Full throttle miss b71 50hp Evinrude

" When the throttle is in wide

" When the throttle is in wide open position I get a seeming slight miss, so I back it off just a hair and it clears up and runs well. Not a problem at full RPM but under load of more than a couple people, it can not get up enough RPM to clear out. Seems to cut out on the upper cylinder. Ran smooth with top wire disconnected, intermittent miss with bottom disconnected at full throttle. Ideas to check?? "

"Kent.... If anyone's been

"Kent.... If anyone's been fiddling around with the full spark advance timing stop screw, it's possible you have it set to exceed the timing specs.

You state, and I quote "Ran smooth with top wire disconnected, intermittent miss with bottom disconnected at full throttle". What wires are you speaking of..... spark plug wires?

Joe "

" Yes, I am referring to spark

" Yes, I am referring to spark plug wires. I ran it with each disconnected to attempt to determine if only one cylinder was misfiring. It only seemed to misfire when running on the top cylinder alone. I said it "ran smooth" with one spark plug wire removed, meaning it ran evenly or seemed to fire evenly on the bottom cylinder but misfired or ran unevenly on the top cylinder. "

"Kent.... Using that test syst

"Kent.... Using that test system (removing wires), switch the s/plugs to see if the problem follows the plugs, then switch the coils. If the misfire follows the coil, that would indicate the problem is with the coil. Those engines are designed whereas (if you look at it carefully), you can use the actual engine ignition components to trouble shoot an ignition problem.... and it does sound like that's what you've encountered.

Disconnect the coil primary wire and the coil ground wire before doing the following test, otherwise you'll get a false reading.

You should have continuity (ohm meter) between the HT S/plug terminal and the coil ground wire, and between that same HT S/plug terminal and the coil primary wire. If not, find out why. Sometimes the spring like terminal within the rubber boot loses continuity with the inner wire within the spark plug lead, and can be corrected. But if continuity is non existent within the coil itself, that could cause your problem.

A sharp breakup would be an ignition problem. The usual exception would be that a fine water spray would be entering one cylinder.... not enough to shut it down completely, but enough to interfere with the s/plug electrode.

If you're not using Champion L77JC4 plugs with a gap set at .030, give them a try. Let us know what you find.

Joe"

" i got this problem and i fou

" i got this problem and i found the second piston ring has broken up, the top one was ok giving me a good compression reading, but when i put it in the water with 2 or 3 people on it, it would sound ok at half throttle but she would miss if i openned it up this was the same on both cylinders. i also found the the jet in the bottom of the carb was blocked this was before i found the piston ring problem. "