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Cooper Mainstream Running Lean


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#1 beardylondon

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Posted 21 July 2020 - 08:58 AM

Over lockdown I refurbed my head, did valve stem oil seals (which stopped it smoking), ground the valves back in, put it all back together. After some advice on here, as I wanted to keep it as original (and quiet) as poss, I kept the cast Cooper manifold, and used a Maniflow down pipe to connect to twinbox RC40. I kept the standard air filter and haven't touch the needle. Tappets are set to 12 thou.  It has brand new plugs (the correct BPR6ES ones from Minispares) and I set the timing and it runs a bit lean.

 

Could it be worth changing the needle?


Edited by beardylondon, 21 July 2020 - 09:02 AM.


#2 cal844

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Posted 21 July 2020 - 09:03 AM

You may need to, What do the plugs look like? You may find the plugs look OK but in my experience minis like to run a little rich to be happy

#3 beardylondon

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Posted 21 July 2020 - 09:45 AM

Thanks, plugs look like this

 

plugs.png



#4 jaysmini1983

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Posted 21 July 2020 - 11:19 AM

i would say its a nice golden colour, maybe a touch lean, just adjust the needle slighlty, 1/4 turn richer and take for a test run.



#5 cal844

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Posted 21 July 2020 - 02:26 PM

Yup they need to be richer. Is the dashpot oil topped up?

#6 beardylondon

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Posted 21 July 2020 - 07:59 PM

I thought the carb screw only adjusted idle, not mixture. Yeah I’m pretty sure I topped dash pot up, will double check.

#7 cal844

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Posted 21 July 2020 - 08:25 PM

Mixture is adjusted overall, regulated by the needle. Give it a quarter turn (or 2 flats if on a HS carb) rich and try it first. If that doesn't work you need a richer needle (back off the mixture to where it is now).

Edited by cal844, 21 July 2020 - 08:26 PM.


#8 Dusky

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Posted 21 July 2020 - 08:38 PM

That looks almost perfect with ethanol fuel. The golden brown color is only favorable with non ethanol fuel.




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