sleeper_dave

A lot of the gas stations around here have 10% ethanol in the fuel. Some of them have it in there and don't post it. Personally, i try to avoid it, but I can't always. For example, last weekend I put 10 gallons of 94 octane E10 on top of the 30 gallons of gasoline that were in the tank all winter.

Ethanol needs to run at a richer a/f ratio than straight gasoline.

I'm also aware of the potential problems with the fuel system.

My boat's a '91 Fountain with a 502 mag, carbed.

If i run 10% ethanol, will I have a problem with my fuel system? Can the pump handle it? Do i need to change any of the fuel lines?

Will i need to adjust my carb to run a bit richer? How much? I think the motor might be running a bit rich as it is, anyway.

Hydrocruiser

Ethanol, when mixed with gasoline, causes the mixture to evaporate very quickly. That forces refiners to dramatically alter their gasoline to compensate for the ethanol. (Throughout the year, refiners adjust the vapor pressure of their fuel to compensate for the change in air temperature. In summer, you want gasoline to evaporate slowly. In winter, you want it to evaporate quickly.) In a report released last month, the GAO underscored the evaporative problems posed by ethanol, saying that compensating for ethanol forces refiners to remove certain liquids from their gasoline.

In short..avoid it if you can.

Griff

I would say that most of your running rich problem is due it being 94 octane. It won't burn as completely and will not make as much power as 87 octane in a stock 502 mag.
It will be fine to run it, although it would not be a preference. Also, do not store the boat for more than several weeks with ethanol.

Payton

What have you done to your engine that it reqires 94 octane? I ran a 10% blend,87 octane,in my boat 454 mags all last summer. no troubles at all. I did not leave the ethanol in over the winter.

sleeper_dave

I don't run 94 octane. Normally I run 89. But the 30 gallons of 89 sat in the boat all winter, and the octane level likely dropped a couple points. So i put 10 gallons of 94 on top to make sure i'm not running 85 or 86 octane.

Is 87 okay to run in a stock 502 mag? The timing is bumped up to about 31 total advance vs. stock 28.

Payton

I think stock timing is 34* total. 10* initial and 24* advance. I may be wrong.
87 octane is all you need. 89 and you will have a sooty transome from the unburned fuel.
If you added fuel stabilizer when you winterized, I would simply fill up with fresh 87. If not, then fill up with 89.

sleeper_dave

My book says the 502 has 8 initial and 20 advance. I know the module in it gives me 20 advance. When i bumped it up to 31, running 89 octane last year, i gained 2-3 mph.

I'll try 87 and see how the boat responds. I'm cautious, though, because i don't have an EGT gauge, or a knock sensor, and i can't afford another new motor.