ukrally

Hi Guys,
I have just bench run in my new 120 fs II pumped which has been sitting in my loft (attic) for about ten years along with the retlas 70" spitfire waiting for me finish building, sorry to babble on with the story.
Problem I have is full throttle running on the bench or in the model. The engine has now done about 5 tanks of 10% nitro and 18% synthetic oil.
Starting is easy and it idles nicely at around 1700 on a 16x6 prop, half throttle is good and smooth with a extra puff of smoke from idle to half throttle transition. With the throttle open to about 90% it pulls about 8000rpm buts its difficult to remove the rich surging but can be just done, the needle valve does not seem very responsive ( currently running at about 1 1/2 turns out)
The biggest problem is when the throttle is opened from 90% to 100% (IE up to its stop) the engine just stops instantly, no missfire or lumpy running ect it just stops as if it were switched off. Iv'e tried the needle valve richer and leaner but it makes no difference at all. It will still do this even with needle valve out to 3 or 4 turns or closed untill fuully closed
I suppose I could set the throttle ATV not to go beyond 90% but that would be cheating and not finding the real cause of the problem and not using the engines full potential.
After ten years I guess the warranty could be void even though its never been run before this week :-)
Any ideas would be greatlt appreciated ..........thanks Mick

Bax

My Feedback: (11)

Your engine has the high-speed needle set much, much too lean. We open the high-speed needle about 1 to 1-1/4 turns when initially starting and lean it from there. When properly-leaned, the high-speed needle will be about 3/4-turn out from closed. The surging indicates that the engine is just too rich.

With that engine, if it's been sitting for a while, the regulator diaphragm will have dried. That makes it regulate badly until it's had about 4-6 tanks' worth of fuel run through it. Those tanks will be 12-16 ounces, each.

Here's how to set the carb:

Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.

One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.

To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.

At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.

With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.

Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.

ukrally

Thanks for the advice Bax, I'll try it out tomorrow if its not raining for a change (typical English weather) and let you know how it goes.
thanks again Mick

ukrally

Hi Bax,
Just a progress report,I removed the diapham and soaked it in fuel overnight to ensure it is in its normall plyable state. The engines still runs poor as if its too rich as you suggested but if I lean it more it just stops as if I have cut the fuel off. Its been like this since day one and I reckon there is a fault somewhere in the metering system as it will only run up to half throttle no matter where the needle valve is set
I lost Patience with it today and another club member has taken it away to tinker with it, I'll let you know how we get on
Cheers Mick

bob_peterson

My Feedback: (2)

Have any of you had trouble with the pump itself. The pumps are pricie and I do not want to invest in another one if that is not the problem. The engine had been running fine and now it will not start. It is not getting enough fuel to the carb. Do you have a way to check the pump out to see if it is working properly? Any advice would be appreciated.

Bax

My Feedback: (11)

The FS-120 Surpass II had a gear-driven pump. If you remove the fuel line that connected it to the carb, filled the tank and spun the engine with a starter, it should really push some fuel through it. If it does, then there's nothing wrong with the pump, and you have to investigate the carb/regulator. The #C-13 carburetor and its parts are no longer available from us or from O.S. in Japan. They've been discontinued since 1996. The FS-120 Surpass III came out in 1997.

bob_peterson

My Feedback: (2)

Thank BAX. Sorry I made a mistake. I had been looking on a lot of threads for the O.S. Max 91II/pump trying to find a solution and did not realize I was on a 120 thread. I have the same question on the 91.

Have any of you had trouble with the pump itself. The pumps are pricie and I do not want to invest in another one if that is not the problem. The engine had been running fine and now it will not start. It is not getting enough fuel to the carb. Do you have a way to check the pump out to see if it is working properly? Any advice would be appreciated.

We have taken off the fuel line to the carb and spun the engine over and the fuel only dribbles out. It does not stream out. Can anything be done or are we up for a new pump? Can the pump get clogged and is there a way to free it up? How does this pump work.

Bob

ukrally

Hi Bob,
My OS 120 pump engine has been a long nightmare story from day one but I hope you learn from my experiences with it.
Following on from my last post, foolishly I let a friend tinker with it and he lost a couple of O rings from inside the regulater ( he did actually get it running OK for a short period by tinkering with the diapham)at which point I lost even more patcience and sent it to the UK OS sevice agent for an estimate hopeing he would replace the O rings and regulater diaphram. NO CHANCE !!

Don't forget this engine was brand new, estimate one was to replace the pump and regulater £230 or convert it to an economy engine at £116 his advice was to convert to economy type (no pump) he would not sell me the diapham or O rings due to it being OS policy. He said very few of these pumped engines actually work ok and its normall practice to convert to economy.

I phoned the agent and said bugger that, just send the engine back and I'll sort it myself............ I wish

I could only get the engine back in bits as he has to totally strip it to give a proper estimate, plus a bill of £35 foir stripping it down. At which point I thought I may as well bite the bullet and have the economy convertion rather than spend money for nothing, its like being held to ransome !

Iv'e now got the engine back in economy version and it runs fine as it should have done at the begining but it now stands me at nearly £500 and I could have bought two engines for that price.
Needless to say I will never buy another OS engine, they may well be quality engines but customer relations is is quite disgusting in my experience. OS should never have sold these pump engines knowing they were a problem.

Sorry to sound so negitive but back to your engine problem, I'm guessing the pump itself is not the problem as mine had a massive amount of fuel returning to the fuel tank when bench running it ( try bench running with clear fuel pipes to see the fuel flow)
I would suggest the regulater is the main fault but OS won't sell you the parts to recectify it ( my perfectly good pump ended up in the scrap bin at the agents)

POSSITIVE !!! the spitfire had a maiden without crashing and the engine ran well, just a few tweeks to do (more nose wieght)

Hope I've not depressed you Bob but I needed to get it off my chest.:-)

Good luck with the engine and let me know how you get on.
Cheers Mick

Bax

My Feedback: (11)

The pump on the FS-91 Surpass II is a diaphragm pump. If you only get a dribble of fuel out of the pump when the engine's spun with a starter, then it's likely clogged with debris. No way to fix it, you'll have to send the pump assembly to us for replacement if you believe it's a warranty issue, otherwise, you'll have to purchase a new pump unit.

The pump has not been a thing of concern.

bob_peterson

My Feedback: (2)

Bax
What does it take to convert the FS-91 Surpass II with pump to the FS-91 Surpass II without the pump. Is it just a matter of buying the OSMG2432 45984000 O.S. Engines 60P FS91SII Carburetor only?

Bax

My Feedback: (11)

You'll need a carb, rear cover, and intake manifold, according to our parts lists. They have the same case and head.