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Petrol
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mcafee
Malton North Yorkshire
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September 16, 2020 - 7:46 am
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I have a B175 fitted with a Bones CDI which I set up with the head off and used a dial guage to set the timing accurately and found that it ran beautifully using premium grade fuel.My local garage no longer sell premium grade petrol so I now use standard grade but found that the engine was running a bit rough with signs of pinking.I have retimed the engine by retarding the timing by 2degrees  and find that the engine runs as it used to,has anyone had similar problems?

David

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Peterg
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September 16, 2020 - 11:43 am
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I had the opposite. My Gold Star ran fine on regular and then when I took it abroad, where preminum is much cheaper, found it didn't run so well

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SpacedMarine
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September 16, 2020 - 11:10 pm
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Was thinking quite a bit about this recently.Unleaded e5 has 5% ethanol.I have a brand new amal on my d14.The book says pilot screw should be 1 3/4 turns out and timing should be 16.5 degrees.

My timing has been set with a dial indicator so should be bang on and yes it pinks slightly.To get the mixture right it needs roughly half a turn on the pilot screw.

Take into consideration that ethanol stochiometry is roughly 8;1 and petrol is 14:1 and the fact that it burns 50% faster would explain needing a slightly richer mixture and slightly less timing.

I worked it out that if the book was correct for standard petrol a back of the fag packet calculation for e5 was about 16 degrees and a slightly larger pilot jet.

What's 7/16 in mm again?

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SpacedMarine
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September 17, 2020 - 11:58 am
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Its actually 9:1 afr for ethanol sorry I'm also guessing the lack of lead in the fuel means timing cant be as advanced  also

What's 7/16 in mm again?

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Sponge
Lancashire (A chip shop somewhere near Preston)
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September 17, 2020 - 2:01 pm
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This bears out what I am finding with all my BSAs - Although I can get 97 octane from ESSO the bikes run better (ccoler and smoother) with a larger pilot jet, slightly larger main jet and about 3-4 degrees retarded.  This even holds true for the A10. 

When I pull the spark plugs they read OK with these settings whereas with stock settings they were showing signs of overheating.   

I wish I understood the science behind this but the arguments above seem pretty conclusive. Well done Spacebootneck once more for working it out. 

Sponge 

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SpacedMarine
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September 17, 2020 - 2:52 pm
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Ta sponge.Whether my maths is correct or not I just figured it out as a rough percentage.

As regards running cooler that would make sense with a richer mixture and shorter burn time.Lots of the turbo car brigade in the US and Aus run e85 ethanol as they can use higher boost and the engines run cooler theres just the issue of getting parts that are ethanol proof.Wonder how long before the ethanol content rises over here?Seems a bit of a scam as you get lower mileage plus theres a lot of farm subsidies involved under the smoke screen of being environmentally less damaging and general corruption.Just think how much cheaper food would be if they weren't growing fuel???

What's 7/16 in mm again?

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