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Run on / pre ignition.

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Oh my!   Any tips please I have adjusted and re adjusted timing and mixture. Still my TR4 is running on / getting hot. I use a strobe light and have tried leaning the carburettors but nothing helps. I'm running an unleaded head, SU carburettors and Accuspark eletronic conversion in the distributor. Can anyone help please?    Mike

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When is it getting hot Mike - during normal running ?  Have you an electric fan fitted ? If so does the car always run-on or only when the fan is running ? 

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Thanks for your comments.

Honestly, my very old and very basic strobe light (no angle setting), relies on my measurement / mark approximately 8mm before the pointer against the timing mark on the pulley. Any advice on that would be gratefully received. This gives me smooth running, no jerking at high torque at low revs and the car pulls well.

I have an electronic fan and it cuts in on a short run, cool evening and that is when the run on is worse.

I have had a pretty recent engine rebuild so I don't think coking is an issue but I'm a pretty inexperienced home mechanic / enthusiast.

Btw, I think I have over-leaned the carburettors ???


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"Leaning the carburettors" would make it run hotter, not cooler.   Rob may be on to the cause with the electric fan actualy keeping the engine running due to it acting as a generator - depends how it is wired in.  Is the radiator blocked ?


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Hi Mike,

a lot of car and engine producers solved that with a „petrol to the idle jet stop valve“ or with a „air to the idle jet stop valve“.

The earliest I know is the VW beetle from the 50-ies.

Sadly SU and Strombergs have no idle jet, but Mercedes Benz and Volvo solved that on the Stromberg 175 CD with a petrol off valve direct in front of the main jet in the 70-ies to 90-ies.

I use 2 of them on my SUs and switch the petrol of to stop the engine while the ignition is on.

This works lovely, I reported.

Ciao, Marco 

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14 hours ago, Hamish said:

Go for premium fuel.  Helped my previous engine. 

Yes, 97 octane or above in my mildly tuned 4A or else it will sometimes run on.

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