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John Adams
Yet to post message
Username: john39a

Post Number: 1
Registered: 10-2009
Posted on Monday, 24 May, 2010 - 08:54 pm:   Edit PostDelete PostView Post/Check IP

Hello All,
I have a Silver Shadow SRH17323 - Queensland registered. Has anyone got any suggestions / ideas re the following - I can't slow the hot engine idling speed below approx 900 RPM. Throttles are synchronised and have been confirmed as fully closed. The idling speed adjusting screw has been fully backed off. The choke opens and the cam is completely off the cold idle adjusting screw. There is no tension in any of the throttle linkages. The timing has been checked and confirmed at 5 degrees BTDC. Could float chamber level (although checked also) have something to do with this?? I will welcome any suggestions.

Thanks in anticipation

John Adams
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 596
Registered: 6-2006
Posted on Monday, 24 May, 2010 - 11:19 pm:   Edit PostDelete PostView Post/Check IP

Air leak?

Intake air temp blend flap.
Speed control vac hose?

Have you got small spring loaded valves on the butterflies?

Have you blocked the distributor vac hose? Is the diaphragm Ok?
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Peter Colwell
Frequent User
Username: peter_colwell

Post Number: 92
Registered: 3-2005
Posted on Tuesday, 25 May, 2010 - 05:46 am:   Edit PostDelete PostView Post/Check IP

I had this problem once on a different engine, but one also fitted with twin SUs. The problem was solved when I released the two carbs from one another, ie. allowed both throttles to close on their own. As soon as I released the clamp that ties the linkage together the revs dropped to about 200. I then locked them together again, and gradually raised the idle speed in the normal manner to the proper level.
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Jan Forrest
Prolific User
Username: got_one

Post Number: 138
Registered: 1-2008
Posted on Tuesday, 25 May, 2010 - 05:58 am:   Edit PostDelete PostView Post/Check IP

I recently had a similar problem with The Old Girl (SRH24518). It turned out that the adjuster on the hot idle cam (the one attached to the choke flap) wasn't allowing the A bank carb butterfly to fully close even with the flap in the fully open position.
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John Adams
New User
Username: john39a

Post Number: 2
Registered: 10-2009
Posted on Wednesday, 26 May, 2010 - 09:58 pm:   Edit PostDelete PostView Post/Check IP

Thanks to all for the advice. I will try it all as I have been stumped trying to work this out.

Paul - I'm still doing Silver Shadow maintenance 101 - you mentioned the speed control vacuum hose. Where can I find that - sounds like a dumb question but I don't know.

Thanks again to you all for your ideas. I'll try them and keep you posted.

Kind Regards
John
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Jan Forrest
Prolific User
Username: got_one

Post Number: 140
Registered: 1-2008
Posted on Thursday, 27 May, 2010 - 12:41 am:   Edit PostDelete PostView Post/Check IP

The speed controller (called The 'Speedostat' Cruise Control Mechanism) is located on the right hand side of the engine bay and can be identified as a largeish rubber bellows arangement with a bead chain attaching it to the throttle linkage. To make it work it has a slender rubber tube going to the inlet manifold where it employs the depression to reduce the pressure on one side of a diaphragm, which is open to the atmosphere on the other side, to pull the chain and thus open the throttle wider. A small analogue computer then compares the current speed to the set speed and allows or denies the partial vacuum to continue to operate on the diaphragm.
Obviously a leak in the pipe or any of its joints will allow unregulated air into the manifold and so weakening the fuel mixture which can then alter the idle speed. Occasionally the bellows or the diaphragm can develop a leak with the same results.
Sometimes the chain is removed by someone servicing the car who then doesn't replace it properly so either the cruise control doesn't work at all, or it's put back too tight and so forces the throttle open even when the control is off. The correct adjustment is that the chain must not be taught or have excess slack in it. You have to pull the connecting arm towards the bellows, attach the chain on the last bead and then check that it goes all the way back without having a lot of slack in it. If it does just move the chain one link at a time outwards until it doesn't and still doesn't pull on the bellows then leave it there.

(Message edited by Got_One on 27 May 2010)
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John Adams
New User
Username: john39a

Post Number: 3
Registered: 10-2009
Posted on Thursday, 27 May, 2010 - 08:47 pm:   Edit PostDelete PostView Post/Check IP

Hi Jan,
Thanks for the info re the cruise control - unfortunately though this car doesn't have cruise control. However, have you given me some ideas re air leaks so I am grateful for the input.

Kind Regards
John

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