm) i can do about 30 MPH. And the engine bogs way down with the throttle wacked and smokes a bunch(i think my neighbors hate me because of it), but up to about 3000 rpm it runs like a champ.
 

KrazyKX

Member
Sep 18, 2005
4
0
So i finally got this stupid thing figuered out, had to drop a bunch of of sizes of main jet. Went from a 138 to a 98 and the thing runs like the perverbial raped ape. So if anyone has an idea why a smaller jet on a bigger motor works better and could let me know then that would be greatly appreciated... thanks for all the help you guys provided...... thanks again
 

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