Re: 1976 johnson 35 surging
Your explanation points to a fuel problem, being either a air/fuel leak between the fuel pump and the fuel supply, a faulty fuel pump, or a fouled incorrectly adjusted carburetor.<br /><br />I'm assuming that the problem does not consist of a sudden instant change in rpms which could be contributed to ignition or a slight amount of water entering a cylinder, nor is it a case of the engine suddenly screaming away due to cavitation/ventilation (prop drawing air). If I am in error here, let me know.<br /><br />From what you've said, it appears that the surge is a slow gradual up and down surging of rpms, which as I've said above, would pertain to fuel.<br /><br />Compression should be in the 100+ psi range and even on all cylinders..... is it?<br /><br />With the spark plugs removed, using a spark tester of some kind, set to a 1/4" gap, the spark should jump that gap with a strong blue lightning like flame..... a real SNAP! Does it?<br /><br />Spark plugs should be Champion UL81J plugs, set to .030.... are they? Any other s/plugs will not function properly.<br /><br />Does pumping the fuel primer bulb when this problem takes place have any effect, if so, what effect?<br /><br />Fuel pump... leave the hoses intact but remove the pump from the engine mounting. Attach nuts to the back portion of the mounting screws so as to seal the pump as if it were mounted. Pump the fuel primer bulb. If fuel escapes out that back pressure hole in the pump, discard it and install a new one. I don't recommend rebuilding it as one would not know if a slight goof was made, resulting in a continuation of the problem which would have you diverted off on a false nerve wracking path (been there).<br /><br />If all is well so far, and even if it isn't, double check the carburetor work, making sure that the fixed brass high speed jet is absolutely clean (located in the bottom center portion of the float chamber).<br /><br />(Carburetor Float Setting)<br />(J. Reeves)<br /> <br />With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.<br /><br />(Carburetor Adjustment - Single S/S Adjustable Needle Valve)<br />(J. Reeves)<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 />Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.<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 />Now, what are you going to do with the rest of the day? (grin)
