TR2/3/3A TR3 1991cc engine emits black soot from exhaust

[cguild]

My '60 Morgan with TR3 engine is emitting black carbon soot out of the exhaust, even at idle. I thought it was due to a rich carb mixture even though it was recently professionally tuned. But then I noticed the Champion RL87YC spark plugs were gapped less than .030" whereas Champion specifies the gap at .039". I changed the gap to .039" and the car ran well and the carbon emissions stopped. Then I read the Triumph manual and a number of TR3 owners' threads and both sources agree that the proper gap should be .025". When I changed the gaps back to .025" the black soot emissions returned worse than ever. Can I get away with an increased gap on these plugs or should I be looking elsewhere for a solution to the black soot emissions?

 

[Andrew Mace]

Is your ignition "stock" (i.e., points and condenser as opposed to electronic such as Pertronix)? Regardless, I don't think I'd argue with the .039 plug gap if it seems to solve the problem!

 

[RichB4493]

Your muffler may be retaining mositure/condensation. Does it happen consistently or only during cold startup? I was having that issue and regapped my plugs and made sure my point gap and timing were appropriate. I also rescinded my carbies. All is good.

Not sure where the forum experts will land on this suggestion but you can drill a small hole at the low point in your muffler to let condensation drain out. I didn’t do it yet but it was next on my list.

 

[cguild]

The ignition is stock, not electronic. I did notice some condensation with the soot the last time I checked the exhaust, but that's the first time I've noticed it. I've only checked it after cold start-up so next time I'll check it after it's run for awhile. RichB - what measurement did you regap your plugs to?

 

[RichB4493]

The ignition is stock, not electronic. I did notice some condensation with the soot the last time I checked the exhaust, but that's the first time I've noticed it. I've only checked it after cold start-up so next time I'll check it after it's run for awhile. RichB - what measurement did you regap your plugs to?

.025

 

[Hamish Racing]

Gap them to what works for your set up.
You obviously have a good high tension elec set up
And it’s the points gap that regulate your dwell angle

Sound like it needs an Italian tune up. Ie go and drive it like you stole it and get the revs towards the red line through the gear to help de-coke the engine and headers.
Then pull the plugs and have a look.

I run points and condensed and a .032 plug gap points half that.

 

[cguild]

I worked my way down from a gap of .039 to a smidge over .030 (.032??). No carbon emissions after cold start nor after a run up the highway. I think I'll leave it at that and see how it goes over the long run. Thanks to those who gave me their thoughts.

 

[CJD]

The problem with increasing the gap is that it takes exponentially more voltage to jump a larger gap and more amperage to accomplish the spark. Higher voltage loads the points, condenser, and coil and wires. Of course, the spark is hotter with a wider gap. Thus you have a compromise between the equipment longevity and spark heat. The stock parts will last years with .025" gap and annual tune-ups. If you run better at .039, just realize you will reduce the life of the parts...somewhat. How long is somewhat? Hard to say.

An interesting story...the GM HEI ignitions were introduced in the mid 1970's, and originally designed to be able to run a super-hot .125" plug gap. The lawyers had to limit the gap to .060", as the amperage was reaching lethal ranges! It just shows that everything is a compromise, whether it's trading spark heat for extending the life of older, marginal parts, or saving lives from what is possible with modern parts?!?
.

 

[Got_All_4]

I had a similar problem with my TR3 way back in the 80s after I restored it. Black soot would fowled out my plugs constantly. Went to a hotter coil and wider gap. I think 32k. Worked but was now blowing out condensers. Then went to Petronics and not a problem after that.

 

[Sarastro]

One thing to keep firmly in mind: these cars worked just fine back in the 1950s as configured by the factory. Fixing a problem by changing some factory setting may seem to fix something, but it's really just misadjusting to compensate for a problem. The result is never as good as getting it running as it should.

I suspect that, for some reason, you are getting incomplete combustion. Since increasing the spark gap seems to fix it, the the problem is most likely ignition. If the car seems to be running well, it's probably not a bad coil or cracked distributor cap or such--that would cause rough running. But maybe too much resistance in the high-voltage wiring could do this. You probably have resistor wires, including the one from the coil to the distributor, resistor plugs, and maybe even resistance in the rotor. These resistances can be around 5000 ohms each. I suggest no more than 10,000 ohms total in that wiring, the entire path from the coil terminal to the spark plug gap.

You might also try a different brand of coil. I've measured a number of them here in my lab, and I've found that most are pretty similar, but occasionally one is significantly different. The standard Lucas coil and Lucas Sport coil have the best characteristics of the ones I've measured. The Bosch "blue" coil is OK too, if you can still find one. The coil must have no more than 3.5 ohms primary resistance.

Probably not the ignition capacitor, but I would replace it on general principles. Also, make sure there is no additional resistance in the primary circuit (no ballast resistor, for example).

That's all I can think of at this moment, but perhaps its enough for you to get the idea.

 

[cguild]

Thanks Sarastro. I haven't measured resistance in the wiring but I had wondered if the gap difference between what worked (.030+) and what the manual recommended (.025) was due to Resistor plugs that require a wider gap. The car came to me with Champion RL87YC plugs and those are the ones I had to increase the gap to over .030+ in order to stop the carbon in the exhaust. I just replaced those plugs with L87YC and gapped them at .025. I now get a little carbon at a cold start but when warm the exhaust is clean.

 

[Sarastro]

I've never heard that resistor plugs need a wider gap, and I can't come up with any reasoning why they would. If the resistance is not too high, its effect is pretty much negligible. The resistance has no effect until the plug fires, and when it does, the spark voltage is a function of the plug gap and shape, cylinder pressure, and probably some other things. The resistance just sucks up some of the available energy and shortens the life of the spark. Widening the gap will increase the spark voltage, but then the spark duration will be even shorter.

Here's where I'm coming from: my Porsche 912 got new ignition wires recently. There was 5000 ohms in the Bosch rotor, 1500 in each wire, another 1500 in the wire from the coil to the distributor, 1500 ohms in each plug. It's getting to be a lot, but still less than 10,000 ohms total, so I think I['m OK. I have calculated the loss in the wiring to be about 10% of the spark energy. But it would be easy for this to be much higher if the resistance were higher.

BTW, if you wonder where this is coming from--I'm an electrical engineer and I've been computer-simulating ignition systems and measuring coil characteristics for some time now. The effort has taught me a lot and even dispelled some of my own previous misconceptions.

 

[cguild]

You're certainly infinitely more qualified than I am when it comes to electronics, Sarastro. I'm a civil engineer who can barely make a radio work when I turn it on.
My comment about a wider gap for a resistor plug comes from the RL87YC plugs coming pre-gapped at a recommended .039 and the L87YC plugs coming with a .025 gap out of the box. When I looked up resistor plugs I read something to the effect that they sparked slower (or cooler or something) so needed a wider gap for more voltage (which I assumed to be a hotter spark). When I increased the gap on the resistor plugs the carbon emission from my exhaust disappeared. I thought that was a good thing but then I learned that the increased voltage put more wear on the other electronic components.
I then bought the set of L87YC plugs with the .025 gap recommended for my engine. I now get some slight carbon emission at start-up but it disappears once the engine warms up. With the RL87YC plugs gapped at .025 the exhaust emission was full of black carbon all the time. When I widened the gap of those resistor plugs to between .030 and the .039 recommended by Champion the carbon emission disappeared. So I just assumed resistor plugs need a wider gap.
Regardless of all this I appreciate your tutorial on resistance. Frankly, it's a subject I've never fully understood so any and all enlightenment is a good thing.

 

[mctriumph]

Often not suspected, is resistor wired dizzys can have the wires burn out. The set screws in the cap
often shear the core of the wire on install. Fold the bare portion of the wire back 1/4 inch and blunt
the set screws which will now require Loctite to stay in place,since you dont want to over tighten them.
Also I prefer NKG plugs over any other, they are just that much better( IMHO & experience).
Mad dog