What kind of fuel does everyone run? I've got a 2000 225 Opti-Max. Do you run Regular, Plus or Premium?? I know my outboard is rated for 87(regular) octane, but I usually run plus or premium to be sure it runs clean. With gas prices going up I'm thinking of running regular, will this effect anything? Thanks  

things ive read states running a higher octane doesnt make a difference and sometimes decreases performance. i run 87 octane every time.

I run 87 in mine.  I will put a can of Seafoam in 1 or 2 times a season.  It helps keep everything clean and prevents build up.  The savings on using 87 over 93 will easily pay the $8 for the can of Seafoam.

I run 87 always.  I ask about this before and I believe that someone on here said that you should use what its rated for.  If its rated for 87, use 87.   I also heard that 91 burns "slower" than 87, so it could acutally do more damage than good.  But someone help me out here.  Just wait, someone will come through here in the clutch.

87 Octane with Stabil everytime I fuel up.

I run 87 always. I ask about this before and I believe that someone on here said that you should use what its rated for. If its rated for 87, use 87. I also heard that 91 burns "slower" than 87, so it could acutally do more damage than good. But someone help me out here. Just wait, someone will come through here in the clutch.

it takes more energy to burn 91 than it does 87. how in the end that effect power im not sure but i agree. 87 octane should do the job nicely.

Compression, displacement and timing are three of the key factors that determine octane requirement. 91/93 octane burns too slow and will not make a full burn in a low compression motor dumping unburned fuel out the exhaust. Unburned fuel equals loss of power

87 octane will burn too fast in a high compression motor, causing predetonation, which can destroy a motor by hammering the rods needle bearings into the crank, breaking rings, melting the edge off the pistons etc.

The engines timing and compression is set by the manufactor to burn a certain octane fuel and it does a motor no good to run anything other than the recommended octane, unless you have gone in and modified the motor to increase/decrease the compression

You will see small bore carb engines like 9.9, 25's etc running 130+ pounds of compression and running 87 octane but a big bore motor running as low as 80 pounds of compression with 87 octane.

With computer controlled DFI motors, they are able to get the compression up to 125+ pounds and still run 87 octane because of the much more accurate fuel and timing control. That's why a 225 DFI motor will have a better hole shot and midrange torque than a 225 carburated motor.

Note: that's also why you have to be very careful about trying to run old gas in a DFI motor. Doing it can get very, very expensive. Gas loosing octane very quickly and they don't build a whole lot of fudge factor into DFI motors. A lot of blown DFI motors are blamed on the injectors, ECU and all kinds of things but many times, it was simply the fuel was a few months old no or not enough fuel was added to offset the old fuel.  I should mention if adding fuel to that's been in the tank for a couple of months, is one time I would recommend adding 91/93 octane, at least two or three gallons for every gallon in the tank.  Personnaly,  If it's more than two months old, I pump it out, even though I do run SeaFoam at one ounce per gallon in every tank.  

Compression, displacement and timing are three of the key factors that determine octane requirement.  91/93 octane burns too slow and will not make a full burn in a low compression motor dumping unburned fuel out the exhaust.  Unburned fuel equals loss of power

87 octane will burn too fast in a high compression motor, causing predetonation, which can destroy a motor by hammering the rods needle bearings into the crank, breaking rings, melting the edge off the pistons etc.  

The engines timing and compression is set by the manufactor to burn a certain octane fuel and it does a motor no good to run anything other than the recommended octane, unless you have gone in and modified the motor to increase/decrease the compression

You will see small bore carb engines like 9.9, 25's etc running 130+ pounds of compression and running 87 octane but a big bore motor running as low as 80 pounds of compression with 87 octane.

With computer controlled DFI motors, they are able to get the compression up to 125+ pounds and still run 87 octane because of the much more accurate fuel and timing control.  That's why a 225 DFI motor will have a better hole shot and midrange torque than a 225 carburated motor.  

Note: that's also why you have to be very careful about trying to run old gas in a DFI motor.  Doing it can get very, very expensive.  Gas loosing octane very quickly and they don't build a whole lot of fudge factor into DFI motors.  

Dude...i want your brain!  

Not to hijack....i actually think it will be valid to this conversation....what are you guys' thoughts on ethanol in the gas?  

I think you will find most modern outboards will handle up to 10% alcohol. Older motors have a very hard time with it. It dries out hoses, and ruins gaskets and seals.

All fuel systems are having a hard time with it because it's desolving the old shelac buildup that's been forming in the tanks, line etc from 100% gas that has formed these deposits and giving the carbs hell. You will be very smart to put a good filter in your fuel line and change the filter often. If running fuel injection, it's even more critical to keep the filters change. Also, I've read some of the plastic tanks are not really suited for alcohol bases fuels either but have not experienced any problems. However, not many stations in my area area pumping alcohol fuels (yet).

Very nicely put Way2slow, that completely answers my question. I guess in a normal mind you'd just think that the higher octane would burn cleaner and more efficient, but I see what you're saying now. Thanks A Lot!

It depends on the compression levels in your engine.  My dodge V6 is rated for 87 and in the owners manual is says to use 87 and not to use 93 for a long period of time.  But my dad's corvette you have to put 93 in it because it is a high performance engine and it wouldn't run right with 87.  So I think if it is rated for 87, use 87, but if it is high performance engine (sports car, drag racing, etc...) then you need to use 93 in those engines.

Very good information Way2slow.

Thanks, John.

Here's a good link from Mercury about Ethanol in outboards. Kinda adds more to what way2slow said.

http://northamerica.mercurymarine.com/serviceandwarranty/outboardfaqs/ethanol.php