Car: 88 festiva with 227K miles For those unaware this is a Mazda B3 SOHC carburated 4cyl
Symptom: Misfire and Blue (oil) smoke.
When: Only happens at first startup after car has sit for a while (at least 8 hours). It starts ok, runs fine on all cylinders, for about 15 - 30 seconds. Then it starts to misfire. If I try to drive away I get a cloud of blue oil smoke. It then clears up and runs fine. No oil smoke, no misfire. If I just let it idle, it will misfire for a long time, and then blows even more smoke when I finally hit the throttle. It really only seems to clear up if I rev the engine a bit.
I have adjusted the valve lash, changed the oil and filter, replaced the plugs with NGK copper. Dist cap looks newish as well as wires ( but I have not changed them)
When I pulled the plugs, they looked fine for the most part. no fouling, color looked normal, they weren’t worn horribly.
I initially thought that it was a carb issue, but the smoke has gotten worse, so I am thinking maybe something is sticking? I get some clatter at startup sometimes (not valve noise) but it goes away as soon as the oil gets pumping (like 1 second) and it is pretty inconsistent when that happens. I am still getting over 30mpg in mostly city driving, and power levels seem ok most of the time
I am leaning away from valve seals, because in my experience they dont cause misfires and for the first 30 seconds there is no smoke at all, but am I in the wrong here?
Any thoughts from you master mechanics? I feel like a compression test might not help because it only happens in certain circumstances…