LargeScale88

Is it worth buying the os 91 pumped? Whats so great about the pump, besides pumping fuel???

Thanks For all tips and hints!!!!

ChuckW

The pump is good for keeping a steady fuel supply regardless of the plane's attitude. They can also allow placement of the tank further from the engine. Like everything else, they have their place. For typical sport flying though with a good engine, they aren't absolutely necessary.

Gray Beard

My Feedback: (-1)

Everything Chuck mentioned. I go for pumpers mainly because of the tank location, they just don't care where you put them. The pump pumps and the regulator regulates so I am able to set my tank over the CG and have it low or high. Inverted engines don't flood either. I like the YS system a lot better then the OS but they both work very well. Some of my planes don't require anything special as to tank location so I run the non pumped engines in those. It just makes my life simple.

LargeScale88

I'm gonna use them for a b-17, do they bring in the right amount of fuel for the weather conditions?

Thanks

Gray Beard

My Feedback: (-1)

Pretty much. I tune for 110 degrees for about 5 months out of the year. When the weather drops from 100+ down to the low 60s I do have to fatten up the high ends about one click at a time until it's in the low 30s or high 20s. By then I have gone fat about 4 clicks. This time of year I am starting to lean them one click at a time as needed. This is both YS and OS. Other people may not need to do this. For me it is no longer a surprise so I kind of expect it as the weather starts to drop here. If you are worried about this you may want to give electric power a thought because there are no perfect gas or glow engines. There is a difference from engine to engine of the same brand, one may be perfect and the other one may give you problems.

jay2000dakota

Personally, I don't care for O.S 4 strokes. Saito's are lighter, make more power and run better then O.S. In my opinion Saito 4 strokes are superior in every aspect. Run 4 Saito 100's in that beast and you'll have more the enough power.

AllTheGoodNamesAreTaken

My Feedback: (180)

There's a completely unbiased post...[sm=thumbs_down.gif]

MikeL

My Feedback: (3)

There's nothing wrong with making a suggestion.

Gray Beard

My Feedback: (-1)

Seems we just went through something like this in another post. We all have a favorite, some more then others. I have several engines without the pump and they are just fine. Does depend on the set up of the plane though. The pumps are something that almost never go out but you can have problems with a regulator diaphragm every couple of years. OS requires the owner to send the carb/regulator into them for replacement. Money money money!!! YS you can get every part for the engine if you choose. I keep several YS diaphragms in stock in my shop, old style and new. If your YS starts running different it's usually just the diaphragm and it takes me about three minutes to replace one. Wouldn't it be nice if OS would trust there customers well enough to know how to remove those two screws and spring. Only new four stroke I would buy today is the YS just for that reason. Well, other reasons too but that's what really put me off. Saito?? The thought never even crosses my mind. Don't even want to know what I think of Magnums!!

summerwind

i can speak from experience about the OS pump system...........when they are right they run great, but they don't stay that way. i went through 2 pumps and a regulator and then it only maintained the tune as long as i flew it every weekend.
no power gain.
personally for a plane that means a lot to me i would go with YS. tune it and forget it. the YS will run the same everyday whether you run it once today and then run it again in 2 months from now. the torque and consistency of these engines is fantastic. the YS is not for needle tweakers though, they don't need to be tweakered.
if used properly they will solve any tank issues period.

the OS pump system is garbage...............don't trust it on a anything but an ARF you don't care about.

sorry, but 2 OS 91 surpassII's with pumps led me to believe they are too finnicky to be used in anything of value.

Gray Beard

My Feedback: (-1)

It can happen, they are just machines. I have gone years without any problems with them then one day they just go nuts? I have never lost a pump though. Yesterday I was flying with one of my very old YS 1.20 NCs and all was well but the idle was acting funny?? As I was rolling back into the pits the engine started to sputter then went dead, that just doesn't happen. When I tried to adjust the high end it just wasn't helping? That was the clue I needed to replace the diaphragm. This can happen about once every year or three and doesn't give any warning. The engine just starts to act funny and you know what it is right away. It's just a two screw and $3.00 fix. Other then that I have never had a dead stick in the air with this engine. They aren't perfect but they are the best four stroke engines I have ever had, tune and forget!! I do check the valve lash every year but they even stay put.

FLAPHappy

My Feedback: (209)

I tend to agree with summerwind. I don't care what engine you have, it will malfunction at sometime. Pumped or not, engines will fail for a reason. Why? Fuel, oil, humidity, air temp, altitude, carb adjustments, take your pick. These commen failures occur with any engine, not only R/C engines.
I'm not a pro by any means on this subject, that is MHO.