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A mate followed me from a pub classic car meeting last night in his Urraco.  

it was a little wet and only the 2 of us there in classics but still great fun even  with aero screen. 

he followed me home in a spirited drive and suggested that I had flames from my exhaust !!

his text said 

flames from your exhaust ....how rude !!!

running rich I presume with a crackle on the over run. 

Should I be worried.

its a large bore stainless single box exhaust.

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Flames in exhaust are caused when suddenly throttle is released in combination with a very low pre-ignition value 0° or even negativ value...

the sudden release of the throttle makes the engine run rich, un-burnt fuel explodes in the exhaust, and not in the combustion chamber.

....the sound may be cool but your spark plugs don't like it.

You may not be able to compensate for running rich, which actually is normal, but you may want to check your ignition in combination with MAP pressure.

Jochem

 

 

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Jochem

it was happening down our Cheshire lanes so very much an on off throttle style. 

So it would make sense that it may appear under those conditions but after all my  fuelling issues it was great that it felt like it was working again. 

I’ll check my running timing again. 

Thanks

H

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If the flame was steady and not the flash of a backfire I'd check the timing, could be too retarded. If timing is OK running very lean can cause sustained exhaust flame.

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Rich was demonstrating at the Alma's last meeting how the stainless down pipes on his TR4 glowed cherry-red-hot.  Might the combination of on/off spurts of unburnt fuel in the exhaust and glowing red hot pipes not result in such flame bursts, without any timing issue or air leaks ..which I would have thought Hamish would otherwise have noticed in the car's starting and performance ? 

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A cam with really wild overlap will do that if the engine is run at road rpm. Unburned mixture enters the exhaust during the overlap period. At race rpm the overlap is too brief to allow that.

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44 minutes ago, Peter Cobbold said:

A cam with really wild overlap will do that if the engine is run at road rpm. 

No need for wild cam. It can be done with standard cam. As I mentioned before, it is all in the timing. Retard too much will do this. 

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Chatted to my mate who followed me and it was very sporadic and he thought at times of sudden wide open throttle snap closure. And it was as the light was fading in the evening. 

No wild cams or such changes. 

Not overly worried about as it’s better than the fuelling misfire I did have !!!!

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15 minutes ago, stillp said:

Is that misfire sorted now Hamish?

I hope so - fingers crossed and any other technical talismans and the gods of classic car fault finding I can put that one behind me

after blowing through the fuel line I had a couple of fast competition runs at aintree 

I have since substituted the old  rubber joining pipe with modern fuel proof pipe and had my spirited drive out on Tuesday evening. 

Perhaps I can try a motorway prolonged run this weekend to see if it manifests itself again. 

It did happen on the motorway at the aintree lunch time test so ......?

 

just a wet  ( leaking ?) oil cooler to sort now <_<

Edited by Hamish
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1 hour ago, Hamish said:

Chatted to my mate who followed me and it was very sporadic and he thought at times of sudden wide open throttle snap closure. And it was as the light was fading in the evening. 

No wild cams or such changes. 

Not overly worried about as it’s better than the fuelling misfire I did have !!!!

If the dashpot oil is too thick it can slow the descent of the SU piston upon sudden butterfly closing and gives an over-rich mixture briefly

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3 minutes ago, Peter Cobbold said:

If the dashpot oil is too thick it can slow the descent of the SU piston upon sudden butterfly closing and gives an over-rich mixture briefly

20:50 engine oil a candidate then ?

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