Re-examining Fuel and Fuel Mix Ratios

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Re-examining Fuel and Fuel Mix Ratios

Postby Schoobytwo (Bruce) » Sun Feb 21, 2016 9:42 am

Hi All,

It almost the end of another year and again, I have witnessed a winter where more than one Diablo has scorched a piston (or two :o ). Yet mine have run without issue and I wonder if it is just luck or something else. So I am writing this post looking for some feedback from the experiences of the forum to form an opinion of the matter.

First I want to start out by presuming a motor does not have any vacuum leaks. Motors have new seals and gaskets and have had the crankcase pressure tested for verification. Motors that have the ignition systems set up right and are using a spark plug with the proper heat range (I always use a Champion D-14). Carbs are original in design which means if they are not an HR3A or HR14A, they are one of the HR carbs that are similar in that era. Also want to presume that carb jets are running at the approximate factory settings which is idle jet out 3/4 turn and high speed jet 3/4 to 1 turn out. Basically saying that the motors to our knowledge are repaired and set up to the best of our abilities.

So if that is the case above and a motor burns a piston, what can only be left to question is the fuel and fuel mix ratios.

Many have opinions on the effect of ethanol in our gas mix today. Some have opinions on lead versus lead free. I don't have thoughts on the lead versus lead-free, but I was recently talking with a good friend whom I respect his knowledge much and he feels fuels with ethanol burn hotter than fuels without. Now many people have stated how hard ethanol is on gaskets and diaphragms, but I don't remember a conversation about the heat comparison of fuel with ethanol verses without.

My recommendation in the past is to use a regular octane fuel as in my head, I'm thinking the higher the octane, the hotter the burn. His thinking took me aback when his opinion was just the opposite. He says octane does not produce a hotter fire in the cylinder but ethanol does, therefore we should always be using a premium fuel without ethanol. I'm very interested in opinions here.

Regarding the fuel mix, original Diablo and Hirth fuel mix ratios back in the 60's was 16:1. Remember that 1 quart to 5 gallon mix? That was 20:1. I and many others run 24:1 and I've never recommended running leaner than that. I've heard all kinds of rational to run 30:1, 40:1 or even 50:1 when using high quality oils. I've never bought in to that as oil is cheap. And I believe today's oils are much cleaner and thus run much cleaner than in the 60's, so I don't think I come home smelling like an oil can. With a few more motors burning up this winter, I'm thinking of richening up the recommendation to 20:1.

So the bottom line of this discussion is hear your thoughts on using premium fuel with a 20:1 mix - Pros and Cons.

Bruce
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Re: Re-examining Fuel and Fuel Mix Ratios

Postby BillNH » Sun Feb 21, 2016 3:18 pm

I've always run my old 2 strokes at 20:1, that's 1 qt to 5 gal (20qt). I never had a problem below 40 deg F.
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Re: Re-examining Fuel and Fuel Mix Ratios

Postby Barrie2777 » Mon Feb 22, 2016 2:29 pm

I run my hus-skis with a 32:1 ratio, premium gas and CASTROL 2 stroke snowmobile oil. I have never burnt a piston.


Henroit Filion,(HUS-SKI mechanic in 1963) told me that it was the gas which kept the piston cool therefore a lean mix is the problem and not the oil ratio.
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Re: Re-examining Fuel and Fuel Mix Ratios

Postby BillNH » Mon Feb 22, 2016 2:35 pm

That would be right. Anytime you have any engine with excessive carbon build up, you lean out the mixture to burn hotter and remove it.
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Re: Re-examining Fuel and Fuel Mix Ratios

Postby kmskidog » Mon Feb 22, 2016 9:59 pm

Hello all, here is my two cents worth. Most piston failures are caused by lean running, not the ratio of oil. Now saying that, there is a minimum amount of oil required to protect the engine. I run almost all of my 2 stroke engines at 40:1. But, I choose a high quality oil. I will never run oil packaged by 4 stroke oil experts. I am talking about companies like Pensoil, Quaker State, Mobil, etc. They do a great job of blending oils for vehicles and other 4 stroke engines, but they only sell 2 stroke oil to complete their product line. They do not understand the needs of a 2 stroke engine. I also will not run generic packaged oils, they are cheaper because the blend is cheaper. What I do run is OMC or
Mercury outboard oil at 40:1. I have never had an oil related engine failure. Buying a large amount of broken snowmobiles throughout the years, almost all piston and bearing failures I have seen have been related to running lean. Leanness can be attributed to an incorrect carburetor setting. Many times if the engine has float type carb(s), the leanness is often caused by deposits in the bowls which plug off the fixed jets. But, many times in these old engines, the cause of failure is air leaks to the engine from damaged or worn out seals or damaged intake gaskets/carb flanges. It is crutual at the time of waking up an engine that has not run for an extended period of time, to pay attention to and replace faulty seals and gaskets. Keep in mind that excess oil creates carbon in the engine. Carbon is abrasive to the engine, causing the engine to ware out faster, so using too much oil causes other problems including fouled plugs and engine ware. Octain, the higher the octain, the slower the burn, the lower the heat. By slowing down the burn, you retrieve more power from the fuel. Ethanol is extremely bad for engines not designed for it. First of all, it burns faster and hotter. Second, it takes the flexibility out of rubber parts like seals. If seals loose their flexibility, they are likely to develope an air leak. Ethanol will many times breakdown the rubber in carburator flanges, which can again result in cracks and a subsequent air leak. I never use ethanol in small engines unless I have no other alternative.
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Re: Re-examining Fuel and Fuel Mix Ratios

Postby jayvee43 » Wed Feb 24, 2016 9:59 am

kmskidog wrote:Hello all, here is my two cents worth. Most piston failures are caused by lean running, not the ratio of oil. Now saying that, there is a minimum amount of oil required to protect the engine. I run almost all of my 2 stroke engines at 40:1. But, I choose a high quality oil. I will never run oil packaged by 4 stroke oil experts. I am talking about companies like Pensoil, Quaker State, Mobil, etc. They do a great job of blending oils for vehicles and other 4 stroke engines, but they only sell 2 stroke oil to complete their product line. They do not understand the needs of a 2 stroke engine. I also will not run generic packaged oils, they are cheaper because the blend is cheaper. What I do run is OMC or
Mercury outboard oil at 40:1. I have never had an oil related engine failure. Buying a large amount of broken snowmobiles throughout the years, almost all piston and bearing failures I have seen have been related to running lean. Leanness can be attributed to an incorrect carburetor setting. Many times if the engine has float type carb(s), the leanness is often caused by deposits in the bowls which plug off the fixed jets. But, many times in these old engines, the cause of failure is air leaks to the engine from damaged or worn out seals or damaged intake gaskets/carb flanges. It is crutual at the time of waking up an engine that has not run for an extended period of time, to pay attention to and replace faulty seals and gaskets. Keep in mind that excess oil creates carbon in the engine. Carbon is abrasive to the engine, causing the engine to ware out faster, so using too much oil causes other problems including fouled plugs and engine ware. Octain, the higher the octain, the slower the burn, the lower the heat. By slowing down the burn, you retrieve more power from the fuel. Ethanol is extremely bad for engines not designed for it. First of all, it burns faster and hotter. Second, it takes the flexibility out of rubber parts like seals. If seals loose their flexibility, they are likely to develope an air leak. Ethanol will many times breakdown the rubber in carburator flanges, which can again result in cracks and a subsequent air leak. I never use ethanol in small engines unless I have no other alternative.


Here is my 2 cents. Also. Ditto with everything you said Skidog. Slow down the burn, get max power and keep top of piston cooler. The rest will stay in place, the walls and skirt will stay together. No Ethanol. EVER!!!!!! Bad. :o

I'm an old dog when it comes to the older outboards also. OMC, Mercury and Yamaha of today. Keep carbon build up low, and piston cooler. (That my friends is the formula) :P
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