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OS Surpass FS .91 inverted question

Old 02-02-2010, 09:30 PM
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Default OS Surpass FS .91 inverted question

Hello
I am mounting my OS Surpass .91 Fs inverted in my plane.
As a result of that the carburetor air intake is facing up.

My question is this:

When I prime the carb before starting the engine , in the normal position upright, I see the extra fuel draining out the carb air intake.
I then energize the glow plug, flip it and start.....no problem there ....

Now that the engine is inverted, where the excess fuel goes when I prime the engine before stating ? is it going to sit in the carb and flood the combustion chamber?
Could someone explain how to prime an engine inverted?

Thanks for all the help...

Fabio
Old 02-02-2010, 10:17 PM
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Default RE: OS Surpass FS .91 inverted question

This is my technique for inverted four strokes. I have several in 3d ships that are mounted inverted and cowled.

I don't ever prime the intake because the chance of hydraulic cylinder lock is too great. I always pull the engine through by hand just before I start the engine to ensure that the cylinder is not full of fuel or oil. If I need to choke the engine to draw fuel through the lines into the intake, I momentarily put my finger over the exhaust outlet on the muffler while cranking with the electric starter which creates suction in the intake and draws fuel through the carburetor. You can see the bubbles in the fuel line moving quite rapidly when you choke in this manner. By starting with a dry engine, you prevent cylinder flooding. The other way to prevent this is to invert the airplane while starting on some sort of stand, but I think that's a big hassle.-Just my 2 cents...
Old 02-03-2010, 10:23 AM
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Default RE: OS Surpass FS .91 inverted question

When a four-stroke engine is inverted, then the intake manifold points downward. You just have to be very careful when priming. Add a few drops of prime, then turn the engine backwards to allow any excess fuel to drain out the exhaust port. You must be very careful because fuel can cause a hydraulic lock. If you try to start the engine, you can potentially bend the connecting rod.

Once the engine has been turned backwards, you can carefully prop it by hand a few times to make sure it's clear. Then, connect the battery and turn the engine over to start it.
Old 02-03-2010, 11:04 PM
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Default RE: OS Surpass FS .91 inverted question

Thanks for the tip.
My engine is in a cowl, but your suggestion of turning the engine backward to purge any excess fuel from the carb, is a great idea.

Thanks for your quick support.

Fabio

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