What kind of gasoline do you use?

When I first got my XJ it ran okay, but it buzzed at certain rpm's. I remembered being told that in 1981 regular gas had a higher octane rating than it does today, so you should use mid-grade gas in older vehicles. I tried it, and lo and behold my bike does run smoother and with more power on mid-grade. I've also heard that premium may be too much octane for most older bikes. Any thoughts?

 

I use the highest octane that the pump has.

 

I've been running 89.

 

High Test.
I'm getting better performance with it.
The Regular was making a sound I'm sure would lead to trouble.

I'm treating this Old XJ to the Good Stuff.
Just like I did with my new MGB, back in '72 ... when Sunoco had that 260!

 

high octane

 

I read that the higher octane gas may not be the best though because it is older than regular. Most cagers don't put premium in their cars and therefore it sits in the storage tanks longer whereas the regular gets turned over much more.

What are your thoughts to this?

 

I think it all comes out of one tank, anyway ... the higher octane rating is baloney and steeper price just makes you feel more important!

 

The highest octain I can find. Around here that is 89. Gets better performanc as well as better mileage.

 

I run the highest also, treat my baby good. It is 93 here. Never tried anything else.

 

I have heard that the gas comes from the same tank, but at different levels, not sure if top or bottom in the tank is higher octane though. I only use the high octane in mine, lately with seafoam additive to clean it some more.

 

I just had to throw my 2 cents in here!Contrary to popular belief/myth higher octane fuel doesn't come out of the same tanks but it can dissapate a small amount when sitting in the tanks but doesn't lose any octane! I work in the fuel business and I get asked this quite often. Also my 1980 XJ 650 runs nicer on high octane and way better mileage too.But being a cheapskate I often put the cheaps stuff in and then kick myself after(lol)
Hope this helps a bit!

 

I put in 89. My bike runs like crap on 87, but I don't see any real difference between 89 and 93 so I stick with 89.

 

87. I can try some other flavors, and I have in the past, but I'm not sure I noticed much of any difference.

 

I use premium, which is 93 octane. I've been back and forth all summer between 87 and 93. Mileage-wise not much difference but performance wise it sounds and runs a bit better on premium. I buy about 2.5 gallons a week so the price difference is barely noticed.

 

premium,,I try to stick to the name brands,,,,I don't buy the agument it's all the same.
an yes I remember sunoco 260,,,,an still buy sunoco alot but I've been on a Marathon kick latly because I heard they don't buy mideast oil
an I once owned a 69 MG miget,,,1275cc 4 cylnder motor it was a motorcycle with 4 wheels type fun nothing but premium an loved to run with your foot flat on the floor,,,,,of course everything I drove love to run flat footed back then...I weighed 120 lbs back then I don't think I could fit in 1 one now at least not comfortable,,,,but that car was fun in the turns

 

I run only 87 octane regular in my Seca, and she runs great. The factory manual calls for regular, and that's what she gets.
One of the most informative pages on octane ratings can be ound here:
http://www.faqs.org/faqs/autos/gasoline-faq/part3/

Be sure to check out the section on using mothballs as an octane booster!

 

87
but give her a bit of 89 when shes a dirty girl(wink wink)
mild differance, but benifit is arguable.
depends if i have the extra .50 to use the better stuff

 

I read the section on Mothballs. It seemed to say that to use them to increase octane in your tank also leaves residue as it needs to burn up at such a high temperature. Sounds like I will be leaving that alone as I have no experience tearing my carbs apart, and don't wish to learn until I have some space and a bench to do them on. Dispather, Have you used mothballs before in your bike?

 

I'm so impressed I actually know something about this. We build gas stations all the time, so here is what I know.

There are two unleaded tanks at most gas stations. Here we have our choice of 87, 89 or 91 octane ratings. The one tank holds the 87 and the other holds the 91. They mix in a valve to create the 89 octane.

As I far as I know about all this, high compression is needed to get the most out of high octane fuels. I run jet ski's a bunch and know that if you don't have a high compression head you are just waisting your money. most people only notice a change when they move 1 grade up from normal, but most people don't see high enough compression to notice any change beyond that. I currently own a subaru turbo car that requires 91 at the pump. I notice a huge difference in the power and sound of the engine when I use something less. 89 is okay, but you get down to 87 or even 85 it is just crap. These bikes don't have the compression to require 91 octane gas. You may just be waiting your money, or at least that's what I've been told.

 

I use 91 here, the highest I can get. Mostly because the mid grade has 10% ethanol, and I accidentally pushed that button once, and it made my yammy run like garbage. I won't even bother with the normal 87 stuff. I used to have a carbed car, and whenever I put the stuff with ethanol in it, it ran like garbage too.

 

Here in new zealand we have 91 octane and 95 octane, I use 95 in my xj, i think the the lead content in the 91 is to low and it needs to have additive to increase the lead content, so i dont touch it as it could damage valves etc. Would be interested to know if this would be the case from any experts out there

 

You guys still put lead in your gas???
We haven't had lead in gas in a very very long time around this part of the world!

 

its un leaded but some older vehicles dont seem to run on it that well and you can put an additive in it which i assume increases the lead content. I think the unleaded fuel can damage some older engines resulting in excessive wear to parts. i was wondering if others had the same results with there fuels or excessive wear

 

No gas here has lead and the additives are lead free as well, they contain mainly kerosene. The additives are to prevent damage to the head where the valves seat. Older engines heads valve seats are made of soft metal where the new ones have hardened valve inserts thus lead (or additive) is not needed.

I have used the 3 grades of fuel in my XJ, 95 ran OK but left soot in the head and pipes, 98 sooted up so bad that after 30 or so Km the bike started running bad and after a couple of sort trips would not run at all due to the plugs fouling. 91 the bike runs fine. Regular is what is called for (by Yamaha) in these bikes (apart from the turbo or you have upped the compression or you have the Ethanol problem).

As my bike is EFI I know jetting is not affecting my findings.

Octane rating explained

 

Here in Eastern Canukville, we get 87, 89 and 91. Tried all the varieties and found that 89 & 91 simply waste cash. I get no better mileage and maybe worse and the bike is harder to start. The higher the octane, the higher the resistance to burning, so unless your Yammie experiences spark knock, regular is the way to go.

 

I must be confused as that is certainly not what I have been led to believe. In fact my understanding is that the higher the octane the faster it burns producing more heat.

 

I use the highest octane at any station I go to. :wink:

Chuck

 

" "It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion).

A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content by volume (per litre or per gallon). This is because ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl group for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. To a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

In the case of alcohol fuels such as methanol and ethanol, are partially oxidized fuels and need to be run at much richer mixtures than gasoline. As a consequence, the total volume of fuel burned per cycle counterbalances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred maximum power air/fuel mixture of 12.5:1, it will release approximately 20 MJ (about 19,000 BTU) of energy, where ethanol run at its preferred maximum power mixture of 6.5:1 will liberate approximately 25.7 MJ (24,400 BTU), and methanol at a 4.5:1 AFR liberates about 29.1 MJ (27,650 BTU)." "

 

Hey olebiker, this was an tidbit gleaned from R&T's Dennis Simanaitis in one of his Tech Tidbits articles years ago. The reason that straight hi-octane gasoline reduces or eliminate spark knock (aka pre-ignition) is because it will not light off early. It resists early ignition due to pressure and temperature better than low-octane fuel. Dennis and I (and Rick) are not just pretty faces - Dennis is an engineer and I am...well, a grocer...that wants to be an engineer. Thanks for your Super-Tech answer, Rick. XJB counts on you for a reason.

 

What Rick said was far over my head. I know for a fact that higher octane burns faster it must be that compressing it causes delayed ignition. I'm still not sure I believe it though. I am not an engineer but take a gallon of low octane pour it out and light, now try that with higher octane. Better stand back a bit as I have seen a guy get singed trying this out.

 

What Rick said was a quote from the Wiki artical I posted a link to above.

Read the whole artical and also follow the links from it for more information.

These bikes require regular, the problems arise when ethonol is added the ethanol needs to be much richer to run.

Also read:

http://www.prime-mover.org/Engines/GArt ... ctane.html

and

http://www.offroaders.com/tech/octane.htm

 

Yeah, the chemistry is over my head as well. Keep in mind that the two examples feature entirely different conditions (liquid fuel vs. atomized fuel, 9:1 compression vs. atmospheric pressure) and in the open flame test alone there can be a lot of variables.

There may be more energy in hi-octane gas but also keep in mind that the ignition points for each fuel are low enough that a match, a spark or a blowtorch are all going to get the job done to make it light off. The difference is ignition under pressure and hi-octane resists that better.

Diesel resists it even more. That's another discussion entirely.