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Old 02-24-2013, 07:17 PM
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Default Rebuilt engine, new gas, good compression, good spark... but no!!

     

91 CR 250R

Heres it to you straight...

Brand new over bored cylinder and new piston (MAYBE 2 HOURS ON IT)
new gas mixed at 32-40ish:1
New spark plug today

Rebuilt the engine like yesterday and it ran good but leaked coolant out of the head gasket... fixed that and today got fresh oil in the trans and a new spark plug. Ran great from 3-about 6:30 pm then it did its usual runs decent and get on the throttle and bogs out as in... i am at half throttle then i open it up and it will struggle to gain rpms and then just eventually sputter its self out...

So this means good compression, what i think is good fuel, and a spark that looks fabulous but it still does this!!

Could it just be something simple as not riding it hard enough or could it be something like antifreeze finding its way into the cylinder?? All i know is that if i were to put a new plug in it right now it would take 2 kicks tops to start the dang thing!!! Please respond, thanks
Also i ride it as a putter but then more often then not i get on it and normally it will run ok until this happens...
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Old 02-24-2013, 07:56 PM
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Ok a good starting pointing in my opinion is find out how you are sure coolant is not still getting into the cylinder? If you suspect the head is warped then I'd suggest getting the cylinder and head checked. Next thing I would ask for is a plug reading. My cousins bike had similar problems ( along with others ) a bad float height, incorrect jetting, not riding hard enough, are so things that contribute to a bike fouling and dying out like you state.
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Old 02-25-2013, 04:27 AM
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If you just lugged it around you could have a lot of premix in the crankcase accumulated.

Normally if you loose coolant your level would drop in your radiators, does it?

Something not running more than half or 2/3 of throttle would make me check, swap the coil.
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Old 02-25-2013, 05:21 AM
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Don't get mad but I noticed something in your post.
32-40ish?
Could your rebuild be "ish"?
Could that attitude perhaps gone into your build?
I mean, do it right and know what you have.
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Old 02-25-2013, 09:09 AM
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32-40ish as in it depends on how i ride... 32 for hard riding wich i dont normally do and 40 for just riding in the trails

I wouldnt rebore my cylinder and put over 10 hours of work in a bike i dont care about

---------- Post added at 09:09 AM ---------- Previous post was at 08:24 AM ----------

The plug reading is a little black with a back ground of brown on it... signaling a slight richness. But if i let it sit for like 20 minutes after riding i try and ride again but i cant get passed 1/2 throttle before i bog out and have to put a new plug in...

Rebuild was successful the compression is excellent with a 195 reading.
Im assuming i am just to easy on it.
Does anyone want a cr 250 in texas
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Old 02-25-2013, 09:31 AM
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why dont you fix the overly rich condition? if you are coming back to it and having trouble getting it started and being able to take throttle it sounds like it is flooding, float needle and setting usually fixes that.
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Old 02-25-2013, 11:44 AM
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Ok when i take the carb off and take it apart how do i set the float hight... i know how to fix the jetting... Just go down on the main right
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Old 02-25-2013, 12:02 PM
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there is a good pictorial in the knowledge base here on ATM by faded on setting the float. while you are at it, screw the enrichenor (choke) down all the way, it wont idle but that causes flooding too on the pj carburetor as they age. 16mm should be the float setting and just do it as his pictorial shows and test that it is shutting off. this will eleminate that as a problem.
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Old 02-25-2013, 02:26 PM
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Sorry you took my comments personal, just pointing out what I read.
btw-the main jet is but one component of jetting a carb.
Should be a manual floating around somewhere or someone could give you the stock settings.
Also, rejetting should be done when you change ratios.
I suggest pick one and stick with it.
My personal preference is 32:1 Klotz.
My 2001 CR250 is a shredder.

Your problem could be something simple.
Get the manual and check the stock settings.
If your bike is stock start there.
Question, did you check all the tolerances before you buttoned it up?
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Old 02-25-2013, 06:41 PM
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Tolerances? Explain... i am still quite a newby when it comes to fine mechanical work with dirt bikes

---------- Post added at 06:41 PM ---------- Previous post was at 06:35 PM ----------

So basically setting the float is checking for wear on the inlet needle pin and if it is out of spec bend the float assembly in the direction needed?
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