Topic: Using pre-77 cab insluators on post-77 carbs

[mrosso]

I have a set of new carb insulator rubbers I bought a while back for my '71 CB750. I just bought a set of '78 carbs off of ebay. Can I use the '71 insulators with the '78 carbs?

[fuzzybutt]

no, the 77/78' carbs have a larger diameter.

[sohc4]

On the engine side, all the carbs have the same diameter, but the '77/'78carbs have a larger dia on the airbox side.

But - the earlier insulators are longer than the '77/'78s, they will give you a headache if you are using the airbox.  No problem if you have pods or stacks, though.

[scondon]

On the engine side, all the carbs have the same diameter, but the '77/'78carbs have a larger dia on the airbox side.

But - the earlier insulators are longer than the '77/'78s, they will give you a headache if you are using the airbox.  No problem if you have pods or stacks, though.

78 carbs are bigger on both ends, just measured to confirm. Am guessing it's the same for 77 carbs(CB750).

'76 carbs outlet-  37mm

'78 carbs outlet-  41mm

Axl, that you? 

[sohc4]

Yep, it's me.  Hmmmm - I didn't measure them up but I know I had mounted '77 (K7) carbs using the earlier insulators 

[scondon]

Yep, it's me.  Hmmmm - I didn't measure them up but I know I had mounted '77 (K7) carbs using the earlier insulators 

 The only "pumper" carbs I have are from the "F" models, though I thought from discussions here that the "K" carbs had same dimension. I am certainly prepared to be wrong on this as I hate spreading mis-information


   Either that, or years of putting bikes together have given ya "Popeye" strength

[eurban]

Don't know how they compare to the earlier carbs but the F2/F3 and K7/K8 carbs are identical as far as the size of the fittings on the airbox and the engine side of the carbs.  F2/F3 have larger diameter spiggots that screw into the head.

[scondon]

Don't know how they compare to the earlier carbs but the F2/F3 and K7/K8 carbs are identical as far as the size of the fittings on the airbox and the engine side of the carbs.  F2/F3 have larger diameter spiggots that screw into the head.

  That's how I remember it. Thanks,eurban   Haven't forgotten about taking piston pics, just need some time in the garage to clean and compare them. Will post when done.

[sohc4]

Yep, it's me.  Hmmmm - I didn't measure them up but I know I had mounted '77 (K7) carbs using the earlier insulators 

I stand corrected - sorry    Now, the question remains, how did I get these '77 carbs onto the earlier insulators?  Must have had that extra helping of spinach before 

[Terry in Australia]

To install 77/78 K or F carbs onto a K or an early F (F/F1) head, you need K7/K8 insulators. been there, (last summer) done that.

Another problem that you may encounter with the conversion is that the F2/F3 airbox (and presumably the K7/K8 item) which you'll need as the K0-K6/F/F1 airbox won't fit the later carbs, is slightly larger in width than the earlier item, and you'll crack your left sidecover trying to install it. I did...........