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Rob Rawe
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J.H. shop manual has no reference to fuel octane rating that I can find.

Can some one tell me what is recommended?

JH #14120

answerman
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Joined: 09-10-2012
Location: Little Chute, Wisconsin USA
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I'm pretty sure that my owners manual specifies a minimum of 91 octane. Plus, for whatever it's worth, "premium" is usually ethanol free, which is important in a car of the JH's vintage as the ethanol can cause havoc with the fuel system and seals and such.

subwoofer
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Joined: 04-01-2008
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The stock JH 907 has next to no compression (8.5:1) and still fast combustion chambers, so octane rating is not likely to be an issue. I run a higher compression 907 (9.4:1) from a Lotus Eclat and see no issues on regular 95RON. My VW flat-4 in the family barge has 10.5:1 compression, slower chambers and still runs with no issues on 95RON...

But beware of alcohol content, since it eats gaskets and fuel lines if they are not compatible, and fuel lines from the 70's are most likely not!

--
Joachim

Jim Ketcham
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Remember that the JH manual specifies RON. In the US the octane rating on the pump is (R+M)/2., that is, the average of the Research Octane Number ( RON) and the Motor Octane Number (MON). Since the MON for typical fuels is about 8 numbers lower than the RON, US "regular" at 87 (R+M)/2 should meet the 91 RON requirement as specified in the JH manual.
JH fuel lines are steel and should be okay with ethanol. Aluminum and certain elastomers do not seem to like ethanol, but I have not experienced any problems with E10 (10% ethanol) which is what we see in the US (in all grades) in non-compliance areas.



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