Old KX Problems...Noob to bikes-PLEASE HELP!!!

[Redneck Ron]

The bike is a KX250 air cooled which i believe to be a 1979.

I guess I will start by saying it is hard to get it started.When I am able to kick it over good and I keep it running in neutral once I shift I would keep it revving to let her take off but once it was fully engaged in gear it does the oh so famous wing...wing...wwuh and stalls.I suspect this has to do with the carb or the other problem I am about to explain but then again I dont know much about bikes yet.

(This is my main problem)Now also besides that problem it blows the oil out of the cases oil supply somehow somewhere and then it will only keep a minimal amount of oil in it.Well right now from the cylinder up is taken off and the cylinder,head and head gasket seem to be in really good shape.The base gasket seemed like crap though.It seemed rubbery in one spot right near the front left hand side stud in the case.Also in the pocket that is in the case right next to that stud had oil in it.The gasket covers that pocket so I suspect that may be where the oil is coming from.But also the exhaust ports flange that holds the pipe in place on the cylinder was not even completly bolted on.It had only 2 out of 3 bolts in it,one of which was too long so it did barely anything.It was in one spot probally 1/8" off the cylinder.At first i was thinking this was where the oil was blasting out but someone told me the cases supply of oil shouldnt be coming out of there.I though it does though and by the looks of the cylinder I could see how it seems it gos there.I dont know...

Now finally I think this is the last big problem.When it seems to be running and it doesnt die like explained in problem one sometimes it will either stick or go up by itself to a wicked high rev which makes the hair stand up on my back since it sounds like its gonna blow it.(I am sure it would if I didnt stop it by shutting it off)I think this may also have to do with the carb.

Any help is greatly greatly appreciated since I have enough money to fix this its just i want to make sure that when its all back together it runs good and doesnt have the problems still.

Thanks everybody!!!
Ron

 

[viking20]

Clean the carb completely , and check the float height , if you havent got a manual you can probably get one , it all helps.
Be sure that the throttle cable is in ok condition , and that it has a little free play.
The crankcase seals at both ends of the crank could be leaking. At the ignition side , air will be drawn in , and at the cluth/gearbox side oil will enter the crank case , if they are leaking. This will also make the bike hard to start , and could be the reason for a higher and/or more unstable idle than normal. I would think they can be changed without splitting the cases....
You can learn alot by trying to fix this bike yourself , but dont spend too much money on it , you will never get it back !
Also , Eric Gorrs site ( Forward Motion ) has some excellent articles on different kinds of engine rebuilding , you could get a lot of good , general knowledge from reading these articles !
Good luck !

 

[Redneck Ron]

Sorry it took so long for my to write back.I dont have a computer available to me at my house so I had to wait.Anyways last night I put new gaskets in it and when I took it apart before that I found that the clutch side crank seal was pushed out.I was told if it gos back in tight it might be able to be used.It did and it is still in very well when I checked again.Now my carb is overflowing more than usual and filling the cylinder full of gas.I was told I just need to find out what the problem is inside the carb now.It would start but wouldnt run for long and at different settings on the adjustment screws it would run only on idle(die if you gave it gas)then it do a little low power sounding backfire and quit soon after.Either way it wouldent stay running.Also why do I only have 2 screws?Shouldnt I have 3?One for idle,one for low speed fuel and one for high speed fuel?

Any more help from anyone would be greatly appreciated.

Ron

 

[viking20]

There is no-one who can tell you if the crank seals are ok , I would change them unless the bike runs fine after you are done with the carb !
Reg the carb , I have never worked on a dirtbike that old , but it sounds like the float valve is leaking. Check there isnt dirt/crud between the needle and seat. Sometimes it is possible to polish the needle and seat with tooth-paste , or some kind of polish for chrome and alu. That is , if the needle is made out of metal. If the carb still over-flows , try tapping the side of the floatbowl with a screwdriver. You might need a new needle. It would be helpfull if you could find out what the float height should be , and adjust it , if nessecary.
There is a guide at the Forward Motion site ( link on the left ) explaining how the different carb circuits work , but there is certainly no screw to adjust high speed.
There is a throttle stop screw , to adjust the idle speed. Then there is an airscrew , to adjust the idle mixture along with the slow jet.
The needle position and the Main Jet takes care of the upper register , but read the guide........

Good luck !

 

[Redneck Ron]

Thanks!I will have to try again when I get home tomorow.

Ron

 

[Redneck Ron]

Oh...I forgot to ask something.Once I attempt to clean the carb up what should I adjust the screws to?I have been told to turn them both all the way in then one full turn out for each one.Is this right?

Ron

 

[viking20]

Seat the airscrew lightly , then back it out 1,5 turns. The throttle stop screw , is just there to let you adjust the idle speed , and I would rather have it out a bit too far , and then adjust when the bike is fired up.

 

[Redneck Ron]

Havent replied in awhile I know but anyways I got it running.My new question is about a new problem although its less severe.From take off and into midrange this bike could kill but now its all revved up quick and I know it aint going as fast as it should although the revs are high.Could the clutch be toast and slipping at high revs?It does that in every gear.Also I heard the clutch whining bad so I added more gear oil.BTW since I got the bike running well it hasnt kicked back at me.The old problem turned out to be the coil that is in the motor was loose and only had one timing bolt in.

Thanks for your help so far!

Ron

 

[Halfast816]

A simple way to check for clutch slipping is to ride in third while applying the front brake and throttle at the same time. If the RPM of the engine starts climbing while the bike slows your clutch needs new plates and springs.

 

[Redneck Ron]

First off I havent got the chance to try that last suggestion yet since my uncle is hunting outback (Dont want to scare the deer,you know! :) ) but I thought of some more info to add though.

I forgot to mension before that the gear oil that I put in the tranny appears to be muddy now, like a grey color, and if I remember right last time I put trans oil in (Before the complete rebuild) I forgot what I did till after and realized I was running 2 stroke motor oil in it.I am sure that had a negative effect on it.

Also, I have been riding the bike some today,no more than 15 minutes at a time for maybe a total riding time of 30 minutes, and it seems if I let it sit for awhile twice now I had to push start it so it ran like crap and died and then kick it over and over again to get it started and then it sorta clears up and runs o......k........

I am at the point now where i am either going to sell my other toys and get a newer bike or fix mine up really good and have an awesome vintage MX bike.

Thanks,
Ron

Forgot to add sometimes it grinds into first when i first start the engine up and put it in gear but it doesnt seem to after it has been riden a little ways.