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02 WR250F Starting trouble, 290 Big Bore.

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Hey there!  I'm new to Thumper talk as a member but have read many help topics over the years, time to bite the bullet and get on board!

Well To start I'm not new to working on bikes, Ive always done all the basic work on my Yamaha's, 3 to be exact.   YZ250F, WR450F and now a WR250F.  I'm also an HVAC Tech by trade so the electrical trouble shooting experience helps. 

I just bought this 2002 WR250F and It only started once and ran for about 30 seconds, sounded good.  After that it wouldn't start, it gave a few false burps but nothing.  Popped a few times on third kick with out starting but I was guessing it was fuel I dumped in by opening the throttle.  I got spark!   To my knowledge, what i was told by seller and from what I've seen upon opening it up, it has a 290 big bore kit, new valves- (I checked clearenses, intake in spec .13, exhaust say's .17-.22  I have .23) Not sure if thats a determining factor??  It also has newer cams and a decompression cam.  

NOTE, I HAVE NO EXPERIENCE WITH 290 BIG BORE KITS, JETTING REQUIERMENTS etc...

This may be the entire issue.... I took my carb off my 2002 YZ250F and put it on this bike because I know it works.  I wanted to try and get it going since the carburetor that came with the bike was in a thousand pieces when i bought it.  (Parts needed and on order, waiting).   There is not much difference but...???    So i guess this is where the rest comes in.  I went through the entire electrical system and ohm'd out everything accept the CDI box.  see pictures.  I couldn't find anything in the manual as far as checking ohm's. ??  I would think it would say but I didn't see anything.  

So here I am, is it just the carburetor?   I mean it did run, it started with out the choke on like second kick and ran for 30 sec hand off throttle!  I kicked my brains out two separate days checking different things and nothing after that.  Please help! HAHAHA!

Thanks!!

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Edited by Thrasher MX
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Now that is a big boar!

 

You can't "ohm out" the CDI...   it either works or it doesn't.   

There is no procedure for testing it and the manual simply tells you to replace it if all the other tests come up good...  i.e., process of elimination.

if you are getting spark the CDI is probably good.    Valves sound close enough that it should run.

Could be the carb since you said you had it trying to start a couple times.  Maybe the pilot jet is clogged or there are parts missing or not installed correctly...

 

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That's a big ass boar. Haha,  I need to edit this. Lol!  I would think carb issues if I didn't just pull it off a bike that was running like a top a few days before.   There is a slight difference between the YZ carb and the WR carb.   

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18 hours ago, Thrasher MX said:

That's a big ass boar. Haha,  I need to edit this. Lol!  I would think carb issues if I didn't just pull it off a bike that was running like a top a few days before.   There is a slight difference between the YZ carb and the WR carb.   

 

hmmm...   yes you did say that about the carb.   I just saw the part about your carb in a million pieces    lol

This one may be hard to sort out, especially if you never saw it running properly before you got it.  Who knows what the previous owner did to it and isn't telling you!

 

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i had a similar problem and it turned out to be a fouled spark plug. sometimes we look for the big problems when in reality its something small

 

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i had a similar problem and it turned out to be a fouled spark plug. sometimes we look for the big problems when in reality its something small
 


I was thinking that this morning. I'm going to pull the plug out of one of my other bikes today and give it a try. Just because it fired once doesn't mean much.

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I was thinking that this morning. I'm going to pull the plug out of one of my other bikes today and give it a try. Just because it fired once doesn't mean much.

I can also pull the CDI off my YZ250. That's the next step after the plug swap.

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Update, I switched out the decompression cam using my YZ250F decomp cam. The guy at hot cams was saying they've had issues in the past and they occasionally fail causing the hang up and of course not starting.

 

So, I swapped it out, no more binding and and bam, Fired right up! ....but wait! It ran for about 30 seconds and stalled out. Tried to start it for several minutes, it acted like it wanted to start then it did for about 1 second, I tried to kick it over and it locked up. I pushed down to try an start it and it got harder and harder to push, now The kick start won't even move. Piston/rings must be bound up??

 

I'm thinking whoever installed the big bore kit messed up big time. Looks like I'm pulling the damn thing apart. Has this ever happened to anyone and if so what did you find?

 

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