V
viking02
Guest
1996 Mercruiser Magnum 350 with the original Carter carb professionally rebuilt. Ran like a champ at 3200 rpm for the first 30 minutes, then started backfiring through the carb every 10-15 seconds. I suspected too high a float level, pulled the sparkplugs which look mostly like "carbon deposits" in the Haynes chart. When I did a compression test, I got between 142 and 160 lbs, except no 7, which doesn't even move the needle. I cant even get a whoosh from the open sparkplug hole. It still runs like a champ, even idles pretty good. Could the no 7 problem be independent from the backfire? How can I determine a lifter problem from a valve problem? What kind of tricks are there before the head comes off?