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egp8111
Joined: 25 Mar 2010
Posts: 49
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 Posted: Mon Dec 12, 2011 10:34 am Post subject: Carb synch issues |
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I can't get the carbs on my 912ul to synch at both idle and about 4000rpm. If I adjust it for one setting it runs rough at the other. I'm using the dual throttle cable from ACS . Any suggestions ?
thanks,
EG
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Vic Peters
Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine
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| Posted: Mon Dec 12, 2011 11:42 am Post subject: Carb synch issues |
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Clean and adjust idle mixture jets and screws first.
[quote] ---
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Vic
912ul Xtra
Maine
Too old to cut the mustard but not the cheese. |
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Tue Dec 13, 2011 5:20 am Post subject: Re: Carb synch issues |
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You should have no problems syncing at 3500 and then at idle. Some of you use a very thick throttle cable (i'e. vernier type) and or have to tight a bend in the cables. Many times it isn't the carb that won't sync, but the throttle cable that causes you grief. This will usually let you set the high sync, but will make the idle sync tougher to zero. The issue is that each time you pull the throttle cable back and forth it never exactly goes back to the same idle point on each carb which makes you think they aren't synced. I just did an RV12 and that's what's wrong with that throttle cable system. The cables are thick and there are bends which makes the cable bind just enough to drive you crazy on a sync at idle. You may need to physically push the throttle arms back into an idle position by hand to get them all the way down instead of allowing the throttle in the cockpit do it.
If you have thin enough cables and no tight bends and the cables move freely then syncing the idle shouldn't be an issue. Start with the mechanical sync to get you close. Some carbs are a little more finicky too. Instead of moving one side idle stop screw you may need to screw one out a little and one in a little. You may not be able to just move one screw.
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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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mortweaver(at)sbcglobal.n
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| Posted: Tue Dec 13, 2011 5:30 am Post subject: Carb synch issues |
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The carb sync procedure from Rotax does not address those installations, like yours and mine, where it is not possible to achieve even throttle cable pull throughout the full range of travel. Tether your airplane (I use heavy rope attached to lower landing gear legs with wheel chalks) and sync your carbs in upper RPM range only. Forget the low RPM range since the goal is to achieve smooth engine operation in RPM range where the engine is under load. I frankly do not care what my Carb Tune tool is indicating at engine idle (which is smooth with little prop loading). I go for close to 5,000 RPM to do my carb balancing and like very much the results I get both at cruise in flight and at engine idle. If it were up to me, I would change the published carb tune procedure as I have a header tank in my XP and can not route the unequal length throttle cables to achieve even carb throttle arm pull through out the range of travel.
Dave Weaver N912GR
--- On Mon, 12/12/11, egp8111 <egp8111(at)aol.com> wrote:
| Quote: |
From: egp8111 <egp8111(at)aol.com>
Subject: Carb synch issues
To: rotaxengines-list(at)matronics.com
Date: Monday, December 12, 2011, 12:34 PM
--> RotaxEngines-List message posted by: "egp8111" <egp8111(at)aol.com (egp8111(at)aol.com)>
I can't get the carbs on my 912ul to synch at both idle and about 4000rpm. If I adjust it for one setting it runs rough at the other. I'm using the dual throttle cable from ACS . Any suggestions ?
thanks,
EG
Read this topic online here:
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