carb fitting confusion downdraught head/intake length

hi everyone, happy new year


just about to fit my new premier amals


got two types of manifolds the original bigger ones for the monoblocs, ad some slim ones that I bought with new studs

studs hit the carb ticklers on the 930's the advice of the local norton shop

was to go gasket-------tunfol heat insulator------ gasket ---- tunfol heat insulator----- gasket---- metal manifold with balance pipe ---- carb so the nuts dont hit

what I was wandering should I still have a gasket on the side of the metal manifold spacer to the carb noticed the carb has an o ring

or should I use the original monobloc metal spacers instead of all that lot?

whats the thought process behind the thinner spacers then padding it out with cork spacers? compared to the original manifolds

any pics or info would be amazing as Im dying to get them fitted


Thanks in advance,

tom

Re: carb fitting confusion downdraught head

I'd use the original Monobloc spacers. They should have a heat dissipating gasket closest to the head, then the alloy spacer, and then the carb.
The rest of that business, just sounds like an air leak is bound to happen.

Re: carb fitting confusion downdraught head

Hi Tom

I have a 68 650ss which came from the factory with twin Concentric 930s mounted. Will take a photo shortly and post it here.

Glen

Re: carb fitting confusion downdraught head

brilliant thanks Glen really appreciate it

Re: carb fitting confusion downdraught head

The air filter is a K&N item from Britcyclesupply , about $50. There is a stock airfilter available however it is a Rube Goldberg affair with many pieces and great expense.

The spacers/manifolds have nipples fitted for balance pipe. This helps to give a smooth idle.

Glen

Re: carb fitting confusion downdraught head

I'd asked the same question, elsewhere, and was advised to go, (from the head) gasket, insulator, gasket, ally spacer then carb (O ring fitted). The studs were too long so I put more thread on the head end (5/16ths BSW) and cut them down to suit. I've not got the premiers as of yet (as you can see the head's not even been fitted yet) but tried the fitment with another carb. So the same as Worntorn's from stock by the look of it.

Re: carb fitting confusion downdraught head

Very short little manifolds, aren't they.

I know there is not much room, but has anyone tried for a longer set of manifolds.
Working on that old formulae that says that ~14" is the optimum length for best performance - on full throttle.

Re: carb fitting confusion downdraught head

Cheers lads really interesting isn't it how some advice can be different I think Im going to go for that set up that you both are using if norton did it an so forth Ill see if I've got enough thread to cut down on the carb end as the other end is fully screwed in.

Just dug out my original norton paul dunstall tuning book John the previous owner gave me forgot i had it as i keep it wrapped in a box :lol:

Dunstall said, concentric is best suited 650c engine is the 930mm

mentions jets and an stuff then says


just as important as correct settings are the induction tract lengths for road use the spacers between the cylinder head flange and cabs should be 1 1/2 inches long

in racing grater emphasis is placed on prventing engine viration affecting float bowl elvels and upsetting carburations fourtunatley the race cam needs a longer induction manifold which gives us a chance to use flexible
inducution pipes 3 inches long to isolate each carb from the head

sorry bout the pants typing trackpads stickin on

really interesting point of discussion though as to how things have moved on since dunstall's thinking