O.S 8AA/9B Carbs

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Martin Fields

Well-Known Member
Joined
May 21, 2012
Messages
124
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

8AA.jpg

9B.jpg
 
The 8AA is the same.
default_smile.png
 
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.
 
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.
 
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

7.5cc Pegasus Evo-a.jpg
 
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
 
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
 
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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
 
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 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.
 
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
 
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