four stroking muggy

[idc1967iow]

What is the main cause of 4 stroking at very light throttle,i am using a muggy 186,delly phbh 26mm ,ancillotti pipe ,elcctronic kit, any ideads where i can start ,even if i can reduce it a bit would be a start it is driving me mad ,she goes ok ,starts good ,just this 4 stroking problem.

Thanks all
Ian

[WINTERMODEL150]

Hi,Sounds like the mixtures too rich,what jets have you put in the carb?

Dean