Best octane gas?

[pamcopete]

voodoorider

Well, I also used 93 Octane in my trusty '78/E when I first got it, thinking that more is better, but after a little research, and listening to the exhaust, I concluded that the 93 Octane was still burning when the exhaust valve opened, which, to me, meant that I was not getting all the potential power and economy from the gas. Now, I'm sure I could have compensated for this by advancing the spark, and perhaps spending three or four Saturdays fiddling with the advance to get it just right, but, what for? I don't run the engine very far up the HP curve, and changing the advance would mean that I would have to use 93 octane to avoid pinging and get the same mileage that I could get with 89 or even 87 octane without the hassle.

[XSv650]

My 2 bits...

I've noticed that 91 and higher octane fuels tend to not break down as fast or turn to varnish as quickly.

I have a Honda mower that I abuse every winter by leaving the fuel(91) in and she starts right up every spring with 2 pulls, same goes for my leaf blower and log splitter...

[10ecjed]

pamcopete,
My 1980 650G runs like crap on 87 and 89 octane here in MD. The here gas does contain 10% ethanol.
93 oct. runs the best on slow back roads and on the highway. I am running a little lean though. I am going to adjust that when I can get to the garage with out crutches.
10ecjed

[voodoorider]

10ecjed, It's got a lot to do with ignition timing. Most people think high octane is cleaner and won't have as much carbon buildup, but that's only if it's all being combusted. I read a lot of articles on this after seeing this thread. For an engine without high compression ratio you can have just as much, if not more carbon buildup in your piston chambers by running high octane. stock xs650's don't have a high compression ratio (high being 11:1 or greater), but if you set your timing to the marks, a lot of people are telling me that this bike's timing was set too advanced from the factory.....so you may need higher octane if you're timing's too advanced....to avoid pinging. I'm running 89 now, timing retarded a bit. I never had pinging with 87, but I do think the valves are a bit quieter with higher octane, but that's maybe my imagination......

Google "high octane gas ignition timing".....there's some interesting things to read.

[jscribner]

May 19, 2008 21:22:16 GMT -5 @pamcopete said:

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.

Thank God I found this! I've been chasing this ghost for months in my '80 Special. I finally just started swapping the plugs at each oil change (or sooner) I tried everything, tweaking carbs several times, and always had one plug a little richer than the other. Now I think I know why!! I definitely recommend the 93 octane fuel, and I burn Lucas gas treatment with at least every other tank of gas. Seems to help. It's probably like Mystery Oil, just more of a local brand (made someplace here in Ohio). Pamcopete, you are awesome!
John Scribner

[voodoorider]

Thank you Jscribner for finding this gem of knowledge for myself also! I have a boyer with a dual output coil and my right side is always hotter than the left. You said it.....pamcopete is awesome!

[10ecjed]

voodoorider, I can not change my timing.TCI. I have ACCELL dual output coil. I am going to try reversing the plug wires also.
10ecjed

[10ecjed]

Does ethanol in gas create more or less carbon build up?

[voodoorider]

10ecjed, Here's what I found.......ethanol will dissolve carbon buildup as it burns. But also...."When ethanol was first introduced in the 1980s, some cars experienced deterioration of some elastomers (rubber-like parts) and metal fuel system components.".....Ethanol is somewhat corrosive to certain rubber and cork materials found in older cars with carburetors......Ethanol may also eat the coating inside most older gas tanks, so a separate plastic cross-link polyethylene tank is recommended (but not necessary). Another thing that isn't good is that ethanol can absorb water and take it through the engine.....

but if they put it in the gas, what can we do about it?

[pops]

It's my understanding that ethanol is not routinely added to premium grade gasoline (91 or 93.) So if one uses only premium...no ethanol associated problems.

A good way to check gasoline for alcohol addition is to put some water in a see-through tube, mark the level on the tube. Then add some gasoline on top of the water, seal the end of the tube, shake the tube vigorously and let it settle. If the interface where the water meets the gasoline moves from the mark on the tube, that's an indication of the presence of ethanol since the ethanol would rather dissolve in water than in gasoline.

pops

[voodoorider]

The "Hot Spot" gas stations around here don't put ethanol in the 87 octane, only 89 and 93 have got it. I googled this a bit and found that some states, such as Oregon for example, gas was mandated to have e10 in it by the end of 2007. It says Portland has been using e10 blended fuel during the winter since the early 90's.....Denver also. I guess it varies by region and it's not just the high octanes who are excluded from the e10.

I usually use Shell here in NC, next time I fill up I'll ask about it.

[southernman77]

I travel all 48 states and pick up all kinds of additives as I travel, read the back of the bottle and you will see must of the stuff can be picked up at a paint store. I buy injector cleaner by the gallon, I have 5 dirt bikes and 5 street bikes. I never buy less than Prem and when I rebuild my 1970 daytona it will be airplane gas. 2008 1200R 2001 ZG1000 1980 XS650 1981 XJRJ750

[xsjohn]

Wouldn't put anything but premimum in mine after trying the cheap stuff many times...the bit slower burn makes mine run smoother.......for sure........

xsjohn

[sarah1]

Very interesting posts here on gas quality VS timing.
As i am restarting to tune my 79 from scratch, meaning no mufflers, pamco ignition and all other variable removed from the equasion i just run the fuel i am going to run in it on a regular basis.
100 low lead or 115/145 purple av gas
Pete how much marvel oil do you put into the tank?

Il let you know how it runs.
Sarah

[pamcopete]

sarah1,

Well, the recommended amount is 4 oz. per 10 gal, so a 2 gallon fill up is a little Less than an ounce, or about a cap full per 2 gal.