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Searched but couldnt find the answer I was looking for on the site so have to ask the question.

I have just bought an '82 900MHR out of Japan and I dont know what octane fuel I should be running in her. I dont know yet if the valve seats have been hardened or whether she is in original in this area, or in fact if the seats will need doing.

My '78 Darmah is having head work done at the moment to allow unleaded to be used in her but she is very old and I am unsure if the '82 will need the same work.

Someone out there with more knowledge that me will know the answer to this question.

I am in Oz where we only have ULP on tap but in various octane ratings.

Cheers.

Hi Jaffa,

I use standard or super unleaded with Millers VSP additive - 6ml/l of juice if that's any help

Thanks for the advice Welshmally, I will track the additive avenue down.

Any idea about the valve seat/guide hardening issue?

Cheers.

I use the 98 0ctane fuel and a good quality upper cylinder lubricant/lead substitute aditive in my 82 SS. To be honest I rekon all vehicles would benifit from upper cylinder lubricant. Remember Redex??? Was all the rage in the old days...........but I digress. I have run lower octane, 91 and 95 and have noticed a difference with pinging and power. I have an old XR500 Honda for bush bashing and that being a big single runs like a swine on lower octane. Very harsh and rough.
Valve seats in older bevels appear to be an aluminium bronze material. Some people call it yorkalbro, well thats what it looks like to me, and it is very common in marine aplications(not as a valve seat though). It is quite hard and resistant to corrosion and has a very high heat expansion rate so the alloy does`nt expand more and let it go. My understanding of lead free fuels is it`s the valves and guides that suffer as they were lubed by the lead in the fuel. I must say in my experience I`ve never seen a valve seat erroded. Recessed, cracked, missing corroded yes.....but it was`nt the fuel. Heads converted for lead free fuel I`ve seen just had bronze sleeve inserts put into the guides, but they were car heads.