Choke Adjustment

Benson, NC

#1 Dec 14, 2012
Can anyone tell me how to adjust the choke on a 78 Shadow II? Simple the better. I am a relatively new
RR owner. In cold weather, I have to restart the car several times in the mornings before the choke will come on. When it does engage, it runs slow and rough for several minutes before it will begin to have the fast idle. Once warmed up, a tap on the accelerator will cause the engine to come back to normal perfect idle.


Jan Forrest

Rotherham, UK

#2 Dec 15, 2012
The choke on a Shadow isn't completely automatic. You are supposed to floor the loud pedal and release it before starting the car in any weather conditions. This sets the 'choke flap' in the air inlet trunking to a closed position (on).

Benson, NC

#3 Dec 15, 2012
Understand pressing the pedal before starting (as this is what I do)and I hear the closing of the choke. Why do I have to restart the car several times before it will start on a cold morning. When it does start, it will run rough for several minutes, then fast like it should? After pressing the pedal, it returns to a smooth perfect idle.
Jan Forrest

Rotherham, UK

#5 Dec 22, 2012
I know I responded to this question several days ago and I could see it before I went away for a couple of days, but now it's disappeared.

So, let's try again.

The first thing to do is to check that the choke flap is actually closing fully - or at least as fully as it's supposed to. There should be just a hint of a gap to permit enough air through for the engine to start of course. Loosen the large Jubilee clip holding the air trunking to the mouth of the central air horn and then remove the trunking. You will now be able to see the flap position. If that's good then you will have to look elsewhere for the cause. If it isn't then there's a turnbuckle adjuster on the right hand side which makes it close more or less depending on which way it's turned. It has a tiny BA sized locknut at each end which have to be loosened before it can adjusted. Only try this if the hoke flap isn't fully closing as it's all too easy to mess up the setting.

Check that the long air trunking is in good condition especially on the underside where it's exposed to the heat of the engine. That's where mine went! It can perish after 30 odd years allowing too much air into the inlet manifold and weakening the mixture too much. A good used trunking can cost well over £100 (?US$160+?)from a breaker's, but an upgraded version can be obtained for a fraction of that price from Demon Tweeks in the UK and I would expect that there will be an equivalent outlet in the US.

Alternatively the air filter in the front wing could be missing (same effect) or blocked which would richen the mixture and cause poor starting and running. After that it's a matter of checking all the little things:
Distributor(s)- some cars have 2
Spark plugs and plug wires
Ignition timing
Condition and placement of the various little hoses that plumb into the inlet manifold for a bit of negative pressure

As a Shadow owner you really should get hold of a copy of "The Shadow Owner's Companion" by Jon J. Waples. It's written for the average Rolls owner who likes to do some of the necessary maintenance on his car. You could also download a copy of the official Shadow workshop manual from here
It's written for the well stocked workshop and often refers to rare and expensive special tools, but it does go into far more detail that the companion. As I write this the site appears to be down - possibly for maintenance - so it shoulod be back up again in the not too distant future.

That is about it for now, but don't be shy in coming back if none of the above sorts out the problem.
Jan Forrest

Rotherham, UK

#6 Dec 22, 2012
The site is back up again and this is the direct link to the manual's chapters
They're in PDF format so you will need a PDF reader. There's a free one available here


Tell me when this thread is updated:

Subscribe Now Add to my Tracker

Add your comments below

Characters left: 4000

Please note by submitting this form you acknowledge that you have read the Terms of Service and the comment you are posting is in compliance with such terms. Be polite. Inappropriate posts may be removed by the moderator. Send us your feedback.

Rolls-Royce Discussions

Title Updated Last By Comments
1973 silver shadow 1 (Jan '13) 7 hr eddy g 10
SU carbs Aug 28 Futility2006 1
brake pressure 1 failure in a rolls royce silve... Aug 26 NEWORL 1
1976 silver shadow II (Jul '10) Aug 25 Futility2006 18
rolls royce silver shadow (Feb '07) Aug 3 Matt 69
Poll hlm oil leak spirit 95 Jul '16 Bob 1
Rolls Royce silver shadow ll transmission will ... (Apr '14) Jul '16 carole 26
More from around the web