I have this ongoing issue and I am running out of solutions. It is an irritating intermittent misfire. So far I have done the following to address the issue:

- Replaced points with Lumenition Magnetronic system
- Replaced coil, twice - becasue I fried the first one by mistake
- New set of Huco ignition leads
- New distributor cap and rotor
- Adjusted valve clearances
- Cleaned the carb and put in a new needle and seat valve
- Removed, cleaned and tightened all earth points
- Removed, sandblasted and tightned holders and connectors on the fuse box

This weekend I checked the spark plugs, again. Two plugs were giving problems intermittently. So bought four new NGK BP6ES's and fitted them. The car ran smoothly for the first time in a long time. But then... after about 50 km's (about 30 miles) the problem was back.

Anyone know what else could possibly be causing this problem?

Hi, Darrell -

Looks like you've done just about everything I can think of.

The fact that new plugs started out OK may be a clue. Something may be fouling them. How about your fuel? Any condensation in the tank? Filter's clean?

The carb was cleaned and a new needle and seat valve fitted about 100 miles ago. There was no major sediment in the float chamber. I replaced the fuel filter at the same time. The spark plugs I removed were nice and clean with the correct deposits on them to indicate a healthy running engine.

What do the new plugs look like now? When comparing the old to the new from the same cylinder is the fouling consistent?

Is this the same problem you were dealing with a few months ago... now resurfaced?

If nothing else, why not try fitting the points again (at least for a while) as a test.

I'm not familiar with Huco wires apart from hearing the name around VWs. Are these solid core wires or resistor wires? How about the spark plug terminals/ends... are they standard or resistance type? I ask because you're running standard, non-resistance type plugs. Something in the system probably should have resistance (plug wires, plug terminals, or plugs).

Not familar with your particular car (though i did own a Mini years ago).

Do you have a stock fuel pump?
If not, what is your fuel pressure?

Appropriate fuel pressure for these cars is about 1.5 to 3 lbs.

Too much fuel pressure will force fuel passed float valves and cause rich mix, eventually fouling plugs.
Just a guess.

I had a similar problem once, intermittant misfire at high-ish RPMs. The solution was elusive, even with a professional mechanic on it.

Cracked distributor cap was the culprit. Crack was not visible until the cap was very closely examined.

You indicate that a new cap was fitted, so this probably isn't your problem. However, it may be prudent to double check that cap just for the heck of it.

Let us know . . .

Thanks for the input everyone.
To answers everyone's questions:

- ChrisS: There was no fouling on the plugs. The plugs were normal - but two were not firing constantly. Four new plugs sorted out that issue.
- Doug: Yes, same problem has come back. I put the points back when you suggested it previously and the problem is still there. In fact she is still running on the points as I have not had time to put the electronic module back. The Huco wires are resistance type plug wires.
- aeron: It is a stock fuel pump. Not sure what pressure it has though

Well, based on what you tried last time, and how you've isolated it to two cylinders, and that when you put new plugs in the problem temporarily went away... I think Chris may have the best idea.

There have been several threads on the various forums discussing the dismal quality of the modern replacement dizzy parts. It's pretty well documented that getting a good rotor these days is pure luck. It might be the same with the caps. I believe you've tried everything else, it's probably time to try a new cap and rotor.

Great minds think alike
Ordered new this morning. Will let you know if they help.

Do you have a good ground circuit for the ignition. Is the distributor where it is mounted in the engine getting a good ground, unpainted metal? Is there a ground strap from the engine to the chassis, or frame? Might want to consider a supplemental ground wire.

I pulled all the spark plugs. Number 2 and 3 cylinder - badly fouled. Number 1 cylinder fouled - but not badly. Number 4 cylinder - text book perfect! Bear in mind that these plugs have done no more than 20 miles!

Why are the plugs so different? Any solutions to this persistant problem?

Valve guides?
Oil running past?
What year?
Crankcase breather passing too much?
Do you have a means of checking voltage at the plugs?
(I have an old clip-on Snap-On tool that does that).

Do the deposits burn when you hold your Zippo under them?
As in fuel?

Are the deposits oily?

Tried a hotter plug?

Coil wired right?
Reason I ask is you would not believe the odd problems if the primary wires are reversed. (not necessarily Minis)

Engine coming up to temperature okay?
Like, not running without a thermostat?

Okay gents. I have a Healey that did the same thing and everything was tried, almost a year of intermittent problems. About a couple of months ago my mechanic took out the distributor and refurbished it. Voila - Agatha is performing like she's back on the Lemans circuit. It never occurred to me or husband that the problem might be in the distributor. Just a thought.