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MGB 70 MGB runs rough - sputters & backfires esp. cold

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All right, I have just spent some "quality" time with the B.

Before I started it would start, run roughly, spit & cough & backfire.

After a bit of work it wouldn't start at all.

After a bit more work I got it back to how it was when I started. :frown:

Here is what I know:

The points were set a bit tight, I adjusted them to .014
When it "idles" it backfires and spits a bit of fuel spray out the carbs.
When I can get it to run up at 4000 - 4500 rpm it runs a little rough but not as bad as at 'idle'.

When I turn the key on and manually open the points I can't see a spark.
If I open up the points by turning the engine a bit then cross between both sides of the points with a screwdriver I do get a spark.

Meter from plate to ground = 0 ohms

Meter from points to coil = 7 ohms (what should it read?) That's to the wire that connects to the side of the distributor via the spade lug.

Meter from one side of points to other when closed = 0 ohms
 
I put in a different coil - it ran the same (if not worse).
I could almost get it to run. :pukeface:

I put the old coil back in and it started but it ran but very badly. I couldn't get it to rev up like before, however it wasn't backfiring this time.

I thought I had a winner when I started the coil swap and found the lead to the positive side slipped out of its connector.
I put on a new connector but that clearly didn't fix anything.

I suppose I will order a new cap, rotor & condenser just for grins.
 
RickB said:
Meter from plate to ground = 0 ohms

Meter from points to coil = 7 ohms (what should it read?) That's to the wire that connects to the side of the distributor via the spade lug.

Meter from one side of points to other when closed = 0 ohms
Click to expand...

7 Ohms???? 7 Ohms seems very, very, high. There should be almost no resistance along that path.

For grins, disconnect the power input wires on the other side of the coil, make sure the points are closed, and repeat your test measuring from the low side of the coil to ground. Disconnecting the wires on coil (+) will eliminate any influence from upstream components and will give you a resistance reading just through the white/black wire, points, and breaker plate earth lead. It should measure close to zero Ohms.
 
I've ordered a new cap, rotor & condenser so they will be here tomorrow and that's the earliest I will get back out to that car. I'll do as you say when that happens.

Btw for those of you who are following along at home...
I found the top of the coil was not loose as I first thought - it was simply loose in the bracket so it turned a bit.

It's getting dark here now, and I've gotta get something to eat & maybe a couple beers. :wink: Full Sail makes a fantastic "Wassail" winter beer, and it's on sale!
 
It Lives!!!

New cap = no difference
New rotor = no difference
New condenser = no difference
Jumpering tach out = no difference
Jumpering ign switch out = no difference

After all that I was beginning to see the end of the rope so I metered things that really "looked" like they were right to see if the meter agreed.

With the points closed I was getting odd readings, like they really were not closed.

I opened and closed them several times and got differing readings.

Next I pulled the points out and hit the contacts with a file, the meter then showed closed when they touches and open when not.

After reinstalling the points and making sure everything else was right I tried it and - IT RAN!!!

I guess sometimes it's just that one "obvious" thing that puts you over a barrel.

Thanks again for all the help here.
 
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