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20 HP Rolls Royce carb


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For others out there who may not know~~~

Rolls~Royce autos in the 20s-30s had two seperate carburetors~~~

One two stage unit that actually ran the car ~~~


An extra starting carburetor !

This was used instead of a typical cold starting choke.

The inside dash starting carb control turns a long shaft that goes through the firewall & opens a gas-cock style valve on the starting carb base to the engine's intake manifold.

This extra starting carburetor then sprays an additional extra rich gas/air mixture into the intake maniflod.

This starting carb takes the place of a normal butterfly choke for cold engine starting !

It is a much more precise system for getting a much richer mixture for start-up and cold running before the engine comes up to normal operating temp.

To fix your stuck starting carb valve you need to remove the control shaft linkage comming out of your firewall & loosen-up the large nut &, spring at the base of this extra starting carb ;and lightly tap to remove the big manifold/carb tapered gas-cock style valve unit that is part of this starting carburetor. It is located where this extra small carb attaches at it's mounting base to the intake manifold.

Once apart~

Clean the tapered valve and it's seat with very fine steel wool and paint thinner or other solvent; and grease with a very light coat of gas-cock grease.

Heating & AC , plumbing supply houses sell gas-cock grease for this purpose on gas heating systems !

Do not adjust the small jet needle valve on the top of this small carb !

These R~R starting carburetors work very well indeed ! They are much better than a typical simple choke butterfly found on most other carburetors !

As typical of all Rolls~Royce car designs of this era they are very precise and perhapps overly complex.

It's a very simple repair indeed !

Hope this helps ! ?

If not ~~~

Call me after 9:00 PM Eastern US time !

I will talk you through this repair and your Rolls~Royce starting carburetor operation.

I have been around these ultra high quality Full Cassic Rolls~Royce cars for 50+ years !

I own two today~

Good Luck !

Edited by Silverghost (see edit history)
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  • 5 years later...



can an anybody help, I have a 20hp 1928,. The carb appears to be flooding when you try to start it.  It's not the needle  valve in the float chamber, we have replaced all that and checked it all seals off.    When you try to start it petrol runs out the bottom of the carb, taking the carb apart everything is soacked in petrol.   


Could the starting carb not be turning off and causing this?


Any help much appreciated 



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Using the auto vac.  We have checked the auto vac and everything is working as it should there.   


Have checked tge the suction valve is working and not overflowing petrol into the inlet manifold through the suction pipe 

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