halflight

My Feedback: (5)

Recently built the Ben Buckle Elf. Having a heck of a time to get a decent idle with the inverted OS 40 four stroke..seems to bog down no matter what I do to the low end adjustment. Tank is as low as possible. This engine (new) runs and idles great on a test stand upright.
Anyone have a similar problem with inverted engines. It has the OS F plug.

Insanemoondoggie

I`ve been fighting my inverted OS LA 25 in my Cub. I went with a plug that has an idle bar and this help get the idle down to 3000 rpms or so , any idle lower than that and she drowns .
After a gallon of fuel it is getting much better. I must say I`ve gotten rather good at deadsticks on landing with it.
If your 40 is an LA, more than likely you need to run the bleed screw all the way open, go with a higher idle till you get some fuel thru it and maybe run a lager diameter lower pitch prop so you can keep the rpm,s up but still land without a dead stick.
Thats what I ran into, may not be what your dealing with , but it sounds like the same.
Thats a very nice looking plane, way cool looking.

SGC

You need the tank top just below the main needle and run pressure of the stumpy muffler, mine will idle to a slow tickover an keep running for 20mins after which it'll throttle up cleanly
Stewart

glowplugboy

My Feedback: (17)

Higher nitro fuel such as a YS/Saito 20/20 ( 20% nitro, 20% all syn oil) will help quite a bit with idle and throttle transition on your four stroke. If the engine is new, it may not be broken in yet, but if you built an Elf, you already know that.

Sport_Pilot

My experiance is that ringed engines need to run several gallons through before they run well inverted. Till you have I suggest a Thunderbolt four cycle plug. Mine ran a lot better inverted with that plug, you can buy them from Hobby People. The max power will be less with that plug, so after finishing a couple gallons of fuel you might want to try the OS F again.

glowplugboy

My Feedback: (17)

I agree completely with Sport_Pilot. The Thunderbolt Brand four stroke plug is one of the best four stroke plugs available, and one of the least heard of brands. With 20/20 fuel and a TB plug, you should be good to go until the engine ring gets seated. I use them in high output four stroke pattern engines with excellent results and great durability.

Sport_Pilot

That Thunderbolt plug is the hottest four stroke plug, not the best plug. Keep in mind that that plug is way too hot for most applications and power will be off a bit, especially with high nitro. Because high nitro means more oil dripping down through the engine and putting out the glow plug, I don't reccommend more than 10%. With a four stroke the vent is now on top which means more oil will collect in the crankcase, which means more to get past the rings into the cylinder. So you can get away with less oil as well. I have used 16% oil with no problems, the crankcase still gets full enough to vent oil out the vent line. Though not as often.

John 38

I am currrently running a saito 90 , OS 90 and a magnum 90 4 strokes all inverted and get no trouble on standard fuel -10% nitro and synthetic oil ( plus 2% castor) and never experienced any running problems ( ignorance is bliss ) plugs are either F or No 3

I do store models nose up to avoid oil pooling into plug. I keep the saito model inverted between flights as left too long - it will oil up

Engines have been well run in , but generally I have always installed inverted to suit model lines and have experienced only oiling up if left standing too long with engine in inverted postion. I believe oil burning off may well leave residue affecting plug and engine performance. If I do get an oily plug, I take out and wash with fuel

hope this helps

John

Sport_Pilot

Getting the plug oily when off is no problem, just take it out and wash it with fuel as you mentioned. The problem is with engines that are breaking in or are worn out and oil from the crankcase flows past the rings while idleing, this pours into the plug and the engine quits. Or the plug partially fills and you get poor transition. A hot plug works, but is not necessary when the engine is very well broken in. You might not notice this when the engine is mounted upright as it runs well after just a few tanks of fuel. But the compression and thus the ring seal preventing oil from getting past doesn't actually reach its peak for several gallons of fuel. I have had stubbon ones that did not run well after running a gallon of fuel, but they would run well enough to fly with that Thunderbolt plug. You just didn't let it idle for more than a minute.