BigBadJon

is there anything special that needs to be done for a gasser engine when taking it from 1,400ft elevation or about 7,000ft elevation?
i know my nitro engines just need a turn of the needles, but everything else i have thats 2 stroke gas, bikes,quads etc. have to be rejetted and dialed back in.
the engine im referring to is a zenoah g62.

w8ye

My Feedback: (16)

There should be a minimum of effort required. You may not even have to adjust the needles.

rangerfredbob

My Feedback: (13)

just retuning should do it, these things don't have replacable jets like your bikes and such.

bcchi

You could advance the timing a little 3or 4 degrees.Maybe lean carb a little. Test fly before doing anything.
BCCHI-Riverton Wy.5400ABSL

Eganwp

My Feedback: (1)

Lean your needles!

karolh

With such a big difference in elevation change I suspect you will have to lean your needles as the opposite applies to me, as when I go from my home base of 3,000' to just above sea level I find that I have to richen my needles just a tad.

Karol

Sport_Pilot

You would richen the needles not lean them? Less pressure to push the thicker fuel through so you have to richen.

w8ye

My Feedback: (16)

Sport

Every engine I every ran at a higher elevation had to have the mixture leaned out.

From the deal that the air is thinner at a higher elevation, to maintain the same air-fuel ratio would require less fuel.
================================================== ================
The carbs on most of our model gas engines have a atmospheric balanced demand regulator in them that partially compensates for the thinner air.

Tired Old Man

My Feedback: (1)

Less O2 demands less gas to achieve the best fuel to air ratio. Higher=leaner. Oxygen is less dense at 7,000' than it is at 1,400'. Temperature effects that density as well.

JoeAirPort

My Feedback: (41)

Part of what you're saying applies to the metering diaphragm vent port (atmospheric pressure is the metering diaphragm's constant reference pressure). But the air induction is more affected by the pressure change. I can't see why the fuel would get thicker though.

Tired Old Man

My Feedback: (1)

Fuel viscosity will not change at all and specific gravity will not change substantially for that small of an elevation change. If a carb is well adjusted to begin with a 5,600' change in altitude would require only a small adjustement at most. Our carbs pretty much self compensate to very high altitude levels. This is something I deal with daily.

AA5BY

It seems to me there are two dynamics (perhaps more) at work. There is the issue of Oxygen change and I agree that it would call for a leaner mixture as is typical to many carbs. However, the Walbro uses a metering system on the float needle that is unlike float bowl carbs in that it uses atmospheric pressure as the constant in providing flow/pressure metering ahead of the adjustment needles.

When examining the Walbro, we see that greater atmospheric pressure leverages the float needle open for greater flow/pressure. Reducing atmospheres then lessens the flow/pressure requiring opening or richening the needles. The question is which dynamic has the greater affect and nets a change in which direction?

Tired Old Man

My Feedback: (1)

From a multitude of experience with this specific subject, the effects are greatest on the mixture.

jedijody

My Feedback: (1)

The beauty and genius of the regulating diaphragm carburetor is that it does compensate for altitude and atmospheric pressure changesall by itself, the only factor requiring minor mixture needle adjustments is the oxygen saturation level in the available air.

Antique

My Feedback: (4)

Love this forum Simple question, simple answer..
Dude asks a simple question, gets into a scientific discourse on density, viscosity, etc.....
Lean the damn needles slightly, you will be good to go...
If you don't understand carb needles do a search. There must be 1000 threads on carb adjustments...

Lnewqban

.............and your engine will deliver less power, ...................and your wings will need to work harder (move faster and/or keep higher AOA) to sustain flight.........

RPool

I love Antique's answer! Lnewqban...in response to your signature line, I know a kindness you can do us...

bcchi

Wrong,Wrong,Wrong Ask Ralph or Jody.
BCCHI

karolh

They already responded. It's just the same ole same ole, you can take a horse to water but you can't make him drink.

Karol.

Tired Old Man

My Feedback: (1)

Most of what I do lately is working with high altitude use engines tuned from a near sea level reference. Ain't no one in this forum runs a Walbro as high as I do. Mine have to work, there's no option of landing to re-tune the carb. 7,000' isn't even halfway there.

gibatta

My Feedback: (1)

Gentleman:

We fly at 13070 feet above sea level (In La Paz, Bolivia) and here are some tips:
. ANY gas engine will work no matter the size, but it will loose power power proportionally with altitude. In our case we loose around 20 to 25% of its power compared with sea level.
. In most cases you don't touch the LOW needle, if it is already been set up at factory, this applies to zenoah and dle engines. what you do regulate is the HIGH needle. but it has to be set up 200 to 400 rpm less at the rich side of peak power due at high altitude there is less air to cool the engine. In other words: set up the needles as if you are at sea level trying to find the highest peak and THEN set up a little rich on HIGH

Any further details I will be more than glad to post

Gary

Super08

My Feedback: (2)

Oh boy here we go with "factory settings" again.....

Tired Old Man

My Feedback: (1)

I agree the engines develop less power at high altitudes. That's a fact of life with normally aspirated, sea level engines.

I disagree with not adjusting the low needle, and setting up rich of peak. Failure to adjust the low needle sets the stage for "wet" fouling of the spark plug if the engine is run for extended periods of time at mid to low throttle settings. Running rich of peak sacrifices as much or more power as the higher elevation extracts, and again fouls spark plugs. That makes no sense. Cooling air can be maximized to handle the heat generation. A standard cowl opening can not do the job by itself. Unfortunately model engines are limited by their availble ignition and spark plug types and cannot reach their full potential at higher altitudes. Has active in flight engine telemetry been used to verify the engine temps? Without a data plot for the entire flight there is nothing to relate temperature to and actual temperatures over the course of several flights is mandatory in determining what you're engine is doing. A high/low recorder is not a good tool for this kind of information.

Even at 13,000', you're still flying in my "basement".

av8tor1977

My Feedback: (6)

A bit off subject, but with a large change to a higher altitude, you will notice significantly higher landing speeds, just so that doesn't surprise you. The airplane will have a longer take off roll as well.

The above amazes me everytime I go from near sea level to flying at or above 5000' msl airfields, even though I know to expect it. After flying for a good time at higher field (and density) altitudes and then going to sea level, you can almost "feel" the much thicker air through the performance of the airplane. The actual stall speed is the same for the airplane, but your ground speed will be higher, hence the extended landing and take off distances.

AV8TOR

Lnewqban

Done, RPool; I have changed my signature line!!