Any multi-cylinder engine that has one carburetor will not give equal distribution of the fuel mixture to the cylinders. One cylinder will always be leaner than the others, and one cylinder will always be richer than the others. The other cylinders will be somewhere in-between. You can only set the engine so that the leanest cylinder is not too lean and let the other ones run where they will. On older engines, where compression may be down a bit, you may have to resort to an on-board glow plug battery to keep the engine running well at idle.