McCullough Eager Beaver - What oil mix?

[ericm979]

Often the limited carb adjustments are already as rich as they can go and are still a little lean on 50:1. 40:1 is not much leaner fuel:air ratio but if it's already on the edge....

The special carb tools are under $10 for a set on ebay or amazon. I pull the limiter caps off and trim or discard them as appropriate.

Electronic self adjusting carbs will have no problem tuning themselves for 40:1.

Based on my two stroke motorcycle experience I prefer to run high quality synthetic oil at 50:1 in saws used for felling and bucking. If I was chainsaw milling I'd go richer on the oil. Chainsaws have a low power output per CC compared to dirt bikes. And they're fan cooled so they don't overheat like an air cooled dirt bike at low speeds. Hence they don't need as much oil. I've run anywhere from 24:1 for road race bikes to 75:1 for water cooled trials bikes.

Excess oil will cause faster carbon accumulation in the engine and exhaust system.

Old saws' oil specs are for oils commonly used in that time. Sometimes just plain 30wt. Two stroke oil has come a long ways.

 

[ericm979]

Interesting.... So it would be running leaner, but does that still mean hotter (as we typically think when lean) if there's more oil?
Would you burn the top of the piston, but no scratches/scoring?

Yes leaner fuel:air ratio means hotter temps. Evaporating fuel sucks up a lot of heat. The oil does not evaporate or burn like fuel.

Whether it's leaner enough to cause engine damage depends on how lean it was already, how hot it is, etc. Engine damage from running lean fuel:air can include damage on the top of the piston from detonation, and/or damage on the side from ring sticking due to piston deformation. Since it's hard to hear two stroke detonation and once it happens things often progress quickly, the engine usually gets run until the piston seizes. Then there's be damage on the piston skirts.

 

[xyz123]

My 550 545 32:1 and AT adjust on it's own. Guess what no issues like the guys running them 50:1 with bearing etc.

If I had them today it would be 40:1 as all my stuff is.

So dont try and sell me that crap wont adjust or limited. On carbs with epa stops just pull and adjust the dang things.

The MT 441 I worked on other day was running sweet with 40:1 I did for a guy.

 

[xyz123]

IMO just adjust your carbs or your AT MT will do it for you for your mix you use. Simple IMO

Reason I went to 40 is when I dump folks crap mix out. I tune their saws. Well when I was running 32 I had maybe 2 saws in my time working come back to being to rich once the owner put 50 in them. So I readjusted their saws to their mix.

So now I tune them with 40 and never had one come back saying was to rich if the mixed their 50.

 

[Storm56]

Tuning a 2 cycle engine is one of those things that you have to get a "feel" for. There are plenty of you tube videos to teach you what to watch for.

Most 2 cycle engines today are set on the lean side for emmissions and have "limiters" on the adjustments. It is simple to remove them so they can be properly tuned. Echo is particularly bad in this regard even though they make excellent products.

I generally set my stuff up a tad on the rich side, gives a bit of a safety margin. I use my stuff enough that I can tell if something has changed and adjust accorgdingly. Ethanol free gas if you can get it is much better than the E-10. Run at least the 89 octane, 90+ is even better.

I have never lost a 2 cycle engine due to a lean condition in 40+ years of owning them. But I learned how to tune and pay attention, and I run them a lot. If in doubt, richen it up! Worse thing that will happen is a fouled plug, much better than lunching a piston or worse ruining a cylinder.

There are quite a few things that can cause an air leak in a 2 cycle and cause your mixture to go lean and burn up an engine. A 2 cycle runs the strongest just before it starts to seize. If your engine starts running like the proverbial "raped ape", shut it down immediately and get it checked out.

 

[Storm56]

Forgot to add, bad fuel has likely ruined as many engines as running lean. Use stabilizer and keep your fuel fresh!

 

[YardBikeBob]

Don't know a thing about your chainsaw. However, I have a fetish of mid-70's D400 Lawn Boy 2-cycle mowers. They recommended 16:1 ratios then. The reason is that, although there are conventional bearings for the connecting rod, the crank end bearings were a bronze bi-metal bushing. Keeping those oil soaked was always a good idea.

Do your homework before assuming you're smarter than the manufacturers' engineers.