F vs R carbys

Ok guys I’ve got a brain teaser for you here, I have a set of F and a set of R carbys, I was planning on using the R carbys on the bike as they are practically brand new and look to be exactly the same as the F set(I’ve stripped both and both sets are from Australian bikes).

I’ve just noticed the main jetting in the R set are all 145 (where the F carbys are 145/150) and the slide springs are all the same length, somewhere in between the longer and shorter length of the F carbys slide springs.

So has Mr Honda decided that it was not necessary to jet the front and rears differently and that a spring length inbetween the two was fine for the R models?
Would this be fine to put on my F model or should I rejet and respring them so they are the same as the F model carbys?


Hi Tony (Planty),
Mate when I rebuilt the set off the “RE” motor I swapped them for the set that was on the “FE” motor as they were in better condition and exactly the same. The “RE” carbs were running 140s mains in the front two cylinders and 145s mains in the rears. But when I put them back together I ran 140s in all mains. Ran a better colour rear plugs with no problems.

Thanks Paul, I ended up swapping springs and jets from the F to the R carbys, all running well.