Here's @Mattax plugs and what Shrinker had to say:
Do they look familiar:
View attachment 1716240894
There is nothing happening in the cylinder. Theres no air being compressed. Its not even making enough bang to seal the rings, its even starting to look like its going to oil up the #3 plug soon. The general grey appearance is exhaust gas, its not even got enough blowdown to get rid of the exhaust.
You have a narrow LSA cam with not much duration that shuts the intake valve very early and you dont have enough compression ratio. So the cylinder isnt getting filled, and its not compressing what air its got in there enough. You not running on 1970's fuel anymore so bring the design up to the 21st century.
Cruise conditions with enough squeeze in a cylinder will give TAN sparkplugs on unleaded fuel. People say unleaded doesnt color plugs, BUNK -RUBBISH -BS. If you set a cruise mixture thats richer than stoich as a test and cant get a tan plug then your never going to burn a WOT mixture with maximum effect.
The manifold vacuum is a big part of getting a balance right between cruise and WOT. The narrow LSA destroys manifold vac. You need vacuum for cruise especially if you dont have compression. Stock motors have lots of vacuum and usually more compression pressure than what a lot of people get with hotrod engines. So thats why they run better.
Increasing the air flow of an engine is the way to get more power but it must be done without deterioration of the other factors.
Your plugs dont look like you have a distribution issue they look like you have a worn engine or one thats not equally built. Once you drop into this range of combustion issues your wide open to small variances, all of a sudden those small variances create glaringly obvious burn differences. It can be variances with any component of the whole system. Very difficult to find and fix.
Greg from @carby tuning techniques had this to say:
Hi Mattax,
That engine doesnt have any heat energy.It just doesnt have any grunt.
Those plugs show that its not squeezing the fuel and its not vaporising it very good either.
You need to get rid of that manifold,and put a single plane on there and raise the compression so that you can convert the liquid fuel to a gas.
Its a typical undercompressed cylinder that the plugs show.When you cant get brown colour on the plugs the engine just cant convert enough of the HC.
Its not so much your carb, its more the engine under it that is not up to speed.