Hi

I have a 1950's Coventry Victor 4 stroke Flat 2 cylinder marine petrol engine in my boat. It is not running smoothly once warmed up. I have noticed that 1 spark plug is always blackened with soot (not oily) and suspect that this might be a clue. The other spark plug is always clean when inspected.

I have spent a considerable time improving the cooling water flow around the cylinders and am happy that both are running cool.

Please could anyone suggest possible causes for my sooty plug?

Thank you

Keith

Hi Keith,
It’s a shame that you are not getting answers and or help from the forum but it’s not surprising as you rarely see responses.
I don’t know about your engine specifically but the fact that one plug is sooty and the other is clean needs investigation.
Perhaps you could swap the plugs to see if the same cylinder is giving the problem.
Then I sense that this cylinder/plug is not getting a good spark and or running rich.
I think that the carb feeds both cylinders equally so it’s unlikely to be that.
I’ve seen a picture which seems to show magneto ignition. Is that correct? Worth double checking to see that you have a good spark on both cylinders.
Do you have access to a Gunson Colourtune? That would enable you to check the burn in each cylinder when it’s running.
You also say that it’s uneven when warmed up. Is that with any choke applied for example?
Keep going! It’s probably something simple but tricky to find.
Have you checked the compression in each cylinder and valve settings?
Remember that with fuel mixture, compression and a spark at the correct time such an engine will run. Therefore if it does not run it must be one of those which is missing.
Hope this helps,
Malcolm

Hi Malcolm
Thank you very much for your reply. That provides some great ideas of things to look out for. Engines are definitely not my forte, but I am finding through necessity, that I am learning fast. I had never heard of a Gunson Colourtune. I have now watched the video and will be investing forthwith.
Thank once again
Keith