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Re: 1948 Iron 4G Coil Ignition

Posted: Sun Sep 01, 2019 12:25 am
by brenton.roy
john.whiting wrote:I do not see how the original magneto capacitor could be in the circuit.
Good point. I don't quite understand whether the magneto is providing an initial spark which is amplified via the CDI or whether the magneto is disconnected completely and is just a housing for the CDI? My apologies for steering toward questions, not answers.

Re: 1948 Iron 4G Coil Ignition

Posted: Mon Sep 02, 2019 4:00 am
by chris.matthews
Hello Everyone,

I might have posted something like this earlier today - Digitally Challenged Again.
The Magneto serves as the place for the Contact Breaker. The windings, condenser, HT Pickup etc are not used.

Lacking a Greaser Dashpot 464261 I made a locator - a bit like the locator for the speedo cable at the gearbox.
I have checked it does not impeded the rotation of the Distributor Drive Shaft.
Feeling quite pleased with myself that the shaft was no longer free to wander up & down, I tried to start.
Petrol On and a couple of kicks to draw the fuel into the chamber.
Ignition On and commence serious kicks First Four Kicks produced some sign of life - it fired and ran for about 4 seconds each time, but would not pick up.
Dozens of subsequent kicks produced nothing at all - not a glimmer.
I have sparks at the plugs.

Plugs remain Bone Dry - with my other bikes they would definitely be very wet and need cleaning.
These dry plugs make Local Brains Trust convinced its a Carb Problem and not Ignition.

Baffled I tried a couple of starts using Local Easy Start - not a glimmer, either with squirts through the Solex or direct into the cylinder.

I checked ignition timing - I find it very difficult to get 8mm BTDC - it always moves when tightening the nut in the timing case - currently its about 6mm - frankly I thought that was 'near enough' - surely I should see some signs of life.
I have manual A/R and timing is set Full Advance.

Paul - can you please scan and send the Cheval Articles on Coil Conversion ?
I have never been inside the Converted Magneto - I think that's coming in the near future.

Bright ideas are most welcome
Best regards
Chris
Tokyo
1938 MSS Velocette (pig to start, but a great ride)
1939 VB (running-in after rebore).
1948 4G (Dead).
1952 BSA B31 (easy starter and easy ride - rigid & teles)

Eas

Re: 1948 Iron 4G Coil Ignition

Posted: Mon Sep 02, 2019 6:29 am
by john.whiting
What I can see in the pic of the points is a stock standard cam and points ,just like I would see if I took the cap off the dizzy in my forklift..........make and break...intermittant earthing of the coil primary as the points make (close).....this is how coil ignition s have worked ever since Charles Kettering of Delco Labs designed the first one for Cadillac in 1916.....There is no hint of CDI in the pic,and a normal electronic system would have a magnetic pickup in place of the rocker arm.......I suggest you toss the alleged CDI ,and run straight coil system.,diagrams of the setup shown in books about cars ever since 1916......stick with negative earth,as it give a slightly better spark.......and fit a capacitor somewhere across the points......even taped to the ignition coil is ok,provided the case is earthed.

Re: 1948 Iron 4G Coil Ignition

Posted: Mon Sep 02, 2019 6:58 am
by chris.matthews
Hello Folks
I have no idea where CDI or Electronic crept into this - my system is the traditional coil system with negative earth, condenser is mounted on the coil 0 which is earthed. I have sparks at the plugs - but I don't have a running engine...…...is it Ignition (Timing or Weak Spark) or Solex/

Best regards
Chris

Re: 1948 Iron 4G Coil Ignition

Posted: Mon Sep 02, 2019 9:12 am
by john.whiting
You have replaced coil and capacitor,checked all the circuits,so its down to timing now........either the firing order is wrong,or the timing is ...........possibly 180 deg out..... if 180 out,just swap leads on the diagonal.

Re: 1948 Iron 4G Coil Ignition

Posted: Thu Sep 05, 2019 8:17 am
by paul.jameson
One last item to check on the carb before you start on the ignition system. I had a long chat at the Annual Rally with Otto Mederle and Jens Buesse who have studied the Solex carbs in great detail. One point to check is that you have the small slot in the gasket which goes in the joint secured by the 4 screws. See attached photo. If the slot is not present in the gasket, the bi-starter will not work properly.

Bi-start gasket and slot.jpg
Bi-start gasket and slot.jpg (147.56 KiB) Viewed 4571 times

Re: 1948 Iron 4G Coil Ignition

Posted: Thu Sep 05, 2019 8:00 pm
by Pete.Silson
Chris,

Is the small screw that holds the rotor arm taper to the top of your distributor shaft tight? Silly question but it caught me out and, if the screw is loose, the rotor arm taper can slip to the point where the rotor arm points to the wrong cylinder. It is surprising how far off the rotor arm angle can be before it actually stops the engine but, if the angle is slightly wrong, starting can become very erratic.

Just a thought - Pete

Re: 1948 Iron 4G Coil Ignition

Posted: Fri Sep 06, 2019 5:28 am
by chris.matthews
A few quick items
Pete - Rotor arm screw - it undid OK, but difficult to break the taper, a bit of heat helped and now its separated which simplifies setting distributor timing.
Paul - Gasket mod, yes I did this .
Paul - By the way can you send me the Coil Conversion Article (or a reference to Cheval - I found Marcus conversion to Electronic, but I can't find coil conversion.
John - maybe its 180 out. I reset the distributor timing by 90, and it fired and ran.
The CB conversion done on my bike has a 2 lobe rotor and roughly speaking the points are closed 80% of the time - and this gets the coil very hot.
We really doubt the effectiveness of this arrangement, surely it should only be energized 20%.
We believe this arrangement is cooking the coil, making subsequent starts difficult. Hence the desire for the coil conversion article.
With best regards
Chris.

Re: 1948 Iron 4G Coil Ignition

Posted: Sun Sep 08, 2019 6:43 am
by john.whiting
The normal cam for two breaks per rev is a round with two flats opposite sides.........seems the maker just ground two lobes off a four, and as you say,its causing the coil to overheat.

Re: 1948 Iron 4G Coil Ignition

Posted: Fri Sep 13, 2019 10:53 am
by Paul_Linden
I’ve been following this thread with great interest, as it has reached into the furthest corners of “it won’t start” leaving no stone unturned, but success is elusive. Chris, please keep us updated, thanks, Paul