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Jul 16, 2019 1:41 pm
Registered since: Jan 17, 2008
Location: -


Subject: Problem with Coil ignition conversion
Due to magneto issues I have temporarily set up a coil conversion on the Saloon, using an old defunct Bosch magneto as a distributor. At first it worked well, but suddenly stopped. I've tried everything to get it functioning again. I've changed the coil and condenser and cleaned the points and reset them to about 15thou. In a static test the plugs spark nicely. I have tried flicking the points open with a wire attached between the rotor arm and the distributor block and each plug gives a nice blue spark. When I spin the engine on the starter I get a couple of sparks from nos 2 & 3, nothing from 1&4, and then nothing from any of them. Similarly a working magneto sparks on the bench,but not on the car. I've also swopped the plug leads, to no effect.
I've never experienced this problem with the Tourer - can anyone help with advice?
 

Jul 16, 2019 4:48 pm
Peter S30 Offline
Global Moderator
Registered since: Nov 27, 2007
Location: Germany


Subject: Re: Problem with Coil ignition conversion
Dear Roger, sounds to me like the distribution part is the problem (high voltage shortcuts in the old Bosch magneto-distributor somewhere) ?. I have one of Johns coil conversions to swap in case but so far normally running on a good magneto (which I prefer).
 

Jul 17, 2019 11:08 am
h14 Offline
Member
Registered since: Nov 30, 2008
Location: Chalandray, France


Subject: Re: Problem with Coil ignition conversion
Hi Roger,
Could be a problem on the low tension side. Poor connection, corrosion etc. Specifically in the ignition circuit, as if the engine is spinning over as fast as it normally does, one must presume that the heavy current starter circuit terminals are sound. If starter speed is slower, check those terminals as well. Try running an earth connection from the magneto to the engine block.
Good luck!
Laurence
 

Jul 19, 2019 10:06 am
bill Offline
Member
Registered since: Jun 08, 2011
Location: -


Subject: Re: Problem with Coil ignition conversion
I had a similar type of problem with a distributor and it was the rotor arm. Renew/replace this and see if this helps ?
Also be aware that even if you get a spark at the plugs when they are out of the engine this doesn't mean that they will spark when they are under compression !
 

Aug 01, 2019 9:13 am
Registered since: Jan 17, 2008
Location: -


Subject: Re: Problem with Coil ignition conversion
Dear all,

Many thanks for your comments. We think that the low tension ciruit is the issue. The magneto was a moving coil type, so the armature should be insulated from earth. It is probably leaking when under load.

Luckily we have got the two magnetos working, that came with the car, so one of these will go back while I dismantle the one used for the coil conversion.

Roger
 

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