1988 rm250 rebuild issue

Hi, i just rebuilt a 1988 rm250, replace crank piston crank seals, complete new gasket kit, the whole 9 yards.


so now i have a few problems..

the bike was hard to start at first and the dealer told me to put some kawasaki fogger in there and that would start it up, so i did...a bunch of times cuz it didnt start the first time i used the fogger, took me a bunch of tries but finally got it.


1) when the bike starts up it idles really high ,and slowly idles faster and faster (things i have debuged, turned air screw in and out, had no change, and throttle cable dosent appear, or feel to be kinked) 


2)  alot of white smoke comes out of it, no blue and white just all white. smells a little weird too


whats really scaring me is that i REALLY hope i did not install a crank seal wrong, i double checked and everything, so i dont know if crank oil is getting in there or not, and another thing could be coolant is getting in there, but like i said i put new gaskets on everything and put yamabond where there needed yama bond, included the base cylinder gasket.\


i dont know if its the fogger just burning thro the engine, but i have started it up 4-5 times to try and fix the idle problem and all i see is a big cloud of white smoke coming out.  i really REALLY hope a crank seal isnt installed wrong :(



ok after doing a bit more research there is oil coming out onto the expansion chamber on my bike from the exhaust port, which from what i have read on other peoples bikes it means the right crank seal might be installed wrong. can someone clarify this???? im going to be pissed if i have to split the cases again :'(


please help!!

Edited by kyle5647

Im far from an expert,but thats what my yz did couple weeks ago when I messed up the inner lip of the right side crank seal,it smoked SUPER bad,tried to foul the plug and there was oil coming out from the pipe flange at the cylinder. One way to tell is if you happened to have just replaced the tranny oil,you can drain it and see if the same amount you put in-comes back out. If its noticeably lower,Good chance its that seal.I only ran mine for 2heat cycles and a 45 min ride and it was down 150ml of the 750ml I'd just put in it. If it is sucking the oil,may consider repacking your silencer now too. Just a thought.

so do you have any ideas why it would be idling high??

Possibly an air leak? Have you inspected the intake between the carb and cylinder? I only ask this cause few yrs back I had a 83Rm 250 that was missing the airbox and the kid I got it from had just put a k&n type filter on it,from just hanging there the carb slowly began to create a crack at the top of the boot/intake and the idle would stay high when you would let off the throttle and idle all crazy high. Perhaps same kind of situation happening? Just a guess. I've also read when the crankseal on left side leaks it can cause a high idle similar to what your explaining.

Hopefully someone more knowledgeable will chime in. Maybe try the search option here on hard starting high idle,maybe find something there also.

Edited by yz250 947

Just thinking,did it run ok before you did all the work? Or had you not heard it run prior? Your sure the cable isnt adjusted holding the slide open?

dam...2 crank seals...holy crap.. lol thanks man i will do some more research and post here to what the issue is

and no i bought it as a project and it didnt run, funny thing, when i bought it the right side crank busted which caused oil to come in the case

I hope you find it to be simple man! I'm still asking questions here too,so hopefully one the vets here give opinions. Alot of knowledgeable folks here.

Could always do a leak down test. Theres posts here on how to build a leak down tester super cheap.

one other think, do you think i could be burning coolant?? cuz it didnt smell like it was burning oil, i wouldnt say it smells sweet, (i dont even know what the "sweet" smell would smell like if you know what i mean)  i have seen 4 strokes burn oil and it smelled nothing like what came out of my 250..wouldnt say it smelled sweet but i can def say it didnt smell like oil..but idk ill have to drain the coolant and see if that makes a difference

Is the coolant level low after you run it? Antifreeze in exuast is a very distinct smell,its definatly a "sweet" smell I think you'd recognize. Whats the plug look like? Is it oily? If the coolant is staying full,I would check trany oil level. Seeing how it just got rebuilt and you know you filled with proper amount,drain&see if same amount comes back out.

Edited by yz250 947

i havent ran it for more than a minute but i will def. check today.  i will upload a pic of it runing if it helps

ok so i fixed the white smoke problem, the spacer where it goes over the crank seal was installed the opposite way and now it starts on first kick!!! :D :D but it still idles really high...now when i start it it just automatically goes up really high, i looked at the carb slide when it was on and i gave it throttle, and it when back down all the way like it should.  the air screw seems to have minimal affect if i turn it just a microscopic turn in or out it will either make the engine die or rev even higher.. any help??

Man that's great you figured it out!! I'm stoked for you!

Maybe try asking this idle question in the intake/jetting section.

I'm thinking air leak somewhere. Use the search option for building a leak down tester, its like 15$ to build and you'll find it....if all else fails.

Edited by yz250 947

Sounds like an air leak.

check to make sure the intake boot is crack free, even a small crack will open up once it vibrates.

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