Aviation gas (100 octane low lead)

Anyone run avgas (100 octane low lead) in their xj650? I can get it at the airport locally and I seen where the engine was designed for lead gas.

 

I would think that would be very expensive and illegal. My bike runs very well on plain old 87 octane unleaded.

 

If you are referring to the emissions label inside the side cover I do not know why it says leaded gas. These bikes were built in the early 80's and I believe leaded gas was long gone in the US by then.

I have read somewhere on this forum that the 91 research octane = 85 or 87 pump octane.

I filled the tank on my Maxim with 93 octane not long after I first got it and it felt like it didn't like it, though maybe it was just my wallet feeling sick.

 

Unless you've done something to increase your effective compression ratio (domed pistons, added a turbo, higher lift cams), there is no reason to run AvGas. On a stock bike you'll actually lose power since higher octane fuel will take longer to ignite with stock timing and compression.

 

I'll parrot SQLGuy. Your engine has no need for higher octane. Octane is not an indicator of greater power potential; it's a measurement of how resistant a fuel is to premature ignition. The lowest octane fuel that you can get at you local gas station is all you'll ever need for a stock XJ.

BigT. Leaded gas was still available in the US into the early 90's. Our engines don't need the lead since they came with hardened valve seats.

 

91 research octane this is whats on my side cover do not know about being equal to 85 or 87 octane.
those are my pump choices 85 oct 87 octane and of course 91 oct.
I can also buy high test no ethanol down the street $$$ I put it in after running tank down to prime for winter storage

 

Pump octane in the US is given as an average of RON and MON (which are different methods of testing octane). This is somewhat unique in the world (surprise (not)). 87 pump octane is equivalent to 91 RON. The easy way to figure what US pump octane you should use (when given a RON rating) is to multiply the RON rating by 0.95 (rounding to the nearest whole number).

 

The higher octane is primarily to cut down on spark knock and pinging , Being an aircraft mechanic I have used 100LL in race cars but unless you have higher compression of 9.5 or higher not really needed. I have tried it in several bikes no difference than 87 octane although I usually run mid grade , but it is up to you .