General Two Stroke Question

[Mek-a-nik]

I'm no expert when it comes to 2 strokes.

I looked at a 2008 Homelite saw today. (The one I mentioned on the Flo Jet thread.) Complaint was that it won't idle down. It started easily. The first thing I noticed was excessive smoke. I asked the owner what ratio he had in it. He said, "16:1". I told him that was from the "old days" of 2 strokes. Anyhow, it didn't run badly. It did idle somewhat high, though.

First thing I did was put some 50:1 mix in it (Echo oil), and try it again. It started and ran almost perfectly. I only made slight low and high speed adjustments. I explained the things that can happen by running too rich a mix: fouled plug, carbon build up, frozen rings, clogged exhaust screen.

Will a rich mix make it idle high? I mean, I saw the results of changing fuel. But could something else have occured?

[bgsengine]

OIl does not burn as readily as gas - richer gas/oil mix = leaner fuel/air mix (with lots of unburned oil residue) - fuel system is delivering the same amount of volume to mix with air, but too much of that volume was displaced with poor burning mix oil - think on it a bit I would not be surpriced at a slightly high idle - it'd have to idle a little faster anyway to stay running - and as well, even a tiny tweak to mixture adjustment can make a huge difference, so it could be a little of both the fresh mix plus your adjustments.

[Mek-a-nik]

Funny, I even mentioned to him that the wrong fuel/oil mix can affect the air/fuel ratio, for the reasons you mentioned. I never took it to the "next level", thinking that it could affect the running.
Cool!

[wristpin]

At the time that unleaded petrol (sorry, gas) was introduced into the UK we were selling Victa two stroke mowers and started to experience various problems with what had hither to been reliable trouble free engines. To cut a long story short we found that in nearly every case the owners had been adding "a bit of extra oil" to the mix to compensate for the lack of lead!
Trying to explain to them that they were effectively upsetting the fuel to air ratio was met with a certain amount of disbelief and this was further complicated by adding that the lead was partly there to "preserve" the valves and valve seats neither of which were present in their engines. We stayed away from any discussion about the anti knock aspect of lead in fuel - was just going to complicate matters further!

[Mek-a-nik]

I see that a lot; I explain something to people and they look at me like, "yeah, sure pal". Sometimes to the point that they will disagree with me. "Well, what am I doing here, if you know how to fix it?"

[KE4AVB]

I don't try to explain it too much anymore as some customers do tend think they know more. I tell them I can only present them with real life info instead of the theories that I heard. There is so much mis-information out there that is hard to overcome at times.

I would think that these lower compression engines would idle a little higher due to the increase compression cause by extra sealing effects of the extra oil but that is just a thought; too many variables that make my head spin.

It like the Husky 345 I just completed the repairs on. Customer said he contacted several shops after I gave him my diagnosis of what cause his engine to lock-up and they all said it was impossible for the cover plate to come loose and jam the piston. Under normal conditions it would not but in this case the cover plate was installed at the factory incorrectly which led to the failure 8+ years later. It had finally work it way out of partially hold by the Crank bearing seal. The strange thing is how the engine never gave any problems without that cover plate being in place.

[OverKnight]

First thing I did was put some 50:1 mix in it (Echo oil), and try it again. It started and ran almost perfectly.

Is it safe to run an engine designed for a gas:oil ratio less than 50:1 on this mixture? I have the two-stroke engines requiring 24;1, 40:1 and 50:1 ratios. I use the Echo oil for all three mixtures, but it would be great if all could safely run on the Echo 50:1 blend and not have to keep three different gas cans.

[bgsengine]

First thing I did was put some 50:1 mix in it (Echo oil), and try it again. It started and ran almost perfectly.

Is it safe to run an engine designed for a gas:oil ratio less than 50:1 on this mixture? I have the two-stroke engines requiring 24;1, 40:1 and 50:1 ratios. I use the Echo oil for all three mixtures, but it would be great if all could safely run on the Echo 50:1 blend and not have to keep three different gas cans.

yes - you may need to "dial in" any adjustments a tad but - those mix ratios were determined *at the time the machine was built* using the most modern oil at the time - 2 stroke oil has improved by leaps and bounds and that is why the ratios have been able to thin out - However, thinning out your mix ratio will also increase the volume of gas being fed to the carb, so, as mentioned, you may need to fine-tune some of those carbs after changing to 50:1 mix In fact the oils are designed to be mixed at the ratio they were sold at - so the echo mix at a 24:1 ratio is gonna be a huge waste of oil and money

It isn't so much the volume of oil that is needed, it is the lubricating qualities. you have to remember back when they first made 2-cycle engines, oils were pretty much the same thing you would put in your engine crankcase... these days 2-stroke oil is far more specialized and different formulations for different applications as long as you are running a high quality brand 2-stroke oil *designed for* the type of equipment (chainsaw mix oil in small handheld machines, outboard oil in outboard motors only, snowmobile oil in, you guessed it, snowmobiles!) - you can run it at the ratio it was formulated for with no problem.

[OverKnight]

Thank you, bgsengine, and Mek-a-nik, sorry, I didn't mean to hijack your thread. Hopefully my questions will add to the good information your thread started.

What kind of dialing-in do you mean? The carburetor? I have a Husky tiller with a Tecumseh TC300 engine, which I purchased at least 15 years ago. This is the engine that requires the 24:1 ratio. I also have an MTD snowblower with a Tecumseh HSK845 engine, also purchased about 15 years ago, which requires a 40:1 ratio. Will the carburetor mixtures for these need to be made more lean or rich? What about the spark plugs; would a hotter or colder heat range be advisable?

Thanks again.

[KE4AVB]

What kind of dialing-in do you mean? The carburetor?

Yes, it is the fine adjust of the fuel mixtures.