Kawasaki Motorcycle Forums banner

1 - 20 of 42 Posts

·
Registered
Joined
·
28 Posts
Discussion Starter #1
got a 1990 kx 250 that i bought off a guy. bike runs strong but smoke a good bit. its a blue smoke so i know its oil. im thinking topend rebuild b/c i can push my kickstarter down with my hand really easily. this is my first 2 stroke and i have a question on it. should i put a new topend kit in it or just new rings. i have built many car motors and 4 stroke wheeler motors. but never a 2 stroke. just wondering what everyone thought. o also it takes like 20 kicks to get it to fire. seems like quite a lot to me since my 450r kicks on the first or second kick. just a few questions and any help is greatly apreciated.
 

·
Dirt Bike Dad
Joined
·
144 Posts
20 kicks to start? You can push the kickstarter down with your hand? Sounds like the compression is gone = new top end needed.
2 Strokes will always smoke (some people call em 2smokers) because they burn the oil used to lubricate, that is normal.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #3
I know they burn oil in the fuel but and smoke a bit. but this thing is like fogging for mosquitos when you hammer on it. which is why I think blow by and some spooge is comin out the exhaust. anyone know where I can download a manual for this one
 

·
Registered
Joined
·
917 Posts
you should search more about this type of rebuild.

You have to know what is inside your cylinder, what walls are made off.

If compression is low, then you could get blow by, difficult to start.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #5
like I said this is first 2smoker but im not afraid to tear into any motor. do most od yall replace piston and jug. or rings only or piston only and bore jug. just wondering what everyone else is doing.
 

·
Registered
Joined
·
67 Posts
First do a compression test. You need to know the compression absolutely - don't rely on your downward pressure of your hand. If it's less than 110lbs you need to take the top end off to check for wear. You'd probably wanna be 125lbs plus to start consistently on the first 3 kicks. If you don't have a micrometer to bring it in to a MC shop to have the cylinder-piston clearance checked out to see if it's within specs. If it's within specs but close, just go for rings, top end bearing, head gasket and base gasket. That should top out around $50. If the cylinder is Nikasil plated and you are out of specs, your choices are either to have it Nikasil re-plated or have it sleeved. Both options are fairly costly and together with new Piston, rings, gaskets, etc., and you could easily be into it for $500. If $ is no object, have it re-nikasil'd. It will last much longer and you won't be having the thing bored out every other year with new OS pistons etc. Cost is worth it...
 

·
Registered
Joined
·
28 Posts
Discussion Starter #7
i am going to do a compression test tomorrow. and go from there. also my rear tire seems to hop pretty bad under hard acceleration. any thoughts on this?
 

·
Registered
Joined
·
46 Posts
like I said this is first 2smoker but im not afraid to tear into any motor. do most od yall replace piston and jug. or rings only or piston only and bore jug. just wondering what everyone else is doing.
you cant rebore the KX cylinder is got a special coating,when the bores fine and you want to just replace the piston and rings just give the cylinder and good scotch briting to take the glaze of but if the bores worn you will have to get it replated and new piston and rings,check all the powervalves and and the teeth on the powervalves arent chewed up,and always use synthetic oil because mineral oil ends up by jaming the powervalves and then strips the powervalve teeth,when i got my 94 250 everything in the motor was had it,i had to replace the cylinder,powervalves, crank,clutch,bearings seals etc but i hope you have better luck
 

·
Registered
Joined
·
28 Posts
Discussion Starter #10
you cant rebore the KX cylinder is got a special coating,when the bores fine and you want to just replace the piston and rings just give the cylinder and good scotch briting to take the glaze of but if the bores worn you will have to get it replated and new piston and rings,check all the powervalves and and the teeth on the powervalves arent chewed up,and always use synthetic oil because mineral oil ends up by jaming the powervalves and then strips the powervalve teeth,when i got my 94 250 everything in the motor was had it,i had to replace the cylinder,powervalves, crank,clutch,bearings seals etc but i hope you have better luck
pulled the jug and piston today after doing a compression test. compression would reach bout 90 and that was it after pumping it like crazy for 10 times. jug looks pretty good. everything actually looks pretty good it seems. checked the reeds and they look fine as well. im going to take the piston and jug to local shop and have them check them to see if i need rings or rings and a piston. anyone have a service manual i can download. also it hops more on pavement that dirt. thanks
 

·
Registered
Joined
·
28 Posts
Discussion Starter #12
finally got my piston to cylinder wall clearance checked and its with in spec. its a stock jug with stock bore. im just going to put a set of rings in it for now. question on that though. can i put oem kawi rings in it since its a wiseco piston and just use wiscos gap measurements or what
 

·
Registered
Joined
·
67 Posts
My suggestion is only use like-kind rings to piston. If you have Wiseco - use Wiseco rings. If you have OEM Kawasaki - use OEM Kawasaki rings. Insure that you are using the correct ring size as well. You may be stock and you may not be stock.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #14
i know its the stock bore. so im not too worried about not being stock. any reason for using same piston and ring. only wonder b/c on drag cars its not true at all. just wondering
 

·
Registered
Joined
·
67 Posts
For a couple of reasons:
1. Different manufactures use different ring width.
2. There are several different styles: Keyston, **** and perhaps others
3. There are different coatings and materials such as chrome, steal. I don't know if you have a Nikasil plating or not and you want a softer ring than the plating.
But I guess, I just trust the rings that are made for the piston to actually fit and be correct.
 

·
Registered
Joined
·
46 Posts
i know its the stock bore. so im not too worried about not being stock. any reason for using same piston and ring. only wonder b/c on drag cars its not true at all. just wondering
Hi,good to hear your kx doesnt need much work,it wont cost you much to get running properly,goodluck
 

·
Registered
Joined
·
28 Posts
Discussion Starter #17
pulled the piston it was actually a .20 overbore. had a wiseco piston in it. so i replaced it with another and a set of rings, honed the cylinder barely to taking the glazing off, put the new rings in and buttoned her up, still smokes a bit and still hard to start. the actual compression feels a bit higher though. still spooging some oil out the exhaust as well. any ideas?
 

·
Registered
Joined
·
67 Posts
Carb's are not my forte as I seem to do more with trial and error but I'd put go through this checklist assuming you have at least 110psi on the bike:
1. Bad gas, bad pre-mix ratio (20:1 to 40:1 - lots of opinions on this), If you did not mix it and it came with the bike or is older than 6 months - don't use it. Obviously use 2-stroke oil and not automotive motor oil...
2. Wrong spark plug
3. Enricher (choke) is not operating properly (stuck on)
4. Running way too rich - needs to be rejetted.
 

·
Registered
Joined
·
917 Posts
is it hard to start after it is warmed up?

The jetting may be too rich, what does the porcelain of the plug near its base look like?

How many turns is the air screw set at?
 

·
Registered
Joined
·
28 Posts
Discussion Starter #20
ok got her cranked up and ran alright in the bottom end. however the power valve is acting up i believe. no powerband feel at all. rode it for a little bit thinking maybe it was cold and then it died on me. just puttered out and quit. on the power valve if you pull the plunger shouldnt it spring return. also pulled the plug and it was fouled. had a bit of oil on it and was kinda black. porcelain looked good though. put a new plug in it and it still wont crank. i know its getting spark b/c i pulled the plug and grounded it to the jug and its sparking on every kick. nice new filter on it too. compression is about 170. you can see fuel flowing from petcock to carb. after kickin a couple times fuel starts comin out the overflow on the carb. tried puttin some gas in the plug hole and it still wouldnt crank. any ideas?
 
1 - 20 of 42 Posts
Top