Topic: RS34 to F2 head need carb intake rubbers, stock f2 boots too big!

[CB750R]

Hi folks.

I just received my RS34s from Australia, racked and set for the Sohc cb750 however we the seller and myself overlooked the fact my F2 carbs have 39mm outlets not 36mm and my new intake boots don’t fit! 

The Mikuni has a 36.55mm OD and my head inlet spigot has a 36mm OD is there a set of intake boots that will fit this combo?

Photos below for reference,  I’ve been searching and see maybe the k7 boots fit but would like to confirm before I hit "buy it now"!

Thanks in advance for your help folks!

[scottly]

The spigots on all the other 750s are smaller than the F2/3 spigots, so the K7 boots won't work.

[madmtnmotors]

The K7, K8, F1, and F2 all used the PD "keyhole" carbs. My F2's and K8's have the same size outlets on the carbs and I have swapped carbs and boots between the two. I do not know what size the outlets are on the earlier round top carbs.

[CB750R]

Oh fun... sounds like I may be making some sleeves...

Looks like Schedule 40 1.250" inch Aluminum pipe is 42.164mm OD and 35.052mm ID so will just need a little a little work on the lathe to make sleeves to fit the Mikunis to the stock F2 intake boots.

Unless the supplier or the masses have a better solution?

Good news is the ID of the Mikuni and the F2 intake port are virtually the same so no major choke point created.

[MRieck]

Sorry for not getting back to you grant....I've been in Texas attending a memorial service for Keith Byers. Going to try to do some bike inventory tomorrow with Jim Sawtell of Jes Built. Quite a few sandcast bikes and that's just for starters......an unbelievable amount of parts.....it is staggering.
 The unmodified RS-34's fit perfectly in the F2 OEM insulators. Unfortunately those intake spigots are unique to the F2. As has been mentioned the K7/8 insulators have the larger ID for the carbs but fit the K and early F intake spigots.
 I haven't seen those RS carbs from Australia before but if I remember correctly Yosh modified RS's in the 90's had screw in adaptors and other subtle mods.

[CB750R]

Sorry for not getting back to you grant....I've been in Texas attending a memorial service for Keith Byers. Going to try to do some bike inventory tomorrow with Jim Sawtell of Jes Built. Quite a few sandcast bikes and that's just for starters......an unbelievable amount of parts.....it is staggering.
 The unmodified RS-34's fit perfectly in the F2 OEM insulators. Unfortunately those intake spigots are unique to the F2. As has been mentioned the K7/8 insulators have the larger ID for the carbs but fit the K and early F intake spigots.
 I haven't seen those RS carbs from Australia before but if I remember correctly Yosh modified RS's in the 90's had screw in adaptors and other subtle mods.

All good Mike, I’m glad you’re able to be there for your friend. Motor isn’t together yet I was struggling with the rings in the cylinders and managed to oil up the base gasket so I ordered a fresh one. Saw the trick about  using rubber bands to strap the gasket to the underside of  the cylinders so will do that with the fresh one.



 Smallish world Jim will be building a Dohc motor for a friend of mine hopefully his is up next. It’s a shame to hear these carbs were modified for the smaller intakes when that wasn’t required. I’m sure I will sort out a fix!

[CB750R]

After speaking with the vendor and and Mike confirming that the stock RS34 outlet is the right diameter for the F2 boots I was able to gently pry off the outlet adapters the vendor MikuniOz installed. Really happy with his communication with me and helping me resolve the issue.

Just need to clean off the bearing retainer compound from the other 3 ports before they will be ready to go!

[MRieck]

Good to see it worked out Grant