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Quoted from Steve P
95 octane is for mowers.

and cars with more modern fuelling systems 🙂

But seriously, the 2L 6 is prone to running on and fuel quality is one of the factors.  Back when I still had carbs I usually had to stick it in 4th and lift the clutch to remind it I'd turned it off.  LRP (remember that!) was especially bad for it.

Other factors,
- timing may have an effect but the setting that gives least run-on may not be where it runs best otherwise.
- idle speed, set it is low as you can compatible with smooth running without stall risk - should be able to get down to 6 - 700 rpm.
- plug type/heat range
- letting it idle briefly to allow the combustion chamber to cool a little before switching off.

There is also a little trick which involves putting it in 4th gear and lifting the clutch just as you switch off.  With a bit of practice you can get it to stop without a jolt.


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Filled the car up with standard BP unleaded with Castrol valve master added when I picked the car up today! its a very low mileage original with 34,000 on the clock!, previous owner said he was running std 95 with castrol valve master this is how he was running the car and it never over ran and prior to him changing the coil (lucas gold sports coil)  cap points etc that it ran fine, so he thought the over run was down to timing being out a bit?, probably got room for 4-5 litres of super unleaded to boost octane in the tank, would an octane booster additive help?

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Back in the day, these cars ran on 5 Star fuel, during the fuel crisis of the early '70s people were running then on anything, 2 Star, lawnmower fuel and whatever, but you need to retard the ignition timing to prevent pinking and running on on anything but 98RON.


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Tetraboost. Actually contains lead, not lead substitute. Noxious stuff, but can be used as an octane booster too. Can make 100+ octane if needs be. Also helps prevent that nasty ethanol crap from absorbing water into the fuel. My mate runs it in his vintage / Edwardian stuff and it's the only thing that seems to actually work. I'll be using it in my 2000 when it's back together.

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I only use Shell V-Power also as it is 99 octane rating. The Triumph seems to like it, but I've never run her on standard unleaded. She still has her original head etc, no conversion.

There is a night and day difference between using V Power and standard in my Saab. Put standard in and it's a fast car but put V Power in and it goes like it's jet powered!

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