How much smoke is normal?

[gcw47]

Hello to all - I have read that the Gull has been called "The most efficient means of converting fuel to smoke" and I understand that. 2 cycle engines afterall. How much is normal, if there is such a thing? After just getting my newly restored 40 plus to run , I get very large clouds of nice blue smoke. The mixture seems correct as the throttle responds as I think it should, stops the engine when closed, apparently good power, sounds smooth, starts easily, etc. My fuel mix was carefully measured- 12 ounces of oil to 1 US gallon if I got that right. It's not really bothersome, just wondering.
Thanks

[40TPI]

12 ounces of oil to 1 US gallon if I got that right.

Well to be picky, assuming Wiki has it right you are shy on your oil mixture by 0.8 of a US fluid ounce.

Quote Wiki:
The US liquid gallon is legally defined as 231 cubic inches,[3] and is equal to exactly 3.785411784 litres or about 0.133680555 cubic feet. This is the most common definition of a gallon in the United States. The US fluid ounce is defined as 1⁄128 of a US gallon.

In reality it doesn't make a halfpenny of difference whether you have 12 or 12.8 of your ounces in one of your gallons. (We will put aside the semantic argument of whether it should be 90% petrol and 10% oil in one gallon of tank fuel or 10% of 1 gallon of oil added to 1 gallon of petrol - even British Seagull seem to have changed their minds at various times if you check out the wording on their tank transfers)

As you have guessed one persons fog is another persons small cloud so everything is relative. Also different motors in my modest flock generate different amounts of cloud/fog/mist when fuelled from the same batch of two stoke.

Having said all that I find that running a decent quality semi synthetic TCW 3 grade oil at about 22:1 on my 25:1 jetted motors feels just about "smoke free". These are vintage motors and I reckon that running them with that mixture should guarantee that my grandchildren will still be able to enjoy them too in twenty to fifty years time!

Looking back over all the BS published data and advice it is difficult to escape the notion that they were quietly advocating a far far greater quantity of oil than was strictly necessary to run the motors and avoid abnormal wear. I believe they were legislating oil content to protect motors from un-thinking owners leaving them on the back of boats or cooped up in humid lockers for extended periods with the attendant risk of seizure.

So, yes you can run them on straight 30SAE oil at 10:1 , amidst a cloud of blue smoke and also never do a decoke and it will probably never seize even if you leave it in a damp garage but who would subject a vintage motor to that treatment?

It is the opinion and experience of many here that a 10:1 jetted motor will, with careful adjustment, run leaned out to around 15 or 16:1 without any risk to sleeve bearings. The limitation on further leaning is maintaining a mixture tight seal on the main crankshaft sleeve bearings. Crankcases later than about 1967/68 are longer in length and therefore easier to seal with less oil in the mixture and were intended to run at 25:1.

Peter