Merc XR-6 150 Preformance

I spent a week at the lake I fueled up the boat with 89 octane as I have done for 20 years added seafoam per instructions. It preformed like it always does slight suprise was it ran 5800 in summer heat. Well my son had it out and needed fuel put in 87 at Marina on lake. It lost 400 RPM and would only run 5400 and lost it's snap witch made it easier out of the hole and handeling was boreing for me. The outboard runs a 23 pitch trophy blueprinted by SCP. Tach is good I have 2 they both report the same numbers. I just find it strange how boring it got. Am I losing my mind or would this be common?

TLW I have had several surgeries since I wanted to reseal my powerhead still healing up last one they took 1/2 my first rib and a muscle from my neck still have the other side to go. That said I am doing better than I have in years Hopefully I can get this done in a few months. I appoligise for not getting the boat down to you.

Garbage gas is garbage gas...run it out and refresh with good fuel and see what happens, I wouldn't do anything until then, don't try to fix something that's not broken.

not a deal.. hell, i've had both neck carotids done, two stints in leg since December 6 and memory really sucks so i never noticed!

what Pat said.....

When you pump gas from anywhere you really don't know what you are getting these days.
Typically the higher the octane the cooler and slower the burn thus you are actually making less power.
The more ethanol in fuel the cooler yet leaner the burn also making less power. More ethanol or oxygenators in the fuel requires more fuel to make the same power. In carbed motors this means bigger jets and in injected motors, bigger injectors or increased injector duty cycle thru the ECM calibrations.
My guess is maybe you got some 15% ethanol fuel which would certainly account for the sluggish performance of a motor tuned to run on pure gas.

Muzzlebrake in the northeast U.S. you have always had ethanol in the fuel since the 70's I have never had a problem running it in a Merc still don't no matter where I am at. As far as octane goes I run 89 to prevent detonation (spark Knock) I learned this many years ago melted pistons s--k. The myth that it reduces power is just that a myth. My Merc is a 97 where most of the country was running E-10 so no doubt that Merc knew this and designed and tuned approiately for this. The biggest myth especially where non E-10 was used is to blame the lack of proper maintenence on Ethanol fuel lines break down which is why I switched to auto fuel lines as they do not exibit breakdown from fuel and age like those cheap azz marine lines do.

Most people think that because their owners manual say minimum octane recomended 87 is that it is the only fuel you can run. I will direct your attention to the word minimum it does not say only. I have been building and running internal combustions engines both 2 and 4 stroke since about 1976 yep I'm old. This is just my long term experience with these engines nothing more.

No fix Pat & TLW just thought I was crazy as it is the first time this has happened bad fuel is bad fuel.

I just rebuilt the carbs on my Yamaha jet after a scrape with some garbage fuel. Two filters new lines didn't help when you try to run mud through it.

You ain't old enough then. If you were you would know a little more about tuning and internal combustion engines not to mention how to spell.

This is an internet forum not english class. The piston in an internal combustion engine uses the intake charge to quench (cool) the top of the piston so that it does not melt. Any carbon deposit on top of piston causes hot spots. With lower octane fuel ignites prematurely also known as detonation (pre ignition) This is a major cause of melting a hole in the piston. Keeping the engine clean along with running higher octane prevents this.

Now on to tuning in race engines it is very important for carbs to be tuned properly as they run on the ragged edge of their capability. Too lean then boom they explode,too rich no power proper jet selection is very important. The only reason for me to change jets in my outboard would be altitude as it is not a race motor with no mods. I can get into the weeds about how carbs work if you would like... Fuel injection is a different animal modern injection is controled by a computer. You must size your injectors to your build and program accordingly. I can get into the weeds here too if you like.