ratherbflyin

[sm=confused.gif] Help! With all the negative talk about problems with
the 91FX such as air bubbles, poor seals, bad idles, and loss of rpm after low
amount of run time, l'm hesitant about owning one. There seems to be too
many owners with similar problems for there not to be something wrong.
l own other OS engines smaller in size and they run well. Should this engine
be avoided at this time until these issues are resolved? In my mind l shouldn't
be required to change carbs or relocate them and add pumps on a new engine,
especially from a reputable firm like OS and at the price.
Any comments are appreciated, thanks.
Dave

beavertail

If it helps your piece of mind, sure, Why not wait, I have one and it really pulls my Vectorflight 300s, But Ive heard bad comments about it. Maybe I just got a good one.

Spicoli

I have one and love it.In your case I wouldn't reccomend it.It wasn't as easy to setup as I hoped.

Sarah

I have an OS91FX which I purchased because I knew of three OS91's that ran very well at my local club.

I ran mine in on the bench, six runs as per the OS manual, and I found it very easy to set up.

Once in my plane, which is fully cowled, it ran fine for the first few flights then would not idle. It turns out that as the engine was bedding in, it got richer as the piston was sealing better. After adjusting the idle and main needle a little leaner it then ran fine again.

I think the OS91FX may be a little more sensitive to setup than some engines, but not overly so.

I am very pleased with the performance now.

Hope this helps,


Regards,

Sarah

Sprink

Too many people have had problems (including myself) to suggest that it is automatically a good reliable engine right from the box. At a guess from what is said on here about 40% have problems with bubbled in the needlevalve. This is way too much.

Given that this problem has been going on for some time (mines now three years old) I wouldn't hold your breath in waiting for the problem to be solved.

I solved it by cutting the needlevalve assembly off the back plate and sticking it on to the firewall. Since then it has been a fantastic performer and very reliable.

SVFlier

I have had no problems with set up or adjustment of my OS 91 fx engines. The only problem I have had is with survival of the engine after vertical contact with the ground.

nashtm

I love mine - I had some bubbles at the nv but when I installed a remote nv I noticed that the banjo was very loose - so it might not have been necessary.

People at the club have commented on how powerful it is and how well it idles.

Its just a matter of time till some of the usuals tell you what over priced rubbish OS is but in my opinion they are not objective in their approach.

regards
Tim

edge 3644

Hi,
I wonder if sick OS91FX can be any better with different carby. I thought about
one from Magnum XLS91 or GMS 120. Both have identical venturi and mounting dia ring as OS's. Of course front needle valve option, not rear.

SMALLFLY-

My Feedback: (19)

The GMS 120 needle valve is what Im using on my 91 fx now and it works great. The 91 needle valve is an odd beast. When mine was new it bubbled like crazy (2.5 yrs ago) I sent in to hobby services and the "patched it by installing new seals and a piece of tubimg over the valve. They said it still has a few bubles but runs per specs... It ran pretty well for 2 years on and off different planes and a few months ago the bubbles and leaning came back with a vengance. I tried everything I could think of with no effect so I bought a 12 dollar gms remote needle from tower and it has worked great since. I also own a magnum 91 xls and I have only flown it maybe a half gallon plus 3 tanks break in, but it has been a fantastic engine. Turns the same zinger pro 14x6 prop at almost the exact same rpm as my os 91fx (no baffles-stock mufflers) and it's 50 bucks cheaper. I would recommend the magnum 91 xls based on my experience. It looks virtually identical and uses the same mufflers

Taildrager-RCA

After reading all the bad luck many were having with their 91FX I installed a large clunk in the gas tank and large fuel tubing. The first gallon was run through the engine with a very rich setting, then was leaned each flight a bit as the 2nd gallon of 15% Wildcat was used. My 91FX now turns 9,500 on the ground with a 14X8, idles great, good transition and very good power. IMHO this engine needs a bit more running time with a rich setting to let the ring and cylinder to take a set. Trying to run this engine with only 2-2 1/2 turns out of the high speed mixture while break in as the instructions state will cause the engine to over heat, thus the many problems that people have had.

adrian-RCU

bingo!!!!

rsieminski

When there are so many other less expensive engines out there, why bother with the .91fx. I have 2 mag .91's and both spin the MA 14x6 at 10.5K(both are with in a few hundred of each other), the same as the .91fx, but chrome sleeve, and better warrantee. OS makes a great engine, but a bit overpriced, especially when an equal(or better) engine is $80 less. Until OS gets with the program and lowers there prices to be competitive with the other engines, I'm going with MAG, ASP, GMS, LEO, MEGATECH,.... The .91FX is only 20 or $30 less than the MVVS .91(not even in the same class). If I really wanted to get a real powerful, great .91, I'd get a Jett at $360.

Get a Mag XLS .91, and don't worry about lg clunks, or lg fuel line, . . . std equipment will work. If you ever have troubles with it, send it back, they'll fix it or replace it. Spend the extra $80 on fuel, props, whatever.

beavertail

What is the low end needle valve setting that works for you guys, My was too rich at a factory setting.

Joey

Sprink

If it is too rich, lean it out till it is ok.

I have to say that your question really anoys me. Nothing personal I have seen so many people on here asking about needle settings as in how many turns. This is not a valid question IMO as each engine is different, even when talking about the same engine make and model, and more importantly each engine is run differently. eg the choice of fuel plays a big part in needle settings, you are tuning the engine to the fuel you are giving it.

I do not know how many turns mine is out, I don't see the need to measure it. I set it to what I want and leave it alone.

There is plenty of advice here on RCU on how to set the needles, I thought I new it all until I started to use RCU and realised I was still only a beginner. If you can determin it is too rich, it suggests you have some idea as to what to do, you will be better off working out what works for you and your engine.

Flypaper 2

To add to what Sprink says, just a change in the weather, temp, humidity, requires different needle valve settings. Just a matter of learning to read your engine.

Taildrager-RCA

Beavertail: Joey, as to your very valid question, I have my low end mixture screw set 1/8 -1/4 turn leaned from the factory setting depending on the tempature and humidity. I peak my high mixture then richen 300rpm, then set low end mixture to best transition. I then again peak and richen. This should get you in the ball park.

beavertail

Sprink, If my question annoys your british ears, then dont read it.

edge 3644

Hi,
I finally tried yesterday both carbs i.e. from Magnum XLS91 & GMS120 on the
OS91FX. Both have NVA's in them, (no stupid remote valve). I must say that now OS installed in Excite 90 works very well with any of these combinations. I could do very funky stuff at full throttle for 15 min on 14oz tank with engine running very consistently. After landings OS wasn't exactly cool, but I think within the norm.

orleck

My Feedback: (1)

I too was/am worried about the OS .91 FX "problems". This will be my third plane. My other engines are OS40LA and a OS46FX. I am waiting for my new OS 91 to be delivered from Tower. Should I keep it or send it back for something else?
I was going to use it on a second hand plane I had bought at a RC swap meet. It is a Robinhood 80 vintage 1985. As per box: the wingspan 80in, wing area 1180sq.in., weight 10-12lbs. recommended engine 75 to 108 two cycle. It has floats but I plan to start is as a land plane until I get familiar with it. Can the 91 handle the job or should I send it back? Any other engine recommendations? I don't want to spend much more that I have already for the 91. Thanks