Has anyone any experience of fitting 1 3/4" twin carbs to an 1800 B series? I have been told that this conversion is OK for the racing boys but it causes a lumpy tick-over, loss of bottom end grunt and high fuel consumption. Is this correct? Has anyone done this conversion an been happy/unhappy with the result?

Hello Paul,
I don't have first hand experience, but the reference book on MGB engines by Peter Burgess says pretty much the same. If you are heading for a +80 bore, race modified head, hairy cam you will see a benefit but only above 4000/5000 rpm and nothing below.

I'd disagree about high fuel consumption if you fit them to a fairly standard engine set up. The SU will only supply what the engine demands. For me why go to the effort which will include changing the maniflold, and then rejetting and time consuming setting up of the jets and needle tuning.
I'd stick with the 11/2" twins and tune them. Another excellent book is the Speedpro series on how to power tune SU carbs by Des Hammill. I have done a review of this book recently for the next edition of the NGOC magazine, should be out soon.
Happy tuning, Dave Holland

Thanks for the feedback Dave. I am not so much interested in the increased performance but have acquired a brand new old stock set of carbs from an 1800s landcrab. My quandry is, do I make them secondhand by fitting them (losing the 'new' value)and be disapointed with the result or, sell them and invest in reconditioning a set of 1 1/2" carbs.