I have a 70 OS 4 stroke I would like to mount inverted, will it start and run this way

Yes

Ditto

No problem, they work just fine inverted.

The problem that happens is that people fail to make sure the tank is centered about the needle valve.

If the tank is high the engine floods and in an inverted situation the tank is rarely low but if it is low, the fuel runs back into the tank.

Either way with the engine/tank relationship not correct, there is hard starting.

With a pumped OS four stroke engine the tank position doesn't matter.

G'day

I have a Saito 40a mounted inverted in a Tiger Moth. Many people told me it would not work because it has an airbleed carby AND it is mounted inverted.

Fortunately they did not tell the engine and it works perfectly. The secret is to not flood it.

I also had an OS FL70 mounted inverted in a P-40. It too ran perfectly though not for very long. Sadly, the plane did not survive its first flight.

I hope the op re reads your post.

Thanks guys for all yoour thoughts, inverted it is

I have found there is also a problem using them if not well broken in.  This is not just when it will run out a tank of fuel with a good idle, but when it has a good seal even when cold.  If not the fuel and oil will collect in the glow plug and make starting difficult.  Even when started the lower compression can cause more issues when inverted.

Well the engines do work inverted OK. unless you have a rare engine with the oil sump in it, or a float bowl style carburetor, they all work inverted OK.

But some caveats though;
   With most 4 stroke engines, the carb is positioned such that when inverted any fuel from the fuel tank that dribbles into it, will flow down into the intake manifold and into the engine if the intake valve is open. But when right side up, the fuel simply drips down and out of the carb.  A two cycle engine is the opposite, in that when inverted the fuel drips out and away, but when right side up, the fuel could flow into the engine's crankcase.

Then as mentioned, when inverted old oil residue or fuel etc can migrate down to the glow plug when the engine is inverted and the plane is in its horizontal attitude at rest.

But if you always turn your prop by hand first before you try starting the engine, these problems tend to go away as you can detect a hydraulic lockup before you try to start the engine.

Fuel tank location is always critical whether right side up, sideways or inverted. do try to get a good fuel tank position in relation to the carb. A Inverted engine position tends to be more critical of the fuel tank location and causing a siphon effect to start.

Engine orientation does not matter if it's tuned properly.

The trick is to learn exactly how many prop turns it takes to prime it. too few and it won't start. too many and you'll flood it.

As Mike Early said, it is all in the technique. If you can get that in your noggin', then even a two-stroke glow engine is a piece of cake to run inverted.


Ed Cregger

It also helps to keep the glow driver on a little longer. Ihad a 4 stroke that needed about 20-30 seconds of warming up. It ran flawlessly after it warmed up. But it would some times die if Itook the driver off too soon.
ED

I broke in my ASP 91 4s inverted from the begining....and I had no problems at all, and been flying the plane over the year without a single problem...

It just takes about a turn of the prop with the muffler blocked ...glow..bounce against compression and I get music

I am running a Magnum 1.20 inverted and it hand starts with one flip and runs beautifully UNLESS I FLOOD IT. If that happens, I can just forget starting it until I clear it out. As pointed out above, it's all in the priming technique. Learn what YOUR engine likes and go for it.