2-Strokes and ethanol

[LA F2 Flyer]

As I get closer to my first engine run, the issue of ethanol levels in the fuel here in my sate of California has been raised by other folks using Polini engines.

Polini recommends (strongly, at that) not using fuel with higher than 5% ethanol to run their engines, or run the risk of holed pistons, etc. Fuel here in California is 10% ethanol (everywhere, that I am aware of).

Short of driving to another state to buy my mogas (and from what I understand avgas isn't ideal either, due to the lead content fouling 2 stroke plugs), it seems my only option is to buy ethanol-free TruGas from the local Home Depot at roughly $35 a gallon (gulp).

Hoping some members have other (better) suggestions.

I am also curious to see what types of fuel builder/flyers in other states are dealing with or have available.

[Allen Sutphin]

Quit racking your brain over 10% ethanol. Use 91 or 93 OCT. 87 is truly 10%, 91 or 93 is not. I've ran it in my Rotax for 12 years with no problems and always use 91 or 93. A lot of the stories you hear are from 25 years ago.

[LA F2 Flyer]

The topic only comes up because of a recent Facebook conversation I had seen concerning the Polini and holed pistons. Apparently several other Polini owners have complained about similar issues; engine seizure, sudden stoppage, etc. Polini's response was to avoid using ethylated fuel. Not sure if this might have been unique to Polini engines or not...just relaying what I had read and thought it could spark a conversation. (See what I did there?)

[Allen Sutphin]

Old fuel is more harmful than ethanol fuel. At todays prices its hard to dispose of 3 or 4 gal of gas. Most just go ahead and run it. Of course, anything more than 10% is a no-no. And there are additives that can lessen the ethanol effects on an engine. A marina is a good place to get non-ethanol gas.

[Badland-F5 Pilot]

Didn't know about the marina. Makes sense since many small outboards are 2 stroke. I've looked into the ethanol issue and it appears it's not the ethanol itself that's so bad for the engine but more about the water that the ethanol absorbs that's a problem, causing corrosion issues. Most rubber seals and gasket material today can easily handle the ethanol. Keeping the fuel from being contaminated by water appears to be the big issue. I've checked into additives. One of the least expensive but appearing to be one of the better additives is HEET. Comes in a yellow bottle at Wally World. It out performed Stabil and several other higher cost additives.

I've also read about the issue with the Polini holed piston problem. I wonder how many of those are from people not watching their CHT/EGT, and they simply burned up the engine on full power for too long a period of time? Both Peer and I've owned and run 2 stroke motorcycles. I've never had such a problem, but also, never ran them at full throttle for a long period of time. They weren't designed for that. Two strokes are great for massive power in short bursts. I'm thinking, that may be the real issue. As long as we watch how long we keep the engine at full power, watch that CHT/EGT, the Polini and other 2 strokes most likely will be fine. There are a lot of people flying them to point to a real engine issue or maybe it's an issue but marginal and manageable?

[Allen Sutphin]

Most of the run-of-the-mill additives are alcohol based. One doesn't need to add more alcohol to the fuel. I've been using an additive called Startron in my engine for years.

[LA F2 Flyer]

I raced two strokes and as a result DID run them at high RPM for extended periods of time, and I was using ethanol gas without problems. Which made me curious as to why the Polini might be so susceptible to issues from ethanol. Todd may have nailed it with the "water attraction" issue. It was never an issue with my race bikes because most of the fuel was used in a day, and the rest removed and used elsewhere afterward.

[Allen Sutphin]

Old fuel, bad timing, can both burn holes in the piston. But the gas/ethanol usually gets the blame. I am not familiar with the Polini engine or the timing setup so one would assume its a type of CDI ignition with a small advance in the timing system. Just me, but if I was spending 30K on an airframe, I would seriously look at another 2 stroke or even a 4 stroke. B&S makes some industrial 4 stroke engines in their racing division that are in the 35-40 hp range. My 503 ran flawless from day one as did the Hirth.

[Badland-F5 Pilot]

The good part - a lot of options. The bad part - a lot of options!

[LA F2 Flyer]

Allen, there are a lot of options out there, that's certain. The biggest issue for me is staying under the 254 limit. I bought the Polini used from Chris; it was on one of his earlier builds which he had sold with a different Polini hanging off it (water-cooled as I recall). For now it fits my mission, which is basically buzzing the hilltops around El Mirage lakebed. If I have an engine-out, I really can't miss the runway.

I would love other suggestions that don't break the bank (or the weight limit).

But I had heard good things about the Polini and the price was right. The downside seems to be that they need to be babied (from the sound of things).

[Allen Sutphin]

A few things about 2 strokes, they have very few moving parts to go bad compared to a four stroke, get fresh oil with every breath, run like a turbine above idle, cheap to overhaul and with proper operation and maint, dependable. And no four stroke can match the power/weight ratio of a 2 stroke. Spend a little bit of time learning the inside and out of your engine and you'll have very few problems. People spend up to years building their airframe and countless dollars, yet won't spend a few days or a month learning their engine. Maybe even go as far as spending a couple days going thru an overhaul with a good shop.

[Badland-F5 Pilot]

Good to know information Allen. The only Polini that I've heard of issues with is the 303, a fairly new engine. I possibly may go with a Polini after some information I found about the 1/2 VW that I don't care for. I've learned that the engine even when well balanced with a crank counter weight still has a lot of vibration. This isn't so much of an issue for me, but from what I understand it is for the propeller. Because of the vibration composite props are said not to be able to used on a 1/2 VW. Only wooden props can handle the vibration. If correct, that means much more weight. Like Peer, that's not something I like the sound of. The other issue is that even the 45 HP 1/2 VW is said to provide a low climb rate in the 200 to 300 fpm area. That doesn't sound so great to me either. I was heading in the direction of the 1/2 VW, but may fall back to the Hirth F-23. I won't gain much in the way of weight savings (78Lbs vs 82Lbs), but I agree that with proper care, two strokes are reliable. Since I know the Hirth can run a composite blade and may provide a better climb rate than the 1/2 VW, it may be the best way for me to go, except - the F-23 doesn't get very good fuel burn.

Then I find this article - so maybe the Polini is the way to go. Other than not being a flat, opposed, boxer (however you wish to name the design) engine, it does have a lot of positives about it - light weight, low burn rate, reliability, and high torque for short take offs.

https://jameswiebe.wordpress.com/2014/1 ... er-except/

Of course by the time I get my kit, have it completed, who knows what will be available.

[Fritz280]

I have accumulated some experience with the Polini 202 in paragliders that I thought I would share. In my experience ethanol is not the problem. For the rash of paramotors with holed pistons (Polini and all other brands as well) the issue is that paramotors use diaphragm pumps to pull fuel up 24” plus to the feed the carb. Add some G and you are trying to pull fuel up a multiple of that This can exceed 72” in some cases. Now, let’s pause for background, we put water in a pot on the stove and raise the temp till it boils so we tend to think that if you want to boil liquid, you raise the temp. BUT, you can also just lower the pressure to boil a fluid. Near all foods will have tiny print of high altitude instructions because the boiling point is lower in the low pressure conditions found at high altitude. Auto fuels are formulated with a certain Reid Vapor Pressure, RVP will determine at what conditions the fuel (or portions of the fuel) will boil. Auto RVP is different in different locations and at different times of year all over the country and the best it can be is 7.8psi the worst (most likely to boil) is 10.5psi with the +1psi for 10% ethanol content. RVP is low (less likely to boil) in avgas (5.3psi) it is also the same year round and everywhere that’s why it seems to solve all problems and may be the best choice. The polini motors don’t need 100 octane or alcohol free, they need a consistent and certain supply of fuel. Badlands aircraft have the fuel tank behind the pilot don’t know the number of inches rise to the fuel pump or what kind of fuel pump Chris is suggesting. I would run a small electric pump such as a Honda NS250 01-07 or other factory carb motorcycle electric pump. This pump would be located below and close to the tank feeding the Polini factory vacuum fuel pump or a header tank. Actually I wouldn’t use the 202 factory Mikuni fuel pump as it’s rated at 15lph and a 33hp 2 stroke needs 16-18lph at full throttle. Can’t say the pump was 100% to blame, see above RVP issues. I have upgraded to a Dellorto 55lph pump after holing a piston on a longer climb out. Fuel supply, fuel supply, fuel supply hope this helps some folks out.

[Badland-F5 Pilot]

This is awesome information. Thank you for posting it. LA F2 Flyer (Peer) has his F2 almost completed, but is running into problems with his Polini 200. We've been trying to figure out what to expect the top RPM to be with the prop. It seems to be a little low. There's also a hang after revving up and then pulling the throttle down to idle. The engine will stay at high RPM for (I think this is what Peer said) a good 15 to 30 seconds before coming down. We've tried everything under the sun to figure out why this is happening. Anyway I'll let him jump in here, give a better explanation, and hopefully there'll be something hit upon that can help, something we haven't thought of.

Thanks,
Todd

[LA F2 Flyer]

Thanks for this information Fritz! Certainly something else I can try. To clarify the issue, my engine (Polini Thor 200 Evo) currently has a maximum static RPM of 5400 or so. From what I've read online, max static RPM should only be a few hundred RPM below the "redline" of 7500 RPM or so. At max RPM (5400 or so) the engine sounds fine; it doesn't seem to be missing or bogging. It just hits it's peak and stays there.

I also had (have?) an idle hang on decelleration, around 3000-3500 RPM for ten of 15 seconds before the idle would drop back down to 1800 or so.
I've actually tried to pump the fuel bulb during the idle hang to see if it would drop the idle down but it didn't seem to make a difference in the hang. I've since then considered that I may have gone TOO large on the pilot jet and as a result had to open the throttle slide quite a bit to compensate. (I'm not sure if that would create the idle hang, but it's worth a test. Also, after idle the plug would look somewhat clean but also wet with fuel.)

I am currently running the fuel pump that comes with the engine from the factory. It sits remotely on the lower portion of the firewall and uses the pulses from behind the reed cage for "power". And yes, the tank sits well below the carb, not to mention about six feet back.

One thing I haven't tried yet is to squeeze the fuel bulb while at max RPM to see if it effects any change. Would this be a good way to determine if it is in fact a fuel starvation issue?