-
The conversation seems to be ongoing for the oil ratio thing within trials.
As I understand it, it makes the mixture leaner in the sense that the fuel is less oil-rich.
Various sources from the manufacturer recommend 80:1, but I am certain I saw a sticker or note somewhere stating 50:1.
The bike shop initially told me to use 75ml to 5L which is 66.7:1, and told me some guys run as low as 100:1 which would be 50ml per 5L.
The idea of less oil in the premix fuel means less un-burnt oil making its way into the exhaust. Less smoke, less saturation on the exhaust packing. Less fouling on the plug.
Bearing in mind this is the plug that I pulled out last week, after a few hours of running, there is both way too much sooty deposit, and a lot of unburnt oil on the plug. This is prior to making any changes to my running.
1 Attachment
-
pdlouche
-
I think the logic is on the lines of the amount of oxygen available is limited by the swept volume of the cylinder(s), and an excess of fuel leads to incomplete combustion and carbon / unburned fuel in the exhaust part of the cycle with soot deposits around the cylinder head and exhaust. Petrol has a calorific value significantly greater than lubricating oil, so reducing the oil increases the proportion of combustible fuel in each cycle, i.e. increases the proportion of fuel that cannot be burned. Because the oil burns less readily than petrol, the unburned portion tends to be mostly oil, giving an impression of too much oil in the mix.
I can believe this applies to older engines where everything goes through the carburettor and oil levels are much higher (the handbook says 20:1 for my 1952 Trojan!), but it might be different for newer designs where oil delivery is separate from petrol?
In any case, you'll often find complete strangers will claim to know more about your machine than you do, especially if you can't get it going and a crowd gathers...
MrE
Does reducing the oil effectively make the mixture richer in that there is a higher proportion of petrol in the fuel / oil mix? If this is the case you might be doing several things at once which will counter each other?
I don't know about modern 2 strokes, but the older bikes I play with use pre-mix and there's always a range of opinions on this - certainly there are machines on club runs that often suffer from overheating, generally attributed to running too lean, and then you hear things like "it's supposed to be 24:1 but I put a bit extra (oil) in to be sure"...