How do I change one gallon of a 50:1 gasoline mixture to 40:1?

Mixing
RatioGAS:OIL UNITED STATESOIL per 1 U.S. GALLON Gasoline
(128 oz.) *INTERNATIONALOIL per 1 IMPERIAL GALLON Gasoline
(160 oz.) *INTERNATIONALOIL per 1 LITER Gasoline
(metric) 32:1 4 oz. 5 oz. 31.25 mL 40:1 3.2 oz. 4 oz. 25 mL 50:1 2.6 oz. 3.2 oz. 20 mL

Two cycle engines run on a mixture of gasoline and oil. Each engine type is designed to run on a specific gas-to-oil mix ratio.
IMPORTANT: Use only oil that is labeled for use in "Two-cycle" or "Two-stroke" engines. Home Depot and other stores now have "premixed fuel" of gas and 2 cycle oil.
To mix two-cycle fuel, start by putting correct amount of oil in gas can. Then slowly add correct amount of gasoline. Do not try to mix gas and oil directly in gas tank of equipment.

IMPORTANT: Do not use any fuel that is over 30 days old. Do not mix more fuel than you are likely to use in a month. Old fuel can gum carburetors and prevent starting. Always use fresh fuel.

The chart below shows correct amount of oil per gallon that each mixing ratio requires. Expect that yours will be between 32 gas to1 oil and 50 to 1. 32:1 and 50:1 are most popular.
Ratio GAS:OIL UNITED STATES OIL per 1 U.S. GALLON Gasoline
(128 oz.) *INTERNATIONAL OIL per 1 IMPERIAL GALLON Gasoline
(160 oz.) *INTERNATIONAL OIL per 1 LITER Gasoline
(metric) 32:1 4 oz. 5 oz. 31.25 mL 40:1 3.2 oz. 4 oz. 25 mL 50:1 2.6 oz. 3.2 oz. 20 mL

Guess you are asking this because you need to mix your 2-cycle engine oil with gasoline. One gallon = 128 fluid ounces if you are in the US. In the UK, 1 UK gallon = 160 UK ounces.
I totally plagiarized this information from numbers.com.
Not plagiarized: you want to use the correct mixture for your blower to get it to start easily. Your blower probably uses a mixture of either 50:1 or 40:1. I use a product called ProMix Premium that allows me to squeeze the bottle to measure out the correct amount of oil into a gallon of gas. I use two different gallon sized gas containers, one with a 50:1 mixture and the other with a 40:1 mixture. Between the two mixtures, all of my machines will start and run well according to their oil mixture requirements. Usually the machine will have a label on it to tell you the correct mixture, if not, check the owner's manual or instructions.

A pint is 16 ounces, add 1/3 ounce of oil for a 48:1 mixture.

Gary

for a 40/1 mixture use 3 ounces of oil ( 2 stroke) to a gallon of gas for a 50/1 ( which is what I recommend ) its 2.5 ounces to each gallon of gas, if you find that the machine is smoking a little too much,, back up on the oil just a hair,, but I don't think you'll need to

Hi gducci1949...

Use a 50 to 1 mixture...1 pint of oil to 6 gallons of gasoline
Please take time to rate me

Most of these mix at 50 to 1. 500ml of oil to 5 gallons of gasoline should do it. If you don't feel comfortable with this mixture try 40 to 1.

one small bottle of oil from the auto parts store ( i don't know the oz. size)to one gallon to one gallon of gasoline; mixed well

Yours is not a current model and I did not find a manual. The following is an excerpt from a 26cc MightyLite Blower/Vac UT08550/UT08951 "Operator's Manual":
This product is powered by a 2-cycle engine and requires pre-mixing gasoline and 2-cycle lubricant. Pre-mix unleaded gasoline and 2-cycle engine lubricant in a clean 1 gallon container approved for gasoline.
Recommended fuel: This engine is certified to operate on unleaded gasoline intended for automotive use.
Mix Homelite Premium Exact Mix lubricant with gasoline according to the instructions on the package. If Premium Exact Mix lubricant is not available, use a high quality synthetic 2-cycle engine lubricant, mixed at 2.6 oz. per gallon (US).
Do not use automotive lubricant or 2-cycle outboard lubricant.
NOTE: Premium Exact Mix fuel mix will stay fresh up to 30 days. DO NOT mix quantities larger than usable in a 30 day period.
PREMIUM EXACT MIX (50:1)
GasolineLubricant
1 gallon (US) 2.6 oz.
1 Liter 20 cc (20 ml)

If properly adjusted your blower will operate fine on 50:1 regardles of what the manual reads. HTH
Lou

3.2 oz oil in one US gallon yields 40:1 mixture.
2.6 oz oil in one US gallon yields 50:1 mixture.