Practically Classics Forum

My MGB runs really well, starts on the button, ticks over smoothly and pulls well without flat spots or pinking, but I can’t seems to get rid of what feels like lumpy running on very light load, ie cruising at 30-40 mph on the flat.

Engine is over bored to 2000cc, lightened and balanced, 123 dizzy, I have tried various ignition timing settings and 14 BTDC seems the best. The carb’s are good, rebuilt and with richer needles and accurately set up. Plugs are a good colour.

Any suggestions? The fact it runs so well the rest of the time is baffling.

thansk...

With all the tuning that has gone on, have you had the car on a rolling road for a good set-up session?
from my bike racing days, sounds like a bit of over fueling going on to me..just a hunch though

Kev

I have had a comparable problem with an a-series which was caused by low compression on a single cylinder. it sounded fine but a 30psi variance meant it stumbled a bit at 35 in top. Fitting hardened valve seats sorted it.

Indeed - double check the valve clearances then a compression test would be a good start, and take it from there.