New member with high idle engine when hot

[yankystag]

Hello Stag owners on the forum,

This is my first posting after having followed quite some topics thanks to your dedication tothe the wonderfull Stag.

I imported a '73 automatic from the US to Holland this year and since a few weeks I have it on the road enjoying it all. However there is one thing that could not be solved by me or others. Engine idle rpm when cold is normal, however after the engine gets up to normal running temps the idle rpm rises to aprox 2000! You can imagine that my automatic does not like that.

Does anyone have an answer to this problem?

Thanks in advance,

Hans

[V Mad]

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Check if your carburettors have a bypass valve in the throttle 'butterflies'. The valve is held closed by a spring, which can become weak and opens up at idle allowing the engine to rev up, . The easy answer is to solder the valves closed.

[NickA]

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V Mad wrote:

Check if your carburettors have a bypass valve in the throttle 'butterflies'. The valve is held closed by a spring, which can become weak and opens up at idle allowing the engine to rev up, . The easy answer is to solder the valves closed.

Get's my vote as well. I had a TR7 that could rev to 5000 rpm with my foot of the throttle. Quite scary. Rather than solder the valve shut I just replaced them with plain disks.

(I think they were fitted for emission purposes?)

[milothedog]

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If I remember correctly I believe they are fitted to prevent popping back (Like you get on an MGB) under engine braking.

Ian.

[StagnJag]

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milothedog wrote:

If I remember correctly I believe they are fitted to prevent popping back (Like you get on an MGB) under engine braking.

Ian.

If they are, they don't work!!!! (Well not on my Stag anyway!).

[milothedog]

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Or there K***erd on yours Thinking about it When I last balanced my carb's I don't recall seeing any fitted!

Ian.

[TimShoubridge]

imported post

yankystag wrote:

Hello Stag owners on the forum,

This is my first posting after having followed quite some topics thanks to your dedication tothe the wonderfull Stag.

I imported a '73 automatic from the US to Holland this year and since a few weeks I have it on the road enjoying it all. However there is one thing that could not be solved by me or others. Engine idle rpm when cold is normal, however after the engine gets up to normal running temps the idle rpm rises to aprox 2000! You can imagine that my automatic does not like that.

Does anyone have an answer to this problem?

Thanks in advance,

Hans

Hi Hans,

I have no idea but welcome. I work in Almere so if you are in the area sometime let me know and would be happy to meet for a beer.

Tim

[Stag Andy]

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I have a similar problem,my idle when cold or pottering around town is 750,after a good thrash down the motorway my idle will be about 1200,i have plain throttle butterflies and i have tested for an air leak,im a bit stumped....i fix stags for a living and have never had this problem with any customers car. Any ideas guys?????
Its not a sticky throttle either,it does it with the carb linkages disconnected also so not incorrectly adjusted throttles,i can turn the idle screws all the way out with the linkage off and it makes no difference

[yankystag]

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Hi Tim,

Good plan, I'll slip you my email as well.

[yankystag]

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Thanks for all reactions so far, I will check if there is a bypass valve installed, however it probably also has to do with rising engine or ambient temperatures.

At the moment the alternator has to be changed so enough work to do.

Enjoy the heat!

Hans

[Guest]

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TimShoubridge wrote:

yankystag wrote:

Hello Stag owners on the forum,

This is my first posting after having followed quite some topics thanks to your dedication tothe the wonderfull Stag.

I imported a '73 automatic from the US to Holland this year and since a few weeks I have it on the road enjoying it all. However there is one thing that could not be solved by me or others. Engine idle rpm when cold is normal, however after the engine gets up to normal running temps the idle rpm rises to aprox 2000! You can imagine that my automatic does not like that.

Does anyone have an answer to this problem?

Thanks in advance,

Hans

Hi Hans,

I have no idea but welcome. I work in Almere so if you are in the area sometime let me know and would be happy to meet for a beer.

Tim

Sorry to hijack the thread. Tim, just out of interest where do you work in Almere? I commissioned 12 x DRUPS for KPM, Black Box Almere nearly 2 years ago! Stayed in a nice little town called Hilversum, lots of pubs

Jason

[TimShoubridge]

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Hi Jason,

my offices are right by Almere railway station. Hilversum is cool, as are many small towns around. I stay in the centre of Amsterdam which is not so nice.

Tim

[Arbman Al]

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TimShoubridge wrote:

Hi Jason,

my offices are right by Almere railway station. Hilversum is cool, as are many small towns around. I stay in the centre of Amsterdam which is not so nice.

Tim

Seemed alright last time I was In Amsterdam

[444John]

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TimShoubridge wrote:

Hi Jason,

my offices are right by Almere railway station. Hilversum is cool, as are many small towns around. I stay in the centre of Amsterdam which is not so nice.

Tim

We've just finished drilling a couple of geothermal wells in Sonderborg, Denmark and the rig we used is now going to be drilling in the centre of The Hague. Maybe you will have seen it already Tim? Can see a lot of grief with a rig crew in middle of Amsterdam.

[V Mad]

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Stag Andy wrote:

I have a similar problem,my idle when cold or pottering around town is 750,after a good thrash down the motorway my idle will be about 1200,i have plain throttle butterflies and i have tested for an air leak,im a bit stumped....i fix stags for a living and have never had this problem with any customers car. Any ideas guys?????
Its not a sticky throttle either,it does it with the carb linkages disconnected also so not incorrectly adjusted throttles,i can turn the idle screws all the way out with the linkage off and it makes no difference

I can't see howan engine can rev if there is no source of air ie if you shut off all the possible sources of air the engine will cut out. So there surely must be an air leak somewhere.

One possible answer is that you may have a rich mixture, andexcess air is somehow getting through the breather system (the two tubes connectingthe Strombergs to the valve cover).When the engine is cold the excess air makes the mixture too weak for a fast idle, but when hot it provides the ideal mixture and so revs too high.

Whe you get the fast idle speed, did you try blocking off the carb breathers?