it still doesnt like it. says file is to large. the only thing i can think of is if you right click on it it says (size 6.92 kb, 8.00 kb on disk)
yay for a 40-60 sized 4 stroke lol

Now if we could only get one with the YS supercharging system displayed...

Old thread, but the debate is always fresh and fun ..... you guys left one important factor in choosing a 2-stroke of a smaller displacement than an equivalent but the needed 25% larger 4-stroke to get equal performance (as in SPEED, ultimately what we WANT!). And that is the weight savings in choosing a 2-stroke over the BIGGER4-stroke!

Point in fact - I have a BHModels "60 size" P-51 and so does a friend, they are identical in every way in the build, except the motors. I have a <font>SuperTigre</font><font> G75 in mine and he has a Saito 100FS in his. My 2-stroke P-51 blows his 4-Stroker into the weeds, over 16 MPHfaster on a police radar gun. His Saito runs sweet ... when it's not "being a woman" (finicky bit@#); while my 2-Stroke SuperTigre never so much as hicups ever. We both burn through a gallon os 15% Nitro in the same damn time. (so much for the less fuel usage of a 4-Stroke story)

I also think my P-51 sounds more like a Merlin-Packard V12 at full gallop than his Saito does, sputtering like an old Harley.

I used to race some Motocross back in the late 70's while in the USAF, I had </font>Husqvarna<font> 360(cc), which I still have and ride (and keep rebuilding), and I'll take that baby against a KTM500 4-Stroker any day and it will still blow it into the weeds as well, even though the KTM with todays technology is pretty damn light .... but still not as light as a fine Swed 2 stroker ... from the late 70's..
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I found the hard way that 2C engines dont run too well inverted as the carb is upside down. In the case of 4C, the carb becomes right way up when the engine is inverted. Just what I observed

Ameyam

So when your 4C is upright, it's carb is upside down, thus wouldn't work "too well" by your logic, right? Wrong both ways. The only thing affected with any of them is the starting. And once you've got the plumbing right and figured out what they need for choking (some don't need it and work just excellently well, some do and don't work very well) they usually aren't much problem.

There have only been a few engines that are difficult to handle when their carbs point down. Most often, it's when they need manual choking to prime, and since 2 cycles usually have the carb in front, where you can reach the carb easily even if cowled. Only 4 cycles that need manual choking have a problem when their carbs point toward the earth and are inside cowls.

Actually, I and many other at my field have had problems with inverted 2C engines. It has got to do with starting but also with tuning. We found that it would rich at full tank and lean out as you go through the tank. On a 3D airplane, this was an issue.

Apparently others had the same problem. I couldnt keep that engine running at all. When I finally gave up, one of the more experienced members came up to me and told that he had the same issue with the same airplane. So much so that he does not buy airplanes with inverted engines. He takes them if the engine is at 45 or 90 Deg

Ameyam

Actually some of the newer 4 strokes have the same problem as most 2 strokes. Oversized carbs. Because they had less power older four strokes had smaller carbs, thus better fuel draw and throttle response. To get more power some have gone to larger carbs.

If you look at the relationship of the tank to the carb, you can usually solve those problems before you have them.

Why would a specific airplane "always" have the same problem? Think it might be the design? The tank too low or too high?

I very often use uniflow tank plumbing. However, with my H9 Corsair (engine at 9o'clock) I had a siphoning problem. Rerouted the lines and had a draw problem. Actually, it was a priming problem as the lines were not only empty but the carb could barely be finger choked. So I got re-did the plumbing to the usual arrangement. That airplane went from a "leaky" problem, to a "dry" problem, to no problem. The H9 Spitfire engine is straight down. When I was building it, the Corsair was in it's wet phase. The Spit wound up having the same problem as the Corsair when it had the same plumbing. And again as well. In both, that very large tank winds up with enough fuel head over the carb (90degree or inverted) to cause headaches.

Bottom line is that every 6 o'clock engine I've got starts and runs great. But since I like to have the option of uniflow, I usually don't go for 6 o'clock as 1st choice.

There was only one engine in 50+ years that I never got to run straight down. OS produced a 4cycle "lightweight" awhile back and it's downdraft carb was basically a guaranteed flooded engine producer when pointed toward the sky. They did advertise that it started great dry. The opposite was also true. It was a disaster to start wet. If it did, you might wind up sending it back for repairs. They did send me a new replacement. I ran it upright and put it back in the box. Someday I might try it side mounted or upright. Otherwise it stays in the box.

When in put a 4C 91FS in the same airplane, I did lower the tank to about the same level as the carb. The problems seemed to go away but I have flown it only one day since and I didnt go 3D with it.

Will again try it in a month and if it works, I will tell everyone what needs to be done. Its a Flip3D /UCS 60 clone from Phoenix and I know a number of people on the field have it because of the way it flies but dont fly it because the engine issues or because its tail has a reputation for falling off if it is not strengthened with fibreglass cloth. Picture attached was taken on a day when I couldnt fly it further because the tail wheel broke during a dead-stick landing

Ameyam

Exactly!

I run dozens of 2C and 4C engines inverted, and any problems tend to boil down to plumbing or mistuning.

Even tank height differences only affect starting when the engine is on the ground, usually due to minor fuel siphoning.