So, I’m having an issue with my spitfire mkIV and I’m after some advice.
The issue started to develop when I took it out for the first time this year after leaving it for the winter. The car idled OK, but after a very short distance I started to notice that it flattened out under acceleration and seemed to have a bit of a misfire. I got it back home sharpish and started having a look to try and work out what the problem is…
The first thing I noticed was that the spark plugs were all pretty grot (a bit black and damp (oil???)) but they were all consistent. I had a set of new ones that I was going to replace them with anyway so popped those in and ran it out again a short distance to see if there was any improvement on the flattening out/misfire. Well, it seemed to cure the misfire but it was still having an issue with low power. I also checked the mixtures, using both a colourtune and a bit of intuition and it seems like the mixture was burning well (and the exhaust didn’t smell rich or splashy as if lean)
It was also noticed that as I pulled out of our driveway and pulled away there was an amount of slightly blue-ish smoke from the exhaust (not a smokescreen but an observable amount). Again, pulled back home and went to check the state of the plugs. After pulling cyl 1 plug a reasonable amount of smoke started coming out of the cylinder! This doesn’t strike me as normal… In addition, cylinder 1 plug seemed to be back in the same state as before while the others seemed pretty healthy.
I should also say that I’ve done a cold and warm/wet and dry compression test and they all seem pretty reasonable (no outliers and only marginal change between dry/wet). I don’t have a leak-down tester so can’t really give any more info on the compression figures.
So, I’m after a bit of help in diagnosing the problem…
Symptoms:
Smoke under acceleration (slightly blue)
Fouled plug (cylinder 1)
Smoke from cylinder 1
Reasonable compression (no outliers)
Can hold a reasonably steady idle
My thoughts:
Given this is the first classic that I’ve owned I’m hesitant to jump to conclusions, but I’m feeling that of ignition, compression and fuel the problem is to do with the compression side. Mixtures seem reasonable and all plugs/points etc. seem ok so it only leaves compression. From what I’ve read I know there can be issues with both valve seals/seats and also piston rings – does what I’ve described feel like one over the other or neither? Is there some test that I’ve missed that would give a better indication?
Sorry for the giant block of text, but whilst I’m happy to have a go at whipping the head off I want to make sure that I’m barking up the right tree before doing anything likewise, if I'm being a bit of a dolt and have missed something obvious feel free to call me out on it, I'd prefer to suffer that embarrassment if it means I can get the car going again! 😁
Cheers.