Olde-Worlde Ignition Help

sounds like the lead from coil to points is shorting to earth either between the coil and the points or at the points, which would give the same effect as closed points (and make a test light across the coil light up, yet give nothing when you try at the points lead to earth). Run a completely separate lead from coil to points to test the theory.

A good picture of the points set up would help.

Reply to
MrCheerful
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This is the Trabi, so it's 2 stroke, 2 contact breakers and 2 coils!

Not a lot to go wrong, but somehow I've broken stuff.

I got the car fired up yesterday, but only on one cylinder. So I pulled everything apart again to look for issues.

Got myself a set of feeler gauges today, set the points gap, but still not getting it to start up.

If I put a test light across +ve and -ve of the coils (terminals 1 and

15), it lights... which I'm pretty sure it shouldn't do!

I've connected a test lamp from the points (terminal attached to the condenser) to ground and turned over the engine - I'm not getting the lamp to light anymore.

Seems like I've broken something way beyond my knowledge!

Any ideas? - really hope it's something quick and easy to fix before next weekend, as it's the Eastern European Vehicles Rally!

Reply to
SteveH

It will do if the point are made. If you can turn the engine by hand, does the light go out?

When the points are closed, flux builds up in the coil primary. When they open, the flux collapses and induces the spark via the secondary winding.

Since both circuits are the same, fault finding should be easy. As it's unlikely both are faulty.

Reply to
Dave Plowman (News)

Drop the coil off and meter out the primary and secondary windings , compare with the good one, also meter across windings, quite possible the internal insulation has broken down , you should not get a reading across the windings

Meter out the condenser too if you can, quite possible this may have failed .

If your meter cant meter out the condenser bypass it ad check for continuity.

Don't meter anything out with the engine running or switched on, you could destroy your meter.

You have the advantage with two coils , two contacts you have one known good system to take readings off .

Reply to
steve robinson

If you have vacuum advance there is a lead that connects the movable base (that the points live on) to the body of the unit, they can break, but would not give your reported symptoms. and from looking at the picture, that does not have vacuum advance.

Be logical, take a jumper lead to connect battery power to the plus or minus side of the coil (no idea if they are positive or neg earth. ) Then check that earthing the other side of the coil and releasing it gives a spark (plug lead is in with earthed spark plug up the end), if it doesn't find out why, then check that the lead down to the points plate gives the same effect, if it does, then close the points by adjusting them shut and make sure that you get a spark when you separate them, if so then set the points gap and you should have running ability on that set, repeat for the second set. There is so little involved that a meter should not be needed.

Reply to
MrCheerful

It's a brand new lead - and is a stand alone lead, too - so can't sort anywhere!

Here's the points in question:

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I've also run a lead and a test lamp from the condensers to the battery

+ve and turned the engine over (by hand, plugs out) - I don't get a light, which suggests there's a fault on that points base plate - maybe both condensers have died? (it's a new old stock DDR board, so 30 years old!)
Reply to
SteveH

No.

Neither circuit is working! - it's so simple, but such a bloody pain to fix!

Reply to
SteveH

Well, neither set of points or coils are working and I can't find my meter...

Reply to
SteveH

have you tried adding an earth lead from base plate to battery to eliminate lack of earth at the base plate?

Reply to
MrCheerful

No, I realise that (not much vacuum available), it was just a vaguely remembered bizarre problem on a Viva once and who knows what bits are used on something like a Trabant ! They seem to have the same setup as a Jawa motorcycle.

However setting the gap with the points in the closed position is bound to cause problems and can (should) be easily observed and kept quiet about. Full marks for admitting it though :)

Reply to
MrCheerful

What you should find out is the correct dwell angle and set the points to that, no, forget that, just check the timing is right, preferably by strobe and leave it alone. Incorrect timing will probably melt a piston before you realise it is wrong.

Reply to
MrCheerful

There's a mechanical advance under that gubbins.

But I think we've found my issue. I've been setting my points to their 'open' gap when they should be closed! So they never actually close.

Doh!

Reply to
SteveH
[...]

It's a two-stroke, and I've never seen vacuum advance on one.

Chris

Reply to
Chris Whelan

Thanks for that trip down memory lane (Morris Minor van I had in

1970-71) - though sadly the t-shirt no longer fits ;(
Reply to
Robin

Pretty much, yes - the actual breaker bits are used on MZs, Barkas vans, Wartburgs, etc.

I've *never* had to do this before. I may have had bikes with points in the dim and distant past - but never had a car with them before. Even my Fiat 124 Spider didn't have them!

It's a learning process. They're crazy little things, incredibly simple

*if* you understand how they work. I think I do now!

Next challenge - drum brakes. Not played with them for the best part of

20 years - last time they were mechanical, too. (Rear brakes on a bike)
Reply to
SteveH

Straight edge, long piece of dowel or cane.

Find TDC using long stick in plug hole, mark stick. Measure 4mm up from that... insert back into plug hole, rotate engine backwards to mark on stick and set timing at this point.

Repeat on cylinder 2.

You can do a crud setting using marks on the flywheel, though.

Reply to
SteveH

Most small 2 strokes run fixed timing. They don't have vacuum or mechanical advance.

Mechanical advance is mainly used to set timing retarded to prevent kick back. Not needed on small 2 stroke engines. Honda CB125S 4 stroke single with 9500rpm redline like most motor cycles only had mechanical advance, started advance at 1800rpm and was fully advanced by 3400rpm, it wasn't really usable below 4000rpm. A 500cc single cylinder 4 stoke Gold Star will break a leg if it kicks back. Modern electronic 2 strokes have variable timing, it advances from low speed to mid speed but retards at high speed. As this was not possible with simple mechanical centrifugal advance it wasn't used.

Vacuum advance is for load dependant timing. 2 stoke timing is not load dependant. A few British bike at the end of the magneto era had vacuum advance or possibly bikes that had frames with sidecar lugs. Many modern bikes with electronic ignition may have vacuum advance but this is done by a pressure sensor in the electronics and not a mechanical vacuum actuator. Yamaha XS1100 and just to break the rule RD200 2 stroke have vacuum advance.

Reply to
Peter Hill
[...]

Understood.

I had the same problem of that little copper braid breaking on a car once. It was somewhat troublesome to diagnose.

Another time, I had a Mk 1 Fiesta. I had replaced the points at service, and a few weeks later it started misfiring, and became hard to start. I went over everything several times, and eventually found the fly-lead that was part of the points assembly had a crimped connector that was only making intermittent connection.

The points were non-OEM; it was around that time I decided that using genuine parts was often worthwhile...!

Yep, and if unfamiliar with last-century technology an understandable error.

The most complex ignition set up I ever worked on belonged to a 4WD Jeep- type vehicle that had been driven in from somewhere in the east of Europe. I have no idea what make it was. It had a four cylinder two-stroke engine, mounted fore and aft, and the points were operated by a cam on the front of the crankshaft, making them somewhat inaccessible. The were four sets of points, and four coils. As well as having the ability to set the points gap, each set of points were on their own backplate mounted with slots, so the timing for each cylinder had to be set separately. It took me all day to figure it out!

It was incredible to drive. It had no low down pull, so would have been crap off-road, but was as smooth as an electric vehicle.

Chris

Reply to
Chris Whelan

That doesn't compute with your:-

If I put a test light across +ve and -ve of the coils (terminals 1 and

15), it lights... which I'm pretty sure it shouldn't do!

If the points were always open, no current would flow.

Reply to
Dave Plowman (News)

Why repeat on cylinder 2?

Reply to
Norman Rowling

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