MY Cooper S used to run like on 3 cylinders and was horrible, turned out to be Ultimate... Changed to BP95 and all my problems went away.. yes it was many tanks of ultimate..

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Sorry Brett,

Speaking as a Petroleum Chemist, I don't believe your problem was solved by changing brands of fuel..

Other factors were involved.

Cheers

Michael

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67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

bit of un update. sprayed start ya bastard around it is leaking a little around the butterfly shaft but I don't think its enough to cause such bad symptoms. I also did a smoke test on it and the only place leaking is the shaft. I found that if I partially block the intake to richen the mixture it also will rev better.

I borrowed a set of twin 1 1/4 setup bolted it on and she revs nice and smooth. so I think I will get a reconditioned carby. what else can cause issues like this on an su? ive cleaned it out sprayed compressed air through the hose from the fuel bowl so it no blocked no major vacuum leaks, the needle is correct as it has run before, fuel bowl is always full, dash pot has oil

I had the same problem on my 1412 stroker a few years back. It happened straight after I filled up with Vortex 98 (supposedly) as the local woolies. Barely made it home, I pulled the HS6 SU off and put the Dellorto back on. Problem fixed.
Investigation showed the fuel had swelled the main jet's fuel hose almost closed. It was an aftermarket `fuel miser' main jet.
I suspect the fuel (whatever it was) had ethanol or something in it and the jet hose disliked it. I had filled up there many times before.
Moral of this story- fit only genuine SU main jets.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Well after 3 months of bench testing. BP paid out my claim

end of the day, Ultimates 98 octane is achieved by lowering its volatility, compared to lower octane, which has higher volatility..

My R53 would have poor start on Ultimate, switched to Bp95 and problem solved once I got enough 95. And yes the entire full system was changed short of changing the tank, and pipes....

Gary at BP was as surprised as me with his bench results...

My Mk1 S ran like its on 3 cylinders and would take a fair bit to start up, changed to 95 and even Ken at Mini Automotive was amazed at its running and starting abilty since changing fuel...
Cheers Brett

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Brett,

The volatility of a fuel (which changes according to the season of the year by design) has nothing to do with it's Octane rating. That's utter rubbish, who told you that?
Every fuel grade available is made to meet the same, particular very defined specifications whether it be BP, Shell, Exxon or whoever. These companies can and do onsell their product to each other...

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67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

This is the latest email from BP ::

Hi Brett we have done more tests and confirmed that the 98 loses the light components faster than the 95 because it has more of them because the light components are high in octane and assist with cold starting, tests we did indicate that a 98 octane would last about 2 - 3 weeks before the properties changed significantly and 95 would last 3 to 4 weeks at around 25 deg C, so explains why it is not such an issue in winter in the southern states and in summer with summer fuel which has less light components for EPA reasons. Yours friends car driving once a month for a 1971 vehicle that would be carburetted so she needs to drive a bit more often, I have found that running to one third then filling to two thirds and keeping at 2 thirds helps as a fuel management strategy. For her age of car the attached document was written as her car was designed for leaded fuels



regards

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