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honda cr 250 won't start after rebuild .

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Bike used to start within 3 kicks before the rebuild .

Now can't seem to get it to start , keeps fouling plugs .

Have tried the fuel off , choke off and full throttle technique , has sort of given once , but nothing now .

Not sure what's up , did think of trying to bump it but unsure on that idea .

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Make sure you have it timed correctly it might just be off a little I had the same issue with my 250 when I redid it

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Make sure you have it timed correctly it might just be off a little I had the same issue with my 250 when I redid it

Don't suppose you have an idiots guide to this lol ??

I have the manual for the bike but no sure if I followed it right .

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I can type a big long thing but your best bet is to YouTube because I don't know about you but I'm a visual learner and I can read how to do something all day long and still goof up somewhere

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Yeh am like you reading an instruction is totally different to watching it being done .

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Bike still won't start . Tried everything , new plugs , new fuel , air filter ect .

Not even giving any show of firing .

Feel like killing it with fire lol

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When you rebuilt it did you put oil on top if the piston? It might be to thick and just loading up the spark plug. If your confident in your work and the try forcing it to start by bump starting it. Make sure the rings are on also. It might be letting oil threw. Pull your expansion chamber off and try to take a peak out the rings

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Put if the rings are off and the piston is going up and down you might be scoring the cylinder. It might be worth buying new gaskets and taking it apart to check everything

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What year is the bike?  What'd you do in the rebuild?  New gaskets & seals?  Piston & Rings?

 

If your fouling plugs and its not starting it's 1 of 3 things:  spark, fuel, or compression.

 

Make sure your getting spark - pull the plug, put it back in the boot and kick it over (make sure the threads on the plug are contacting metal, I just lay it so the threads are resting on the cylinder, that way you don't have to hold it and worry about getting zapped)

 

Check your fuel - should be 32:1 mix

 

Check your carb - air screw should be backed off 2 turns from seat (could differ depending on altitude and other conditions so might need to play with it a bit)

 

Check your compression - think factory is 125-130 psi

 

If your compression is low, could be a bad head gasket or head torqueing.  When you kick it over there should be some resistance, but like NB500 said if your rings somehow aren't on right you're gonna score up that cylinder right quick (and your compression will be low, the rings create the seal).  How did the piston slide back into the cylinder during reassembly?  When I rebuilt mine it was a b*$!% trying to compress the rings all the way so it would slide back in (I also didn't use a special tool, but popsicle sticks).  Also the break in the rings need to meet at a certain point on the side of the piston (there should be a little hole in the ring grooves on the piston head).  I would pull the head off and turn it over a few times if you have any doubts that the rings are unseated, with the head off and the bike in neutral it should kick over nice and easy so you can see if its smooth or not.

 

Good luck.  -Rob

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Edit:  Bike should run with 130psi compression, ideally should be 150psi and up.

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Don't trust pulling the plug out and holding it (grounding) against the cylinder because it may fire outside the cylinder bc there no pressure on it like there is when it's bolted in its a lot harder for the spark to jump the gap inside under pressure than it is outside the the only pressure outside is atmospheric pressure so go buy or borrow a spark tester believe me I've been there done that and the spark on the outside will lie to you same goes with cars good luck I had the same problem on my 1988 cr500 i borrowed a spark tester from school and the spark would NOT jump the gap if you can't borrow one they're pretty cheap at harbor freight

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Cheers guys not had a chance to work on the bike as been busy with my kids as it's the Easter holidays over here in Scotland .

Going to try all your ideas and and see how that helps .

Am really puzzled as to why it won't start .

New gaskets , seals , barrel bored and honed to 68mm wossner piston 67.94mm , new fuel , air filter , plug , water pump bearings and seals replaced , new anti freeze , new oil .

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Did a compression test and not sure how accurate the gauge was but it's only reading 40 psi ?????

Something is seriously wrong , do three kicks and that's the max it gets to but doesn't drop even after an hour !!!!

Am totally lost .

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Did a compression test and not sure how accurate the gauge was but it's only reading 40 psi ?????

Something is seriously wrong , do three kicks and that's the max it gets to but doesn't drop even after an hour !!!!

Am totally lost .

For compression tests you should hold the throttle wide open and kick 5 times consecutively. No way 40 psi can be right, hopefully wide open with 5 kicks will give a better reading.

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If your compression is low, try another gauge. Make sure the throttle is open when kicking the bike over.

 

It usually is something simple. Make sure that your ignition/timing is set properly. I have looked for air gap specs on these bikes and cannot seem to find anything from the factory but I put my ignition/stator as close to the flywheel as I could.

 

This may sound stupid but do you have your exhaust plug in? I once rebuilt my bike and kicked for 30min and it wouldn't run. Pulled the plug and it fired on the second kick.  

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