Got a 2006 250 rev 3 with low use having trouble with an erratic running when warmed up pulls through gears fine but looses response just off tick over goes droggy n plenty pinking Almost like it's too rich but with pinking at same time to date I've changed Crank bearings and seals rings case gasket cylinder gasket new plugs of differnt heat range stator and cdi brand new and good used coil Inc lead n cap kill switch disconnected 2 carbs Reed block assembly flywheel new air filter tank drained tap cleaned out can't pick up on any air  leaks spraying carb cleaner around it problem was there before rebuild n suspected Crank seal I am thinking it needs a  crankcase pressure drop check. Just pulled head wondering if rod was bent piston comes up square but not  level with cyl top ie 2 to 3mm lower is this normal 

 That seems normal. Looks like you have tried everything. I worked on an `06 that just never seemed to hit right just off idle. Never did figure it out. Owner let it go cheap. Never heard any more about that bike. Let us know if you ever figure it out. Change the ground? Check wiring harness as could be pinched. I also had an `03 that I swear did not have any real power. It ran ok, just not as good as others. And it was a 270.

I think you have changed so many things, it's not the same bike...

Just off tick-over is in the carburettor range of the slide cut away, and to a lesser extent upon the needle position in the slide.  You could try moving the needle up a notch, but maybe the answer is to get a slide with less cut away, to make it richer in the transition.

I assume the previous owner has not put the High Compression head on it, which would need higher octane fuel...?

As far as I know the head is standard I've had it 6/8 years id say it went like this gradually just wouldn't run right low down at a trial. Had 2 differnt carbs one brand new from 07 250 which I'd say is  like a motocross bike in comparison swapping stator n cdi is all the loom involved with spark. I added a separate ground to coil and thought I'd fixed it but nope. On a cool day it could  take half hour or more to occur on a hot day as today 10 mins 

Edited May 20, 20188 yr by zerorev3rev4
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Although not the same type of bike I had a similar problem with a cub put a slide with less cutaway cured the problem until the lad that rides it change the exhaust and the fault returned So it is something else easy to check My 200 rev 3 goes off tune when it needs cleaned and repacked  

Edited May 20, 20188 yr by naichuff
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Perhaps the exhaust is grunged up

Can't visually see a fault with exhaust definitely not oiled up more on the dry side. Tried the new carb from other bike which runs very good and no difference 

You need to pull the silencer apart to really see.  Or try the silencer off the other bike?

Can see straight through silencer I did have it apart to check wadding which wasn't that old 

check breather pipes from carb this can cause weird problems if blocked

Had 3 different carbs on it now but yes had that before with snow. Done a leak down test and holds 25 psi no signs of a leak 

Don't know if you want to take the head off again, but that ring of carbon at the top of the cylinder could be glowing, and causing the pinking...   Or is the fuel very old or of low octane rating..?

Also, is there a specific way of getting the coolant back into the cylinder once you have taken the head off..?   Maybe you have an air-lock, causing overheating...?

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Fan works as it should coolant level OK no loss or pressure build up fresh fuel tank n tap cleaned carbon on piston top is prob only after 3 to 4 gallon use so soon recarboned up fuel is standard not high octane but not from super market did try hi octane but wasn't much better if any 

Probably not what you want to read,but we had a2007 rev3 which wouldn't run right when hot and it defied all our attempts to fix it too.Gave up with it in the end,too frustrating 

Seem to think this water gallery across front of Crank case has been blocked off could this cause the problem. Case getting too hot?