A car battery charger does charge at too high of rate for a motorcycle battery. You will need a trickle charger for that.

Seriously have you tried bump starting it!?

Oh and don't bother with a compression test its a waste of time. You could go down the "leak down test" route. But seriuosly get a mate to push you and bump it. I know it sounds unlikely to be be a spragg clutch if it sounds like its turning over but your problem does sound very familiar.

Going to start by checking piston / rings/ valves & seats as was planning to this anyway so have started by removing rads,water pump,cams but the 4 bolts(hex heads) that you access under the cams are tight as hell!! I take it these need to come out as was planning on removing the complete head & then breaking apart on the bench or does the complete motor need to come out or better to come out??

On my 06 TE250 the head and cylinder came out with plenty of room with the motor in the bike. I did not even remove the radiators.
I did remove the subframe bolts, exhaust, and gas tank to allow the carburetor enough room to slide out of the rubber intake manifold. Even left the throttle cables connected and just moved carb to the side. That was a little tight.
When you get the head off turn it upside down and pour fluid ( I used transmission fluid) in the valve area ( combustion chamber side). If your valves are not sealing the fluid will leak past the valves. Do this on a level surface. If you see the red fluid leaking out your intake or exhaust ports you have valves not sealing.

I did have the same problem with my TE510 and check your intake manifold boot a very small crack can do this kind of problem.(make the mixture very too lean)

I super glue it (while I was wating the new piece) and it come back to life ...
You may attached the engine head to it , this is what I did

Make sure you don't just have a spark, but have a STRONG spark. Also, make sure your plug wire isn't arcing out of the boot and wasting your spark.

I had fouled race plugs on an old GSXR- I went digging everywhere for a fix- then I swapped one plug and it seemed to kick some.. swapped all 4 and it ran fine.

When tested though, the old plugs still showed a (weaker) spark.

-Dave

Hi all,
have finally sorted out checking piston & rings etc & found the rings were well worn so put a new piston kit in & re seated the valves as the inlet valves were leaking bad but all good now,engine back in,check valve clearances but still very difficult to start so went back & re check basics,what I have found is that the spark although strong can be intermittent,when you hit the starter the spark very nearly drops out but when you release the starter the spark comes back strong for that final second or so untill the starter stops,have cleaned up all electrical connections & earths,including coil but not sur how to test coil or rectifier (not sure how but have heard bad rectifier causing spark problems) ...any ideas please.

One (temporary) trick is to pull in the compression release lever if yours has one as you first hit the starter button. Takes the initial load off the starter motor, once it is spinning the load is less and the voltage is highest, could give you a stronger spark and faster startup. If that seems to work better then that is a clue about what might be happening and where to look further.

Assuming the piston and head rework is all good I would look toward proper carb and choke operation including leaks in the intake manifold as mentioned.

As above if you find flicking the compression lever is making it fire you may have a prob with your spragg clutch. I have asked you this a few times now... Have you tried bump starting it in second with a friend pushing??

Hi Svenn,have only recently got all the bike back together after the top end overhaul so will give it a try tomorrow I hope,excuse my knowledge but how would the spragg clutch effect poor sparking when turning the engine over??

Just so you know battery has nothing to do with quality of spark, other than how fast it turns motor over. It's a magnito ign as in take the battery out and kick it you'll have spark.
Kick only bikes must have carb adjusted properly or you will kick your brains out getting them to start. E start bikes need it also but by working the throttle can figure where it wants to start and run, the fuel mixture screw is the must adjustment for proper starting as far as carburation.
Later George