Will preface this with an apology for the long spiel
I am far from an expert, but I do have more than a passing interest in oils
A few years ago, I read the original document from a conference back in the mid 70s, when a group of engineers, (surrounded by a careless API system with ATP TC loose classification of 2 stroke oils) put a proposal forward for standardized measure of 2 stroke oils, including the engines utilised to test them - one being a honda bike engine, the other being a small Suzuki generator engine.
This plan ended up becoming the JASO ratings measure. It was well into the 80s by the time this occurred from memory.
There are 4 JASO ratings:FA - probably you could now say oils in this grade are FA - F***ing Awful - they are the base level .
The sole FA rated oil left on the market is Shell Greenskeeper
https://www.repco.com.au/en/oils-fl...oke-engine-oil-0-2l-300012346/p/A5325174 FB - better lubricity, a bit lower smoke, less carbon.
Oil like Penrite Greenskeeper, Castrol Garden 2t, generally mineral oils
FC - much lower smoke, lower carbon, better detergency to keep engines clean
Most semi syn oils - penrite Hi-per, Castrol Activ, most of your lawn oils sold by bunnings, GA spares, Jakmax, etc.
VICTA 50:1 2 stroke oil is JASO FCFD came out in the early 00's - same as FC but better detergents.
So it is practically ashless, great lubricity, no buildup of carbon, and can help to (in theory) scrub carbon out.
Mostly are full syn oils - Penrite MC2st ester, Castrol TTS/Power1, Stihl oil (ultra) and husqvarna (LS+ is semi syn)
Putting aside smoke and carbon for a minute, the basic need for lubrication is the primary need on many of the engines we are using. Ball/needle roller bearings are great from reducing oil requirement. All Victas post 1976 have them on big and little ends and mains.
BUT pre 76 models use at least sintered brass little ends (up at the gudgeon). A bush needs more oil than a roller bearing.
Who is to say what a lot of these little 25cc chinese line trimmers have in them (most are needle bearing but probably pretty poor quality high friction ones)
Then there is film strength - we are asking a tiny bit of oil to go through a motor, lubricate (by my count) about 5 bearings on a FC engine, then get in/around piston rings, around the gudgeon, lubricate the cylinder walls, and still have a bit left to lubricate the exhaust side of the cylinder after ignition.
There are engines out there which are very prone to clagging up the exhaust spark arrester (echo especially).
Stihl Ultra oil is also bad for this when you don't run them flat stick.
There are engines that are easy on oil, and ones that are hard on oil. If its tuned properly and is smoking hot, use less oil.
No amount of tuning will get my Husqvarna 125bv leaf blower to run well on 25 as it does on 40.
Margin of error is another point - I know for a fact when i squeeze the penrite bottle up to the graduated line in the little top measurer part that when tipped, only about 90% of it will come out. No problem for me as I use a mixing bottle, but if you are squeezing then tipping 20ml into a 1l bottle of fuel without checking, your 2% mix (50:1) is now 1.8%
On 25:1, your 40ml is becoming a 3.6%
I have seen enough of
stupid marketing decisions to just err on the side of caution. I have an ozito earth tiller that says 40:1, but the previous model (same engine different colour) said 25:1. Same with my GMC chainsaw saying 25 and my identical ozito saying 40.
I have a armful of old ryobi Ryan IDC motors - half say 25, 1 says 32, one says 35, one says 40 and another says 50. I have seen an earlier one say 20:1
The engine stayed the same (mostly - aside a stupid compression release), marketing decided that as long as they don't cark it too quick, low smoke is a benefit.
I use Penrite MC2st Full synthetic FD. Its about $22 on special for 1l - I use between 1 and 2l per year. I run near what the manufacturer says - except 16:1 - that is from a time when the oils were so poor that the exhaust side would be fried - or 50:1.
I mix 3 bottles of fuel - 25:1, 40:1 (which is actually 35:1) and 50:1 (which is actually 40:1)
I often will get a decent puff of smoke on start up (from victas on 25:1), but none when running in any of them.
Cannot recall a properly carboned up plug - they all come out pretty clean. My technique for running is exactly what everyone says not to go - I rarely use full throttle on hand helds and only full throttle on mowers about 1/4 of the time
I did kill a plug last year on a victa powertorque. Was scalping the hell out of the lawn. a few weeks prior I tried doing it with a 190cc quantum and it had a coronary and couldn't do what I wanted.
I put about 2 tanks through it and got about 25+ catchers off of only an 80sqm area. Full throttle the whole way at low height of cut.
Towards the end it started backfiring up the snorkel and died. Was worried I had cooked the motor as the plug a tad dry, but with a new plug it finished off fine, and a piston inspection through the exhaust port revealed no change (aside from a lot of carbon being burnt out). that was on 25:1 - 50:1 might have seen a different ending.
