Understanding the engine terms “rich” and “lean”?

[^TANK^]

Nothing to do with the oil, just the ratio of petrol to air.

Please could you explain further to why a precise measure of 50:1 petrol to two stroke oil is neccesary then please?

 

Lots of explanations on the tinternet. Enjoy

I have searched but ended up very confused hence why I posted here.

[treequip]

Please could you explain further to why a precise measure of 50:1 petrol to two stroke oil is neccesary then please?

 

 

I have searched but ended up very confused hence why I posted here.

 

The oil lubes the engine, too little and you will get damage, too much and it will gas you out and foul the spark plug with unburnt deposits

[^TANK^]

I understand it a lot better now, thanks for the quick replys guys.

 

Two-stroke oil - Wikipedia, the free encyclopedia

[GardenKit]

Air/fuel mixture ratio applies to both 4 stroke and 2 stroke engines.

Most 4 strokes ( except stihls 4-mixy thing) use lubrictating oil in the sump to lubricate the engine.

2 strokes in general, especially those in our industry, require oil to be mixed with the petrol at a certain ratio. This oil lubricates the engine on its passage through.

 

Most modern oils are formulated to lubricate effectively at a convenient 50:1 ratio.

Too little will result in 'lack of oil siezure' whereas too much will result in build up of carbon and gungy oil deposits.

 

Too little oil in the mix will slightly richen the air mix, as there is a little more volatile fuel present in a given volime of fuel. Too much oil, equates to less volatile fuel so the air mix is very slightly weakened. Hence the strengh of the fuel/oil mix will effect the engine tune.

[miker]

i always add a touch more 2 stroke oil to my mix on really hot days when using 2 stroke equipment ie 5ml extra in a 5 litre mix

[Marc Lewis]

how do you tell/know if your saw is running too rich or too lean?

[Steve Bullman]

In general terms "rich" means fuel-rich from stoichiometric or lambda-1 or in laymans terms more fuel than required for calculated complete combustion in regards to air / fuel ratio. Lean thus means more air and less fuel in relation to a/f ratio - and these ratios are different between fuel and engine types; from memnory a 4-stroke gasoline engine is circa 14:1 i.e. 14 parts air to one part fuel. Overfuelling (rich) not only wastes fuel, but fouls the plug, produces more UHC in the exhaust and so on; engine will run cooler too. Running too lean engine will run hotter and more likely to experience temperature problems. In a 2 stroke, some refer to lean as too much oil in the mixture meaning the mix is thus fuel lean - not to be confused with a/f ratio. Not sure that helps much.

 

I got as far as the 9th word

[GardenKit]

I got as far as the 9th word

That far, Steve? I thought it was in a foreign language.

[Hoggin]

how do you tell/know if your saw is running too rich or too lean?

 

One way is to take the plug out and have a look at it...

 

 

At least, that's the way it works for a four stroke.

[agg221]

In general terms "rich" means fuel-rich from stoichiometric or lambda-1 or in laymans terms more fuel than required for calculated complete combustion in regards to air / fuel ratio. Lean thus means more air and less fuel in relation to a/f ratio - and these ratios are different between fuel and engine types; from memnory a 4-stroke gasoline engine is circa 14:1 i.e. 14 parts air to one part fuel. Overfuelling (rich) not only wastes fuel, but fouls the plug, produces more UHC in the exhaust and so on; engine will run cooler too. Running too lean engine will run hotter and more likely to experience temperature problems. In a 2 stroke, some refer to lean as too much oil in the mixture meaning the mix is thus fuel lean - not to be confused with a/f ratio. Not sure that helps much.

 

Thanks for that, really. I was aware of the term lambda-1 but hadn't made the connection with a stoichiometric mix.

 

It follows that using a 50:1 mix is slightly richer than a 25:1 mix. This should in theory become more noticeable in engines designed to run originally at 16:1. In practice, I haven't had to re-tune any yet and the plugs look good even after heavy use. It will be interesting to see whether this remains the case now I've finally found an air filter to fit (and the Allen Scythe can no longer ingest whole nettles).

 

Alec