Hitchcocks Forum

Has anyone used Gunson colourtune on their Royal Enfield Carb bike.Just wondering if it's a worth while purchase.

Be wary, I have heard that they don`t work well with unleaded petrol, of course this information might be wrong.

It’s more likely that it won’t work properly with petrol with ethanol in it. Petrol and ethanol have different stoichmetric ratios such that 10% ethanol in petrol is equivalent to a 7% leaner mixture. Whilst EFI engines adjust for this, with a carb it is unwise to use fuels with differing percentages of ethanol because a carb cannot compensate. Where this leaves a colourtune I don’t know but the old plug colours in workshop manuals etc no longer describe accurately what is the state of the fuelling.

Interesting comment rattlebattle about spark plug colours.My b350 is running as sweet as a nut and kicks first or second time.I am concerned about the whitish spark plug colour which if I am correct used to indicate a lean fuel/mixture.I am thinking of adjusting the mixture or should I just leave it?.