kswanson

My Feedback: (25)

So I acquired a Four Star with an OS FS-91 that had sat for several years.

Needless to say the engine was all gummed up and I have cleaned most of it including the carb where everything now moves as it should.

Problem is that I can get it started but I cannot throttle up.

I am wondering if anyone know what the correct low idle setting should be and the high end too.

Since I took the entire carb apart I am thinking the issues can be easily fixed with the proper settings.

I did take all screws out. There is one screw with a spring on it and not exactly sure what that is and where it should be set for proper run.

Gray Beard

My Feedback: (-1)

The screw with the spring fits into a slot on the drum or barrel and keeps the drum on track when opening and closing. the spring keeps it from vibrating loose. If adjusted too tight the drum is hard to open. It should open and close smoothly.
The normal starting adjustment of the needles is about 1.5 to 2 turns open then adjusted from there. You adjust the high end first then the low end. The valves should be adjusted cold at .04mm or .0015inches to .10mm or .004. New engines come with the feeler gauges. The thin blade should be able to slide between the tappets and the thick one shouldn't. Make sure your at the dwell at TDC. If you pulled the cam then at TDC the dot on the cam should be pointing down at 6 oclock.
If you are still having problems then go into the glow engine forum and then into factory support and ask Bill Baxter. He knows everything there is to know about this engine.
The OS .91fs is one of my favorites in the OS line.

kswanson

My Feedback: (25)

I don't have anything to adjust the valves with. I didn't tear down the whole engine on the carb.

So your saying both the high and low end needs should be screwed in and then backed out by 1.5 to 2 turns?

right now this thing will only idle if the low end is almost backed all the way out.

Gray Beard

My Feedback: (-1)

Two turns out on both needles is where I always start. 1.5 turns in is about where they both end up, maybe a bit leaner on the high end, like any engine it will be where the engine wants it to be.More then two turns out on your OS for the low end points to other problems. Something may be inside the carb blocking the passage.
Most good hobby shops sell the valve adjusting tool kit for about 10 bucks, Tower also sells it. Just like any engine you will need the tools to keep it alive and well.
Go into the OS forum and you will learn almost all you need to know. Once the high end is set for max rpm then you want to back it off and make sure it is about 3 or 4 hundred rpm fat.
I just had a four stroke I had fully cleaned and oiled last year, I used castor oil when I assembled it. This is the first time I have had fresh castor gum up on me and I had a lifter sticking. Heat is your friend in this case and I just used a heat gun to loosen it up and put some fuel down the push rod tubes and rolled it over. That cured the problem.
You really need to read up on your engine so you understand how it works. I use one of those ear flushing bulbs from the drug store to pressure flush things like the carbs when I clean them.
Chances are you just needed to heat up the carb and flush it instead of taking it apart. I'm guessing you may have gotten old hardened castor oil lodged into the low end.
Take the time to go read threads in the OS factory support. Bill is very good at answering questions. You have an outstanding engine but you need to understand how they work.

kswanson

My Feedback: (25)

I will read up on the engine and seek out the tool you mentioned.

Just so I am fully understanding the adjustments for high and low end.

High end you are turning the needle clockwise until closed and then turning it 1.5 turns counter clockwise., same for the low end too?

I am asking becuase if the low end is done this way it will not start. If I do the opposite on the low end it will start. Meaning turning the screw counter clock wise until I can no more and then turning it 1.5 turns clock wise.

kswanson

My Feedback: (25)

So today I was cleaning out the crock pot I cooked the carb in and found the barrel spring that I didn't put back in.

so I took the carb off and cleaned all ports and blew them out with compressed air.

I was reading today that this carb actually has three set screws, one for high, one for low and a minimum low.

Yesterday I did fly the plane and on my second flight the end died mid-air so I am back to trying to get this to run at it's best.

Will be ordering the kit today for adjusting the valves.

What sort of max RPMs should I be seeing out of this engine? What is the ideal prop for flying a four-star 60? I picked up a 14x8 the other day but have not put it on it. Not sure what's on it now.

Last tach I got about 8950 for RPM at full throttle.

Gray Beard

My Feedback: (-1)

89 is about right, a 14 inch prop is about right too but if you look up the instructions on the engine you will find all the information you need. Adjusting the carb is a balance between the high and low end adjustments. People tend to over lean the engines on the ground then in the air they unload and will lean more. The best way to learn how to adjust an engine is to pick out one club member that really knows what they are doing and stick with him as an instructor. I had a great one once I got into advanced flying and set up. You can get some info from the net but if a person isn't standing right next to you and hearing and seeing the engine you could be getting false info. An engine going dead stick in the air is usually a lean condition. Get some hands on help at your local club.

kswanson

My Feedback: (25)

I got it all back together. I did notice a crack in the exhaust pressure tube so I fixed that. I got it running and thought was running good on high and low ends... right around 9300..... though when I took off it seemed to be as if it was bogged down. flew it for about 4 minutes and then at full throttle it died and I backed off the throttle and then throttled back up and it ran again. did that a few more time in two minutes and then landed dead stick.

Right now I don't have a club member to help. The club I joined recently does not produce a roster and there is only one guy I know and he is an hour away. So for now I am on my own.

jaka

Hi!
The carb has only two needles : One high speed needle and one low speed needle (idle needle).

If the engine has sat for years I 'm certain that the five ball bearings need replacement.
14x6 or 15x4 APC is the prop to use, and only the OS F plug.
Fuel could be 5-15% nitro.
8500-9000rpm on the above props.

speedracerntrixie

My Feedback: (29)

5 bearings?

Bax

My Feedback: (11)

Five bearings are in the original FS-90. The FS-91 was in the Surpass series.

speedracerntrixie

My Feedback: (29)

Well there ya go. I was thinking I missed one when I rebuilt my 91 Surpass.

jaka

Hi!
Oopps!
A front cam OS ! Then four bearings!

People seem to think that it's just cleaning the outside of an engine and taking apart the carb that is important...Nothing could be more wrong!
Itīs the inner parts that is most important and that means replacing the ball bearings!