40:1 or 50:1 two-stroke tools (what to do if you have both)?



Generally they re-use the head gasket - quite often they make their own replacement out of sheet copper, and anneal it every couple times they take it off - just throw it on the fire, pull it out and quench it.
Many of the Mopeds running around in Ougedougou and other cities are OLD colonial era units - Solex, Peugeot, Motobecane, Mobylette? etc from the early to mid sixties. Then there are the later Hondas etc and the new Tomy and other Chinese units. Many of the old ones have very little paint left on them - sun-bleached and worn to a fine patina.
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On Wed, 15 Jun 2011 22:11:43 -0400, clare wrote:

That's also a maintenance requirement (every 30 hours of run-time, IIRC) for the B&S engine in my mower. The head gaskets seem designed to be reusable, at least to a certain extent. I expect it might be a requirement for a lot of yard equipment, but nobody ever bothers :-)
cheers
Jules
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On Thu, 16 Jun 2011 12:59:09 +0000 (UTC), Jules Richardson

I've pulled the head oftermore like 60 hours and not enough carbon to worry about on both Tecumseh and Briggs engines with unleaded gas. Bach when gas was leaded it was a different situation - lead/ash/carbon deposits were sizeable and HARD.
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On Thu, 16 Jun 2011 21:14:14 -0400, snipped-for-privacy@snyder.on.ca wrote:

Interestingly, the local tool shed strongly advises 89 or 91 AKI (octane rating) of not more than 10% ethanol (which, here in California, is almost impossible not to use).
I'm not sure why they are so strong about not using 87 AKI with the two-stroke motors.
When I asked them about the 40:1 and 50:1 ratios, they tried to sell me this 'stuff' in a can which they say lasts forever and has the oil and gas already mixed (so they were of no real use).
I trust you guys - 'cuz you're not making money off of me - and I can trust your advice.
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wrote:

Small high output 2 strokes are high compression motors - and oil mixed with the fuel drops the AKI significantly - starting with 98 MIGHT yeild 87, 91 might give you 89

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On Thu, 16 Jun 2011 22:28:52 -0400, snipped-for-privacy@snyder.on.ca wrote:

I'm not doubting you ('cuz I don't know) ... and I had never thought about what oil does to the octane rating ... but ...
I would 'think' that oil would be harder to burn than gasoline ... so ... adding oil ... I would think ... would RAISE the octane rating.
Are you sure oil lowers the octane rating?
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On 6/17/2011 12:06 AM, SF Man wrote:

Your thinking is correct. the reason they recommend the higher octane is solely the compression ratios.
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Steve Barker
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On Fri, 17 Jun 2011 11:16:30 -0500, Steve Barker

No, it is not correct. Oil reduces the AKI of a fuel. And if you read to the bottom of the bassfisher blog you would see that the error was corrected.
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wrote:

Absolutely sure - and I'm likely one in a thousand on this group that actually understands octane and detonation in an internal combustion engine.
Octane of a fuel has NOTHING to do with how fast it burns - and if it did, FASTER burning fuel would have a higher AKI or octane rating. This is because of the way detonation happens - unburned fuel - endgasses - in the cyl dissassociate into hydrogen and oxygen radicals, which are extremey active and explosive. This only happens with temerature and pressure over time - so if the fuel burns FAST there is less endgas in the cyl, for a shorter time - so less chance of disassociation and detonation. (also part of the reason an engine knocks more at low speed than at high speed, generally speaking.
This is a very "dumbed down" explanation - but it is accurate as far as it goes.
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On Fri, 17 Jun 2011 16:20:55 -0400, snipped-for-privacy@snyder.on.ca wrote:

The Bruce Hamilton gasoline FAQ covers octane ratings in detail: http://www.faqs.org/faqs/autos/gasoline-faq /
Unfortunately, Bruce didn't add a question to the FAQ of: - Does adding 2-stroke oil to gasoline raise or lower the octane rating?
So, I will send him an email asking him to include that in the next revision of the Gasoline FAQ so that we may all benefit.
If he provides an answer via email, I'll post it here.
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On Fri, 17 Jun 2011 16:20:55 -0400, snipped-for-privacy@snyder.on.ca wrote:

Still googling, I find this which backs you up: http://www.off-road.com/dirtbike/tech/two-stroke-gasoil-ratios-20502.html
"When all of the two strokes (the old days) were developed, they all used Castrol petroleum oil at a 20:1 ratio and found that 92 octane gas had the octane reduced to 72 with presence of that much oil. Modern oils wont affect the fuel quite as much, but if you started with 86 or 87 octane regular fuel, you can see where youll end with a very low octane mix. You could end up with a pinging bike."
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