Farmall Cub

On these old tractors is it ok to use unleaded gas or should one add a gas additive ?

Unleaded is fine.

What about octane?
I read that it should be at least 90. That means $premium$ ?

I don't have a Super A but I would be shocked if a 6:1 compression ratio tractor engine needed premium.

I just run regular unleaded gasoline in mine

Regular gas is fine.

Al

382cr62 wrote:What about octane?
I read that it should be at least 90. That means $premium$ ?

There are at least 3 differnt measures of octane. Don't mix numbers off one scale with numbers from another.

I have worked on several engines that were victims of valve / valve seat damage from unleaded fuels. As most of us know the lack of lead can and does cause problems, but mostly in heavy load applications. 10 - 15 years ago I repaired several truck engines mostly big block fords (I'm a Ford guy so that is what I worked on) from the sixties and early seventies that the valves eroded into the seats and were in terrible condition. Most of these were construction or farm trucks pulling heavy trailers, etc.
Others are right about the octane; It will not be an issue on low compression tractor engines. Modern car engines run 2 or more full points higher compression ratio than our old tractors do, with no problems.

Others may not agree with me on this, but here is what I do on a couple of my tractors. I have a cub and a regular A that have belly mowers and see regular use with moderate to heavy loads. I go to my local air port and buy 10-15 gal. of aviation fuel at the beginning of the summer. I mix 2 gal with 5 gal of regular gas, and burn this mix in these two tractors. They really run good and it adds a little lead to the mix.
One other note: I run pure Aviation fuel in my weed eaters, chain saws, push mower, tiller, and my Honda generator. Some may say it is wrong, or a waste of money, but it works great. No more sour fuel after a sitting a month or 2, and there is no alcohol to cause issues with rubber lines and carburetor parts. Many of my small engines sit during the off season. I have had Aviation fuel sit in my generator for over a year and it is as fresh as the day I bought it.
Now the bad part. It was just under $6.00 per gal last spring when I bought it. Now before you say thats too much money think back 25 years, and remember how little trouble we had with carburetors, fuel lines and other rubber parts back when we had real fuel to burn. My time spent fixing fuel related problems on small engines has almost disappeared. This leaves me more time for rusty tractors.
Brad

Fact of the matter is we will not use our tractors enough that lead or no lead will make a difference.

If your tractor goes down with a case of eroded valve seats, it was like that when you bought it. You didn't cause it. It took decades to get that way.

Now before you say thats too much money think back 25 years, and remember how little trouble we had with carburetors, fuel lines and other rubber parts back when we had real fuel to burn.

I can get "100% GAS" locally. Am I better off with it? It is about the same price as the 93 octane "premium".

382cr62 wrote:
I can get "100% GAS" locally. Am I better off with it? It is about the same price as the 93 octane "premium".

A lot of the same people that say to do something to add lead will say to use the 100% gas. IMO you are wasting your money. Most all our gas here now is 10% ethanol. All our small engines still start, and sometimes the gas sets all winter. The old tractors run fine. Maybe it's the climate, I don't know. But we haven't done one thing different since the advent of unleaded, or ethanol, and everything is ok.

Al

I like the 100% gas and use it when I can. And the ethanol is horrible on small engines, I know this for a fact I work on them about every day it reeks havoc with the rubber parts, the primer bulb is the main problem, Stihl has improved the gas lines but the primer still gets soft . We have 100% gas at work, I know the boss would not pay the higher price for nothing.
The new mowers with gas engines seam to do fine.