Re: 79 Mercury Running Rough
It probably sucked-in some varnish or algea, which is plugging one of the carbs.<br />When fuel sits, it can turn into varnish,and can also grow a bacteria,or algae (don't remember which). But it is literally a living thing that is jelly like.<br />First ,try not to run the engine until you solve this problem. With 2 dry cyclinders being carried by the operating ones, the two dry ones will end up damaged due to lack of lubrication.<br />Once you determine which two cylinders are dry (by pullin the plugs after a short test run,and noting the dry ones), Pull that carb,and clean it. It may require a carb kit,so have a kit handy. If you have never cleaned a carb before, or are unsure about the particular carbs, get the shop manual before proceding, or take the carb to a shop near you (a good auto shop is fine). If you are ready to tear in yourself, look for an obstruction in the pickup tube,the venturi in the top of the pickup tube, or the venturi threaded into the side of the pickup tube as the main culprits. But blow compressed air thru everything just be be sure. Try not to change the float level or mixture settngs.<br />You will want to pull the float,but these carbs have springs behind the float needle. The dang things ar touchy,which is why i say "try not to change the float settings".<br />The mixture screw can be turned-in till it bottoms-out, while you count the turns. Then,when you are done with the carb,you can screw it all the way in, then back out the same amount as before. This extra care to avoid missadjustment is only important on multi carb engines like yours. Those old Mercs are marvelous,both in performance and reliability.<br />good luck with her.
