O.S 8AA/9B Carbs

[Martin Fields]

Hi,

I'm hoping that someone out there might be able to help with some advice. I've been looking to buy some new O.S. 9B carbs but it appears they're discontinued now. I think that the 8AA is the same, just with a different fuel nipple position.

All of the images of this carb show it without the fuel mixture needle and a blanking screw instead. Does anyone know if you can fit the assembly to the 8AA to make it the same as the 9B?

I've attached a couple of pictures below of the 2 carbs so that you can see what I mean.

Thanks in advance,

Martin

 

[Don Ferrette]

The 8AA is the same.

 

[Martin Fields]

The 8AA is the same.

Cheers Don

 

[David Bryant]

just curious, what engine are you using the OS carb on?

 

[dwilfong]

The 8AA has a wider bolt pattern on the body.

Look at the part break downs every thing is the same but the body.

It will not bolt up where a 9B did.

 

[Don Ferrette]

The 8AA has a wider bolt pattern on the body.

Look at the part break downs every thing is the same but the body.

It will not bolt up where a 9B did.

I have both the 8AA and 9B here and they have the same 31mm bolt pattern. The only difference is the fuel inlet location.

 

[Martin Fields]

just curious, what engine are you using the OS carb on?

It's actually not for a rigger, but and endurance racing boat (20min qual and 30min final with 12 other boats). I'm running the new CMB RS45 EVO and have tested with the 40A that I used to run on the RS45, but found I could get more out of it with the bigger 9B.

Martin

 

[David Bryant]

just curious, what engine are you using the OS carb on?

It's actually not for a rigger, but and endurance racing boat (20min qual and 30min final with 12 other boats). I'm running the new CMB RS45 EVO and have tested with the 40A that I used to run on the RS45, but found I could get more out of it with the bigger 9B

I see. thanks.

Looking at the spec's on those carbs I believe:

OS 40A throat ID = approx. 15mm

OS 9B/8AA throat ID = approx 11.85mm - 15.75mm (that's what OS site shows)

http://www.osengines.com/parts/carbs.html

 

[El Zorro]

Carb throat ( I.D. ) on the 40A carb is 11 MM or .433 inches. The tech sheet as listed by O. S. is incorrect. I just measured one that I have here.

I would think if you are running enduros you would be concerned with fuel mileage. One would think the 40A would be better suited.........

Dick Tyndall

 

[Martin Fields]

Carb throat ( I.D. ) on the 40A carb is 11 MM or .433 inches. The tech sheet as listed by O. S. is incorrect. I just measured one that I have here.

I would think if you are running enduros you would be concerned with fuel mileage. One would think the 40A would be better suited.........

Dick Tyndall

In the past it's been a bit of a concern, but this 7.5cc boat can carry 3.5 litres (0.9 US Gal). I always pump in and out the fuel and with the 9B is using 2.9 litres over 30 mins. If i was getting close to not being able to carry the fuel needed I can always reduce the nitro content.

Martin

 

[ALLAN YUEN]

Hi Martin I am curious that can you tell me about compare CMB 45 rs and evo which one better fast and powerful? Let me know

 

[Martin Fields]

Hi Martin I am curious that can you tell me about compare CMB 45 rs and evo which one better fast and powerful? Let me know

Hi Allan,

For the endurance racing its been a fantastic upgrade to the RS45. Using the old geared engine I was doing a lot of tuning to induction times and running a 53.5mm prop. The new EVO engine has a lot more torque!!! Without mods I'm going quicker, about 9kph. The reliability has been great as well. I've run the engine all season (70mins per event x 8 events + testing) and everything is great in one piece.

If I ran a .45 rigger the V5 engine is the one i'd try over the Nova. I'm not a Nova hater, i run them in my 3.5 riggers, but the CMB appears to be a strong engine now.

Martin.

 

[ALLAN YUEN]

Hi Martin I am curious that can you tell me about compare CMB 45 rs and evo which one better fast and powerful? Let me know

Hi Allan,
For the endurance racing its been a fantastic upgrade to the RS45. Using the old geared engine I was doing a lot of tuning to induction times and running a 53.5mm prop. The new EVO engine has a lot more torque!!! Without mods I'm going quicker, about 9kph. The reliability has been great as well. I've run the engine all season (70mins per event x 8 events + testing) and everything is great in one piece.

If I ran a .45 rigger the V5 engine is the one i'd try over the Nova. I'm not a Nova hater, i run them in my 3.5 riggers, but the CMB appears to be a strong engine now.

Martin.

I am very interesting about EVO Ask question long or short stroke? How many of ports on sleeve? Flat or dished on piston? Let me know

 

[David Bryant]

Carb throat ( I.D. ) on the 40A carb is 11 MM or .433 inches. The tech sheet as listed by O. S. is incorrect

thanks for confirming Dick. I was wondering whether those specs given by OS site were correct or not.