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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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 Posted: Tue Jul 17, 2007 7:39 am Post subject: Two Stroke Prop and Carb Tuning |
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| Not necessarily. See here:
| http://www.bcchapel.org/pages/0003/pg11.htm
| Richard Pike
Richard P:
How do you do a spark plug check?
john h
mkIII
PS: I changed to subject line to be more in line with what is being
discussed.
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Tue Jul 17, 2007 8:48 am Post subject: Two Stroke Prop and Carb Tuning |
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How DO I it, or how SHOULD I do it?
There's a difference you know... <grin>
I have always heard that the ideal way to do it is to be running your engine
at the RPM & loading you want to check for, leave it there for a couple
minutes, and then turn the engine off and then check it. Since there is a
difference in prop loading in flight than on the ground, that would mean
being right above a suitable strip to chop the engine, glide down, and then
pull the plug out and look at it. That should be the ideal to give you an
unadulterated reading. Probably running it at the RPM you wanted on the
ground would actually work close enough in practice.
The way I do it is I leave my plugs in long enough for them to be
distinctively colored (at least 15 hours) and then take them out and look at
them. (blush, kicks dirt with foot) Which tells me if the engine is running
consistently too lean, (whitish-gray) consistently too rich, (black) or more
or less right. (brown) And since the stock Rotax specified jetting gives me
temps right around 1050-1100, and the plugs are a medium brown, I actually
can't remember the last time I did a plug check. Probably the last time I
actually did a genuine, hard core, do-it-right-or-else plug check was with a
Rotax 277 in the Hummer about 24 years ago.
But thanks for asking...<grin>
Richard Pike
MKIII N420P (420ldPoops)
PS - this is probably the best description of how to do it-
http://dirtbike.off-road.com/dirtbike/article/articleDetail.jsp?id=332655
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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Tue Jul 17, 2007 10:25 am Post subject: Two Stroke Prop and Carb Tuning |
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|
| I have always heard that the ideal way to do it is to be running
your engine
| at the RPM & loading you want to check for, leave it there for a
couple
| minutes, and then turn the engine off and then check it. Since there
is a
| difference in prop loading in flight than on the ground, that would
mean
| being right above a suitable strip to chop the engine, glide down,
and then
| pull the plug out and look at it. |
| Richard Pike
Richard:
That is the way I did it. Past tense.
Haven't done one in a while. I long while.
Normally, the engineers that design and build these things know what
they are doing. Two strokes are unique when combined with an
airplane. Suddenly we have a propeller and prop loading. ;-( For
most of us folks down here near sea level and up to 1,500 or 2,000
feet, that Rotax two stroke is jetted, timed, and equipped with the
correct heat range spark plug to do the job, with nothing for the
pilot/builder to do but dial in the correct pitch to load the prop.
Always the same for me. WOT, straight and level flight, just bump the
red line which is max continuous rpm for me because I fly with a prop
that is not inflight adjustable. This will put my egt and cht right
in the green arc on a Rotax two stroke, and other brands also.
912UL and 912ULS it is 5,500 rpm
Rotax two strokes is 6,500 rpm
Pushing the EGT redline to squeeze more power and less fuel burn is
also pushing the engine failure factor with a two stroke, IMHO.
john h
mkIII
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Wed Jul 18, 2007 5:24 am Post subject: Re: Two Stroke Prop and Carb Tuning |
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Just FWIW,
The same methods appear to work at high density altitudes as well. I fly at about 7000' MSL where I live, the DA is frequently as high as 9000' even in the morning.
Basically, the only change I've had to make to the 503 on my FS II is a leaner main jet as per the Rotax jetting chart. Virtually everything else is the same except a very slightly higher rpm needed to maintain altitude at my cruise speed and of course a noticeable improvement in fuel economy.
Oh, and a much crappied climb rate, but it's still as good as the local spam cans.... 
LS
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LS
Titan II SS |
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