Yanmar YSE8 Air Inlet Popping

[NoDramas]

Hi Guys,
A bit of background:
40 year old Yanmar YSE8, single cylinder.
After the water inlet was blocked by plastic bag we have honed the cylinder bore very carefully and replaced piston rings and all gaskets.
All relevant parts were well oiled before starting. Head was crack tested and skimmed and valves checked all OK. Fuel is getting to the injector. It sounds like it is getting half the combustion it needs (if that makes sense).

Fuel pump is new as well. Motor started and ran for a couple of minutes but stopped, we think due to improper valve clearance which has been fixed.

We have good compression and fuel is flowing we believe the injector to be good as it was tested a couple of years ago.

The issue is that it doesn't quite start but is very close.
Symptoms are that there is a distinct pop/blow back when the air inlet valve opens.

Any thoughts or questions for more info would be gratefully received.
The old girl wants to run, I just need to find how to help her.
Cheers Heaps

[a64pilot]

If it's popping in through the intake valve, it's either a leaking intake valve, too advanced timing of the injection pump or the cam timing being off.
In short your getting combustion with the intake valve still being open a little

[shakey doug]

Are the valve rotater caps in place???

[GordMay]

Greetings and welcome aboard the CF, NoDramas.

[NoDramas]

Originally Posted by shakey doug

Are the valve rotater caps in place???

Good point. Yes they are checked and in place.

[NoDramas]

Originally Posted by a64pilot

If it's popping in through the intake valve, it's either a leaking intake valve, too advanced timing of the injection pump or the cam timing being off.
In short your getting combustion with the intake valve still being open a little

Appreciate the prompt reply!! I'll check it out. Thanks heaps.

[NoDramas]

Originally Posted by a64pilot

If it's popping in through the intake valve, it's either a leaking intake valve, too advanced timing of the injection pump or the cam timing being off.
In short your getting combustion with the intake valve still being open a little

Problem Solved. Compression was very good and we can see teh valves shutting correctly. A few weeks earlier the motor started once and leaked a lot of black smoke (from well oiled new piston rings) into the cabin. Replaced the exhaust manifold gasket. Wouldn't start since.
Held a paper towel over the exhaust and it didn't move at all, worked our way back to the exhaust manifold. Issue was that the exhaust was blocked by carbon at the U bend a chisel and patience and it is all clean now. Will put it back on next weekend. It makes perfect sense now :-).

Appreciate all your advice.