Last year in May, I had a lot of trouble with on OS 75AX on a Phoenic Topstar. That airplane had an inverted installation and the engine never ran right.

Then, during the monsoon last year (which is off-season in our nick of the woods), I got myself a FS91 SII and the same runs quite OK now. Once I swapped out the 75AX, I washed it, by overnight soak for two days in plain methanol and then oiled it thoroughly with sewing machine oil. After a good 8 months in storage, I took it out for inspection today. This is what it looks like. The photos are as is with my N82, it looks a lot brighter in real life as compared to the photo, atleast on my CRT monitor. Can anyone see any problems with the engine?

Ameyam

Run the 75 on a test stand and then come back with that result. I suspect that your problems in that airplane were more related to the poor fuel tank location in that inverted installation one to which the fourstroke may have been better able to deal with.

So test the engine in a stand and see if you even have problem.

John

Didnt seem to have the problem on the test stand at that time. I will again run it and see

Ameyam

It looks like it is in pretty good condition from the photos.

If you feel some compression and the piston turns relatively freely with the glow plug removed, your biggest area of concern will be the carburator.

Don't forget or loose the small thin washer behind the prop driver. It is essential on O.S. engines!

I am betting on it running well in the stand with a reasonable tank to spraybar height relationship.

Often if the fellows convert to an inverted mounting and give no thought to the need to maintain the tank to spraybar height relationship buy remounting the fuel tank appropriately there are al sorts of problems.

More an more we are seeing Arfs now intended to be used with full inverted mounts and even some of these have neglected this need.

John

agree. Eyeball it. What is the location of tank outlet vs carb in 2 cycle vs 4 cycle? ThinK this will give you the answer.

I keep telling people, if you invert the engine, consider inverting the tank.

Tom

When I put the 91FS on the same airplane, I lowered the tank outlet by drilling another hole into the firewall and it did not geve me ant trouble on that day. Hope the same has corrected my problem

Ameyam