David Mutch

Hi Tony. Sorry, haven't checked in for a while.

The fact is I didn't really solve it, but I'd say I've found some mitigations and have some theories:

TL;DR - I think my air filter is just getting clogged with oil, but why that's happening I'm not sure. I intend to fit a catch can, as you suggested but haven't got around to it yet.

1. I think I got a bit confused about the timeline of when I routed the crank case/rocker cover breather into the air intake. I thought I'd done this long before the smoke started, but perhaps it wasn't so long. I've upped the regularity of cleaning my air filter, which helps a lot, but doesn't completely fix the issue and it soon needs cleaning again as it's soaked in oil.

2. I think I underestimated how much I had started using fewer revs because of the problem (I was trying to be kind to the engine because I thought it was on its last legs). I think I posted a video of me doing the old Italian tune up and just revving it for a bit, and the smoke clearing. I've given up trying to be kind to the engine and now the smoke pretty much disappears after 5-10 minutes of cruising (as long as I'm not passing too many moored boats 😜). The problem is much worse when I've been running my engine stationary in winter for electricity than when I'm on the move most days.

3. I did advance the timing as far as I dared, but I don't think this had much of an effect.

4. As I think I mentioned in the post, I changed the injectors. I think this had little to no effect, except on my bank balance.

5. I suspect your suggestion of routing the crankcase breather into an oil catch can would largely eliminate the problem, but I've not got around to it yet.

6. As I said in the post, I have relatively high oil pressure, so perhaps there's more oil mist under the rocker cover than there should be, and therefore too much is being sucked into the air intake (so an oil catch can would hopefully help).

7. As I said in the post, I've checked the compression, and it's good, so I'm fairly confident that the smoke isn't down to piston rings.The fact that the problem is largely eliminated by cleaning the air filter would suggest the excess oil isn't from bad rings, but just from an oily air filter.

8. I guess bad valve stem seals could be contributing to smoky startup, although when I have a freshly cleaned air filter there's precious little smoke, even on start up, so the problem is pretty much down to oil being sucked into the air intake.

Just tagging @Guy J, so he sees this. Hopefully you're the right Guy J!

Guy emailed me and asked me to pass on his thanks for your long reply to him.

Not a lot of help to either of you, but we had a 1.5 in a cruiser with a wet exhaust, and we could never stop black ish exhaust smoke and a constantly black transom, whatever we tried, and that includes prop, injector pump changes and checking the pump timing many times.