Fuel Grade?

This might be a dumb question but i'm new to riding and I just bought a 1982 Yamaha XJ550 Maxim and was wondering what fuel grade to use.

 

The cheapest one at the pump. No need to use anything else, unless you've upgraded the engine with all kinds of high performance parts for drag racing.

 

Higher octane fuel, above the manufacturer's recommendations for your (unmodified) engine, actually decreases performance.

 

I use 93 octane... There isnt a knock sensor on the motor nor is the timing super advanced so I dont think it would make much of a difference. Although I dont have any pinging to knocking or any other sigs that it's really harming performance. Higher the octane slower the burn... But I doubt a loss or at least a noticable loss of performance though.

 

Thank you for your help.

 

I've been told that regular gasoline had a higher octane rating in 1981 than it does today. My bike seems to run more smoothly on mid grade (89) than on regular (87), and my motor is all stock.

 

Wrong thread oops, thanks for the replies though guys.

 

In 1981 when you went to the gas station you'd see two pumps for gas. One was regular, the other would be unleaded. Lead was used in the gas from around the 20's or 30's to increase the octane rating to slow down the buring of the fuel which increased efficiency and by association power. But in the late 70's the Federal Government mandated the use of catalytic converters to reduce emissions. However, lead was (and still is) very toxic to a catalytic converter and gas stations were required to supply a non-lead fuel for cars with them.

The problem with unleaded gas was the lowered octane ratings which meant burn efficiency dropped. As a result, engines were designed with lower compression and thus lower performance and even lower MPG. (In fact a lot of people cut out their cats... no, not that cat you sicko... so they could use 'regular' gas again and gain some performance back). Throughout the 1980's Oil companies experiemented with various formulations to increase the octane levels of their fuels and figured out that that people would pay for higher prices for "Premium" gas. So then you had "Regular" "Unleaded" and "Premium/Plus/Supreme Unleaded". In the 90's (I think), leaded fuel was banned in the US and "Unleaded" fuel took the "Regular" name (which confused a lot of people for a while) and we were introduced to "Mid-Grade".

 

gNaRKiLL,

I started mine tonight when I finished installing new starter brushes. It was 34 degrees f and the garage isn't heated at all. The bike started right up. The trick was to pre-heat the carbs and intake manifolds with your wife's hair dryer. Put it on high heat and high fan and play it over the carbs and manifolds until they are warm to the touch. Starts right up if you don't have any other problems.

Cheers,

Phil

 

The grade of fuel you need depends on your compression ratio. as a rule of thumb from and old hot rodder - i use 87 octane for an 8:1 engine, 89 for a 9:1 engine, and 93 for a 10:1 engine. I use 93 in my 750 maxim when i could get away with 89 because its only 10 cents a gallon more so what am i going to save on a fill-up 30 or 40 cents?

also any engine that has a 12:1 compression ratio is going to hate pump gas. I have a 1970 Challenger with a 440. I use 93 octane and some 104 octane boost to get it to 100 octane, it has 11:1 compression. Years ago i had a 426 Hemi in a GTX back in the days when you could buy Sonoco 260 (100 octane) out of the pumps. That was also a leaded gas. My brother runs a late model racecar with a chevy 350 and they use Cam2 purple (110 octane). I had a 1984 Daytona Turbo Z with a 2.2 turbo motor. It only ran on 94 octane Sonoco. 93 octane Exxon would make it ping. 89 octane anything and it would barely run.

A note on lead... Lead was in the gas to lubricate the valve seats. with the introduction of unleaded gas in the early 70's auto manufacturers began using hardened valve seats (seats that were pressed into the heads, and harder than just cutting a seat into the cast iron head). Our japanese bikes have aluminum heads with steel valve seat inserts - so we are ok.

all in all, you should use the grade of gas that makes your engine happy. If you hear it pinging or it feels down on power, or it sounds like there is sand running through your engine, step up a grade. If it feels like it is "nose-ing over" (feels like it is slowing down as you give it gas and get into the mid range RPM band of the engine) - step up a grade. You can't "over octane" an engine, you need a high enough rating to stop preignition (when the gas explodes before the piston reaches top dead center), but after you reach that level, any higher octane won't do you any good.

 

Hotter plugs won't help. Hotter plugs dissipate heat more slowly, thus they operate at a higher temperature once the engine starts. Hotter plugs will be the same temp as the standard plugs - the temp in your shop.

Mine started just fine today at about 40 deg. It also starts fine well below 30. Haven't tried below 20 because I don't start when it's that cold. I have stock everything.

So lets look at your situation. It was starting and running well with the throttle butterflies being held open by the cable. When you detach the cable the butterflies closed a bit and now it won't start. So, maybe they're too far closed now? Or maybe the idle circuit isn't working right?

Or maybe you used up the last of the gas just as it shut off last time it ran?

So, make sure it has fuel. Turn the idle screw in a turn. Put fuel valve on "PRI" and hit the starter (Don't forget the "CHOKE"). Be ready on the kill switch just in case 1 turn was too much.

If that doesn't work give the screw 1 more turn and repeat.

Of course you need to make sure you have a good charge on the battery.

Once you get it running let it warm up until it will run without the "choke". Then back the idle screw back to where it idles below 1500 RPM. If you can get it to 1000-1100 that is great, but my guess is you'll have more tweaking to do before it idles well down there.

 

The previous owner of mine told me to run 93 or it'll ping on me so I didn't mess with it, I have the same bike and my 550 runs like a champ.

 

I run the cheapest unleaded and my XJ700N runs fine