Mysterious misfire

[Mon Ami Mate]

Wondering if anybody might have any bright ideas on a mysterious misfire problem I'm having with my old Series III.

She runs absolutely normally at tickover and at low revs. Smooth, no problem at all.

Under load though she's misfiring horribly. Not a typical running on 3 type of misfire, but a complete cutting of power. Lift your foot off the throttle and everything catches up, until you put your foot back down again. I guess it has to be either fuelling or electrics. I've taken the (Weber) carb off and had it cleaned out. That hasn't helped. I've replaced the plugs, leads, points and condensor and that hasn't helped either. I'm now out of my comfort zone. I guess it could be the ignition coil or a fuel pump (although she has two tanks and switching between the two makes no difference).

Any ideas?

[100SRV]

Have you checked the fuel sediment bowl for a build-up of dirt?
How often do you use it?
Does it have lumenition or points and condenser type ignition?

[P4T]

Hello

The closest thing to this I have encountered on my 200tdi defender was when I was drawing air into the fuel system due to a incorrect sized jubilee clip on the fuel tank.. Once the source of the air in the system had been sorted it was simply a case of undoing the bleed screw on the fuel filter until just fuel (no air bubbles) flowed out.

Given what you have replaced I would guess your problem lies somewhere in the fuel system.

[camel_landy]

...could also be the vacuum advance on the dizzy.

Do you have a strobe lamp for checking the ign timing?

M

[Mon Ami Mate]

Yes, checked the timing when I changed the points and condensor. THe fact that it only does it under load makes me think it's likely to be fuelling. Wondering if it might be a fuel pump...

[camel_landy]

I wouldn't be overly concerned about the fuel pump as it sounds as though it is working by virtue of the fact that the car is actually starting in the first place. I'd check the condition of the pipe work and the unions first.

Also, do your carbs have rubber diaphragms inside? It might be worth checking the condition of those too.

M

[Mon Ami Mate]

The carb is not very old. I stripped it and cleaned it and it was perfect inside, it definitely isn't that causing the problem.

[mwy1964]

Did any of the parts come in a blue box, in particular electrics!!!!

How does the engine sound when you rev it at stand still?

Did you time with a light or by ear?

When misfiring do you hear a pinking sound ?

You said you had the Weber stripped and cleaned out, new jets and gaskets?

Its a simple engine and works well even when well worn, but there comes a point...

Regards

Mark

[Mon Ami Mate]

Just for interest, it turned out to be the ignition coil.

[camel_landy]

Mon Ami Mate said:

Just for interest, it turned out to be the ignition coil.

Makes sense.

Thanks for the update...

M