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What is the difference between a Bedford MW and OY carburettor


64EK26
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Hi

What is the difference between a Bedford MW and OY carburettor

The MW carb is a Solex 35RZFAIP/C581 and theOY carb is a Solex 35RZFAIP/C583

Are the jet sizes different?

I think the choke actuator is at different angle

Any data on the OY carb jet sizes would be most useful (I have the info for the MW one)

Cheers

Richard

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Thanks Wally

I have done some further digging and have found a 1940 OY parts list, this calls for Solex 35RZFAI/C559

From the Air Ministry publication AP2222 (Book Number 10I/BD3A) 7th ed 1944 which covers MW,OX&OY. The jet sizes etc are

29mm choke.

185 main jet

165 correction jet

60 slow running jet

200 starter jet

150 slow running jet air bleed

85 pump jet (this is on the 35RZFAIP model, P denotes pump)

Needle valve 2mm

Looking at the 1947 MW parts list,

The carb was changed at engine number 12811

From Solex 35RZFAI/C559 to 35RZFAIP/C581, and the jet sizes changed (the C559 is the same as that in the 1940 OY parts list). [Note the P is for the additional pump]

The main jet changed size from size 165 to 135  (which is different to what the manual states, but 165 is specified for the 35RZFAI/C559)

The naming of the jets also varies, so I am getting a bit confused

A later OY parts list that calls for 35RZFAIP/C583 should clarify things, will see if anyone has one of these

Cheers

Richard

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Hi Richard,

Sorry I cannot offer any more info but I'm watching with interest. I had always thought the MW and OY had the same carb, given they had identical engines.  May I ask the reason for your question?

 

Cheers

 

Jim

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Hi Jim

The engine may be the same for both an MW and OY. The engine performance characteristics required for them are different primarily due to the difference in weight. The performance will also alter depending on the air intake system and exhaust system.

I have it on good authority that the correct MW carb will improve the performance of my MWC (which currently has an OY carb fitted)

The main way of adjusting the performance for a given engine is the carburettor. Carburettor design is complex, there is a Solex publication that goes into the basics of how to size a carburettor (see link to pdf file)

Having done some more research, there is a subtle difference between the OY and MW carbs. The jet sizes are all the same, but the emulsion tube is different (I don’t know what the difference is, but it is different, and hence Solex gave them different part number). Tuning/adjusting the emulsion tube will remove engine "flat spots".

Cheers

Richard

Link to Solex publication http://oacdp.org/pdfs/solex.pdf

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1 hour ago, 64EK26 said:

Hi Jim

The engine may be the same for both an MW and OY. The engine performance characteristics required for them are different primarily due to the difference in weight. The performance will also alter depending on the air intake system and exhaust system.

I have it on good authority that the correct MW carb will improve the performance of my MWC (which currently has an OY carb fitted)

The main way of adjusting the performance for a given engine is the carburettor. Carburettor design is complex, there is a Solex publication that goes into the basics of how to size a carburettor (see link to pdf file)

Having done some more research, there is a subtle difference between the OY and MW carbs. The jet sizes are all the same, but the emulsion tube is different (I don’t know what the difference is, but it is different, and hence Solex gave them different part number). Tuning/adjusting the emulsion tube will remove engine "flat spots".

Cheers

Richard

Link to Solex publication http://oacdp.org/pdfs/solex.pdf

Thanks Richard for your explanation.  You've got me thinking now.

 

Cheers

 

Jim

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