That is corect...but it is firing off time for some reason...you never really did clarify once and for all if this was out the exhaust
or back through the intake manifold..if the latter it leans more toward valve isues if the former more toward fuel delivery
isues...and what I took you as meaning from the get go.
Since you only have 70 hours you can sort of rule
out sticking or burnt valves ..and like I said SORT_OF
or in other words were going to look elsewhere first then come back to that if we are stalemated.
However every manufacturer I know of wants a re-checking of valve lash ( the clearance between the end of the valve stem and the bottom tip of the rocker arm in a totaly valve closed position after a reasonable break-in time..This is stated as TDC or Top Dead Center...and checking that in a particular rotation of the four stroke firing order...
As the valves seat farther into their valve seat due to wear and reduce this clearance it can create a no-sealing condition where the valve is not totally closing....This is not called valve sticking this is a valve clearance issue or another part of the "Timing issue" ...but could lead to a sticking valve or worse a burnt one as exhaust
gasses rush by when they are not supposed to or where
they are supposed to in the case of intake valves.
Yours should be done if it hasn't been already.
Hence my first place to check after the Fuel filter
change and while in there doing the pump timming...As you have to pull the valve cover for the later two so It makes no sence not to check both.
Again I hope this helps a little.