73 340 Compression Test interpretation help

Valve guides. Block the breather hose coming off the non-PCV valve cover. You should feel the crankcase build vacuum really quick. If the idle speed changes, this confirms. I'm betting those are probably original heads and starting to show their age.

Here's what happens. You get the smoke when starting cold because while the engine sits static, oil runs down the intake valve stems and wets the backside of the valve head. So when you cold start the engine, the extra rich mixture from the choke washes this oil off and you get a puff of smoke when you start. We aren't so used to seeing it these days, but not too many years ago it was considered fairly normal. Now, with the engine warmed up, you trounce the go-pedal. A cool fuel wet wind howls down the ports washing the back of the valves and the sudden raging fires within the chambers cooks the oil out of the saturated deposits making you guessed it. More smoke.

Here's a quickie diagnosis. Do an "Italian Tune-Up" at about 25 mph, floor it until the tranny shifts into 3rd (65-80 mph) lather rinse and repeat. The first time I bet you get a pretty good cloud of smoke, and the engine will ping and rattle pretty good. The next time, the smoke and pinging should be less. By the 3rd or 4th time the smoke should clear up. If the smoke gets worse, your rings are shot or stuck.

How much oil does the engine use? Anything under a quart per 1000 miles in normal driving means something is wrong. More than a quart in 500 miles, something is seriously wrong. Did the car sit for an extended period of time?

Sure, you can put new valve guide seals on, and I would if it were me. BUT start saving your nickels for a top notch valve job.