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DAquaNut(at)aol.com
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 Posted: Sat Aug 23, 2008 9:57 pm Post subject: Idle fluctuations |
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: Group,
I have a situation with my 447 where after running the engine at 3000 rpm or better, and then closing the throttle, the rpms drop to around 2200 and then slowly come back up to 2500 where I have the idle set. Upon landing it seems like it is going to die when I close the throttle. I would be afraid to close the throttle while flying for fear it would die. Any ideas on what is up?
Ed Diebel Firefly ( 62)
It's only a deal if it's where you want to go. Find your travel deal here.
[quote][b]
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jbhart(at)onlyinternet.ne
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| Posted: Sun Aug 24, 2008 9:32 am Post subject: Idle fluctuations |
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| Quote: | I have a situation with my 447 where after running the engine at 3000 rpm
or better, and then closing the throttle, the rpms drop to around 2200 and
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then slowly come back up to 2500 where I have the idle set. Upon landing it
seems like it is going to die when I close the throttle. I would be afraid
to close the throttle while flying for fear it would die. Any ideas on what
is up?
Ed,
If the humidity is high, I would bet on carburetor ice.
Jack B. Hart FF004
Winchester, IN
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herbgh(at)nctc.com
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| Posted: Sun Aug 24, 2008 10:31 am Post subject: Idle fluctuations |
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I do not claim to be an expert on Carbs...but------
With the mechanical idle screw set all the way in...spring
compressed completely, usually ....the carb idle circuit is no
longer effective...so when you close the throttle...the jet needle
may go so low toward the main jet so as to restrict flow? (that is
your idle circuit now) Check your needle and drop the clip a
notch... These carbs,Mikuni's also, were designed to operate
with engines wthat have clutches or variable belt drives that have
no load at idle... Herb
At 01:28 PM 8/24/2008, you wrote:
| Quote: |
>I have a situation with my 447 where after running the engine at 3000 rpm
or better, and then closing the throttle, the rpms drop to around 2200 and
then slowly come back up to 2500 where I have the idle set. Upon landing it
seems like it is going to die when I close the throttle. I would be afraid
to close the throttle while flying for fear it would die. Any ideas on what
is up?
>
Ed,
If the humidity is high, I would bet on carburetor ice.
Jack B. Hart FF004
Winchester, IN
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sun Aug 24, 2008 10:58 am Post subject: Idle fluctuations |
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These carbs,Mikuni's also, were designed to operate
| Quote: | with engines wthat have clutches or variable belt drives that have no
load at idle... Herb
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Herb:
Maybe for ATVs, snow machines, but the carbs for Rotax and Cuyuna engines
are set up for props without clutches, I would think. I am no expert
either. Trying to use common sense.
Ed D's engine is unloaded when he is in landing configuration. No load on
prop.
I bet if the engine and carb are tuned correctly, he won't have that
problem.
Just guessing, of course.
john h
mkIII
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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jbhart(at)onlyinternet.ne
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| Posted: Sun Aug 24, 2008 11:24 am Post subject: Idle fluctuations |
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At 01:58 PM 8/24/08 -0500, you wrote:
| Quote: |
I bet if the engine and carb are tuned correctly, he won't have that
problem.
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John brought up a good point. If your EGT's are running a little lower than
normal, it might be caused by a slightly over rich idle setting. Turn the
idle air screw out 1/8th of a turn and see what happens. The idle circuit
continues to produce a fuel flow no matter what the throttle setting. If
your EGT's are running a little higher than normal rotate the idle air screw
the opposite direction.
Jack B. Hart FF004
Winchester, IN
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DAquaNut(at)aol.com
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| Posted: Sun Aug 24, 2008 8:00 pm Post subject: Idle fluctuations |
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In a message dated 8/24/2008 1:59:20 P.M. Central Daylight Time, jhauck(at)elmore.rr.com writes:
| Quote: |
Ed D's engine is unloaded when he is in landing configuration. No load on
prop.
I bet if the engine and carb are tuned correctly, he won't have that
problem.
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John and Jack,
Just so we are on the same page. The 447 seems to run fine when the air temp is above 90 which it is most of the time. I have gone back to stock jets except I have a 40 Idle jet because it seems to load up. my egts are around 1000* below 3600rpm. they go up to 1200* at times when at 4100 - 4500 rpms . At 4900 _ 6300 rpm its around 1000*- 1100* I have it propped at 6300 rpm tied down. I dont recall this problem before I installed the 40 idle jet. I guess I can try the 45 idle jet. We have 75% humidity most of the time. When the weather cools the midrange egt temps go to 1250 or better. Not good according to Rotax.
Ed Diebel FF(62)
It's only a deal if it's where you want to go. Find your travel deal here.
[quote][b]
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rowedenny
Joined: 09 Mar 2008
Posts: 338
Location: Western PA
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| Posted: Mon Aug 25, 2008 2:02 am Post subject: Idle fluctuations |
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[quote] John and Jack,
Just so we are on the same page. The 447 seems to run fine when the air temp is above 90 which it is most of the time. I have gone back to stock jets except I have a 40 Idle jet because it seems to load up. my egts are around 1000* below 3600rpm. they go up to 1200* at times when at 4100 - 4500 rpms . At 4900 _ 6300 rpm its around 1000*- 1100* I have it propped at 6300 rpm tied down. I dont recall this problem before I installed the 40 idle jet. I guess I can try the 45 idle jet. We have 75% humidity most of the time. When the weather cools the midrange egt temps go to 1250 or better. Not good according to Rotax.
Ed Diebel FF(62)
Ed,
Sounds to me like going back to the 45 idle jet will help. Seems like your idle and also your midrange is on the lean side and the cooler denser air is enough to slightly over lean it.
Try one thing at a time starting with the 45 idle, if your mid range is still a little hot than drop your clip to raise your needle.
Denny N616DR
[b]
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Tue Aug 26, 2008 1:46 am Post subject: Re: Idle fluctuations |
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| John Hauck wrote: | These carbs,Mikuni's also, were designed to operate
| Quote: | with engines wthat have clutches or variable belt drives that have no
load at idle... Herb
|
Herb:
Maybe for ATVs, snow machines, but the carbs for Rotax and Cuyuna engines
are set up for props without clutches, I would think. I am no expert
either. Trying to use common sense.
john h
mkIII |
Just FYI,
The stock jetting on the Bings on the Rotax works fine on clutch-equipped engines at idle.
The only oddity is that the stock slides have to be bottomed out to get the idle speed down below the clutch engagement speed. The stock slides are setup for higher idle speeds so the idle stop screws have to be all the way out, at least on the dual carb configurations.
There are other slide options with a smaller cutout available from Bing that will allow lower idle settings, but the stock ones will still give about 1600 rpm idle speeds at correct idle mixture settings.
I don't remember having to adjust the idle mixture at all when running the clutch on my 503's, but I did always have to bottom out the slides to get the idle speed down.....
LS
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LS
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