Topic: CB750 Intake spigot sizes

[754]

I did not know there was more than one thread size where they join the head.I sent an early one to a member and he said it fell in.
 So are late F model bigger or are the threads just stripped?

[kmb69]

F2 and F3 spigots are about 2mm larger.

[Old Scrambler]

Is the OD the only thing that is BIGGER?  My F2 head is on ice for the winter so I will have to wait a few weeks to get to it. It would be interesting to know if the ID of the intake ports and spigots are also larger than the standard K-models.

[Sam Green Racing]

Where is Mike when you need him.

Sam.

[Bill/BentON Racing]

I just looked in a 410 /F2 head,nice and smooth and looks bigger,port sticks out in the way,just match to spigot would help!,Can shoot pic if you like,or measure! Bill

[kmb69]

Is the OD the only thing that is BIGGER?  My F2 head is on ice for the winter so I will have to wait a few weeks to get to it. It would be interesting to know if the ID of the intake ports and spigots are also larger than the standard K-models.

Ports, valves, all bigger.

[MRieck]

Better port casting as well.

[Cqyqte]

I would be interested in knowing if the OD of the 1975 F spigot where the intake rubbers clamp is different than the 1978 F or K OD.  As I have 1978 carbs that I want to fit to my 1975 and I don't have any boots.

[Old Scrambler]

Thanks guys.............now to find some high-compression pistons to match the dome.....but no more than a 0.5mm overbore.

[Retro Rocket]

Sorry to dredge up an old thread but, is it possible to fit F2/3 spigots to a K7 head by tapping new threads ..?

[Big Jay]

On the K heads, there are two different thread pitches.

[kmb69]

Doubt if you could just tap them bigger. They are a good 2+mm larger. It's a very fine pitch thread. Probably have to be machined bigger and then rethreaded. Certainly doable.

[Retro Rocket]

Doubt if you could just tap them bigger. They are a good 2+mm larger. It's a very fine pitch thread. Probably have to be machined bigger and then rethreaded. Certainly doable.

Thanks mate, thats what i meant, i figured in the HIPO section i wouldn't have to fill in all the blanks....

[Old Scrambler]

Retro...............I measured the ID of the F2 spigots at 31mm................then bored them to 33mm for my salt-flats motor;D

To improve the intake potential on a K-head, I would think it would be easier to bore the spigot to match the porting. JMR may have some more input, but I would want to know how much larger the port on a K-head can be expanded before I attempted to bore and re-thread the F2-F3 spigots.   Then again, you could re-do the ports to follow Ken at Cycle-X

[Retro Rocket]

Retro...............I measured the ID of the F2 spigots at 31mm................then bored them to 33mm for my salt-flats motor;D

To improve the intake potential on a K-head, I would think it would be easier to bore the spigot to match the porting. JMR may have some more input, but I would want to know how much larger the port on a K-head can be expanded before I attempted to bore and re-thread the F2-F3 spigots.   Then again, you could re-do the ports to follow Ken at Cycle-X

Old Scrambler, I'm going to run fuel injection off a GSXR600 so i was just feeling around, the ID of the throttle bodies on the head side is 38mm and OD is 43mm so bigger diameter spigots and manifolds would help. I would also like to know how far the K8 {392} ports can be opened up and if i can then use F2 spigots...