has os engine with PUMP has any advantage for 3d flying or any other type of flying

I don't have experience with that particular engine, but after flying pattern with YS engines I came to rely on some sort of pressure fed fuel delivery system. The three most common types are the YS, Cline demand system, and the Pumped systems like OS and Perry. Regardless of which you choose, they tend to make the engine runs extremely consistent. You come to depend and rely on the power being there all the time, no matter what the fuel level is above empty. If you 3D, it's worth it in my opinion. All of my profiles have a Cline, and almost all gassers use some sort of fuel delivery system. Advantages vary from tank placement to avoiding lean runs, to just plain old consistency. If nothing else, try one and see how you like it

You can put the tank on the CG to maintain a consistance balance during the flight.

Is these pump systems are reliable or they have some tendency to break down once in a while

Use a YS because if the pump breaks it only costs a few bucks to replace whereas an OS you have to send it in and pay around Seventy bucks for it to be fixed. Besides I think YS is better just my opinion.

Chris Gini

I have a pumped 61 SF and like it very much. I bought it used 3 years ago and never missed a beat. The only disadvantage I see over my previous 61 FX is that the FX "warns" you when the tank is near empty and the SF pump just shut instantly. I crashed my plane because of this (maybe it was me insisting torque rolling low for too long).

Just my opinion here but I think newer OS are of less quality than these older SF series.

I did not notice any difference in fuel economy. I was thinking of it because the carburetor is much bigger than standard (more air means more gas).

It starts really well. I choke it very much and with only fingers on spinner, a small clockwise flip just before compression and it always start first or second flip if choked properly.

Hope this helps.