Grrrrrr frustrated with two stroke!

[danjerman]

Here's the deal, I have a 91' KX250 thats been running a little odd lately. It's never been out since memorial day weekend 2002, but I have been making it run better little by little every weekend. The problem is that whenever I crank it up past 3/4 throttle, right when it hits the powerband (on the main jet), the bike starts puking out a lot of blue smoke and seems to sputter a little bit. I've been fooling with the jetting down low like the pilot and needle clip, but haven't messed with the main lately (I think I've got a 165 main in there now). Its wierd, it sounds like its hitting the powerband, but all the power doesn't seem to be there and theres a lot of blue smoke coming out. It doesn't smoke nearly that much down past 3/4 throttle, it runs fine down there. I just put in a new spark plug, and the top end has had about 30-40 hours of very easy riding on it, and it had fresh fuel last weekend. The only error on my part is that I put some 6 month old premix in with the gas (yamalube 2R), but it still runs crisp down low and through mid throttle, so that leads me to beleive that couldn't cause my smoke problem. I have a few theories:

1) the bike has been sitting so long that it just needs to be wound up a little bit. I don't run it too much on the top end and maybe just needs some good old full throttle time.

2) the main jet is too rich, or something goofy. Might need to clean the carb.

3) the reeds are toast. Although, I took them off and seemed that only a tiny bit chipped on one corner, so little that it exposed hardly any of the cage when closed.

4) the premix did this. It was an open bottle.

I really don't think its the top-end, the crank seals or the head gasket. It's got plenty of power and is still hard to kick. Also, the smoke is BLUE, not white or any other color, just blue.

 

[Glitch]

Are you losing oil? You should measure oil before going in and then when it comes out after a few rides. It might be a crankshaft seal. I would try going down on the main first. If you keep going down and it still does the same, its probably the right hand side crankshaft seal. But before you do anything, you should clean your powervalve and make sure it works.

 

[marcusgunby]

Also if the silencer packing is full of oil it will run bad-try repacking it and if the problem is on full throttle then lower the main jet as thats the jet that effects wide open throttle settings.The reeds will need replacing but its not the cause IMO.

 

[Rcannon]

I had very bad (chipped and split) reeds in my YZ 250. There were no smoking problems. Many others, but not smoke.

 

[Studboy]

What altitude are you at and what is the stock main jet for your bike? Also check your gearbox oil levels, as you may have a leaky seal.

 

[Hon-Yam-Junk]

2) the main jet is too rich, or something goofy. Might need to clean the carb.

It sounds like a new problem is developing? Yes, check the carb, needle, main and float level. After you operate your bike, the gas will evaporate out of the engine crank and leave the oil behind. So when you restart your bike the next day, not only do you have to use the choke for extra fuel, but also burn the extra oil out of engine crank. Check the problem after you have warm the engine and ran it hard at 3/4 or full throttle. If the problem still persists check the carb. I have had ignitions to weird things too.

 

[ram1]

I had the very same problem with an RM 125. No smoke till wide open, then a cloud. Did like you, messed with jets. It was the crank seal. Check your crank seal. I changed mine and it cleaned the bike up, but don't be surprised if you go back to your original jetting spec..

 

[danjerman]

You guys seems to have me convinced that it is a crank seal. That's funny because I just saw some black spooge left on my garage floor after I ran my bike yesterday, and it usually never leaks spooge. Instantly that had me thinking that its burning something more than just gas and premix. Just one more troubleshooting question though, if it is the crank seal, wouldn't I be able to smell the scent of burning oil on my spark plug? I ask because I had an old yamaha with the same problem but much worse, and the spark plug wreaked of burnt oil. Thanks.

 

[danjerman]

BTW, I just replaced the silencer packing, I'm at about 700 ft elevation and the stock main jet in 160.

 

[ram1]

Not always, my RM actually burnt the plugs very inconsistently with the bad seal. Sometimes oily, sometimes kind of dark, but not oily, I guess it depends on how much you get on it before you check the plug. I bet its that darn crank seal...

 

[Studboy]

If the stock main jet is 160 and you are at 700 ft, why are you running a 165?

 

[danjerman]

I was told to richen up th jetting a little bit for winter because of the cold, dense air.

 

[kymx]

how hard is it to change a crank seal

 

[danjerman]

Depending upon what bike you have it can be as simple as taking the engine cover off, or as difficult as having to split the cases. In my situation, I have to split the cases, and I've decided that while I have everything apart I might as well rebuild it all. I plan on putting in a new top end, inspecting all the gears and internals, and if necessary a new clutch could be installed.

 

[kymx]

what about a 1995 cr125.

 

[danjerman]

No clue, you can check your service manual if you have one or you could try posting a new topic in the forums.

 

[cr25096er]

all u need to do it on a cr is remove the engine side cover and clutch n all then pry out the seal.