Misfire

[Monkeyzak]

I've gave up with the electrics for the moment. I'll not drive it at night

Car sat in my garage running fine. Drove it a mile a couple of miles no bother. Then it started misfiring. I stopped and it idled fine. Then when I drove off it misfired again.

What do I check first? Plenty of fuel in it.

[skertonman]

I'd be checking the electrics first. Points and condenser if you're running those, then dizzy cap or rotor arm.

What's it like being revved stationary, or does it only do it under load?

Electric misfires are like a sudden on/off affair, where as I've found fuel to be more a slower loss of power usually at higher revs, as the engine needs more fuel than it's getting, as in whats it like when running out of petrol.

Well that's my two penny worth.

[Monkeyzak]

It has electronic ignition.

Ticks over and revs fine. Select gear. Pull away and it misfired. Rev it really hard and you can keep driving it.

I hope it's not going to be one where I keep replacing bits until I have no cash and a still! Stuttering car.

[Monkeyzak]

So yes only under load.

[saabfast]

What sort of electronic ignition?
Assuming that is retrofit electronic ignition check the rotor arm and distributor cap for carbon tracking. If it has a slight crack anywhere the voltage will track away along very fine (invisible) faults. If they are old it is worth changing them anyway.
The other important part is the HT leads and plugs, again change either if they are old.
I have had similar symptoms when there was water in the tank (from condensation). Hopefully it has an inline filter on the suction side of the fuel pump. Check the state of it. Mine was full of rust sludge and part water/part fuel. Had to empty the tank and pipework. I now put Isopropyl alcohol in the tank when it is laid up for the winter. I absorbs water and mixes with the petrol and burns in combustion.

[John_C]

If the electrics route starts looking like a blind alley, check the fuel. Misfiring from rusted fuel tanks has become a common problem in recent years. I confirmed my own ten years ago by running the car from a jerry can and a long petrol pipe from the pump into the cockpit.

[Monkeyzak]

Checked the timing tonight. It was so far out I was worried it was me that was wrong. My mate who's an old hand at Trs is going to clean the carbs out and set them up tomorrow and check for air leaks. And check the fuel pump

After that if it's still running badly I'll replace the rotor arm, cap, plugs, by leads. Does my car have a replaceable coil if it has electronic ignition?

If that doesn't work then I'll! Report back.

[UKPhilTR7]

That is good that you have got a mate that can do the carbs for you. If you have the option go and watch while he does it. This way the carbs will not be a "black box' which you have no idea how they work. This is a good chance to learn more about them as you will need this knowledge in the future. Before you know it you will be posting carb replies on here too.

I would still replace things like the plug, leads and that if they are old, just to be on the safe side.

[UKPhilTR7]

I have had similar symptoms when there was water in the tank (from condensation). Hopefully it has an inline filter on the suction side of the fuel pump. Check the state of it. Mine was full of rust sludge and part water/part fuel.

I totally agree. I had this filter that I changed a few years ago. I am just glad that the cheap inline filter was there catching the rubbish and that it didn't get to my carbs or past.

[Hasbeen]

One 7 I bought had so much crap in the tank that one of those little in line filters would be so clogged in 150 kilometres that the thing would suffer fuel starvation, & not rev past 3000 RPM.

Another had a developing fault in the Lumenition electronic ignition system. It would never display a fault when near an expert. Each time I replaced something it would be good for another couple of thousand kilometres, only to start with a mild miss when cold again.

It took 3 years to finally cut dead, & allow the problem to be located to it.

Good luck

Hasbeen

[John_C]

I too had dodgy electronic ignition. The car would start fine and would sometimes go for miles before the misfire started. It got worse over time and was down to something in the ignition box overheating. It was the third time in as many years electronic ignition caused a breakdown (the car, not me but I nearly joined in) and so it went back to points and condenser. However, for the Anniversary Run in 2014 Rawspeed put in a cheapo ignition in for me during a rolling road session and so far that one hasn't caused any trouble. But I do carry a standard distributor around in the car for when it does suddenly throw a wobbly.

[Monkeyzak]

Carbs cleaned out. Went for a run with my mate today. Started misfiring again and throwing petrol out of one of the carbs. So going to get the floats and float needles replaced. I'll order plugs and leads at the same time.

He is convinced it's a fueling issue. Its not cheap this classic car malarkey.

There's no inline fuel filter so I'll get one when Im ordering the other stuff

[Monkeyzak]

Hopefully not a problem with the electronic ignition. Don't have the original distributor to swap

[Beans]

... throwing petrol out of one of the carbs ...

What fuel pump is fitted to the car?
I had the same symptoms many moons ago with an electric pump.
Sorted with a fuel pressure valve. But could also be caused by incorrect mechanical pump.

[Monkeyzak]

Don't know what fuel pump or electronic ignition system it is. Is there a way to find out?