I have an OS 46AX engine installed in a Great Planes Venus 40 model. The engine has a three line uniflow fuel system with the fuelling line always plugged with a fuel dot for flight. The inverted engine has an OS F glowplug with a Great Planes remote glowplug connector installed as a result of the fully cowled engine.

Due to the fuelling layout the carb does rest a little below the tank outlet and once fuelled, prior to start with the throttle open, fuel does drip out of the carb. To counter this, I start the model inverted on a stand so that in effect the engine is right way up. However, it is to say the least, a devil to start. What often happens is that after minutes of trying with an electric starter, it eventually fires with the throttle almost closed and runs at very low RPM. Slowly the revs pick up and only then can you increase power without the motor stopping. Once its going all seems well and it runs well at around 11,900rpm on an 11x6 prop.

Whereas this engine used to start easily with a chicken stick after only a few flicks, it now takes a prolonged effort with an electric starter to get it into action. We don't overprime it and there is fuel at the carb which is clean. All starters and batteries are also in good condition. Any suggestions please.

Thanks...Paul.

Only problems that I have had on my OS .46 AX have been solved by switching out the glow plug ...and/or.....the glow plug starter battery...... each time. Rich

Swap the plug for an A3.

How is the idle once it starts?

You may be getting fuel in your pressure line from your muffler, use an A3 plug or #8, Put your tank where it should be for starters.

My friend had to take his remote plug set up off. It had too much resistance and was eating up the juice before it got to the plug. I had a used Venus that was flown with the inverted engine; same problems you have. I mounted my engine upright and got rid of all the problems. Does not look as cool, but deadsticks and such are worse. I learned my lesson with my .46 U-Can. The Venus is a great plane; I still have the fuse and 1/2 a wing. It had a mid-air with a p-51 that ate 1/2 the wing off. From the start of the aileron out was gone on one side and the dam thing kept flying! I stalled it out abour 3 ft over the runway and everybody looked at me wondering why the bad landing; only the other guy thought we came together but his plane was unhurt. Because both planes kept flying everyone ignored the incident thinking a hatch or something came off.

It is not practical to move the tank which is constrained by the geometry of the fuel bay. In fact I was surprised it was designed that way with a sloping floor which prevents the tank being moved down any more. The engine idles perfectly once we have it going and doesn't miss a beat. The problem is just getting it started.

As regards the potential resistance problem with the remote glow connector, I would have thought that the Manufacturer like Great Planes would have sorted a problem like that out prior to marketing. But not to say that is not a causal factor. A few things to check!!

G'day A friend has had a similar problem with a Super Tigre 40 in a Phoenix Twister. The engine is mounted at 225 degrees (not inverted or on its sibe but in between). When we tried to start it, no amount of choking would get it wet enough to start. Fuel was dripping out of the carby but the engine was not sucking any inside. So, I grabbed a small squash bottle I use for fueling small diesels, put some glow fuel in it and used it to squirt some fuel into the partly inverted carby. A couple of flicks showed that the engine was wet - put the glow starter on and one flick and it was running (backwards). So one back flip and success.

So why does this happen? Well the ST 40 has a huge carby inlet. I used to have a ST 45 which used a similar carby but it was sleeved down to give more venturi effect. The GS 40 is not sleeved and just does not seem to create enough venturi effect at cranking speeds. A small prime with the squash bottle gets round this.

My friend now says this is his easiest engine to start. Small prime, connect glow a and check for "bump" then one back flip and it starts every time. This may work for you?

Picture is of the Twister in question. Sadly it no longer looks so fine. He tried to fly it through a tree. It is flying again but it not quite so pretty.

Michael from Oz

I have the exact same engine / plane set up. I have a remote glow and a Dubro remote fill valve and A3 plug. When filling I have to be aware about flooding the carb out. I have the pressure pipe fitted with a Tee piece which acts as a fuel over flow for which I have a collection bottle, this tee sits as low as it can below the carb to stop flooding . The first start of the day is sometimes inverted but after that its good all day.
P.S. I tried a uniflow tank set-up ..........didn't make any difference.

That is called gravity feeding. I've learnt this term a couple of weeks ago and solve the problem with a regulator. Iron Bay works wonder. The engine turns smooth and reliable. I still have issue to have it starts for the first flights, though.

most of my Q500 planes have the engines mounted in a similar fashion. I haven't noted any particular problem with starting them, and yes, sometimes fuel does drip out of the carb once the tank is full, but it doesn't run into the engine the way they are mounted. A good hot glow battery, either flip by hand or with a starter, and they're off and running. If they're particularly stubborn, you can block the exhaust port of the muffler momentarily as you turn it with a starter, it will increase the pressure in the tank and it's off and running.

Paul,

I had exactly the same problem with my 46AX mounted inverted in a Phoenix Tucano. I found that it wasn't getting enough fuel to start and run properly. I would have to put a finger over the exhaust a few times and each time it would pick up some more revs before eventually being able to open the throttle to full. What I do now is really prime it well so that there is fuel dripping out of the carb and she starts no worries. If I find that it starts and won't acclerate, I stop it, prime some more (throttle fully open, finger over the exhaust and hit it with the electric starter for a second or so) and then have another go.

To prevent the fuel running out if the engine when sitting there I ran my fuel line up to the top of the cowl and then back down to carb. That makes it a bit harder for the fuel to siphon out. I also use an onboard glow which has transformed the engine and given me complete confidence to do low throttle manoeuvres without the engine cutting out.

Cheers