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Booster coil buzzing ..no start

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dsavarese(at)elmore.rr.co
Guest

Posted: Sun Feb 25, 2007 7:34 am Post subject: Booster coil buzzing ..no start

When you press the start button, do you hear a buzzing from the starting 

coil?  Also check the wire from the starting coil to the left mag. 

Particularly where it enters the left mag and makes the sharp 90 degree turn 

toward the magneto cap.  Remove the wire from the mag cap and place the end 

close to metal and press the button.  You should have a continuous spark 

jump to ground when you press the start button.  I have found many starting 

coil wires so badly deteriorated that they short to ground when the start 

button is pressed.  You also could have a bad starting coil of course. 

Assuming you have a Yak 52, and although there is a relay in the relay box 

at bulkhead #6 on the right side that could cause the problem, it is 

unlikely the culprit if when you press the start button, the air start valve 

opens and the rotation starts.  That's because both the starting coil and 

the air start valve circuits are through the contacts of the same relay.

Dennis



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dsavarese(at)elmore.rr.co
Guest

Posted: Sun Feb 25, 2007 8:23 am Post subject: Booster coil buzzing ..no start

The points in the mag are what continues the spark to the plugs after you 

turn on the magneto switch.   Not during the initial starting procedure. 

I'd bet it's a bad wire from the starting coil to the left mag.  On the 50, 

it's a much easier job to replace it than on a 52.  The wire is 5 mm, 

braided core wire.  Sometimes tough to find except at possibly your local 

small engine shop that repairs lawn mowers, lawn tractors etc.  If you can 

find it locally, here's a link to where you can find it on the internet. 

http://www.mfgsupply.com/m/c/24-8776.html  You can also use 7 mm braided 

core wire.  But the rubber sleeve on the ends of the 5 mm wire is 

eliminated.  Here's the 7 mm wire. 

http://www.mfgsupply.com/m/c/24-8775.html

Dennis



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jorgen.nielsen(at)mweb.co
Guest

Posted: Sun Feb 25, 2007 12:19 pm Post subject: Booster coil buzzing ..no start

If the same magneto as the 52, the booster coil HT goes into the mag and

connects to the stator (correct term?  Anyway the bakelite/plastic thingie

that turns inside the mag).



This connection in turn is connected to the TRAILING metal pin, and hence

fires with retarded timing, preventing the motor starting up in reverse

which is what often happens if starting on mags.  The normal mags on

connection is via the leading pin, providing advanced timing.



As per Dennis, 9 times out of 10 it will be the wire that is shorting to

ground OR burnt inside.  If after changing out this wire, if it still

doesn't work then check for a crack in the stator - I have had this one.

Rather F^%$#ing frustrating until I realised what the problem was.  Almost

impossible to see.



So before swapping the wire and reassembling the whole thing only to find it

still doesn't work, I would first remove all the air from the system, (close

air valve master and use brakes until no more air is present), then check by

kistening to make sure the coil is working.  Assuming it is, then pull the

mag cover and remove the wire, and check it.



To check the wire, close to the frame / engine mount while someone pushes

the start button, AFTER removing all the air from the system to make sure

the prop doesn't turn.  Should get a nice strong spark.  I cable-tied the

wire to a plastic rod to hold it.  Did not fancy a shock.



If no strong spark replace the wire.  If the spark is present at the wire

your fault is downstream, and the only item left is the stator.



 

 



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