Poor running

As the Harmon Rocket I converted to IC is a tad too fast too keep within the boundarys at the local flying field I decided to remove the electics from my Seagul Pilatus Porter and convert it too to IC. I purchased another SC70 four stroke from Elite Models in West Vale, and made the conversion over the next few days.

Everything went well until the day of the first run. I felt it wise to run the engine in whilst mounted to the airframe, mainly to see what bits would come loose or drop off due to the extra vibration.

First off the engine would not run without the glow clip attached. As soon as it was removed the engine would splutter and die. Faulty plug maybe. New plug installed and engine fired up. Started fine and ran without the clip on. Looking good. Very lumpy running though, not a bit like its predecessor.

I ran 3 tankfulls through with the needle set at 2 1/2 turns out. Very rich and lots of smoke. At the recommended setting of 5 turns out it would not run at all.

I started to wind the needle in a little more on the last run. It ran a bit better and smoother at full throttle but is very lumpy at any other speed and stops often. .

Question time.

I have installed the engine upside down, would this have any problems attached to it in any way.

As the engine is upside down the fuel tank is higher than the carburettor. could this have any bearing on the lumpy running at medium revs.

So far the vibration has caused both elevator and rudder servo screws to wind out and the control horns came adrift. Disasterous had the model been flying. Dab of threadlocker on the screws sorted that one. 

Edited By Dean B on 30/07/2012 00:37:37

Have you balanced the prop and spinner (or try without spinner)

It is probably still running rich at 2 1/2 turns open. The high tank position will not help either.

As Garbo says, balance the prop.

dean-as above also-sounds like the engine is Far too rich........can you get someone who has one to help out....it needs setting up top and lower needle by the sound of it.....when you have it running at full throttle......screw in the needle a click at a time-the engine should start to rev faster and the exhaust should be cleaner---if it starts to falter--open it up one click and that should be the top end set.....Watch your fingers also and be Warned its not uncommon for a four stroke to throw the prop off at high(flat out) rev's if you lean it out too much.....all good fun...

ken anderson ne..1 ......fun dept...

I had the same problem but not as bad on my AT-6 where the tank centreline was about 2" above the carb when I got it. It's much happier and more consistent with the tank moved to be only 1/2" above the needle. Looking at your Pilatus you may need to resort to a Perry pump or similar to regulate the pressure.

the prop is balanced and the engine mount is made of aluminium. Without the cowl on the carb is filling up with fuel. Obviously siphoning due to the tank being higher than the carb. I thought about moving the tank into the cabin much further back and runing longer fuel lines, not sure if this will cause different problems. Whats a perry pump ??

A perry pump is used to pump fuel from a "remote" tank up to the engine....they usually work off crankcase pressure though so I'm not sure they would work with a 4 stroke.....

4 Strokes usually have better "suction" than 2 strokes & draw fuel better so moving the tank might work.....can you not lower it at all?

An optimum installation has the tank as close to the engine as possible & the tank centre line about 1/2" below the engines' carb.....but that doesn't mean other set ups won't work OK......can you run the carb feed so it goes higher than the top of the tank before it gets to the carb......might help reduce the syphoning....

Apart from that as the other guys have said it does sound to be running rich.....my ASP70 runs at about 1.5 turns out.....you often find that the factory settings for the idle are a touch on the rich side too....

I also have to say it looks a fair old chunk of engine to hang off such a slender nose.....the model may simply lack the mass to absorb the levels of vibration you get with an IC motor.....

EDIT:- Perry pumps available as an oscillating version for 4 strokes.....see here.....not cheap though....

Edited By Steve Hargreaves - Moderator on 30/07/2012 14:54:06

That's the type Steve, I was thinking it might help as they act as regulators as well as pumps.

In fact when leeaned out until it starts to falter you shou;ld back off until you just hear a slight loss of r.p.m.. This prevents a lean run as running too weak or lean will make the engine over heat.

On the prop throwing. OH YES! a few weeks ago my OS FS 40 Surpass threw a prop. My assisatnt was adjusting the engine before I could get round the back.

I had on a thick fleece, a sweatshirt and a normal shirt (Well, it is summer) and I get a really nasty bruise on my arm and another on my chest. THis is two minutes after the accident. A day later and I had a big black bruise over a large area.

Some good info here, thanks. I have found the cause, not what I expected from a new engine. The little screw which secures the carb barrel into the housing had dropped out. Missing. The barrel was floating about on the wire to the throttle servo. No chance of getting any adjustment. New screw obtained from Elite models, great customer-service. Took the screw from another engine. Refitted screw with a dab of threadlocker and fired it up. bit of fiddling required but managed to get a nice even top speed and an acceptable tickover. Hopefully the idle speed will get better as the engine is run in more. Needle is less than one turn out but seems ok. Lots of oil and smoke so running slightly rich. feel confident enough to try and fly the model now.

Well Dean, looking at the weather for Tuesday it`s not loking too good. might have to be the weekend now before you can try it out. But make sure that engine is on song. Paul (Driving Instructor). As for customer service Jeff at Elite RC Racing is top man. Always gives me discount no matter how small a item i buy, and wil try get you any part or model you ask for.

Called at the field today, ran a tank through the engine, no stalls or anything untoward so took her up for a fly round. Bit blustery but she performed well. Little bit tail heavy so needs a bit of balance lead taking out. Landed beautifully with no vices. Problem solved. Another nice model.

A Perry pump will not help you with a syphoning problem, it will make the engine run even richer. On the other hand a Cline or Ironbay regulator will take care of that problem. They are both demand regulators, use a check valve to pressurize the tank and a diaphragm to regulate the fuel flow to the carb. As the carb draws, it releases the fuel.

I know fellows that use a forceps clamp to keep the fuel from being syphoned. They remove the clamps just before starting the engine.

Since you found one problem, it is only a matter of adjustment and you will be cruising around the sky at will.

took the engine out of the model to try it on the bench. had a frustrating day at the field with an engine that wouldnt run. Works perfectly on the bench with the tank below the carb. Ticks over beautifully like it should do. have decided to re electrify the porter and put the engine in my next model, what ever that may be. Note to everyone thinking of buyng a Seagul Pilatus Porter, It doesnt work with 4 stoke engines as you cannot get the tank low enough in the airframe.