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                           RotaxEngines-List Digest Archive
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                     Total Messages Posted Tue 03/21/06: 1
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Today's Message Index:
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     1. 10:27 PM - Late Model Rotax 914UL3 Mag Drop  (Horizonspace@aol.com)
 
 
 
________________________________  Message 1  _____________________________________


Time: 10:27:49 PM PST US
From: Horizonspace@aol.com
Subject: RotaxEngines-List: Late Model Rotax 914UL3 Mag Drop

We spent the last month diagnosing a mag drop problem while  commissioning 
our new 914.  If you have a "new" 914, you may be  interested in our findings.

Configuration:  Rotax 914UL3 S/N 4418895 (one year old); pusher;  
Airmaster/Warp Drive 63" CS prop.

Symptoms:  Deep RPM drops (400 - 450 RPM) on both A and B ignition  tests; 
mild detonation in the mid-RPM range (2000 to 4500).  Sluggish  during drops. 

All temperatures and pressures are within specs.

We consulted with several well known Rotax Authorized Service Centers in  the 
US and one in Canada and were advised to try the following:
    - Check plug caps resistance and trim ignition  wire ends before 
reassembly (use dielectric grease to prevent future  corrosion).
    - Check primary and secondary coil resistance
    - Swap A and B ignition modules
    - Synchronize Carbs
    - Synchronize Carbs
    - Synchronize Carbs
    - Check propeller for excessive pitch setting
    - Verify return fuel line is not obstructed
    - Replace spark plugs
    - Clean carburetors
    - Verify float levels
    - Perform float needle valve seal check
    - Check carb vent system
    - Move carb 1/3 throttle needle position from 2 to  1
    - Change main jets from 156/158 to 160/164

We performed all except the last step without arriving at a solution.   As 
best as we can tell, the proper settings for our carburetors are specified in 

Rotax SI-914-015 (pg 3, pp 3.3.2 and 3.3.3).  The document specified  156/158 
main jets and position 2 for both carb needle positions for 914 with  newer air

box (with optimized enrichment system).

We finally consulted with Mike at Rotec Research in B.C. Canada and arrived  
at the solution in a short 2 minute phone call.  Mike told us that the  proper

main jet specifications should be etched on our air box below the model  and 
serial numbers.  We verified that we have the correct jets (156/158)  not 
160/164 normally prescribed for earlier 914s.  He then suggested that  we move
the 
needle settings to position 3 on both carbs to achieve a slightly  richer 
mixture in the mid-range.  We performed the mods, resynchronized the  carbs and

now have a very smooth running 914 with mag drops both below 200  RPM.  We 
suspect variations in manufacturing and environmental factors  contributed to our

problem (near sea level; around 60 deg F ambient  conditions).  We credit the 
Rotax documentation system for the confusion  factor.

Hope this long winded missive help future 914 owners experience a smoother  
engine commissioning period.

Regards,

Tam Pho