1990 RM250 starting problems

[Scotty99983]

Hey as said in my introduction i bought an RM250 rebuilt it with my dad and got it running. i got out on it twice the first time on it was just running it in then the second time i got out on it i was giving it a bit more id say bout half throttle gettin into the power band and then suddenly it died. my dad being the awesome mechanic he is ( he has had bikes all his life and has bout 36 years experience with them and done all his own work to them) he said it sounded like feul problems when it died on me and it wouldnt start it would only backfire a few times. so we checked the plug dried it off and there was still plenty of fuel gettin thru at the time and as we had just rebuilt it we took the top end off just to make sure everything was ok and it was fine. so we decided just to check everything else whilst we were at it and realised the timing had slipped so we sorted that aswell as there was still feul getting to the plug but it would backfire once or twice. so after that we tried to start it again as we rebuilt the top end and it will only back fire at us now and there is very little feul getting to the plug. we are going to strip the carb down and check to see if it has maybe picked up some dirt and clogged the jet which i think it probably has.

but anyway the main thing im writing to ask about it the fact that when it wants to fire there is smoke coming out of the power valve vent tube. is this normal or is there a problem??

help is much appreciated as this is my first ever two stroke motocross bike same for my dad he has never had to work on a two stroke motocross bike (he prefers 4 strokes)

 

[OriginalRider]

Make sure your pv screws are tight if not it will suck air and bog out or wont start also sounds like your jetting you should look in to it how is your plug burning?

 

[Scotty99983]

i just had it fired but it started to increase the revs without the choke on and the throttle was shut. i havent took the plug out to check it yet as im just in for a break lol ill let you know what the plug is like when i take it out. also all the screws are tight.

 

[Scotty99983]

right i just had a look at the plug after it had been fired and it is normal. but we got it fired a few more times and then we got it fired one last time and it done the same increased the revs without choke or without the throttle being opened then the revs died down so i gave it a little rev and then it started to idle ok and suddenly it started spraying oil out the exhaust. my dad said that it was the oil from the clutch/gearbox so we took the oil filler cap off to find some smoke and no oil.

i turned the kick start with my hand a couple of times to see if there was any oil and every time i turned it the smoke would fire out through the filler cap as if compression was leaking into the clutch. so i think me and my dad may have found our problem.

 

[kx2502009]

if it reving up as if it would if u had the choke on your sucking in air somewhere bad crank seals would be a start and new ones can be put in wrong and they will not seal

 

[Scotty99983]

yea my dad read the manual some more and has diagnosed it as bad crank seals. all the symptoms of bad crank seals are there. ill need to get them replaced and see how it goes lol. here we go more money and more big jobs lmao