...all good comments.<P>The behavior is inconsistant, to say the least, and that's the maddening part of it.<BR>Typically, it runs VERY smoothly, and the problem kicks in about 50% of the time when under load. The engine was test driven with an in-line vacuum gauge. No vacuum problem.<BR>BUT the depression chamber (secondary) operates on it's own system, from the venturi on the carb. It's a more subtle vacuum than the rest of the system, and harder to check during a test drive, but the depression chamber won't hold a vacuum, so it's being replaced, and hopefully the problem will disappear. If not, then the investigations continue...<BR>The problem (power-loss, feels like a stuck carb valve) occurs with a very cold engine and any other temp, as well.<BR>All the air ducting controls work, and the problem is not related to any specific RPM, it can hit between 1800-4000 rpm. Most noticible trying to climb a hill in a high gear. But not ALWAYS. I climbed one hill on the freeway in overdrive without any difficulty, caught up to the vehicle in front, eased off the throttle, changed lanes, and then eased back on the throttle, and THEN it lost power! Wierd.<BR>I should pull the plugs and actually take a look inside. I have a compression tester (or used to...), but I somehow doubt there's suddenly a problem there. I lived with bad cylinder scoring, low compression, bad head gaskets, etc, and this looks like none of them. Mostly because the exhaust is clear, no oil smell, and was pollution tested last week with below average hydrocarbons. I'll check the tailpipe for oily soot, etc.<BR>There is NO oil leaking outside the engine, went over it and cleaned it thoroughly this evening, and ran it to look for any sign of oil. none.<BR>I have noticed that my oil pressure is sometimes showing quite low even though the oil level is good. And along with it comes the lifter chatter. Oil pump may be a problem. But again, it's infrequent.<BR>Changed the oil and filter 10 days ago (10-30 Castrol GTX), and the oil level didn't move in 5 days. Then sometime during the next 3 days, 1 liter disappeared. No blue smoke, no spillage. No oil on the ground under it, and it's always in the same parking spot. Even had some newspapers under it to check...<P>If I had to explain it, I'd say that the when the problem occurs with the power-loss, if you push the throttle, there will either be a backfiring, or a sudden loss of power to 1 or more cylinders. Then you pull over and rev the engine for a few minutes to smooth it out again, and all's well. I have this delusion that all of a sudden a lot of oil got sent into the carb at that point, and that's why the power loss to several cylinders (and the recently soiled pcv valve). But HOW can that much oil get burned through a carb that quickly without any obvious sign? Admitedly at night I can't esee the exhaust...<BR>Running the engine with the oil cap of produces a throbbing air movement at the valve cover opening, but if you cover the hole with your hand, you can feel a slight negative pressure. I gather that's ok. A positive pressure would be a problem.<BR>Other idea: could I have bloked oil passages, and the oil is all pumped on top of the head, and getting forced into the carb? Or into the cylinders?<BR>Having needed a lot of helicoils on the spark plugs in the past, I'm reluctant to pull the spark plugs unless it's urgent. And since it runs and idles beautifully under no load, I presume the plugs are good...<BR>The mechanic that's going though it has the Mitsu book, and read through a lot of it last week, and checked everything he could find against Mitsu's published numbers, and SO FAR only the Depression Chamber stands out...\<P>Bicycle time? It's a mix of rain/snow/wind here now. Even walking's ugly, and the busses are full...