Voltage drop at coil

[rhyatt]

Simple test

Clip a wire to the engine head nut or rocker box.
Then then other end of this wire hold onto or clip into the distributor body with a Croc clip

Does this fix/reduce your volts loss ?

[Barnsey]

Yes,  no surprises.  I added a wire from a rocker cover nut, to the spring clip which holds the distributor cover on.  3.5V at the coil became 4V, and 2A became 2.25A.  SO, not quite a smoking gun, but definitely a useful improvement. 

  At the weekend, I'll take the Distributor off and give it a clean,  maybe I'll add some copper grease when I re-seat it.

 To remove the distributor, is it a simple case of undoing the adjuster screw and pulling it out?   

[JulianS]

Put a mark across the distributor/crankcase joint so you put it back in the same position.

[rhyatt]

Just install a dedicated earth wire direct from the battery positive terminal direct to the rocker cover nut.
No need to remove the distributor.
It is held in with its clamp(albeit hidden in the timing cover) and this clamp screw is screwed into the engine so the earth path is there.

So did it start with your earth lead installed ?

[Derek996]

1/  Clean and reseat the dizzy, and go around the wiring remaking all connections.  This might become a full loom replacement, and switch replacement, as on my other bike.

Separate every bullet connection between the battery and the coils and clean the surfaces and refit one at a time. Also check the resistance across the ignition switch when it is switched on. I used to have a Ducati 907ie and every time I used the indicators the rest of the lights would go bright/dim/bright/dim in time with the indicators. It was dropping 1V across the switch but this dropped further with the extra 3.5A load of the indicators affecting the lights.
The voltage drop across the ignition switch was also affecting the ignition and injection circuits. I fixed it properly by replacing the switch with a 30A relay and modifying the wiring so that all the ignition switch did was turn the relay on and off. A bit more drastic than what you need I think.

[shoal48]

I took some measurements after work tonight.  I have the full 6.5V on the engine block, but I am losing 1.5V between the engine and the coil positive.  Most of this appears to be between the engine and the distributor. 
If I measure between the engine and the coil positive I am seeing the 5V which I want.  I guess that this also implies that I am losing 1.5V on the negative side. 

It seems to me that there are three possible solutions. 

1/  Clean and reseat the dizzy, and go around the wiring remaking all connections.  This might become a full loom replacement, and switch replacement, as on my other bike. 

2/  DO a 12V conversion, as a 12 V coil has a higher internal resistance, and all these other traces of resistance will have less effect. 

3/  Go the whole hog, and do a full electronic conversion with 12V to boot.  This should knock it into a cocked hat as there will be no current through the dizzy, all current going via the magic black box. 

  Since advice is in that direction, I will persist with 1 for the moment, but I am strongly tempted to skip 2 and go straight to 3. 

if you are going to check connections in the circuit The batt pos terminal is first, then both ammeter terminals, cable then goes to terminal 12A on the ignition switch, probably brown-white and comes out of terminal 13 probably white,to the pos side of coil. If you monitor at these points with ign on and contacts closed you willbe able see if the voltage drops along the route to the coil and hopefully pin it down to a dirty connector or high resistance in the ignition sw

[Barnsey]

Not tried starting it yet. Time was short.  Resistance from the battery to the engine was negligible, the resistance being between the engine and the distributor, so I think a ground from battery positive to engine might not help in this case, but no harm in trying.  I'll go around and check the connections before I put the tank back on and try firing it up.  It's a pity that there is nothing on the distributor that I can permanently connect a ground wire to. 

[V500]

It's worth bearing in mind that C15's have been running happily for close on 70 years without the "dizzy" needing a dedicated earth.
That said, it's always worth having an earth wire running to somewhere on the engine, moreso if the frame has been powder-coated or painted recently.

[shoal48]

Not tried starting it yet. Time was short.  Resistance from the battery to the engine was negligible, the resistance being between the engine and the distributor, so I think a ground from battery positive to engine might not help in this case, but no harm in trying.  I'll go around and check the connections before I put the tank back on and try firing it up.  It's a pity that there is nothing on the distributor that I can permanently connect a ground wire to. 

Hope you dont mind suggestions, just trying to get a good picture of your problem, looking at your last post but one, you get 6.5v presumably between the batt Neg and the engine casing which is expected and you get 5v between the coil POS and the engine casing. If the points are closed at this point you should be seeing very little voltage at the coil +ve as should be grounded through the points/distributor/engine/frame. Have I understood you correctly in that the distributor is not pulling the coil voltage down to near ground in which case there is resistance between the coil +ve and the engine casing? If thats the case, my first thought would be loose or rusted connection where the points spring terminal is fixed to the distributor connection screw or a corroded terminal on the wire where it connects to the distributor.

With the meter on volts, connected between coil +ve and the engine casing, with points closed (showing the 5v), try putting a piece of wire between the distributor terminal and the engine case, if voltage drops the problem is in the distributor as you suspect. then put the wire between the distributor body and the engine, if volt drops then that proves your diagnosis that the distributor is not making good contact with the engine. If the problem is between distrib body and engine you could do a short term fix and attach a lead to the cap fixing screw and run it back to the earth point under the seat.

If I have misunderstood and you see 5v on the coil +ve with the points open that suggests a different problem because with points open there should be no current draw on the coil so you would see the full 6.5 volts on on both terminals. if this is the case it suggests earth leakage through the dizzy. If you take the connection wire off the dizzy and voltage goes up to 6.5 then maybe failing capacitor leaking to earth or conductive gunk bridging the points.

[Barnsey]

Thanks Shoal,   Yes that ties up with what I have been doing, and I definitely have a drop across the distributor.  Unfortunately this one has the cap held on with a clip. not a screw, so nothing to attach a wire to. 

  I tried slacking off the adjuster screw and rotating the distributor, to see if it would improve the connection, but no dice.  It might be a case of having to remove it.   

  I will be off work tomorrow, so expect an update soon.   

[Barnsey]

An update.  I ran a grounding wire from the supply terminal on the frame, to the distributor and clamped it on with a jubilee clip. 

Actually I was quite proud of this, it was a smart bodge as bodges go.  I cleaned the body of the distributor first with emery, and soldered a piece of copper, from a central heating pipe onto the ground wire, which is clamped between the jubille clip and the body of the distributor. 

 Anyhow,  I have got the current from 2A up to 2.5A.  In theory,  6V into the 2 Ohm coil would be 3A, so I suspect that 2.5A might be as good as I can hope for. 

  I am busy with family stuff today,  so I'll put the bike aback together tomorrow, inc refitting the tank,  and give it a kick over. 

[Barnsey]

An update for this week. 

Fitting a ground wire directly onto the distributor unit, made all the difference.

The bike started second kick.   Now that I have adjusted the carburettor it is starting FIRST kick!

  I have also fitted the new 6V regulator. 

   Thanks to everyone for your help and support! 

[iansoady]

Good result.

I always fit a dedicated earth wire to the crankcase (although have never found it necessary to do so with the distributor itself). Expecting electrons to flow through painted / corroded surfaces and bolts is a bit optimistic in my view. I also run earth wires to rear light assembly and headlight for the same reason.

[V500]

Given that the dizzy is metallic and has a large clean surface area, and the engine unit the same, the resistance should be so low as to be irrelevant.
if you have a measurable drop in resistance with this dedicated earth wire it points to a poor engine/frame electrical path rather than a poor dizzy-engine unit.
Simultaneous posting.

[rhyatt]

you are looking for 7.2 ish volts across the battery when running , to prove the RR is working fine.
but you must do this with a charged battery