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-   -   Unhappy Result on First Engine Start (https://vansairforce.net/community/showthread.php?t=114464)

Tom Martin 06-24-2014 08:07 AM

I totally agree with Steven, your cold start sequence is way too complicated. I have over a 1000 hours with the AFP system with NO purge valve and I have never had a hot or cold start issue.

jpharrell 06-24-2014 08:29 AM

A little more information
 
I will add that I performed the "pull thru" test recommended by E-Mag Ignitions before the first start where you rotate the prop with sparks plugs out of the cylinders but grounded to the case to verify that the 1 and 2 cylinders fire at TDC and the 3 and 4 fire 180 degrees later. But I admit that I was looking mainly for gross timing issues like miss wired spark plug leads or spark well off the timing mark. I am sure the sparks were in sequence and approximately at the TDC mark but it is possible the plugs could have fired a little either side of the mark by a degree or two. If the P-Mags begin to advance at a low as 200 rpm as stated, is it possible that the timing could have advanced before TDC while cranking causing the kickback? I'd like to hear more from those with lightweight props and P-Mags.

judoka5051 06-24-2014 08:59 AM

What they said, And...
 
For what it's worth I used the "B" curve and retarded the engine to split the difference between the A and B curve. So the engine is a little more retarded than the A curve during start and slightly more aggressive during full power. I can tell you that since I did this my engine is very easy to start.

Lance

N941WR 06-24-2014 09:16 AM

Quote:

Originally Posted by judoka5051 (Post 891347)
For what it's worth I used the "B" curve and retarded the engine to split the difference between the A and B curve. So the engine is a little more retarded than the A curve during start and slightly more aggressive during full power. I can tell you that since I did this my engine is very easy to start.

Lance

The "A" or "B" curve has nothing to do with starting. As stated above, below 200 RPM the P-mags fire at TDC.

N941WR 06-24-2014 09:18 AM

Quote:

Originally Posted by Kyle Boatright (Post 891290)
With a lightweight prop, I engage the starter for a couple of prop revolutions and turn on the ignition system while the engine is already spinning.

You can modify the RMSD (Run Mode Start Delay) with the Emag EICAD program (or our EICommander) so that the ignitions do not fire until "X" number of revolutions.

Bavafa 06-24-2014 09:38 AM

I agree with Tom Martin and I would cut the boost pump time to about 3-4 seconds instead of 30 or more seconds.

Toobuilder 06-24-2014 10:04 AM

Concerning boost pump use - I've found that some move more fuel than others, but 45 seconds is a LOT. My injected Hiperbipe needed a good 10 seconds, while the RV will flood after about 2 seconds. The Rocket is somewhere in between.

EDIT - Completely missed the purge valve part - never used one.

judoka5051 06-24-2014 12:20 PM

Yes it does.
 
Quote:

Originally Posted by N941WR (Post 891352)
The "A" or "B" curve has nothing to do with starting. As stated above, below 200 RPM the P-mags fire at TDC.

I retarded the flywheel a few degrees when I initially timed it, so the wider curve does exactly what I said.

Lance

vic syracuse 06-24-2014 02:52 PM

Hydraulic lock
 
Everyone is right here on having you look at the timing, but with 45 seconds of priming there is also a possiblity of a hydraulic lock happening in one of the cylinders.

Vic

cguarino 06-24-2014 03:22 PM

I've seen it
 
I've had my engine kickback during start with 2 P-Mags but never had any damage like that. As a precaution, I set my base timing about one tooth retarded. That way on start it will fire after TDC but once running you can make up the advance with the timing curve. There is also a start delay as mentioned that will allow a programmed number of revolutions before firing the plugs. I wonder if there is something else going on here.


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