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@BrickMan
So now I see why previous owner did not use this thing for 3-4 years. Its a total PITA to get it running right.
Essentially I've got fuel starvation once I go beyond the idle/pilot jet. Starts and idle's like a champ, will idle forever without bother. Runs up from idle fine, then after 1-3 seconds die's off and returns to idle.
So....
cleaned tank, fuel cock, pipe work (vacuum pulls the cock open fine), cleaned carb out twice, cleaned out jets and orificies of carb very thoroughly, float works fine, checked operation of auto choke (does eventually push out and do something*), ignition all fine, oil level, valve clearance and compression all sweet as can be, air filter + oil filter all new and fresh.
It only improves to the point you can actually ride it above 3mph once its been idling for at least 10 minutes. Doesn't matter if the engine is already fully warm, therego I'm assuming its a problem with the autochoke, as its operation goes along the lines of '5-10 minutes to turn fully off after each period of ignition turned off'.
And then when it is choke off (or as off as it will go) you can ride it, but still epic bogging until throttle is pumped a few times or backed off to idle then back on it.
Next step? New auto choke or might even go for manual/cable conversion so then at least have control over that aspect. Fit another fuel cock, could still be an issue as they are renowned for fail. New carb**? Bike has only covered 3k miles but its all essentially cheap eastern parts that hold it together
This is the offender, a 20-26mm KeiHin carb. Only adjustment is idle speed and idle/pilot mixture. The needle and slide move freely, but as freely as a quality carb on a bigger bike, and would assume for a smaller engine if anything it needs to be able to move MORE freely?