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-   -   engine/fuel question (https://www.rcuniverse.com/forum/questions-answers-154/9672271-engine-fuel-question.html)

ShaneLittle 04-19-2010 09:58 AM

engine/fuel question
I am running a OS 46 engine. It has a dozen flights on it and it has been running fine, I started out on 10% fuel and bought a field box that came with a gallon of 15% so I figured I'd use that. Anyway, engine starts fine, runs strong, I have the high end tuned pretty good. What's happening is after flying at half throttle for 15mins or so, I do some touch and goes and the go-around power is right there, no bogging. But when I land, within 30secs, sometimes quicker, as I add power to clear the runway it just dies. It didn't seem to do that on the 10% and that is the only thing that is different. Also, there seems to be excessive exhaust fuel down the side of the plane. Any thoughts on this?


Dr1Driver 04-19-2010 10:01 AM

RE: engine/fuel question
Sounds lean on the low end. Sometimes a different nitro content or different oil mix will change the needle settings.

ShaneLittle 04-19-2010 10:08 AM

RE: engine/fuel question
That being said, I turned the LSN clockwise about 1/16 of a turn, that may have been enough to cause a slight issue. I haven't tuned these engines in years so I was experimenting a bit, but just a bit. :)

Dr1Driver 04-19-2010 10:11 AM

RE: engine/fuel question
That would do it. You leaned it out. It doesn't take much on that low end needle to make a big difference. Put it back where it was and go from there.

ShaneLittle 04-19-2010 10:17 AM

RE: engine/fuel question
Thanks DR1, I guess I answered my own question. It helps to talk it out sometimes. :)

Dr1Driver 04-19-2010 11:13 AM

RE: engine/fuel question
Do the pinch test for the high end. At full throttle, briefly pinch the supply line. If the engine dies immediately, it's too lean. If it runs a while, then slowly revs up, it's too rich. If it speeds up quickly and begins to die, it's about right.

ShaneLittle 04-19-2010 01:02 PM

RE: engine/fuel question
And just because I'm learning I'll ask. The 10/15% rating is the amount of nitro in the fuel? Meaning 15% should have more kick or am I way off base here? Also for a relatively new engine should I be doing anything specific to it on a regular basis? Should I stay with the 10% vs 15%? Just curious.

Jetdesign 04-19-2010 05:30 PM

RE: engine/fuel question
15% requires a more open valve setting; more nitromethane needs less oxygen to burn, therefore would be running lean with no adjustment from 10% settings.

The increase in nitro content is mostly about the ability to burn more alcohol in the combustion chamber, since you can reduce the amount of air and increase the volume of fluid (it has a lower fuel:air ratio).

The only thing I noticed when going from 10%-15% on a .46 engine was a decrease in flight time. I don't believe it is worth the extra cost and reduced flight times for the small increase in power you get.

The increase in power gets more noticeable when you get into larger engines.

ShaneLittle 04-19-2010 05:36 PM

RE: engine/fuel question
Gotcha. I only tried the 15% because it came with the field box I bought. Thank you guys for the insight!

TedMo 04-19-2010 06:54 PM

RE: engine/fuel question
My thoughts are that perhaps fuel is very old and not airtight when it was stored.

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