[]I am having a problem getting the mixture just right on my OS 160FX. The engine runs fine at idle and top-end but there is a hesitation (flat-spot) between half and full throttle. My setup as follows:

Model: CMPRO Katana 140
Fuel: 20% Cool Power Oil, 10% nitro
Prop: 18 x 6W APC
Plug: Enya No 3 (have tried OS No8, OS A5, OS A3)
Fuel System: Cline Regulator,

The engine starts and runs very well with plenty of top-end power, I have tried adjusting the mixture rich (no difference) and a bit leaner (still no difference) I have tried different plugs of the same heat range, fresh fuel, and set the mixture back to factory specs several times but the problem persists!

I don't mind admitting that this has me a bit stumped, I have a substantial number of years in the hobby (33), but have limited experience with a pressurised system.

Can anyone offer a solution as to what might be the cause?

Thanks in advance

Peter

Have you considered a Glow Driver?

Try richening the low end and then increase your idle with trim or try leaning it. If the engine rattles in the air at 1/4 to 1/2 throttle it is too lean on the low end. The low needle affects the midrange a LOT on this engine.

Saw this very problem with a 160 at our field. Turned out to be overheating because the engine was tightly cowled. A baffle was installed to direct all the sirflow over the engine and problem disappeared. Try running it with cowl off and see if it changes symptoms any. If it does you will have a clue to the problem.

My flying buddy had the same problem with his OS 160 engine. He drilled and tapped the head and put a 2nd glow plug in. Worked like a charm. He is a pattern flyer and needs a lot of throttle management to fly his routines. You need to have access to a machine shop equipment to have ths properly done. He does not have on board glow as he is very weight conscious. If it was me, I would have on board glow.
Cajuncharley

Thankyou for the proposed fixes for my OS160 FX problems.

The problem has been fixed thanks to a suggestion via a PM, it's a bit radical (involves replacing the carburetor) but I now have an engine that performs over the whole throttle range.

Once again thanks for the reponses and regards

Peter

Well how about some details as to what the problem was.

OK, sorry about that.

At the suggestion of the contributor I replaced the carburetor with a 7D from an OS 108. I had to drill and tap the body for a 3.5mm screw (as fitted to the 160 carburetor). Fortunately, I had a 7D which had some severe damage to the body, so I just ordered a new body from Tower ($29.00).

Regards

Peter

Ozmodeller,
Was the 108 7D a definate recommendation, or was the choice based on you having most of the carb to start with. I guess my real question is: is there a more prefered carb to use?
Actually I had a similar problem with an OS 91FX, I fixed it by putting a Saito 100 in my UCD!!!

The OS 160 FX is capable of far greater performance than the APC 18x6W can produce. Might I suggest the APC 18x10 or 19x8W prop, or pick a prop from the prop chart shown as each prop will produce roughly the same load on the engine.

Note: my ST G90 uses an APC 17x6.

You can also benifit for this setup by running FAI Fuel with Zero Nitro (3% acetone added), which will provide a substantal cost savings over nitro fuel, with minimum loss in performance.

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Schpankme

The F3A guy's I've seen running that engine are more than satisfied. They're using a Perry pumps instead of the Cline. I have heard about the Cline creating similar problems you're mentioned.
One other point is they're using 2 extra head shims (3 in total). No extra carb or head Vodoo, just stock equipment. I've been very impressed watching and listening to this set up. After using YS's and OS1.40's I'm seriously considering this option as all seem very happy and have zero problems.
Also far more prop than you are using, 17x13's seem to be the norm for pattern... so just add dimention and reduce pitch untill you find a prop you're happy with.

What is the function of acetone in this mix?

Cline regulator is a brilliant device but it doesn't really work with OS 160 FX or 91 FX.
On other engines without rear needle it works great.

ini

Saw this thread late, sorry. My experience (unsatisfactory) with the Cline on this motor caused me to go to a Perry VP 30 pump. The problem I had with the Cline was very similar to yours, except that it also tended to go lean, for no particular reason.
If not mistaken, the 7D carb has the integral needle valve, so you're no longer remote, correct? If so, that may be the reason the CLine is now working okay.

If you have future problems, save yourself a LOT of grief, and go with a Perry on the stock carb. BTW - that motor needs to turn some load, it has gobs of power available. For your application, I'd go at LEAST an 18 x 8 W, or preferably a 10 pitch. You will be happily surprised!

Nosram

The 7D was the recommendation, I was also fortunate in having a damaged example on hand. The engine now exhibits the characteristics that I was looking for which is constant and reliable transition throughout the throttle range. I have retained all the specs as in my original post.

For Aerobob, I have retained the remote needle valve, this was accomplished by blocking off the needle valve thread body with a small bolt.

Schpankme, I had tried many different props including 18X8 Mezjlic and APC 18X10, but for what I was looking for (good acceleration without excessive speed) the 18X6 appears to be the most suitable, I am however open to other suggestions if anyone knows of a better prop.

Regards

Peter

How about some RPM numbers on the props you have tried? What muffler, plug etc are you using?

Are you using that check valve he gives you in his kit? It seems very restricting no matter which way you blow through it. I didn't like it so I put a better one in. Also I thin CA's my elbow fittings onto the regulator inlets and outlets. No more fuel leaks.

Basically I had the same problem with my Moki 1.80 and just ran large fuel line instead of the medium. I re-did the tank with all large fittings and tubing. I also shortened the tubing going to and from my fuel dots. I noticed immediately that the fuel draw was right there for priming. Even with fuel regulators, it's better to use large tubing. That medium stuff can really create a lot of pressure drops on the way to the regulator. That regulator needs a minimum inlet pressure to be able to work right. If the pressure drops too much, it doesn't get the optimal fuel draw. I had my tank near the CG, about 15-18 inches from the carb's fuel inlet.

One thing I learned from all this, don't just check your high end and transition from idle to high end. You have to check all of the throttle positions and transitions. It should also drop right to idle as well. You don't want to find out during a hover on the deck that it can't go from mid range to high end.

As soon as the weather lets me I will get some prop figures.

I am using a Bison Pitts style muffler and an Enya No3 Plug, all other specs are the same as in my original post.

For JoeAirPort, I am using the Cline checkvalve, seems to work OK, I also CA'd the fuel elbow fittings, I have no problems with fuel leakage.

Regards

Peter

I'm sure the Cline check valve is fine but I had a new one laying around in a box and thought I should just replace it to eliminate all possible weak points in the system.

ini,

Acetone as a flame modifier, helps with throttle transitions and starting difficulties in colder climates.

In four stroke engines acetone reduces the tendency to pre-ignite when lean mixtures are used (prevents throwing props).

Acetone when used as an additive (3%) reduces the ability of methanol to absorb water from the air.

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Schpankme

Wonder why they don't just use it as an additive in glow fuel?

PS: Nice knife edge in your avitar.

I use onboard glow drivers on all my planes. They all turn off at about 1/4 throttle. I don't think that would solve a midrange problem.
The Cline I use on my Moki 180 works great with med fuel line. You have to put the regulator very close to the spray bar. It opens using the vacuum created by the motor and will not work if far away from the carb. If using on a remote needle valve setup you insert the reg between the carb and needle valve. This valve keeps pressurized fuel from flooding the engine. The Cline system creates a lot of pressure.

I have a OS 160 that is waiting to go. I will probably use a cline on it also. I use 5% omega bought by the case for 9.50 a gallon.

Carl

Oz,

There are four upgrades you can provide for your OS 160 FX installation, which will greatly improve performance and the ability to utilize larger props.

1.) let the engine breath properly - Switch to the Bisson BGX 3500 Pitts Muffler, which offers a less restrictive airflow and as a side benefit has deeper sound.

Muffler: BGX 3500 Pitts (direct bolt up)
Product #: 4220

2.) stop taking pressure from the muffler for fuel flow - Switch to the VP-30 Perry Pump, it regulates the supply of fuel to your engine with no variation in pressure regardless of fuel level in the tank or its location - never to lean or rich.

3.) return to the original carb - the OS 160 carb has proven to be an effective carb.

4.) swing a greater prop load - the above setup should provide 9400 RPMs with an 18x6W Prop. I'd recommend an APC 18x10 or 19x8W or a 20x6W single blade prop. If prop clearance is a problem, you can use a three blade: 16x10, 17x8, 18x6. These larger props should provide 7800 - 8400 RPM.

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Schpankme

The super Tigre 4500 muffler also works well as does the JTec dual snuffler muffler if noise is an issue. I run either a APC 18X6 or Mezjlik 20X6 prop depending on what I want. I have also used a Bolly 18X10 and custom Bolly 16.5X10 three blade all have different performance. Tried a Mezjlik 20X8 but it was too much prop.

Never needed a pump.

Here's a Prop Chart for the OS 160 FX based on Muffer/Exhaust performance.

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Schpankme

[quote]ORIGINAL: Schpankme

1.) let the engine breath properly - Switch to the Bisson BGX 3500 Pitts Muffler, which offers a less restrictive airflow and as a side benefit has deeper sound.

Muffler: BGX 3500 Pitts (direct bolt up)
Product #: 4220

2.) stop taking pressure from the muffler for fuel flow - Switch to the VP-30 Perry Pump, it regulates the supply of fuel to your engine with no variation in pressure regardless of fuel level in the tank or its location - never to lean or rich.