Real Classic - - Norton Model 18 - Frank Melling

I read the in­ter­est­ing com­ments in RC about fuel. The ethanol fuel thing has been an is­sue with clas­sic race bikes for some time now and we used to get around it by cut­ting 97 oc­tane un­leaded with 100 LL Av­gas (ap­prox 97 oc­tane RON) – pos­si­bly a bit il­le­gal. How­ever, there is now a com­pany in Stock­port mak­ing all-Bri­tish race fuels with no ethanol at all in them. I’ve been us­ing their 107 (min­i­mum) oc­tane Supreme and this could be used to legally cut 97 un­leaded so that if there was any ethanol there it would be dis­ap­pear al­most to noth­ing­ness.

The 107 also con­tains all the good stuff for valve seats and burns very well in­deed giv­ing a prop­erly perky en­gine power.

I ride my bikes equally in UK and in France. Of the two, France is prefer­able as the roads are bet­ter and less crowded and for the most part their gen­eral at­ti­tude to mo­tor­cy­clists is much bet­ter than in the UK. In the UK I usu­ally just fill up with the cheap­est un­leaded, 95 oc­tane, as it is the most eas­ily avail­able. At the mo­ment it’s E5; 5% ethanol. Nor­mally I don’t have any prob­lems with the bikes as long as I re­tard the ig­ni­tion slightly, and use an ad­di­tive to stop the carb gum­ming up and the fuel go­ing off. Even when warm, my 1956 Tri­umph Tiger 100 with its monobloc carb is a first or sec­ond kick starter. Like­wise, my 1959 Morini Cor­saro 125 and the other older ve­hi­cles I own.

Ethanol in UK petrol is likely to in­crease to 10%. In France, ethanol is al­ready 10% and some­times 15% (I have seen a pump with 65%...), the bikes run bet­ter when the ig­ni­tion is re­tarded a few de­grees. This re­sults in re­duced pink­ing. On the bike which has man­ual ad­vance/re­tard, I only put it onto full ad­vance when the en­gine is run­ning at more than 3500rpm which equates to about 55mph in fourth. By ad­just­ing the tim­ing while run­ning, you can tell when the en­gine is smoothest or hap­pi­est (not that a me­chan­i­cal ob­ject can be happy or sad: dis­cuss!). Elec­tronic ig­ni­tion has more of a grad­ual ig­ni­tion curve right through the rev range, whereas the old school bob weights and springs fit­ted to most 1950s and 60s bikes bring full ad­vance very early in the rev range, espe­cially if the springs are a bit weak with age.

On French petrol, when the bikes are warm they can be hes­i­tant to start due (I think) to the way the fuel seems to evap­o­rate from the hot carb. When cooled they are back to nor­mal start­ing, so I try for short stops at the top of hills. Free­wheel­ing for a while and then put­ting the bike into gear starts them up again with­out bother. The carbs have in­su­lat­ing gas­kets of Tufnol to re­duce heat trans­fer. This leads me to con­clude that the fuel evap­o­rates so eas­ily it can­not be good for the ozone layer – de­spite the ethanol be­ing ‘re­new­able’ en­ergy.

I think the ef­fect only oc­curs in car­bu­ret­tor ma­chines as in fuel in­jec­tion the fuel is in a sealed cir­cuit. It would be in­ter­est­ing to hear of oth­ers’ ex­pe­ri­ences and con­clu­sions. Stu Thom­son, mem­ber 2256

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