Ok. I have managed to get my simi inverted 4 stroke to idle over a minute from about 20 seconds initially. I did this by further breaking in the engine, playing with the tuning, switching glow plugs, and switching to a fuel with a lower percentage of oil. So how do you get this thing to run reliably? The engine is a TT F91-S, the fuel is 15% Omega (was Wildcat), the plug is a Thunderbolt FS (was OS-F and Fox Miracle), and the plane is the GP Fokker Dr-1 Triplane.

I have to add here that I have tuned it to the max, I have done the pinch test as well as taching the idle. It idles best just rich of max lean, just as you would expect, transition is great with glow, and without glow before it bogs down which is about after about 20 seconds of idleing. If you run it up to max and shut the engine down immediately compression is better than average for a ringed engine. If you check after it quits after over a minute of idling it will have compression almost as well as an ABC engine, it takes about 3 minutes for it to lose enough compression to stay at TDC. Obviously the extra oil flowing down into the cylinder increases compression. Only adding this because some of you think that an inverted 4 stroke should act just like an upright one, but just as with a two stroke the extra oil flowing into the glow plug make some engines problematic.

go back to os type f ( the only 4 stroke plug) and run more fuel through it . keep trying it will come around

I use mach7 15% fuel same engine as you. I could not get to idle for more then 20 seconds inverted for a while either. After running about a gallon through it now it will idle for about 2 minutes before loading up and dying. I have tried leaning it out more but that does not help and makes it worse. I think it need more run time still as it keeps gettign better but slowly

Pat

Sorry, I have tried 6 different plugs, the Thunderbolt is the best with this engine and fuel. Come to think of it I didn't switch plugs when I switched fuel. I will try the OS F and Fox Miracle Plug again. But, I can tell you my old TT FS did better with a Fox Miracle with 15% Wildcat, though this one did better with the OS F, but best with the ThunderBolt.

Most 4 strokes do not like to run inverted! To get them to do so, you need to really lean out the low end. The cure for most is to install an on board glow driver so that it lites up when under 1/3 power. Spend the money...you wont be sorry.
Or, continue to have problems! Because of the 4 strokes, the plug has time to cool off so it doesnt matter which plug you use( stay with the OS-F!).

deputydog,
If you think I need a glow driver why didn't you vote that way? Even inverted you cannot lean much more than the upright setting. In fact most 2 stroke engines you can get the tuning setting perfect upright and they run fine inverted. I am finding that running a bit leaner does nothing except make transition worse. The engine is not actually totally inverted but at 45 degrees down tilted to the right with the exhaust valve down. Although the plug was getting a lot of oil in it, that no longer seems to be the case. I think its the added viscous drag of the oil in the crankcase. It completly fills the gap between the piston and cylinder and drags. Unless you cut the engine after it is running at full throttle it is stiffer even when the valves are open. Kinda like when a tight engine is first broken in, it needs glow power no matter what the mixture is.

So far I think PatinIdaho has the correct answer, though a glow driver would certainly work. But, I would rather not have the extra weight, and something else to charge up.

BTW What glow driver do you recommend?

Your poll and the subsequent responses don't seem to tackle probably the most fundamental problem with 4-strokes not running very well inverted.

Look at the relationship between your engine and the fuel tank. You need to make sure you fuel level is slightly higher than the centerline of the carburetor. Some inverted engine/airplane configurations forget this important step and you end up with a fuel tank much higher than the carburetor. This causes the carburetor to fill up with fuel when it is not running.

I had a significant problem with my U-Can-Do 3D because of this (inverted Saito FA-100). My solution, and many others, was to add a Cline Regulator to my fuel system. This keeps the fuel from flowing to and flooding the carburetor between flights and allows me to reposition my fuel tank to the CG. Others have modified the airplane to position the fuel tank lower in the fuselage.

IMHO, the OS #F plug is the way to go in most 4-strokes, regardless of manufacturer.

I have bought a new design driver I like (comes from Austria). Its called GLOW4B. Was reviewed by Jim Oddino in RCM in April 2003 issue. Does not require another battery, uses receiver battery, very light. Been using mine about 3 months, works well. Must have at least 1500mAh battery. Not cheap, about $100 Info at www.microsens.at

I'm a little worried about the one's that use the battery reciever, especially since this plane will be crusing around the sky at 1/3 throttle. Rather have a dead stick than have the glow plug drain the reciever battery. Pluss not gonna spend that much on a driver.

Hillja,
If you read my last thread you would know that others have mounted this engine on this ARF without any problems, the center of the tank is about centered on the carb, it will not siphon fuel into the carb.

I'd like to ask a related question here. I recently built a plane with an inverted Saito .30, which has an air bleed idle circuit. It runs perfectly right side up, but is realy fussy when inverted. With such a small plane, an on-board glow driver is out of the question. Should I just admit my mistake and install a two stroke engine, or install a Magnum 30 four stroke that has a two needle carb, or keep running the Saito until it's good and loose? It only has about 45 minutes running time. Tank centerline is right on the carb centerline. I've tried OS F, Fox Miracle, and whatever Sig sells as a four stroke plug, all with the same low speed flooding problems.

Check you tank center line to your carb center line. They can be a bit off but not a lot. I've got a satio 100 mounted inverted in my ucando .46 with NO PROBLEMS. It idles and transitions all day long just perfect. My bet is your centerline is way off. If you cannot change it, then get a regulator.



Neo

3

Ran almost two more tanks through it today. With no more adjusting I got a minute and 25 seconds, tweaked it a bit and got a minute 30. Looks like you are right. The engine is still too tight. Oil from the exhaust is still very dark. I have run about a gallon and a quart through it. The ThunderBolt plug is still the best by about 15 seconds. On the GP Dr-1 the tank is at the center line of the crankshaft, since the engine is tilted only 45 degrees between horizontal and inverted the carb is slightly below the tank stopper, but they have compensated by sloping the back of the tank down so the center of the tank is about the center of the carb. Tweek it just a screwdriver length lean and it only runs a little less than a minute.

Personally don't know why anyone would want to be idling for 1 1/2 minutes. If you are on the ground, you not in the air.



I think it is a tank relationship need to be checked out as well. Inverted is a bit touching on tank location. Put another gallon through it ...... But in the air. Why waste flying opportunities.....

How many times do I have to say that tank location is not the problem. Actually its only a problem in the air doing maneuvers. On the ground you can lean it out all you need with the idle needle, but if the tank is too high it will lean out inverted. I have had this problem with inverted two strokes. But not a factor here, many people have built this ARF with no problems with the simi inverted installation. Running it seems to improve the situation, this seems to be the solution.

I can get mine to idle for around 2 minutes now and thats longer then i need for a taxi out to the runway lignup move control's
then gun it. I use the OS F plug and it is in a TF 182. I have black oil comming out of the exaust normal? i dunno i have been told a out of balance prop will cause this maybe i should check that again. Maybe its to rich or lean by just a hare?

Pat

Ran a Saito 180 inverted with both a Type F and a Miracle.
Tank location was below the carb certerline, no pump or regulator, but an on-board glo driver was installed.

Did have to play with the low speed adj. though.

Black oil means that the engine is still breaking in. The aluminum from the pistion scuffs against the sleeve wearing the softer aluminum away, the higher silicon aluminum still stays. Most engines stop this for the most part before a gallon is used up. So I'm thinking like you that my engine is still to tight to run inverted.

Personally don't know why anyone would want to be idling for 1 1/2 minutes.

You can easily exceed this on the base leg and final. This is a slow plane. You know Red Barron's Triplane? Besides, it does the same thing up to about 1/3 throttle.

If you've run over a gallon through it and your still getting black residue from the engine......you may have a bad engine. My latest 4 stroke broke in quickly in 20 minutes. After that I can see little changes in tuning....but no black residue. I've got less than a gallon through it. It's never missed a beat. You may want to have a profrssional look at it.



Just a thought


Neo

You must have an OS. They break in in 20 minutes and last 20 hours. Saito's and TT take longer to break sometimes a couple of gallons of fuel, but they last over 200 hours.

All my four strokes run fine inverted. It's all in the low end tuning. I finally got my brand new OS 120 to idle for an extended period of time after about half an hour of tweaking the low speed needle valve. The trick is to adjust the low speed needle valve while the engine is idling. Set the high speed needle valve first, then slowly lean out the low end and make sure the rpm increases while you are doing it. If the rpm starts to drop or the engine suddenly quits while you are leaning it out, then you are too lean. Richen the low end by 1/8 of a turn, restart the engine, and check the idle again. If the rpm drops significantly when you remove the glow igniter, then you are too rich. Eventually you will find a sweet spot. Just keep on trying. An on-board glow driver is nothing more than a bandage for sloppy low end tuning.

You will need to richen up the hi end each time you adjust the low on the saito!!
I did'nt vote because I gave you a full explanation.
Sonic Tronics I believe makes a driver system. Depending on a persons expertise with engines and during breakin makes a world of difference on how a 4 stroke runs inverted. You are getting too much fuel at idle and its having its toll on the glow plug. I would not fly with it the way it is! spend the $30-40 and get the on board glow.

Or spend $300 and get a YS . They will run all day inverted.

What toll on the glow plug? plug is fine bright and shiney. BTW rich mixtures are not the only thing that can cause a RPM drop. Too cold of a plug, fouling, fuel with too much oil, and too much friction (such as with a brand new unbroke engine), can also cause an RPM drop. Keep telling me how to tune an engine, but that's not it. Every time I run a tank or two through it it runs longer.

Yep, a YS will run all day inverted, and it doesn't take that much time to find the sweet spot on a YS low end. You get what you pay for.

H'mm the YS .63 would be a good choice. Just never figured on a super charged engine for a plane that will chug around.