Jump to content
Sign in to follow this  

KX 250 easy to start cold/hot, extremely high rev on start, smokes more than should.

Recommended Posts

I've read tons of posts and have several ideas but, no one post entirely fits. I dont have the money to just start replacing everything.

The biggest issue is the smoking, but I think most of my issues are related (Runs strong, smoke, oil spoog, high revs). Messed with oil ratio and brand some without change. The previous owner said he replaced the carb and exhaust expansion chamber (possible cause of jetting issues). Starts easy cold and hot, revs to a point I usually pull the choke back on a time or two to slow the rev. It levels off after 30 sec.

I have a transmission fluid leak case seal drips, I'm going to fix and while I'm in there I might replace the crank seal if it could be the problem. I read the smoking could be from burning tranny fluid thru crank seal, high revs could be from air pulled thru seal until oil splashes up starts to suck oil instead of air. Cant monitor fuild level with external leak, if the crank seal is easy to replace i'll change it just incase. Are there other seals in there worth replacing?

Anyone think I'm onto something?

PS: Changed tranny fluid type and smoking seems worse.

Share this post


Link to post
Share on other sites

sounds like a main seal problem if you change tranny type fluid and it changes the smoke out the pipe,unfortunatly you need to split the cases to change the seals although you didn't say what year the kx was.Stator side seal will suck air only as there isn't any oil on that side and the other it will be tranny oil.If you pull it apart then replace the main bearing as well.

Share this post


Link to post
Share on other sites

The bike is a 94'. I may be wrong about the smoke changing, but it seemed to be worse when I topped transmission off with new fluid. How hard is it to change crank seal? Any further investigating I can do before opening it up. Crank seal and main seal, are they the same thing? I'm pretty mechanical and can tear an auto engine down and make pretty major repairs.

Share this post


Link to post
Share on other sites

Ok as for further investigation you should pressure test the motor. The crank seal and the main seal are the same thing. In the FAQ sticky above there are threads on pressure testing and case splitting and reassy.

Ed

Share this post


Link to post
Share on other sites

I built a pressure tester today and got it hooked to the bike. There is a small plate on the left side (shifter side) of the bike on the head (have heard it called the jug) it's leaking air terribly. When I bought bike it blew oil out there and I put a new gasket on it but the threads were fairly stripped so I chased them with a tap and put loc-tite on the bolts. No surprise their not tight enough. I'll drill them larger and tap them tomorrow. What is the purpose of this plate and what issues could this have been causing?

Share this post


Link to post
Share on other sites
I built a pressure tester today and got it hooked to the bike. There is a small plate on the left side (shifter side) of the bike on the head (have heard it called the jug) it's leaking air terribly. When I bought bike it blew oil out there and I put a new gasket on it but the threads were fairly stripped so I chased them with a tap and put loc-tite on the bolts. No surprise their not tight enough. I'll drill them larger and tap them tomorrow. What is the purpose of this plate and what issues could this have been causing?

there is no issue with the plate, you need to replace you right side main seal that's where the air is coming from

Share this post


Link to post
Share on other sites

Could just be real rich on the pilot jet, does it just rev fast when the engine is cold? Do you need to use the choke to start it from cold? How many turns out on the air screw for your fastest idle?

Share this post


Link to post
Share on other sites

I got what I believe was the resonator cover tapped and sealed. Pressure test revealed a leak at the valve cover and at the center of crank case. Since I'm assuming that's the same place it splits to put in new crank seals in I'm going to go ahead and knock it out in one shot if I have to split the case anyway. I'm going to order complete gasket set w/oil seals and bearings w/seals. Anything else I'll need or should check out while I'm in there? Engine is on my work bench, waiting on parts.

Share this post


Link to post
Share on other sites

There is no center gasket on these bikes so you have to use something like Yamabond4 or something that is the same.

Ed

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×