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PETER DIXON
Frequent User
Username: petenlinid

Post Number: 71
Registered: 8-2003
Posted on Tuesday, 07 August, 2012 - 10:18:   Edit PostDelete PostView Post/Check IP

Continuing my investigation into what is to me the mechanical quagmire of the Rolls Royce engine bay I have so far found the following:

1.There are no damper retainers (piston ball race clips) in the suction chambers of the carburettors. I have driven the vehicle for several thousand kilometres and to the best of my limited experience it has always performed well. Does the absence of these items compromise the carburation process?

2.Subsequent to the above I found that one of the automatic choke solenoid wires was disconnected from the automatic choke assembly. I have no idea how long it has been like that but up to finding it the car always appeared to start properly and run well. I reconnected the wire.

On initial tests the car starts OK but the engine revs higher and it seems to take longer before it reduces. For the most part rev reduction in the past was brought about once the engine had warmed a little by tapping the accelerator. I don't think I have actually ever waited for a long enough period to see if the choke would regulate itself.

I drove the car in this condition for about 90 kilometres and it went fine. I ‘think’ but am far from certain it may have been running rich. This could be pure imagination as there were no visual indications and I am relying on the only exhaust gas analyser I have at this time, my nose.

All advice and comments will as always be greatly appreciated.

Peter.
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Jeff Young
Frequent User
Username: jeyjey

Post Number: 87
Registered: 10-2010
Posted on Tuesday, 07 August, 2012 - 19:39:   Edit PostDelete PostView Post/Check IP

Hi Peter,

I've been led to believe the damper retainers don't actually do much. Mine aren't seated either.

The choke solenoid only comes on when the ambient temp is quite cold (around freezing or below, I think). It's purpose is to augment the "normal" choke, whose bi-metal spring isn't strong enough to counteract the manifold vacuum when it's really cold. Under normal starting, though, the bi-metal spring does all the work (and the solenoid is inactive).

The "fast idle" is a mechanical setting on the throttle linkage and cam, and is different from the automatic choke. If you set the fast idle (by pressing the accelerator before starting the car), then you always need to poke the accelerator to go back to "slow idle".

If you're smelling a bit of petrol, my money would be that the o-rings between the fuel filters and carb bodies are compressed and leaking a bit of fuel down the side of the carb body, rather than that it's running rich.

Cheers,
Jeff.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 375
Registered: 1-2008
Posted on Tuesday, 07 August, 2012 - 19:59:   Edit PostDelete PostView Post/Check IP

I've noted on occasion that either or both dampers can drop off without seriously affecting the engine's running. Fortunately it's just a matter of pushing them back in again. In any case they are only there to slow the response of the pistons should you slam your foot down hard on the loud pedal. That's not the kind of driving I bought my Shadow for - I've got a sporty little 2+2 cabriolet for that! Have you checked that the float chamber(s) isn't/aren't leaking from the top(s)? The A bank one on my Shadow does until the engine starts and then stops as the pressure/level drops in the chamber.

The solenoid is Crewe's usual 'belt & braces' method of doing the same thing twice, but in different ways. In practice it may be a little faster than waiting for the heat to wander up from the exhaust manifold. Is the heat retaining lagging still in situ and in decent condition? If not it can be replaced by glass roving as the original asbestos is now a banned substance.

90 klicks isn't much of a test, so what kind of fuel consumption are you seeing over longer distances? The type of driving conditions can make a big difference - urban, city centre, extra urban, motorway, etc. at best you are highly unlikely to see better than 14mpg (20 litres/100 klicks) while ... spirited ... driving at the 'traffic lights Grand Prix' could bring that down to sub 9 mpg (31.5 litres/100 klicks).

Even when The Old girl has been running quite rich according to my electronic exhaust gas analyzer there has been little in the way of petrol fumes detectable to my biological one. Considering how much of this rapidly depleting resource can be lost through poor tuning it could be false economy for you to not have a decent analyzer. One could repay the outlay in quite a short time.
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PETER DIXON
Frequent User
Username: petenlinid

Post Number: 72
Registered: 8-2003
Posted on Saturday, 11 August, 2012 - 17:05:   Edit PostDelete PostView Post/Check IP

Thanks for the responses.

Jeff,
The smell I was referring to was only that of exhaust fumes. There are no fuel leaks anywhere. Like I said, probably just imagination. The car once warmed up and going runs really.

The dampers are missing altogether. I expect that they are not difficult to acquire. I shall attempt to do so and replace them.

Jan,
The only lagging I can see that is associated with the carburettor/choke pipes is the same as that shown in Chapter U-U51 Fig.U26 of the Workshop Manual. It is in excellent condition. Is it that to which you were referring?

Ninety klicks is a fairly big run for me these days. In the last six years she has averaged just a few kilometres a fortnight to keep things ticking over. Prior to that I did three 1200 kilometre runs to have work carried out by Bob Chapman in Melbourne. I was not at all concerned about the fuel consumption at that time. I recently retired and now have the desire and time to rectify (within my limited abilities) those years of comparative vehicular neglect. Fortunately the engine has only done about 40,000 kilometres since a complete rebuild by Chellingworth Rolls Royce. It should last for a while yet.

I would love an exhaust gas analyser and have been looking to see what would be available for a DIY mechanic. All I have found are units suited to workshops starting at around $5,000 (which my wife who does not understand the importance of such matters says I definitely can’t afford) and some hand held units advertised on eBay costing $250. They do not instil me with confidence. Has anyone out there used similar equipment?

On the subject of the carburettor and choke system I have read the Workshop Manual, all I could find in this and other forums, T1 Topics, and Crewed Jottings. Unfortunately enhancement of my initial comprehension of the matter remains limited. One thing is for sure I will be popping up on this forum on a fairly regular basis in the future.

Cheers
Peter