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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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 Posted: Wed Nov 24, 2010 9:57 am Post subject: Re: Rough running cured with carb heater |
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Hi Dave,
Warm air will richen the mixture and cold air will leans it.
I have seen guys try and tweak their engine temps too close to the max trying to get more HP when the weather is warm. Then they go out on a cold morning and seize their engine and don't understand why. They think the colder air should have kept the engine cooler, but the cold air affects the fuel mixture and it seizes.
It never pays to run your temps too close to max because one little issue can cause a big problem, not to mention faster wear on the engine over the long haul.
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Wed Nov 24, 2010 10:09 am Post subject: Rough running cured with carb heater |
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Dave, you have raising the needle confused with raising the clip. Raising the needle richens the mixture and is done by lowering the clip, Lowering the needle leans the mixture and is done by raising the clip.
Rick Girard
On Wed, Nov 24, 2010 at 11:23 AM, Dave Austin <daveaustin2(at)primus.ca (daveaustin2(at)primus.ca)> wrote:
| Quote: | --> RotaxEngines-List message posted by: "Dave Austin" <daveaustin2(at)primus.ca (daveaustin2(at)primus.ca)>
Thom,
If the air is hotter and less dense, will it not raise the needle as far, and thus lean the mixture? That would also apply as you fly higher.
Dave Austin
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Zulu Delta
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Thanks, Homer GBYM
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joeing701(at)simnet.is
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| Posted: Wed Nov 24, 2010 10:32 am Post subject: Rough running cured with carb heater |
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Hi all.
This is what we thought also and therefore raised the needle and the clip is in the bottom position. Still did not fix the problem.
Good to know we were on the right track.
Thanks,
Johann G.
On 24.11.2010, at 18:07, Richard Girard wrote:
[quote]Dave, you have raising the needle confused with raising the clip. Raising the needle richens the mixture and is done by lowering the clip, Lowering the needle leans the mixture and is done by raising the clip.
Rick Girard
On Wed, Nov 24, 2010 at 11:23 AM, Dave Austin <daveaustin2(at)primus.ca (daveaustin2(at)primus.ca)> wrote:
--
Zulu Delta
Kolb Mk IIIC
582 Gray head
4.00 C gearbox
3 blade WD
Thanks, Homer GBYM
It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.
- G.K. Chesterton
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Thu Nov 25, 2010 5:58 am Post subject: Rough running cured with carb heater |
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> ...Applying carb heat in most aircraft leans the mixture ...
I regret to inform you that you are mistaken. The warmer less dense air from applying
carb heat, combined with the same amount of fuel, results in a richer mixture,
not leaner. This is why as you climb higher into less dense air you must
lean the mixture to maintain proper combustion <
I stand corrected Thom, you are right. With carb heat on you must lean the mixture to have the correct ratio with carb heat on. A little dyslexia there. Thanks! (getting old sucks)
Dick Maddux
Milton,Fl
[quote][b]
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daveaustin2(at)primus.ca
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| Posted: Thu Nov 25, 2010 6:53 am Post subject: Rough running cured with carb heater |
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Dick, we are talking of a Rotax with Bing carbs. are we not? The Bing automatically reduces the amount of fuel as the air thins because the thinner air cannot lift the needle assembly as high against the spring tension. So it maintains the correct fuel/air ratio at any altitude or hot-moist/cold-dry combination.
Dave Austin
[quote][b]
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Nov 25, 2010 7:54 am Post subject: Re: Rough running cured with carb heater |
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...The Bing automatically reduces the amount of fuel as the air thins...
This is true but not entirely so. The CV carb adjusts the mixture somewhat but not does not do a perfect job of it with increasing density altitude. In every airplane I've flown that had engines with Bing CV carbs, as you gain altitude the EGTs start coming down slowly. Not as if it did not have the altitude adjusting function but not as well as once can do with a manual mixture control, either. However, the Bing CVs do a good enough job to not allow the engine to be way over rich at any density altitude up to 10k or so that a manual mixture control is not essential.
Bottom line is that the 912 engine does run gradually a bit richer as density altitude increases, whether it is from warming the air or climbing higher.
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Thom Riddle
Buffalo, NY (9G0)
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Flydad57(at)neo.rr.com
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| Posted: Thu Nov 25, 2010 8:05 am Post subject: Rough running cured with carb heater |
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What? Now this I don't understand. Please explain, Dave. I think you're way off here. The air does not lift the needle assembly. The throttle cable does this.
Bob Taylor
TigerCub N657RT
From: Dave Austin (daveaustin2(at)primus.ca)
Sent: Thursday, November 25, 2010 9:50 AM
To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com)
Subject: Re: Rough running cured with carb heater
Dick, we are talking of a Rotax with Bing carbs. are we not? The Bing automatically reduces the amount of fuel as the air thins because the thinner air cannot lift the needle assembly as high against the spring tension. So it maintains the correct fuel/air ratio at any altitude or hot-moist/cold-dry combination.
Dave Austin
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Thu Nov 25, 2010 8:26 am Post subject: Re: Rough running cured with carb heater |
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| Thom Riddle wrote: | ...The Bing automatically reduces the amount of fuel as the air thins...
This is true but not entirely so. The CV carb adjusts the mixture somewhat but not does not do a perfect job of it with increasing density altitude. In every airplane I've flown that had engines with Bing CV carbs, as you gain altitude the EGTs start coming down slowly. Not as if it did not have the altitude adjusting function but not as well as once can do with a manual mixture control, either. However, the Bing CVs do a good enough job to not allow the engine to be way over rich at any density altitude up to 10k or so that a manual mixture control is not essential.
Bottom line is that the 912 engine does run gradually a bit richer as density altitude increases, whether it is from warming the air or climbing higher. |
I can definitely confirm this. My airport is at 6300' MSL and my typical kicking around the patch altitudes range from 8500 to 10,000 MSL. The max I can get on the EGT's are about 1300-1350F and usually only on one bank of cyls; the other is usually around 1200F. The exhaust baffle stays nice and white with lots of high power operation so I'm not too worried about it at full power.
But it's definitely rich at lower throttle settings especially between 2500 and 4000 rpm. I have to run my idle jets out about 3/4 turn instead of the Rotax spec of 1.5.
Also, the carb vent lines _must_ be at the same atmospheric pressure as the venturies as spelled out in the installation manual up here, or the carbs really do go too rich.....
I havn't tried dropping the jet needle, but that might help some too (I just don't want to take those damn things apart anymore  ).
LS
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Titan II SS |
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Nov 25, 2010 8:26 am Post subject: Re: Rough running cured with carb heater |
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Bob,
On the Bing 54 carbs (Rotax two-stroke engines) the throttle cable is connected to the piston holding the jet needle and thus does directly lift the needle.
On the Bing 64 (Rotax 912 series) and Bing 94 (Jabiru) the throttle is connected directly to the butterfly valve only. The piston and attached needle are indeed lifted by the combination of differential air pressure on the diaphragm and the spring below the diaphragm.
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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thesupe(at)hotmail.com
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| Posted: Thu Nov 25, 2010 8:39 am Post subject: Rough running cured with carb heater |
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Bob, I'm notDave, but I'll give it a shot. In a way, you both are right... that is if you are reffering to a type 54 Bing carb as is used on a Rotax 2 stroke engine.I believe Dave was reffering to a type 64 Bing as is used on a 912 or 914 4 stroke Rotax engine. In that case, he is correct, the slide/needle assembly is not lifed by thethrottel cable but by vacumm above it.Look up the Bing website and have a look at the type 64 carbs and you will see how they work. Take care, Jim Chuk
From: Flydad57(at)neo.rr.com
To: rotaxengines-list(at)matronics.com
Subject: Re: Rough running cured with carb heater
Date: Thu, 25 Nov 2010 11:03:54 -0500
What? Now this I don't understand. Please explain, Dave. I think you're way off here. The air does not lift the needle assembly. The throttle cable does this.
Bob Taylor
TigerCub N657RT
From: Dave Austin (daveaustin2(at)primus.ca)
Sent: Thursday, November 25, 2010 9:50 AM
To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com)
Subject: Re: Rough running cured with carb heater
Dick, we are talking of a Rotax with Bing carbs. are we not? The Bing automatically reduces the amount of fuel as the air thins because the thinner air cannot lift the needle assembly as high against the spring tension. So it maintains the correct fuel/air ratio at any altitude or hot-moist/cold-dry combination.
Dave Austin
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Flydad57(at)neo.rr.com
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| Posted: Thu Nov 25, 2010 9:43 am Post subject: Rough running cured with carb heater |
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Thank you, Thom! I hadn't realized that the subject was the 4-stroke
Rotax's with the Bing CV-type carb. I was thinking 2-strokes with the
Bing 54. Sorry group!
Bob Taylor
TigerCub N657RT
--------------------------------------------------
From: "Thom Riddle" <riddletr(at)gmail.com>
Sent: Thursday, November 25, 2010 11:26 AM
To: <rotaxengines-list(at)matronics.com>
Subject: Re: Rough running cured with carb heater
| Quote: |
<riddletr(at)gmail.com>
Bob,
On the Bing 54 carbs (Rotax two-stroke engines) the throttle cable is
connected to the piston holding the jet needle and thus does directly lift
the needle.
On the Bing 64 (Rotax 912 series) and Bing 94 (Jabiru) the throttle is
connected directly to the butterfly valve only. The piston and attached
needle are indeed lifted by the combination of differential air pressure
on the diaphragm and the spring below the diaphragm.
--------
Thom Riddle
Buffalo, NY (9G0)
Kolb Slingshot SS-021
Jabiru 2200A #1574
Tennessee Prop 64x32
?oEveryone is entitled to his own opinion, but not his own facts.?
Daniel Patrick Moynihan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=321020#321020
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Thu Nov 25, 2010 11:36 am Post subject: Re: Rough running cured with carb heater |
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Rotax 2 strokes are more affected with the warm v.s. cold air than the 912 with the Bing 64's, but they are all affected to some degree. The Bing 64's do compensate, but they can only do this just so far.
This is similar to the compensation cross over tube for the carbs. They can help make things between the carbs more equal, but it can only do so much and that is why the carbs should be balanced every 100 hrs. during the 100 hr. inspection. They will always be off.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Nov 25, 2010 11:52 am Post subject: Re: Rough running cured with carb heater |
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Roger,
ALWAYS is a big word. I have seen 912 carbs stay synched for over 200 hours, as long as the owner does not try to fix what is not broken. 
But, I always do check the balance during annual inspections.
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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