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TR4 just rebuilt motor have tweequed it just a little (as You do).

goes great but wont stop

have tried a moss anti run on valve but that hasent fixed the problem so looking for a bigger anti valve or is there something we are overlookig

Love driving this car but she is doing our head in

Many thanks

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Newly rebuilt!..so it's not excess carbon build up.

I take it you mean 'dieseling'?

1). Check the butterflies are closed right down, AND balanced, and the idle speed is correct.

2). Check the timing.

3). Spark plug grade.

4). Try a higher octane fuel, like Shell V power, or BP ultimate.

5). An excessively weak mixture will cause the engine to run a lot hotter than normal (combustion temp.) so check mixture setting.

Spark plug colour is a good indication, look for the tip to be a nice brown colour and not white!

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Hi Binkie,

your name has just brought back wonderful memories of 'Around the Horn' etc.

 

The anti-run on valve should supply neat air to weaken any mixture that may be getting through. It clearly doesn't work - throw it away.

 

The simple fix is to leave in gear when turning off the ignition and let out the clutch.

 

The complex cure is er... complicated.

 

Is the valve timing correct - not always easy to set up.

 

 

Roger

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It's slow speed autoignition. Slides 84, 120, 121;

https://supertrarged.files.wordpress.com/2016/07/combustion-talk-iwe-2016-v2-ppt.ppt

The two most likely sources of heat are the exhaust valve, especially if the seating has been thinned from standard,

and the spark plugs. Try a couple of grades colder plugs. If that fails than higher octane fuel and/or Rogers footwork are the only simple cures.

( Waterless coolant would also not help.)

Peter

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Peter rightfully mentions Waterless coolant.

I had the same running on problem until I ditched the waterless coolant, then all was fine.

Just out of interest my cylinder head temperature was 30c less running with water antifreeze than running with waterless coolant.

I guess just enough to stop pre ignition.

 

Steve.

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Mine runs on when hot too. I use Roger's method, it's cheap! (Just as long as you have your foot on the brake as well otherwise you are in danger of shunting forward into someone's prized possession!!)

 

When I first got the car the PO (- yes he of the interesting exhaust clamping system!) told me it was because the engine had a high compression ratio (10:1) he was also running it on BP7 plugs. I have switched to BP6 but it still does it.

 

At a recent TRR Wessex meeting I was told that blipping the throttle just as you switch off the ignition was a remedy - but I must be doing it wrong (hand to foot co-ordination obviously not my strong point!!) as it doesn't always work. I can't remember the theory now - I think it was that it fills the float chambers and the floats cut off the fuel supply more quickly (someone more knowledgeable will explain properly!)

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" At a recent TRR Wessex meeting I was told that blipping the throttle just as you switch off the ignition was a remedy - but I must be doing it wrong (hand to foot co-ordination obviously not my strong point!!) as it doesn't always work. "

 

 

Nope, it just puts a plug of neat fuel through the inlet manifold and deposits it onto the upper cylinder walls where it washes the oil off causing excess wear, stick with the stalling the engine.

 

Mick Richards

Edited by Motorsport Mickey
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Peter rightfully mentions Waterless coolant.

I had the same running on problem until I ditched the waterless coolant, then all was fine.

Just out of interest my cylinder head temperature was 30c less running with water antifreeze than running with waterless coolant.

I guess just enough to stop pre ignition.

 

Steve.

Steve,

That fits. A high octane fuel that will kill running-on will have an autoignition temperature only 50deg C higher than a normal octane fuel. The same small temperature shift you have measured.

Peter.

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Mine runs on when hot too. I use Roger's method, it's cheap! (Just as long as you have your foot on the brake as well otherwise you are in danger of shunting forward into someone's prized possession!!)

 

When I first got the car the PO (- yes he of the interesting exhaust clamping system!) told me it was because the engine had a high compression ratio (10:1) he was also running it on BP7 plugs. I have switched to BP6 but it still does it.

 

At a recent TRR Wessex meeting I was told that blipping the throttle just as you switch off the ignition was a remedy - but I must be doing it wrong (hand to foot co-ordination obviously not my strong point!!) as it doesn't always work. I can't remember the theory now - I think it was that it fills the float chambers and the floats cut off the fuel supply more quickly (someone more knowledgeable will explain properly!)

Ben, Try yet colder plugs. As long as they dont foul up there's no harm in going colder. Triumph would specify the hottest running plugs they could get away with to ensure that tired engines in daily drivers did not misfire from oiled plugs and tired sparks from neglected igntion got the best help from the hottest plugs.

A heat shield to reflect exhaust heat off the intake manifold might help, as might cold air directed at the filters. Auto-ignition is quite a subtle chemical event and the temperature drop needed to kill it is not great.

Blipping the throttle can work as the mixture is then set very rich by the SU damper action and the evaporative cooling from the extra fuel can drop the mixture temperature. Difficult to say how much, but a normal mixture would cool the air by about 18deg C ( if the fuel evaporated in the air flow, not off the walls of the manifold).

Peter

Edited by Peter Cobbold
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I'm pretty sure that BP6 is hotter than BP7. Checked. Yes it is.

Yes:

http://www.totallyamaha.com/snowmobiles/aaTECH/sparkplug/Spark%20Plug%20Information%20%20Overview.htm

Peter

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At the IWE Matt spent a long time adjusting everything, but said he couldn't get it 100% perfect because of various improvements?? The engine builder had made.

 

It is now 99.5% perfect and just very very occasionally runs on slightly for no apparent reason.

 

I would recommend a good tune up by someone who really knows these engines

 

Cheers

 

Nigel

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Hi Folks,

because of this thread my engine is running on.

Interestingly when I engage gear and kill the ignition and lift the clutch (without the brakes on) the car lurches backwards.

This suggests that the crank had stopped and then rotated the other way.

 

Has anybody noticed this before?

 

Roger

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Hi Folks,

because of this thread my engine is running on.

Interestingly when I engage gear and kill the ignition and lift the clutch (without the brakes on) the car lurches backwards.

This suggests that the crank had stopped and then rotated the other way.

 

Has anybody noticed this before?

 

Roger

 

Hi Roger,

 

I have mentioned this before on the forum, my engine usually runs backwards, although not always.

 

I have tried many things and the only cure as mentioned above is webers. The TR4A that I owned back in the early seventies was exactly the same even on 5 star fuel. As the problem goes away with the webers, I am convinced the problem lies with the SUs, but don't know why?

 

Cheers

 

Graeme

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Several thoughts.

1 A lot of SUs are set up with the fuel level a mm or so from the jet surface. It can be lowered to say 10mm without making detectable difference to normal operation. But the jet might then resist delivering fuel into the tiny depression in an dying engine with closed butterflies.

 

2Anything that helps liquid fuel pool in the manifold might also supply enough mixture to auitoignite, eg a protruding gasket at SU/manifold join.

 

3The coolant-heated manifold might raise the mixture temperature enough to cause running on, it only needs to be a few tens of degreesC warmer.

 

4 Polishing intake manifolds is a trick for reflecting exhaust manifold radiant heat, but an ali reflector sheet is easier.

 

5 As well as using colder grade plugs, ensuring a good heat conduction path is important:

http://www.stealth316.com/images/spt-heatinout.jpg

Two thirds of the heat is removed through the thread and washer, so I use coppaslip on the thread to try to aid plug heat dissipation.( I would not use coppaslip on alloy heads)

I am not sure of the protrusion of TR4 plugs, ie the length of casing/thread exposed in the combustion chamber. But that does pick up a lot of heat so changing to a less protruding plug design might help kill running on.

 

If high octane fuel kills running on you are definitely got an autoignition issue, and are only looking to lower the mixture temperature at the site of autoignition by at most 50deg C.

 

Peter

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Hi Folks,

because of this thread my engine is running on.

Interestingly when I engage gear and kill the ignition and lift the clutch (without the brakes on) the car lurches backwards.

This suggests that the crank had stopped and then rotated the other way.

 

Has anybody noticed this before?

 

Roger

Roger, Its quite possible. Engaging the drive train slows the crank and the autoignited combustion then has time to build pressure well before TDC. Autoignition is a chemical reaction that requires a lot of time to get going. If I had the RO problem I'd be playing with different plug grades, less plug protrusion, and chopping off the earth strap tip, as the plug is the most likely source of the required temperature of the ignition source.

cheers, Peter

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Mine might run on a little if using anything but Shell V-Power. Using Shell cures it!

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We had a 4a in a while ago that all sorts of people had tried to cure its run on including fitting heat shields and a dump valve. Careful setting of the carbs (Float levels/needles/springs/damper oil level) correct setting of the distributor and the A/R capsule connection and bob weights freeing up and the right springs for them, proper routing of fuel lines and correct plugs stopped it completely. Often its a combination of all of that that will make them run on like a damn. Totally agree that fitment of Webers/Dellortos never have that problem at all.

Stuart.

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Just to add to Stuart's contribution, if you have the wrong springs fitted (too light) that will adversely affect run on and can also give a jerky ride in light throttle openings.

Edited by peejay4A
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