Compression should be off in the affected cylinders. I had a couple of carboned up valves in a 350 Chevy and all the cylinders had 180 except two cylinders.....those had zero. Don
it would have a bad miss for one. intake valve would probably be backfiring through the carb. exhaust valve you may hear a sputter in the exhaust. if it's bad enough you may hear some rattling in the valve cover. whats it doing?
Hss a pretty distinct pop about every revolution in driverside exhaust. Has s very slight but noticeable miss . Only at idle on both .
pull the valve cover off on that side, crank the engine, watch the rocker arms. try to see if one is moving less than the others. could be a cam lobe going down. that will usually have a dead miss under load like you pulled a plug wire off.
That isn't a sbc question but an engine condition question. If you have or have access to a vacuum gauge you can usually tell the condition of the valves with it. Scenario 6 on this page http://www.secondchancegarage.com/public/186.cfm shows what bad valves do on the reading. Running a compression test is probably a more positive indicator. Pull all of the plugs, prop the throttle plates wide open and put the compression gauge in an end plug hole on one side or the other and crank the engine over letting the compression hit the gauge 5 times on each cylinder. Write the readings for each cylinder down for all eight cylinders and compare them. Ideally they will be all even and have compression close to the suggested reading for that engine. All with low compression equals weak rings. one or two cylinders with compression quite a bit lower then the others would usually indicate burned valves. The third test would be a leak down test where you put a fitting in the spark plug hole that is connected to a gauge assembly that reads the amount of pressure loss. That would show if and where you had compression leaks in the cylinders.
The Jalopy Journal
