Re: 1997 Johnson 50 runs rough at 2000rpm
John.... It's unlikely that problem is a timing issue, but it could be a synchronization issue that is associated with the timing.<br /><br />Check to make sure that the throttle butterflies are not open at dead idle, then check the linkages between carburetors to make sure that all throttle butterflies open and close at the same time. At dead idle, both closed, not one closed and one slightly open.<br /><br />Check the throttle roller that slides against the cam. Many of those rollers have a clear exterior coating that will break and flake away. The roller is usually about 3/8" in diameter, if it looks like a smaller black roller (about 1/4" or so), replace it.<br /><br />There is a scribe mark on the cam. The throttle butterflies should just start to open when that scribe mark is dead center with the roller, not before.<br /><br />There is always a possibility that, due to altitute etc, that the intermediate jets at that point which are just starting to mix with the high speed jets, may be the wrong size but I'd leave this area as a last resort.<br /><br />If those carburetors have slow speed adjustable needle valves, the adjustment procedure would be as follows.<br /><br />(Carburetor Adjustment - Single S/S Adjustable Needle Valve)<br /><br />Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.<br /><br />Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.<br /> <br />Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting. <br /><br />When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.<br /><br />Let us know what you find.
