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Morning Chaps

My TR4A's engine runs on after the ignition is switched off -- 

The carbs were completely refurbished 3000 Miles ago. It has Lumitron electronic ignition, new plugs, pretty much tried everything bar removing the head and de-coking. My classic car specialist (complete faith in his ability) has suggested a valve between the head and the carbs to flood the head with air on switch off as a fix ... I'm inclined to agree with him as having just spent a great deal on the clutch and gearbox I'm pretty much tapped out and don't want the expense of taking off the head etc.

Anybody done anything similar? Any other suggestions as to what could be the problem. To my mind it has to be either fuel or ignition ...

Open to anything.

Steve

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Tried the air valve trick, and about every other one. No joy. Probably due to my Burgess head mods. I now use IanC’s suggested solution. Foot brake hard down, 3rd gear, drag the clutch ever so slightly and switch off. 

Edited by peejay4A
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21 minutes ago, stuart said:

Recheck your ignition timing properly and float levels and then give it an Italian service.

Stuart.

+1. I'd add check your valve clearances in case a hot exhaust valve isn't closing properly. What plugs are you using?

Pete

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I fitted an anti-run-on valve many years ago and I use top notch fuel, but I still get run-on and have done for years.  The valve sits above and feeds straight into the inlet manifold's balance pipe.

I pull the handbrake on hard (or press hard on the footbrake), select first gear then gently lift my left foot to slow the engine slightly as I turn the ignition OFF.  Engine still wants to run on, but this regime quells it very rapidly.

As the car runs very well, I cannot be bothered to investigate further - and I certainly would NOT remove the cylinder head!

There are some things one just has to live with!

Ian Cornish

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Many years ago, I had the same problem with a TR4A. The pcv valve seemed to be the culprit. I remove it and reverted to the road draft tube of the earlier TRs. This, along with keeping the idle speed low, solved the issue. You might try temporarily plugging the pcv plumbing to see if this is the cause of your problem.

Berry

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Hello Steve

I had this problem with my 4A for a while. Tried everything you have. Solution was to fit NGK BP7HS fast road plugs that run cooler than the standard BP6HS. Plug gap is 0.025inch. A cooler plug is less likely to cause run on after switching off the engine.

Keith

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The TR makers missed (another time) the point when they had to change to a modern construction like other producers did:

have a idle jet in the carbs and switch off the flow of air or the flow of petrol to the idle jet when switching off the ignition. 

That's all...

marco-z-blick-auf-die-vergaser-und-abschaltventile-von-unten.jpg?w=1000&h=

 

 

Edited by Z320
my bad english writing + photo added
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Keith - I've been running BP7HS, gapped 32 thou, since 1993.

However, with a modified engine, I accept that "there are some things one just has to live with" (as I said before). 

It's difficult to set the tick-over much lower than 750-800 because the engine will tend to stall when the electric fan kicks in or if the alternator is having to power more than just the ignition.

Ian Cornish

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Pierburg "idle switch off valve", they close when I switch 12 Volts on them by a push botton under the dash board.

Mercedes Benz used them with Strombergs 175 CDT carbs on their M102 engine. I slightly modified them with DIY valve housings.

That works lovely since 4 or 5 years.

marco-z-stromberg-175-cdt-skizze.jpg?w=7

Edited by Z320
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My TR4 started running on afew years ago. After trying all the usual things - timing, plugs etc I changed to using higher octane fuel such as BP Super or the Shell equivalent or Tesco Momentum. Since then ( several years ago) it's never run on - not even once!

Cheers,

JeffR

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  • 3 weeks later...

Thanks to all of you  .... I've just got the car back after a refurbed clutch, renewed gearbox and a valve to control the air flow when the engine is switched off, if I let the car idle for 30 seconds after a hot tub this seems to have done the trick, however I used higher octane fuel which seems to have helped. Thanks for all your comments, I will report back when I've done a few more miles.

Steve Young 

PS pic is driving around the M25 last year. 

tr2.jpg

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