limbodancer

I am breaking in a new OS FS 70 Ulitimate. I have already run about 1 litre of fuel through it. There is still plenty of white smoke whether I lean or richen the idle mixture. I still cannot get a reliable idle. My fuel mixture is 10% synthetic, 5% castor, 78% methanol and 7% nitro. Please advise.

MYTHOS

i think, ................ check valve clearances

between 0,04 and 0,10


myhtos

Bax

My Feedback: (11)

1 liter of fuel isn't much...about two tank's worth or so. Your engine will break in over several liters' worth of fuel.

For a four-stroke engine, you want the firsts 20 minutes or so to be run at full throttle with the high-speed mixture as rich as possible with the engine still running. Over the next few tanks's worth, you'll gradually lean the idle towards peak RPM. By the end of an hour, you should be able to lean the engine to just rich of peak RPM.

We usually prop the engine so that it will turn in the high-9,000's or low-10,000's. Start out with an APC 12 x 8 prop or so. Other brands of propellers will turn different RPM ranges.

Smoke emission is mainly a result of the percentage in the fuel, and what kind it is. Even leaned to peak RPM, you should still see some kind of exhasut emission.

limbodancer

Thanks, Bax. I have richen the idle mixture slightly more and found that the response is much better. I reckon in time, the idling will be more settled. Do you recommend petrol in place of nitro for this pumped FS 70 ? This engine will power the CM Pro Passion 3D.

Bax

My Feedback: (11)

NO PETROL! The engine's not designed for it. Adding it to fuel will make the engine run hotter.

A good blend is 16%-18% oil content, 10%-15% Nitro, and the rest methanol. The 15% nitro helps idle a bit, but you won't see much difference in top-end power from the 10%.

pwood

Hi Limbodance

I find the main needle on my 70 ultimate very sensitive. While running flat out, 3 clicks rich of peek and it will die too rich....

The instruction also say not to turn the idle richer like a normal idle screw...to make it richer on the idle you must turn way too rich and then lean to where you want. I.E. lots (+-1 turn) anticlockwise and then back clockwist to where you need.

I have only had 3 flights on mine and am very happy, took some time to tune as i was keeping it too rich on the top end "becouse it is new". 1or 2 clicks rich works for me. I also found it easier with the cowl off. as the motor died i could squeeze the line to the carb and if it picked up and ran again i knew it was rich...if it died i knew it was lean. This helped to set the top and bottom end.

Paul

REV-IKE

My Feedback: (45)

Bill I have a new 70 surpass 2 and it runs perfect and I have had over 50 os 4 strokes in the past few decades and liked them all but I have never had one break 3 header pipes just belong the thread on the head side within 15 flights.I tried every trick in the book.I did notice on my old style 70 the muffler is alot shorter and smaller diameter,no doubt lighter.The extra length hanging out there must no doubt be putting a strain on the header pipe resulting in a failure,I have been running without a muffler,I had to richin the mixture seting up considerably to get the same run I did with the muffler attached which is about 1/4 turn counter clockwise from max RPM.Also everything balanced perfect .I do like the looks of a muffler on my 4 strokes plus to devert the exhaust on the plane,cleanups are better,any input would be appreciated ,Thankyou REV-IKE

panagiotis.p

Bax,
I'm addressing this question to you since it seems that you have the answers. I have an FS Ultimate 70, for a long time, and I never got it tuned correctly for more than a day. I must say that I own several OS pumped and non-pumped engines with no problem at all. Yet this one seems impossible to tune. I use 15% nitro fuel with 18% oil. I have a wooden MA 13X6 on it, it is mounted inverted on a Great Planes Reactor with the tank located above the wings tube (where the CG is and at approximately 10" behind the carb, leveled with it) and I can get 9300 peak. This is not my problem though. The engine runs really hot. I have managed to idle it below 2000 but it dies when I try to open the throttle. When I get the max RPM, I cannot get it to idle, not to mention that almost every time, when the throttle is closed to idle, it takes 5-10 sec to really drop RPM to whatever idle I have set. And, sometimes, after 10 more sec, idle rises 400-500 RPM. Yet, the worst thing is that the carb floods with no apparent reason, whatever the fuel mixture. Not to mention the mess it does.
The pressure provided to the tank by the pump is very high, in my opinion too high just to help fuel flow. I think it is this pressure that causes the carb flood, when the engine doesn't need all that fuel, at idle. Is pressure flowing back to the pump, and there to the carb (somehow) and not through the tank? Would a check valve at the pump-pressure-to-tank tube solve the problem? The high needle is set up right now at 36 clicks from fully closed, and at that point I got 9300 RPM. Yet, although as I said I got a really good idle as well, when adjusting the low, it dies after 3/4 open throttle. I tried every possible compination between this 36 clicks (+ or - 5 clicks) and + - 90 degrees for the low needle, yet nothing.
The problem is, when the engine runs well, it runs perfectly. When it doesn't, it is completely unreliable. So I do not want to sell it, because I have seen really good flights with it. But I'm tired setting it up every time. For your information, the engine was bought late in 2007, and I have now installed on it new pump and regulator and new cylider head with valves (the complete assembly) just to try everything. Engine has run with new parts almost a gallon. Compression was more than enough, really good, as it was before changind cylinder head. Plug is new, and weather conditions are almost always the same (sunny weather in Greece), and I fly at sea level.
Please help, and thank you in advance.

P.S. Does it matters that I have removed the exhaust muffler? Is it needed for some reason? (it was done only to make the plane more tail heavy)
So far I tell you the same as any other with problems

Bax

My Feedback: (11)

There's not a lot we can say. You need to set up the engine so that you get a good top-end and a reliable idle with good acceleration. A very low RPM for idle is useless if you do not have acceleration. Anything below 2,400 RPM for idle would be considered acceptable, lower is better, but you must also be able to open the throttle without the engine stopping.

Prop the engine so that it will turn in the mid-9,000's when leaned to peak on the ground. With a pump, you do not lean the engine to peak and then richen. Lean it as far as possible without detonation or RPM drop and leave the needle set at that point. If you have good fuel, your engine will get plenty of lubrication.

If it will run "all day" at full throttle when leaned to that point, then your engine should accept being throttled-down and having the idle mixture and RPM set. You will not be able to get a good idle unless you can get the high-speed set. Many problems are caused by a too-rich high-speed needle setting, which causes the idle to be unreliable.

panagiotis.p

Thank you Bax for your answer. I will try to do as you say. Although I always use a tachometer to set the high speed instead of the ear. By the way, would it be possible for the engine to drop the RPM (lets say from 9300 to 8800) and then climb again? I mean, once I see it drop, is it final? Or the graphic (of the output) is not that simple? Should I experiment more? I'm asking that because I now have the high speed at 36 clicks open, which corresponds at 1-1/4 open needle, but previously it was set up at more than 2 complete turns, and the result was more or less the same. And that was A LOT richer.
And what about the exhaust missing? Is that a problem? Should I take a video with the best audio I can and upload it? Anyway, thank you again, I will be back with data!