91 versus 93 octane

[gp1200x]

I had head work done on a 97 XP and 99 XPL (plus a complete engine rebuild on this unit) 20 years ago and had PPG work the heads with their PPG Level 1 kit (head rework and carbs modified). I believe I told them to set it for 93 octane but not sure since I also had other skis modified years ago so it could be worked for 91. Old paperwork I have does not give me the answer.

Is there any way to tell which octane I really need to use? I have always used 93 but would rather like to switch to 91 non ethanol if I know I'm safe since I have found that the dried ethanol deposits clogged my accelerator pump lines which I had to clean out. There is only 91 free ethanol gas around here. 93 is 10% ethanol.

It would be nice to know if I can run 91, but not sure if a compression test really gives me a definite answer.

Worst case scenario is i run 93 and drain before winter and put in a little 91 non-ethanol to run it through.

 

[mikidymac]

Well, run the highest pump octane you have.
We only have 87, 89 and 91 here so we all run 91 with higher compression.
And all our gas had some ethanol and not a single issue.

 

[gp1200x]

I read up and found the explanation for the issues with small engines using gas with ethanol. I have other small engines including motorcycles and friends with the same issues. It turns out that the ethanol absorbs water in the tanks unlike gas. When the ethanol in the lines evaporates, dissipates completely, after sitting for a long time unused (which happens up North or unused for a year or two) it leaves water molecules coating the inside metal surfaces. This is what is causing the brass and aluminum surfaces to corrode leaving a white to yellow powdery substance and in the case of copper a green coating. This is a side effect of ethanol gas and it tends to effect small unused engines to a larger effect since it starts to clog small passages for the gas flow in carburetors. Older cars with carbs have larger passages and are usually used year round so the side effects are much less. From what I read most fuel additives usually won't dissolve the white material. I used air pressure and parts cleaner to clean my acc pump orifices.

So my plan is to run the 93 ethanol in summer, drain tanks as I always do and then add just a little pure 91 (Stewarts) in the tank and run it though the carb / engine for a few minutes. Start of summer I'll pump out any remaining gas and water and fill with 93 ethanol. I'm not going to let gas with ethanol sit in my engines for long periods of time anymore...too much work pulling carbs off.

 

[burtshaver2021]

I read up and found the explanation for the issues with small engines using gas with ethanol. I have other small engines including motorcycles and friends with the same issues. It turns out that the ethanol absorbs water in the tanks unlike gas. When the ethanol in the lines evaporates, dissipates completely, after sitting for a long time unused (which happens up North or unused for a year or two) it leaves water molecules coating the inside metal surfaces. This is what is causing the brass and aluminum surfaces to corrode leaving a white to yellow powdery substance and in the case of copper a green coating. This is a side effect of ethanol gas and it tends to effect small unused engines to a larger effect since it starts to clog small passages for the gas flow in carburetors. Older cars with carbs have larger passages and are usually used year round so the side effects are much less. From what I read most fuel additives usually won't dissolve the white material. I used air pressure and parts cleaner to clean my acc pump orifices.

So my plan is to run the 93 ethanol in summer, drain tanks as I always do and then add just a little pure 91 (Stewarts) in the tank and run it though the carb / engine for a few minutes. Start of summer I'll pump out any remaining gas and water and fill with 93 ethanol. I'm not going to let gas with ethanol sit in my engines for long periods of time anymore...too much work pulling carbs off.

That was a really good explanation, here in Ontario we have 87, 89 and 91 Octane at most stations. I run 91 in all my small engines mainly due to the fact that most of my small engines run seasonally and the 91 stores better due to the fact it has no ethanol in it. I had purchased an ethanol tester to verify that the 91 Octane indeed has no ethanol in it. I will sometimes run the 87 in my favourite Seadoo’s for the first part of the season but then switch to the 91 for the later part of the season.

 

[mikidymac]

I read up and found the explanation for the issues with small engines using gas with ethanol. I have other small engines including motorcycles and friends with the same issues. It turns out that the ethanol absorbs water in the tanks unlike gas. When the ethanol in the lines evaporates, dissipates completely, after sitting for a long time unused (which happens up North or unused for a year or two) it leaves water molecules coating the inside metal surfaces. This is what is causing the brass and aluminum surfaces to corrode leaving a white to yellow powdery substance and in the case of copper a green coating. This is a side effect of ethanol gas and it tends to effect small unused engines to a larger effect since it starts to clog small passages for the gas flow in carburetors. Older cars with carbs have larger passages and are usually used year round so the side effects are much less. From what I read most fuel additives usually won't dissolve the white material. I used air pressure and parts cleaner to clean my acc pump orifices.

So my plan is to run the 93 ethanol in summer, drain tanks as I always do and then add just a little pure 91 (Stewarts) in the tank and run it though the carb / engine for a few minutes. Start of summer I'll pump out any remaining gas and water and fill with 93 ethanol. I'm not going to let gas with ethanol sit in my engines for long periods of time anymore...too much work pulling carbs off.

A mostly empty tank with any fuel with ethanol or not will have a lot of moisture in it. You are much better off with a full tank of 93 octane ethanol and Sta-Bil.
Don't over think this or get internet scared. Been using ethanol fuel for years her in Cali as it is all we have without a single issue.

 

[gp1200x]

That was a really good explanation, here in Ontario we have 87, 89 and 91 Octane at most stations. I run 91 in all my small engines mainly due to the fact that most of my small engines run seasonally and the 91 stores better due to the fact it has no ethanol in it. I had purchased an ethanol tester to verify that the 91 Octane indeed has no ethanol in it. I will sometimes run the 87 in my favourite Seadoo’s for the first part of the season but then switch to the 91 for the later part of the season.

We have all octane levels around here but all have 10% ethanol. The only place where you can get non ethanol gas here within 100 miles is at Stewarts which is 91 octane and higher priced than the 93 ethanols but my only option. I wish it was 93 for my cars too.

 

[gp1200x]

A mostly empty tank with any fuel with ethanol or not will have a lot of moisture in it. You are much better off with a full tank of 93 octane ethanol and Sta-Bil.
Don't over think this or get internet scared. Been using ethanol fuel for years her in Cali as it is all we have without a single issue.

Did empty and full tanks over the years and use sta-bil every year but it doesn't seem to really make a difference. This is probably the third time I had to blow out the acc pump orifices with them clogging from sitting too long.

 

[Grim]

Question...doesn't the ethanol gas cause the green goo we are seeing in the gray lines?

 

[mikidymac]

Question...doesn't the ethanol gas cause the green goo we are seeing in the gray lines?

Not especially as in time they all do it no matter what fuel you have. If you still have Gray lines they need to be changed no matter what fuel you are running.