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  #1  
Old 01-11-2017, 09:16 PM
yankee-flyer yankee-flyer is offline
 
Join Date: Jun 2009
Location: Dayton, OH
Posts: 828
Default Rotax engine problem

here's one for the knowledgeable Rotax guys. At the 400-hour inspection, both carbs were removed, cleaned,and new gaskets fitted by an A&E who's had thew long Rotax training course. He also set the floats using a new tool from Rotax. Ever since, when I do the normal cold start sequence (worked fine before) the engine will start on full choke, but after a few seconds it stumbles badly, like sparl plus misfiring and RPM drops. Going to half choke immediately helps for a half-minute, then the RPMs drop WAY into the yellow arc. I've got to go to no choke at all by about 30 seconds in order to keep in running, even with OAT at 30 deg and no temperature movement on any of the displays.

I don't see how it's possible to "over choke" the engine-- I'm thinking mixture is too rich.

Any thoughts at all? Thanks.

Wayne 120241/143WM, 420 hours.
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  #2  
Old 01-12-2017, 01:59 AM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Default

You might consider asking this question in the Rotax Forum http://www.rotax-owner.com/en/rotax-...ical-questions
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
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RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 302
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  #3  
Old 01-12-2017, 03:16 AM
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Gagarin737 Gagarin737 is online now
 
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Default

I have never used the shoke for more than approximately 10 sec.
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  #4  
Old 01-12-2017, 03:44 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Default

In cold weather I bleed the choke (enrichment) off in steps as the engine warms. If choke is removed too quickly during cold engine start the engine will run rough.
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 302
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  #5  
Old 01-12-2017, 05:53 AM
h&jeuropa h&jeuropa is offline
 
Join Date: Jun 2008
Location: Kalamazoo, MI
Posts: 181
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Wayne,

It is very easy to assemble the choke assembly backwards. You might want to have the A & E take them apart again and be sure they are correct. Have a look at chapter 3.3.11 of the heavy maintenance manual for guidance.

Jim Butcher
Europa XS, Rotax 914 - 800 hrs
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  #6  
Old 01-12-2017, 06:45 AM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,534
Default Another question - -

Were the carbs re-sync'd after reinstalled ? When cold do the EGT's match fairly closely ? When warm, do they match fairly closely ? Gives you a very good idea of how well they are sync'd.
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  #7  
Old 01-12-2017, 07:58 AM
yankee-flyer yankee-flyer is offline
 
Join Date: Jun 2009
Location: Dayton, OH
Posts: 828
Default Yes

Carbs were re-synched, EGTs and CNTs match well, and engine operation is good once it's warmed up.

POH AND recent Rotax Service bulletin call for full choke at start, then ease off to 1/2" and maintain that until the engine is "warm". That has worked fine for6 years and 400 hours.

Wayne
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  #8  
Old 01-12-2017, 09:48 AM
JBPILOT JBPILOT is offline
 
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Location: Jesup, Iowa
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Default Wayne - -

Then I would check to see if the Enrichener 'disc' is in correct position. There is a center punch mark on the external portion of the shaft. It should be toward the cable hookup end of the arm. Easy to check.
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  #9  
Old 01-12-2017, 08:35 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
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I've always been reluctant to do much to the carburetor other than inspecting the bowls and replacing the diaphragms at 5 years. It seems that if they are working well it is best to leave them alone.. just my opinion.
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  #10  
Old 01-13-2017, 06:24 AM
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tomkk tomkk is offline
 
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Location: Port Orange, Fl
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Quote:
Originally Posted by RFSchaller View Post
I've always been reluctant to do much to the carburetor other than inspecting the bowls and replacing the diaphragms at 5 years. It seems that if they are working well it is best to leave them alone.. just my opinion.
I agree. I disassembled mine for the 200 hr inspection and they were like new. They were clean, gaskets and O-rings in great shape, etc. Not only did I pretty much waste my time, I took the risk of messing something up - I didn't
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