Update for those who own this engine or interested to know what helped.
Basically I teared down the entire engine and looked at every bits. The biggest issues with these engines in my opinion is poor assembly and quality control, despite being produced in low numbers. But after hours and hours of work I managed to make it work to the level I am happy with and represents the real r90s character.
Things I have done:
× Replaced both piston rings
× Replaced sparks with Iriduim type
× Replaced the valve pushrods with a more accurate lenght to control intake and exhaust valves better
× Adjusted crankshaft position and pushed it towards the rear of engine by .7 mm
× lapped all valves
× adjusted the ignition cable by bringing the head towards the spark to increase ignition
× took carb apart and filed the HSN screw to sit it more tightly
× Added silicon gasket to both parts of each cylinder block to prevent air and fuel leak
× Shortened the fuel line, this helped with faster fuel pickup and less HSN
× Adjusted LSN to bring the idle speed to as low as possible without stalling to represent the low idle character of real engine
× using mixture of zippo and VP 50:1 fuel with ratio of 3:1. That achieve the best ignition with minimal spark fouling . These engines have low compression and weak ignition. I don't know why the suggest 95 octane fuel but it's defitenly too high to suit. I personally beleive the best option is lighter fluid mixed with 2 stroke oil or marvel mystery oil as suggested by many
TIP ON CARB SETTING: if after priming the engine doesn't start at 1/4-1/2 turn from close, there is an issue somewhere. I start the engine from cold with 1/2 and throttle 1/3 open. I let it warm up with few throttle up moves, then slowly reduce the carb to 1/4. It should pur and run slow on lowest throttle position, might seem stalling but let it settle. As the engineering is not precise you won't have the exact replication of very low smooth idle as it would on the real engine , but close enough
One issue that still exists is the spitting fuel spray from car intake and I think it's as I managed to get the engine to the level I'm happy with, I will leave it as is for now. The casting of cylinder head is different in each cylinder when you look closely, unless a precise sanding is done ( with no point of return) the valves and suction on both cylinders won't be exactly equal.
That's why I rather have these engined as kits option too, so those of us who are OCD can make it near perfect !
Hope this helps others with the same engine