Need HELP with timing

[gasser]

I just put a new 300 top end on my 07ec250 (large ignition). It started right up and seems to run strong off the bottom with a moderate bog around 1/3 throttle. I did a throttle chop and plug check and the new plug was a grey color on the electrode and insulator. I've read that the grey color is a result of pre-ignition and timing needs to be adjusted. I don't have a timing light or anything to measure advance so any tricks or advice would be greatly appreciated.
jetting: 40/175, CCK middle position, oil 43/1, plug B7ES, rain/sun switch in sun position. Temp 69F and sunny, altitude 800ft

P.S.
#1 Piston (Vertex "A") did seem a little tight in the newly replated "A"cylinder
#2 I did set my float a little lower because it had been overflowing when parked on sloping ground. Maybe I set it too low.

 

[rpduc]

I'm no jetting expert but this winter I rejetted for ice and I had what I would describe as a lean "bog" at 1/3 throttle (if I've interpreted what you mean by bog). One position richer on the needle clip took it out.

Your jets seem a little lean compared to recommendations in the excellent post that Pobit posted a while back. He ran bigger jets than you have in there for both main and pilot. 178 main and 42 pilot with the CCK needle clip 3.

That set-up worked very well to tame the hit on my MC 250. It was "unruly" in the woods with the stock N1EG needle

 

[iancp5]

It does seem a little lean. I'd try Pobit's jetting first. In terms of the ignition - are there no marks on the flywheel and case? You could try rotating the pickup in the direction of rotation that will retard it but in my experience there is very little scope for this as it can't retard much but maybe mine was already retarded a lot. There was a thread on ignition timing on here somewhere with different CDI's but unfortunately the results are a little inconclusive. Is the CDI for your model year the same for 250 & 300? If it is you shouldn't need to adjust.