Best octane gas?

[chevyy1212]

Just wonderin whats the best octane choice for the XS .. Thats all.. thank you

[5twins]

High test is best. Mine will run on the midgrade and only ping occasionally but will ping a lot on regular.

[chevyy1212]

Premium it is then.. Thanx alot for the fast response

[tomterrific]

Every year I ask XS650 and Brit bike owners who have holed pistons what gas they use. 87 octane comes up allot. For 20 cents these guys could have saved their engine. Old bikes need high test!

Tom Graham

[Don Murray]

Couldn't you retard the timing a tad and eliminate the pinging on regular? I use regular in my 72 all the time and have no pinging. Maybe because I don't use much throttle unless the revs are up.

[XSv650]

On a similar tangent...

Does anyone here include a lead additive to thier bikes fuel, especially early '70's models?

And if so, what brand yields the best results?

[eric123]

I put Marvel Mystery Oil(MMO) is every tank, in every bike I own...I also put a little in the oil too...

[Don Murray]

Also I would check the timing with a timing light to make sure advance is not happening too quick. Weak advance springs could cause the timing to advance too soon and make it ping.

[compa]

May 8, 2008 11:03:33 GMT -5 eric123 said:

I put Marvel Mystery Oil(MMO) is every tank, in every bike I own...I also put a little in the oil too...

What does this do for you?

[pamcopete]

I use Marvel Mystery Oil in my gas, but not in the oil because of the wet clutch. It is mainly an upper cylinder lubricant and carb/ fuel system lubricant. I notice small improvements in things like the operation of the petcock and throttle. Can't really say if it does anything for the cylinders, but it's kinda like praying......it don't do no harm! I used it in my faithful '78 standard and it's still going strong after 78,000 miles. No way to tell if it would have made it that far without the "Mystery".

Of course, like any foreign substance in the gas, it actually will reduce the effective octane rating. I use 93 octane in my '81/H for ping protection and because I happen to believe that name brand 93 octane gas is "better" than cheap low octane gas. Like, it's only 2 gallons to fill up and I get 50 MPG, so why risk engine damage to save a couple of dollars?

On the other hand, most Japanese motorcycles were designed for markets where the motorcycle was the family transportation and gasoline quality was iffy, so they will work with just about any octane of poor quality gasoline that's sitting in a can losing it's "aromatics" in the noon day sun, so the octane and even the quality of the gasoline will probably not stop the engine, it just won't run as well, but you can still strap the chickens on the back and go to market!

[tomterrific]

I am on a list for Triumph Daytonas. A fellow just bought a good runner and on his second ride he lost power and the bike eventually stopped running. I'll spare the all symtoms and the thread but i asked if he had used 87 octane. He did. He pulled the heads to see two holes, one in each piston crown. I'm sorry to say this but anyone is a fool to run low octane 87 when 93 octane costs just 20 cents more.

Tom Graham

[Don Murray]

I doubt lower octane gas by itself will burn two pistons unless the engine is tuned for high octane and is worked hard and long. Lean jetting and/or too fast timing is probably contributing, and if they are off enough, high octane won't save you. Also if it's timed for low octane, then high octane will reduce power and might even make it run hotter. The important point is that the timing needs to be correct for the octane rating (burn rate). If the engine specs say use 93 then that's what the stock timing is set for.

[Six-Five-O]

May 10, 2008 18:40:59 GMT -5 Don Murray said:

I doubt lower octane gas by itself will burn two pistons unless the engine is tuned for high octane and is worked hard and long. Lean jetting and/or too fast timing is probably contributing, and if they are off enough, high octane won't save you. Also if it's timed for low octane, then high octane will reduce power and might even make it run hotter. The important point is that the timing needs to be correct for the octane rating (burn rate). If the engine specs say use 93 then that's what the stock timing is set for.

That is interesting. What octane does the factory recommend?

[grizld1]

In the very educated opinion of Gordon Jennings, factory ignition settings of the period tended to be slightly too far advanced. Add to this that XS650 factory timing marks can be off by as much as 2* due to variations in rotor keyway machining, stator mounting, etc., so that reliance on factory settings and fuel recommendations may not yield an optimal combination of fuel and ignition timing. You can find the setting you need for the fuel you're using by reading the deposit line on the central electrode of the plug; see Jennings' article at www.strappe.com .

[pamcopete]

Well, things get a little more complicated with a dual output coil setup, like the TCI system on '80 to '83 models or an after market system that uses a dual output coil, because in those systems, one of the plugs gets a positive voltage and the other gets a negative voltage, which means that the metal from the center electrode transfers to the ground electrode on one plug, but goes the opposite way on the other, depositing metal from the ground electrode to the center electrode.

One of the plugs runs hotter than the other as well in a dual output coil system, and one of the plugs requires 40% more energy to fire than the other.

So, if you have a TCI equipped model or an aftermarket dual output coil setup, then you should swap the plugs at each oil change to equalize these differences.