88SS Carburation

Hmm... difficult. If the ports have been done properly they will be opened up the full length to the valve seat, and the only way I can see to return them to standard would  be to build it all up with weld and then re-work them smaller, which is an awful lot of trouble to go to to get a stock cylinder head.

I think that I would get, or make, a pair of the standard 1" bore carb spacers that fit between the carbs and the head, and mount my two 26mm carbs, set up for a standard 88SS, on those and try it, following basic setting procedures as per manual,  if it works OK then it ain't  broke, if not, then it would probably be more economical to look for another head, as expensive and scarce as they are, returning a tuned cylinder head to stock is not really a practical option IMHO.

If you try the 32mm carburettor option, then go rich,  standard  88SS jets plus a couple of sizes, one slide cutaway less in the bigger carbs, lift the needles a notch and start from there, it would be a case of suck it and see, determined by trial and error.

I hope somebody more knowledgeable  than I has some better ideas.

32mm is really too big for an 88. I have raced an 88 successfully on a normal non-downdraught head with a 1" carb. Once you go above 28mm (which is still a bit big) the inlet air velocity is reduced which means that the pressure reduction reduces the petrol vapour component of the mixture, hence as so rightly stated above you will need bigger main jets than standard to achieve the correct mixture.

Tuning for speed, though antiquated, is still well worth a read. 

I would try sprung  steel sleeves  bedded in devcon or similar , not much you can do about the big valves.  I occasionally ride my  1966  250 on the roads  ,  29mm TT carb and and ported to a  40(!!) mm inlet valve. Definately not  easy  especially if out with  20 vintage bikes  in the lanes ,all stopping and starting.  I will be sleeving my inlet  and fitting a  smaller carb to enable me to carry on enjoying the beast  as I edge ( faster and faster!) towards 80  years .  What year is the 88 ?  ,the early splayed port 88/99 SS head is cheap and availiable.

The ports in the standard 88SS and 650SS heads are over size for the original 1+1/16" Monoblocs.  They came from the factory fitted with cylindrical sleeves, which the owner could remove if he decided to fit larger carbs for racing.  Original Part mumber 23874.

I am fairly sure RGM sell the sleeves.  I can't remember the inlet size, but is it possible yours have not been bored out?  If the RGM sleeves rattle about, you should be able to make and to fit simple cylinder sleeves. They have a slot to avoid the valve guide.

I made my missing ones from flat aluminium rolled round a bar (probably a broom handle), because a previous owner had thrown the mystery objects away.

RGM do have the sleeves, 06-7860, and they are remarkably cheap for original NOS parts, but of course they will only fit original unmolested ports. 1 1/8" is approximately 28.5mm, 32mm is approximately 1 17/64", an appreciable difference, in order to sleeve it, it would need to be pretty much round to start with, or you would first have to bore it round assuming it has been hand finished, and I would be reluctant because there cannot be that much metal left, of course breaking through would not in itself be disastrous, but a big crack when pressing sleeves in would be.

I would try them as they are, if it doesn't work then Robert is no worse off than he is now.