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Hot weather tuning

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Old 08-02-2011, 03:32 PM
  #1
dave de
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Default Hot weather tuning

I had my engine running great over the cooler months. Last to trips to the field with much hotter weather & a little humid but not real bad, I cant get my engine to run. It will start, then at full throttle die. I,m guessing with hotter more dense air I need to richen the hi??? anything I should do with the low?? thanks guys. I know most of you are flying in hotter conditions than me, & I need some tips.... when I got back home I was able to re-tune & get it running great....where I live its probably 25-30 degrees cooler than where i fly
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Old 08-02-2011, 03:47 PM
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Default RE: Hot weather tuning

could be the low end too? if you can reach full throttle then it fizzles out....high end lean.... if it dies while you advance the throttle abruptly, low end lean

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Old 08-02-2011, 04:00 PM
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Default RE: Hot weather tuning

Though I had a hard time comprehending it 50 years ago, hotter weather has a higher density altitude than old weather. Humid weather is usually a higher density altitude and also the barometric pressure is typically lower.

http://wahiduddin.net/calc/calc_da.htm

When the density altitude is higher, you need a leaner mixture because there is less oxygen.

All this theory aside, you need to adjust your needles for the engine to run best.

The metering diaphragm part of your carb adjusts automatically, within limits, for any changes in density altitude.
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Old 08-02-2011, 04:21 PM
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Default RE: Hot weather tuning

Yep. Hotter and/or humid (and/or higher msl true altitude) would tend to make an engine richer, not leaner.

Could it be overheating?

Have you checked your filters, including the screen in the carb?

AV8TOR
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Old 08-02-2011, 04:23 PM
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Default RE: Hot weather tuning

Dave, Try it without the cowl on. Sometimes the carb intake is restricted by the cowl that the hot weather turns out to be the last nail. You may have to cut some of it away to get enough air into the engine. Dan.
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Old 08-02-2011, 04:39 PM
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dave de
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Default RE: Hot weather tuning

whats up Dan....I tried with the cowl off at the field & thought I had it running, when i put the cowl on It cut out again. When i got home I did cut the cowl more, I,m sure i did not have it open enough.
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Old 08-02-2011, 05:02 PM
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Default RE: Hot weather tuning

Your cowl could be effecting the vent for your metering valve especially if you may the air intake larger without making the outlet larger?

You may want to put a remote vent on your metering valve and run it back into the fuselage?
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Old 08-02-2011, 05:32 PM
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Default RE: Hot weather tuning

I could understand it running a little ratty compared to winter, but Carlsbad has pretty balanced year round temperatures. The part where the engine dies tells me there's more involved than simple tuning. BTW, the diaphragm was designed to compensate for a 6000' altitude delta .
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Old 08-02-2011, 05:49 PM
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dave de
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Default RE: Hot weather tuning

like I said earlier, the field I fly at is 25-30 degrees hotter than where I live. And an hour drive from Carlsbad. Other than that, you are correct, Carlsbad has the best climate....
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Old 08-02-2011, 06:26 PM
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Default RE: Hot weather tuning

Dave, Trim away the cowl to get air into the carb. Make sure the opening faces forward to some extent. I live a mile and a half from the beach and drive 55 miles directly east to Chino to fly at the Prado dam. During the summer time the temperature differential is usually around 25 degrees and sometimes 30. My engines are all well exposed. Dan.
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Old 08-02-2011, 06:51 PM
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dave de
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Default RE: Hot weather tuning

Its strange, I thought the engine would burble or run rough if was to hot...... it seemed like it would actually go into a higher rpm, like your were pinching the fuel line and just quit. So today I made a much bigger cut out in the cowl & have it running strong at home.......so from what I,m reading, it sounds like if I have the same problem on Friday, I'll try to Lean the needles a little bit...which one should i try first if the cowl does not do the trick.....
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Old 08-02-2011, 08:07 PM
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Default RE: Hot weather tuning

All the DLE's at the flying field burble (4 stroke) in mid range when just cruising along in level flight. So do the DA's

On my engines, I tune the low speed needle as lean as I can and still get good acceleration when I give it the throttle. I lean to the point of acceleration problems and then richen back up enough to straighten things out.

On the high speed, I like to know where the two stroke four stroke point is in acceleration as that is my reference point. I try to lean not far from there but I listen very carefully for sagging. The engine must accelerate well.

I pay little attention to the mid range burble.
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Old 08-02-2011, 08:47 PM
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Default RE: Hot weather tuning


Quote:
ORIGINAL: w8ye

All the DLE's at the flying field burble (4 stroke) in mid range when just cruising along in level flight. So do the DA's

On my engines, I tune the low speed needle as lean as I can and still get good acceleration when I give it the throttle. I lean to the point of acceleration problems and then richen back up enough to straighten things out.


On the high speed, I like to know where the two stroke four stroke point is in acceleration as that is my reference point. I try to lean not far from there but I listen very carefully for sagging. The engine must accelerate well.

I pay little attention to the mid range burble.
Same here W8ye..... the one engine i own that burbles the least would be my 3w80....but there is a spot in the lower rpm band right above idle where it does it.... i can lean out the low end and get rid of it pretty much but then my engine will die when i throttle up.... i have learned to live with it... i only use that rpm range on landing approach anyhow
i have a buddy that is really annoyed by burbling, my brother and i tell him its pretty common to have a spot in there but he is still getting after it
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Old 08-03-2011, 02:42 PM
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Default RE: Hot weather tuning

Tell him to buy a metering spring selection kit from Walbro and have at it. That should keep him busy pulling carbs and changing springs for the next 8 months or so. If you normally ride to the field together you'll have more room in the car.

The sarcasm in the above was to illustrate the end result isn't worth the effort.
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Old 08-03-2011, 06:48 PM
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Default RE: Hot weather tuning

Here is words from Pe Reivers


pe reivers
04-20-2011, 03:47 PM
but will he swim in it?

BTW,
The notch in the throttle plate, located over the idle jets will concentrate the airflow and provide better idle mixture, allowing the idle needle to close more. However, this also results in leaner midrange because then more air bypasses the idle jets. For some carbs, this is the cure for rich burbly midrange

The above is what I did to get rid of mid range burble. I enlarged the moon on the throttle plate just a tad.... .005 of a inch. It worked good. Capt,n
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