Morris Minor Owners Club

installed unleaded head , idles super but under load there is a very slight misfire you only feel it when the road is smooth such as a new stretch of dual carriageway , as a undulating surface masks it, i did 50 miles in it yesterday so it doesn't affect use but its annoying. put new condenser,points,coil etc on . Any ideas ?

Was the misfire present before you chnaged the head and ignition components? What was the reason for changing the ignition parts? Have you checked compression after changing the head - did you re-torque after heat? Are valvr clearances set correctly?

it wasn't misfiring before putting head on but put new bits on because ive had one or two condensors/coils go before , I did retorque after first heat 44lbs , and valve clearences have been checked 2 or 3 times, it is perhaps a bit more tappet than before I replaced the head

Why did you change the head? Perhaps sticking valve(s) in this head - if that's the only change.

head gasket went and was recommended to put unleaded head on as everything appeared ok, ive had the car 16 years

Hmmm -well 'unleaded' head is totally unnecessary - but still have to assume that if the ONLY change is the head - then sticking valve is a possibility. Try with 18 thou valve gaps - and can you get a compression test? What colour are the plugs after a good run - maybe it's just running too weak.

Ill try with 18thou gaps, plugs are a light biscuity colour.

Colour sounds ok - maybe slightly weak. You could try a little richer. What size engine ?

its a 1098 , I will enrich the mixture first then try the valve clearance

If you have the original ignition components then refit those and see if the problem goes away.