Best B12 Carb Upgrade

[Brians 7/12]

Greetings… soooooooo… I have a set of standard carbs… I’m looking for more oomph… though not internally or Turbo/Supercharger or Nos… Yet 

Stage 3?… or RS36… or FI conversion?… does FI help power wise over the other two or just mainly for less carb issues? 

educate me please 

If FI is way forward I’m guessing any other tuning as mentioned above would still work? 
 

Lastly cheapest but yet preferable way of doing this?… Many Thanks 

Edited January 1 by Brians 7/12

[wraith]

Stage 3 if you have filters and full race exhaust, is the cheapest.

RS36 very good up grade but again best with full exhaust.

FI will do the lot depending on body's you use but is the most expensive 

[Brians 7/12]

I have everything Stsge 3 including filters exhaust etc… so no extra £’s required… it’s whether I should throw £400 on maybe GSXR 38’s… £800 on RS36’s… or £?? on FI?… & wether it’s worth FI over the others for more or same bhp !? 

[Duckndive]

What bike ? as RS36 on a powerscreem are very tight apparently 

[Brians 7/12]

7/11 

[badger]

38mm carbs are 30 odd years old even if you found a mint set they're not great. Rs36s new are decent, heavy on the road imo but if it's not a daily does it matter?

Efi is the future but a pile of money and a load of wiring but will be a lot more reliable and fuckable with. 

I'd go fuel injection if monies not important personally but pro's and cons to each

[Brians 7/12]

Cool… so ball park price for FI from scratch 

[clivegto]

1 hour ago, Brians 7/12 said:

Cool… so ball park price for FI from scratch 

@Arttucan supply what you need 

[nickmac]

1 hour ago, Brians 7/12 said:

Cool… so ball park price for FI from scratch 

When l casually asked the same question last year 2 grand was the answer.

Not sure how close that would be, that would be me giving the bike to someone as a customer. Obviously the more you do yourself you could trim it down but I don't think it would be cheap.

 

[Brians 7/12]

11 minutes ago, nickmac said:

When l casually asked the same question last year 2 grand was the answer.

Not sure how close that would be, that would be me giving the bike to someone as a customer. Obviously the more you do yourself you could trim it down but I don't think it would be cheap.

 

2k 

[Dezza]

RS's are basically bolt on and away you go. Just a little bit of faffing about required with pilot screws. They work well on a B12 with a well designed exhaust. BST 38s are also apparently a good upgrade but I have not done this so have no direct experience. I do have a set and they are physically a pretty huge carb. They may cause clearance issues on a 7/11 as they're very tall and being CVs are going to be a whole lot more hassle to set up than RSs. And in good condition they're rare are unicorn shit, and require the corresponding carb rubbers, which 2nd hand are even rarer and as new items (for GSXR1100s with BST40s) cost a fortune.

[wraith]

I was also told to fit a FI system to do it myself would be around 2k but you won't have the poor fuel problems you can get with carbs, I was told. Also I think you need to know your way around a laptop to set them up?

Which puts me out of the fitting bit

Not had RS carbs in a oil cooled bike.

I've got gsxr 38mm on two of my bikes, one a gsx1100f engine the other a b12 with DOT ported head and gsxr cams, love the carbs and did at one point put some b12 36mm CV on the GSXF engine to see the difference, but they only stayed on for a day as the difference was that different, it felt like jumping off a 1100 onto a 750 then back to the 1100.

But like has already been said, they are hard to find getting old so will need parts (not all are available) and they carb rubbers you can't get new and you don't see them second hand.

So I'd go for the RS carbs if you don't have the 38mm.

What's the best carb rubbers for the RS36 ?

Edited January 2 by wraith

[Brians 7/12]

34 minutes ago, wraith said:

 

I've got gsxr 38mm on two of my bikes, one a gsx1100f engine the other a b12 with DOT ported head and gsxr cams, love the carbs and did at one point put some b12 36mm CV on the GSXF engine to see the difference, but they only stayed on for a day as the difference was that different, it felt like jumping off a 1100 onto a 750 then back to the 1100.

 

That much difference really?… sounds interesting… shame you have no experience of GSXR38’s vs RS36’s 

Still got usable low/mid?… or just all or nothing top end 

[Brians 7/12]

Also would GSXR38’s fit in a Powerscreen frame/engine? 

[wraith]

2 hours ago, Brians 7/12 said:

That much difference really?… sounds interesting… shame you have no experience of GSXR38’s vs RS36’s 

Still got usable low/mid?… or just all or nothing top end 

All depends on gearing, on the GSXF engine (in my Kat) I'm running 48t rear and 15t front and get a good all round power, well the way I ride anyway. And will lift the front end in the throttle in 2nd.

As to fitting a gsx1100f frame (power screen) that will be very very tight, I put b12 carbs and engine in a GSXF frame and had to lift the tank at the rear about 4mm so the carb top (on the b12 carbs) didn't hit the fuel tap. As the gsxr 38mm carbs are bigger you will have to deal with the carb height.

[Arttu]

On 1/1/2026 at 8:03 PM, Brians 7/12 said:

Greetings… soooooooo… I have a set of standard carbs… I’m looking for more oomph… though not internally or Turbo/Supercharger or Nos… Yet 

Stage 3?… or RS36… or FI conversion?… does FI help power wise over the other two or just mainly for less carb issues? 

educate me please 

If FI is way forward I’m guessing any other tuning as mentioned above would still work? 

Generally speaking EFI doesn't make more power than carbs if all other factors are equal. In the best case there might be a small power advantage with it but that isn't guaranteed. But one advantage is that you can size the throttle bodies for maximum peak power and still get good low end torque and throttle response. With carbs there will be more compromises between these. 

The biggest benerits are ability to tune fueling for all situations with minimal compromises. And with data logging you get much better idea what's actually happening in the engine. And if you add turbo/supercharching or NOS in the picture these benefits get even more significant.

Regarding costs here is cost breakdown for one turbo EFI installation:

 For N/A engine you can maybe make it slightly cheaper since you can use injectors, fuel pump and pressure regulator from some donor bike. Also there are somewhat cheaper ECU options too is you are aiming for lowest possible budget. But getting below 1000 €/£/$ will be challenging without major compromises.

[DAZ]

My thoughts are how much power do you ultimately want ? A well set up 1216 with ported head, gsxr/kent cams, a decent exhaust and 36mm cv carbs usually claims 145 -160bhp depending on the owner/dyno and that seems to be the sweet spot as regards £/bhp , bigger carbs cams and valves will no doubt get more peak power but probably at a loss of tractability in comparison to the more street orientated combination , peak numbers are ok but I feel average hp over the rev range is more important , a simple case back when the b12 was launched they claimed 100bhp as standard , so was a cbr600 which was nicer to ride ? Obviously the b12 not just because it wasn't a horrible Gurls blouse  but because it made more torque or mathematically more average hp  

[Duckndive]

RS36 's will spank CV carbs hands down 

Edited January 3 by Duckndive

[Upshotknothole]

I've got RS carbs and BST38s. BST38s are good stock carbs and not hard to jet with a kit, but RS carbs are race carbs. Pros and cons to both, but as was mentioned, the BST38s are really big carbs. You could also go with Yoshimura TMRs.

https://www.yoshimura-jp.com/product/n-100983?lang=en