rcflyer400

The instructions for these engine say to use a fuel of 5-15% nitro and no less than 20% oil content for break in, and then to use at least 18% oil content fuel after break in. I have a gallon of Omega 4 stroke fuel, 15% nitro and 17% oil content according to tower hobbies data. Will this fuel still be adequate for break in and use after break in? The owner of my LHS was telling me it would be, but I don't want to damage either engine.

Also, how could I possibly increase the oil content? For instance, how much Sig Castor would I need to add to increase the oil content to 18 or 20%?

carrellh

Add 5 ounces to a full gallon for 20.12% oil content.

rcflyer400

Thanks for the info. I actually found online the SIG castor specifications, 5 ounces increases oil content by 3%, just as you said.

JCOKEEFE

My Feedback: (2)

[8D]I use the same fuel for break-in as I do for normal flying, i.e.,
Cool Power 15%, for my OS 4 strokes. Have never had a problem.
You run them slobbering rich and alternately a bit leaner while
breaking in on a test stand. I will run 2 tanks of fuel using this
process.

rcflyer400

I have seen several people write that as long as you run an engine slobbering rich for break in the oil content shouldn't matter so much. What does slobbering rich mean, i.e, what rpms should the OS 120 run when breaking in, and the OS 70 as well? And then how much should I lean it out when I alternate between rich and slightly leaner - a few hundred rpm?

JCOKEEFE

My Feedback: (2)

[8D]I will quote the owner's manual for the FS-120S-E, not word for word:

"Start & adjust engine as detailed in instructions. Open throttle fully and run the engine
for no more than 5 seconds with needle valve tuned to produce near maximum rpm, then
immediately slow down engine by the opening the needle valve approx 1/2 turn. The
rich mixture, so induced, will cool the engine, at the same time providing increased
lubrication. Allow the engine to run rich for 10 seconds, then close needle valve again
to near maximum rpm for another 5 seconds. Repeat this process using the needle
valve, while keeping the throttle fully open, then begin to extend the short periods of
high speed operation until two full tanks of fuel have been consumed. For the first
flight have the needle valve set on the rich side. With each successive flight, close
needle valve very slightly, until after ten flights, the needle valve is set for full
power. Do not over-lean the mixture".

My use of the word "slobbering" rich means that when I break in a new 4 stroke,
I probably open the needle valve more than the 1/2 turn quoted in the OS
instructions above. There is a noticable decrease in RPMs and a very wet exhaust
as a result, thus the description "slobbering rich". I have never used a tach to
determine how lean the high end setting should be. I open the throttle and
adjust the high end needle valve until I "hear" the engine running at full power
and then back off from that by opening the needle valve about a 1/4 turn max.
If you lean the high end needle valve too much at full throttle, you will hear
the engine start to lose rpms and you want to avoid doing that. I like to run
my engines, in flight, on the rich side.

rcflyer400

Thanks for the clarification. I do read the manuals and try to adhere to them.

The 91FX 2-stroke is broken in the same way with richening and leaning, and when i broke mine in I think I didn't richen the mixture enough. No damage that I know of was done because after I ran a couple tanks through and the engine was still not tuned corectly I decided to open the HS needle out 1.5 turns and the engine literally woke up and started to run great. Mind you, i followed the manual exactly and started with the needle valve out 2-2.5 turns to begin with. Well mine is out another 1.5 turns from the 2.5 original turns. That's why I am leary of the leaning and richening procedure that OS mandates, because my 91FX at 2.5 turns was too lean to start with.

In the end, I just don't want to damage these engines...it would be too big a hit to the pocket of a poor college student!!