Topic: Boring CB750 carbs

[754]

Used to be  a few that did this.

Anyone know how big they went??, how good it worked?

Seems  like it would be a reasonably cheap mod for those that want a bit more power. The sock bores looked a bit like a figure 8, I assume they ended up round.

I have bored lots of carbs, but not a four cylinder set.

[JMURACN]

If you have experience with it i wouldnt see why you couldnt do it yourself.  i'll probably end up doing it to my set eventually... because apparently i enjoy rejetting carbs or something.

[754]

A couple reasons.

I dont run stock carbs, not for a few decades.
On mine I can change my crbs from 30mm to 32mm in ten minutes, and go bigger if I get bigger venturis.

I think they were bored to 29 or 30, generally there is a point where you will break through into a passage. at which point carb is junk or you need to sleeve the passage, that and the fact that this is the only carb I have seen that does not use a round hole..

They would be great to run on a sleeper, running stock carbs would make the bike look a bit less modified.. sometimes a good thing..

[paulages]

come on, they're not that boring... 

[dusterdude]

i understand the desire to bore them,but at want point will the slides not cover the bore?

[754]

That is easy, you can see that part.

[MRieck]

 Monty Campbell ( X pipe fame) did them if I remeber correctly. They were called Maxi-Bore carbs.

[fuzzybutt]

Monty Campbell ( X pipe fame) did them if I remeber correctly. They were called Maxi-Bore carbs.

big dollars too, something like 400-500 a set

[754]

Interesting..
 You know when you bore a Mikuni 40 that it can go to 44 as it is the same body.

 I think that when the first guys bore one like the CB carbs they sacrifice a set to see how far they can go, or use a thickness tester. Mitutoyo has anMU guage I think it is, will test wall thickness.. sonicly I think. The nice thing boring on a mill is you can move the bore sideways to stay away from a passage if need be.. bored quite a few Keihins for Harleys.

Maybe on the CB they only took out the sides of the figure 8 making an oval...

[MRieck]

Interesting..
 You know when you bore a Mikuni 40 that it can go to 44 as it is the same body.

 I think that when the first guys bore one like the CB carbs they sacrifice a set to see how far they can go, or use a thickness tester. Mitutoyo has anMU guage I think it is, will test wall thickness.. sonicly I think. The nice thing boring on a mill is you can move the bore sideways to stay away from a passage if need be.. bored quite a few Keihins for Harleys.

Maybe on the CB they only took out the sides of the figure 8 making an oval...

I believe you are correct. I have only seen one set of those MaxiBore carbs and that was in 1981 or something

[gerhed]

come on, they're not that boring... 

Nothing boring about these babies !

[Triffecpa]

I have a set of stock carbs that are over bored.  They came on a CB750 road racer that I bought last year.  They were bored to 31mm.  Not certain what year of carbs they were, but they were not pumper carbs and they came attached to a single plate with a linkage. So I would guess early 70's vintage? 

Tracy