i just got my 1990 MC21 running but it does not run on the lower (front) cylinder until rpm exceeds 5000. above 5000 it goes well when under load, but at no load it stutters. it has fresh fluids, plugs and battery. it is all original with 6600 km. All the lights and guages work fine. Temperature guage reads just below 70 degrees c when running, going up to 80 if left idling. i've put 100 km on it thinking it is carburator related and might clean itself up. Troubleshooting guide for poor performance at idle/low speed gives the following protocol:

check ignition timing
check carb air screw
check for leaking intake mainfold
test cylinder compression (top cylinder is 155 psi, front is 140 psi)
clogged carburator

Any words of wisdom before i dive in? Seems to me i should just start with carburator cleaning. I'd like to avoid it as i have no experience cleaning carbs.