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  #11  
Old 02-20-2021, 09:10 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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If the mag was 20 ATDC, it is possible that the previous owner sgnificantly increased the advance on the light speed to make up for the essentially missing spark (20* retarded = might as well not be there). If that were the case, setting the mag back to 20 BTDC, would create a VERY advanced timing.

Total timing on a dual plug system is a composite of both of the advance settings.

Larry
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  #12  
Old 02-20-2021, 06:35 PM
Robb Robb is offline
 
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Location: Nevada City Ca
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I am going to get in contact with Lycoming and Slick and see if they have any input. I agree I may not need an impulsed coupling mag on this engine. Not sure why they originally installed it but will find out. I did send the mag out to be rebuilt.
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  #13  
Old 02-21-2021, 08:10 AM
Robb Robb is offline
 
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My engine data plate shows 20 degrees listed on it
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  #14  
Old 02-21-2021, 10:20 AM
abuura abuura is offline
 
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Since you mentioned having a Lightspeed system, and regarding impulse coupling, according to Klaus (Lightspeed founder) “Timing curve extends from 15 to 42 degrees BTDC. Full retard for starting holds the timing back to TDC. After starting, the system advances according to RPM and manifold pressure”.
Klaus also advised me to set the mag (Slick 4371) to 22 degrees BTDC. Joe Logie (Champion/Slick tech) says "25 degree advance is normal, change to 20 would have little/no effect".
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Last edited by abuura : 02-21-2021 at 10:22 AM.
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  #15  
Old 03-02-2021, 07:24 PM
Robb Robb is offline
 
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I will post on what we finally figure out whats wrong and I get the mag back from the 500 hr service. Still dont have a definitive answer. Hopefully it will help the next guy that has an issue.
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  #16  
Old 03-03-2021, 05:54 AM
vic syracuse vic syracuse is offline
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The D4A5's were originally sent with impulse mags. There has been some concern that there are possibly harmonics on that engine that could cause the impulse mag to disintegrate and cause serious damage to the engine, up to and including catastrophic failure. That's why the change to non-impulse mags coupled with a slick start (or electronic ignition).

We see a large number of these engines come through the shop on RV-10's during the year, and some of the engine builders set the timing at 20 and some set it at 25. Haven't figured out a rhyme or reason for that, except that obviously they run cooler when set at 20.

I did some testing a few years back and determined that 23.5 degrees timing on this engine seemed to be the best, and Klaus had the same opinion.

Just sharing....

Vic
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  #17  
Old 03-14-2021, 03:34 PM
Robb Robb is offline
 
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Well I received the rebuilt mag and installed it today. Set the timing to 20 degrees after using a dunce cap to make sure the starter ring was correct and it was. Long story short it fired up great with 100 RPM drop on the new Slick 6351 magneto. It is still a mystery to me why it was firing off at 20 degrees ATDC with no issues in flight or run up. It is way smoother now and maybe it was the impulse coupling? Who knows
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  #18  
Old 03-14-2021, 05:58 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Robb View Post
Well I received the rebuilt mag and installed it today. Set the timing to 20 degrees after using a dunce cap to make sure the starter ring was correct and it was. Long story short it fired up great with 100 RPM drop on the new Slick 6351 magneto. It is still a mystery to me why it was firing off at 20 degrees ATDC with no issues in flight or run up. It is way smoother now and maybe it was the impulse coupling? Who knows
Timing should be set to 20 deg BEFORE top dead center, not after. E.g., turning the prop in its normal direction, the mag should fire before TDC.
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  #19  
Old 03-15-2021, 06:15 PM
Robb Robb is offline
 
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Installed the new mag after having it rebuilt. Set the timing to 20 BTDC as listed and it works perfectly. Not sure how it even ran where it was. I guess Ill never know but its fixed now. Must have been something really messed up with the old mag. All new lower fine wire plugs also
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