I'm working on my 32cc 4-mix conversion and I'm having trouble to get the engine to run good.
I'm certain the the timing is correct, the lobe is pointing up or down at TDC, and when it's pointing down, the arrows on the cam are pointing at the marks on the crankcase. I've tried original Zama carb and also WT-456. To make engine to start the mixture has to be very reach, it will not start in any other way. The engine has good compression and hand start easily, as long the mixture is set very reach. After starting the engine reach any attempts to lean it out will result in the engine stalling. There is noticeable "blow-back" through the carb when the engine is running, but as mention earlier the timing was checked and double checked.

I'm running the engine with open exhaust. I'm also running the engine on electronic ignition the ignition timing is set at 28 deg. The plug is CM-6 ( the only one type I have on hand to work with the ignition plug cap), this plug is much shorter that the stock one. Can the wrong plug to be a main problem?

Any help is greatly appreciated,