What to do about low runtime?

[marked23]

DavidH suggested that I might be running rich as a result of my confession that I get 8 minute flights on my Fury (OS91csps).

This is what I have:
Fury Extreme
OS 91csps (stock carb... no cateye mod)
OS #8 plug
Using the pump with tank return.
CY MPII
Cool Power 30

This is how I tune:
Set the idle needle on the rich side of center.
Set the high needle to rich.
Repeat:
lean a few clicks
hover
look for tail kicking due to a lean "missing" sound
Then richen a few clicks
Done

In my novice/intermediate opinion, the engine isn't yet running too lean when the tail starts kicking. It's just that the tails starts kicking before I can fully lean it out. So I just fly it rich.

I get about 8 minutes of flight time. I know if I lean the main needle further I will get tail kicking due to engine misses.

So what other things can I do to increase flight time? Shims? Different plug? $ to OMI? Move to Reno or Denver?

Alternatively... What can I do to decrease the tendency of my engine to miss as I lean it out? What causes that? Is it detonation by too much compression or too hot a plug? Or a cold plug? Or not enough compression?

-Mark

[DavidH]

Mark,
Add the third needle to the carb. That is why you can't lean the engine out like it should be. The mid range is running lean and you have no way to control it. Add the needle to control the return line and you then can adjust the main needle leaner and run the engine like it needs to be run.
I used the PS motors for 6 months before converting them to Cline system. They did the same thing you described till I installed the third needle.
You can find the needle on Rick's R/C site under OS engine parts. It cost about $25 for the assembly. Do a search and you can find most of the PS motors have this needle installed on them.
That is why your using fuel so quickly. A full tank of fuel in the Fury is right at 20oz. If a tank only last you 8 mins, then your burning 2.5 ozs a min. I would think there is plenty of unburnt fuel pouring out you muffler when the engine is running.
The engine should burn about 1.5 to 2 ozs a min at full throttle in forward flight.

David

[marked23]

I presume this is it?
Link to Rick's OSM0165 (http://www.ronlund.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=heli&Product_Code=OSMG0165)

This needle sets the back-pressure of the return line... thus setting the fuel pressure at the carb, right? (I'm asking)

So what's wrong with the factory setting via the stock return line back pressure... is it too high or too low? If it's too low, I could use some smaller fuel tubing on the return line to get the same effect, maybe?

I'm not being too cheap to buy the needle... I just ordered it. I just wonder if there are options to deal with this without adding another thing I need to fiddle with. It just seems so complicated.

-Mark
[/url]

[DavidH]

The mid range without the needle to control the flow is too lean.
You could probably control the flow with something else but it would a trial and error type deal.

Fuel does not flow thru the return line all the time, only when the midrange has an excess amount than needed.

The needle will allow that amount to be controlled more precisely. This needle will work opposite of what normal needles do. You will turn the needle in clockwise to richen the mixture and turn it out counter-clockwise to lean the mixture.

The setting that is standard seems to be about 1.5 turns open from fully closed plus about 3 more clicks open.

David