first off, CV carbs are never an upgrade. Most people are trying to go the other direction. They are a good street carb for a bike that you would bungee a milkcrate on the back of, but they are not a performance carb. The big complaint about them is because they are vacuum actuated there is throttle lag - you can sometimes be caught waiting for the carbs to catch up to your inputs. I have heard of guys with cv carbs going smaller to get more throttle response (restriction = higher pressures, the cb900F guys will switch to 750F carbs for this reason) so I don't think these big honkin 36mm Cv carbs are going to help. If you are running an aftermarket cam, your mill may not generate enough vacuum to work the carbs effectivley.
That being said I doubt your bike will even be able to take advantage of 36mm direct control carbs. The biggest restriction in a cb750 is in the head so unless you have massive amount of head work done a stock set of cb750 carbs will support motors up to 900ccs (although you will want the 77-78 cb750 carbs with the accel pump).
If you are jonesin for a set of high performance carbs and don't want to pony up for CRs or FCRs, 1977-79 GS750 carbs are mukuni VMs with an accelerator pump, much better in design than the kehin cb750 stockers and are slightly bigger. There is a lot of info about those carbs if you are willing to use the search function.
Dynoman sells the adapter rubbers for the gs750 carbs to mate to a cb750 head. YOu will have to run some kind of....<shudder>....pods, but at that point you just may be taking advantage of it.
the reason i was interested in these carbs was i could get them for a song and dance.
i need to look into the 77-78 carbs. didn't know they were an upgrade.
my motor has the following...
810CC 12:1 compression pistons
Yosh road and track cam
yosh port and polish head (yeah, that was a very long time ago!)
yosh timing chain and tensioner
4 into 1
stock carbs jetted up.
i had read an article on sohc forums about head porting and they reported to see the carbs as a flow restriction. it started to turn wheels in my head and thats why i thought i'd see what the experts say.
Don't get me wrong, i think it performs great but reading that made me think it may be bottle necked by these carbs. i respect your input geeto, i realize you have a ton of experience on these machines. so thanks in advance for any reply you can give.
yeah the yosh cams are pretty lopey and don't pull crap for vacuum. CV carbs would have made you unhappy.
The 77-78 cb750 carbs are only a slight upgrade. They are really a copy of the gs750 carbs and the only advantage is the acceleratior pump. You have to run the 77-78 carb rubbers to fit them to earlier heads and as long as you need to buy different rubbers then you might as well buy the rubbers for the GS750 carbs and swap over to them as mukuni VMs kick ass.
someone here posted a spotters guide in one of the threads for the gs carbs. look for it, it will help.
The later 73 and up carbs are sometimes viewed as a restriction but the truth is they really are no different than earlier carbs (except for the cable setup). The head is the primary restriction but once that is taken care of the next step in line is the carbs. Guys who have stock heads and big carbs rarely see a gain (even if the bore size is increased) and guys with headwork and stock carbs will get a little gain but not live up to their potential. heads + big carbs make a whole 'nother bike.
If you can dyno it now and then dyno it after the carb swap. betcha you see a huge jump uptop.
If you have the money (about $650), a pair of CRs will make that bike an animal. Pure. Fucking. Animal.