Bought the subject motor recently to replace a '66 80 hp V4 Johnson on a '66 aluminum AeroCraft. The Johnson is still running strong, but is way too much of a gas hog for my taste (2+ mpg). Have only run the "new" motor on muffs. Starts immediately. At recommended synchronization settings, idles at 1700 to 3000 rpm. Runs very "rough" similar to bad out-of-sync carb situation. Runs rough at idle and when revved up. Although, only occasionally "lean coughs." Can bring the idle down to less than 1000 only by severely retarding the ignition which causes even rougher running, of course.
As for the ignition system, I'm tentatively ruling that out at present. The spark is hotter than a firecracker on both cylinders, is in perfect specified time, and is steady as a rock under the timing light. As a dumb check, I've also pulled the plug wires on each cylinders while running and the darn thing continues to run at an elevated idle on one cylinder. Also have checked cylinder two under the timing light and it's perfect also. Don't suspect power pack. I won't rule ignition out, but I'm presently looking elsewhere.
BTW, compression is 140 psi both cylinders cold which is a big part of why I bought this motor where-is-as-is.
So, suspecting an air leak or severe carb malfunction, I did the following. Replaced the upper crankshaft oil seal. BTW, no sheared key or other anomaly with the flywheel. Removed and disassemble carbs. Ah ha. Obviously had been recently gone through. Clean as a whistle and everything in order to my eyes. No doubt previous owner looking for same source of problem as I am. Removed intake manifold and reed valve assemblies. All in order and in good condition including gasket. No visible disorder in bottom end of crankcase. Replaced intake manifold gasket with a new one, but used a thin coat of Blue Halomar gasket sealer just to be double sure. Also replaced carb-to-manifold gaskets using gasket sealer. While at it, removed and carefully inspected VRO and hoses. Re-clamped hoses. BTW, oil intake on VRO has been blanked off so the unit is just functioning as a fuel pump.
Following the above work, I double checked synchronization and upon start-up, samey same. Checked ignition timing with light again. Samey same - perfect. So now I go old school approach. Alternately blocked carb intakes with rag. Not the severe impact you would expect. Definitely getting air somewhere downstream of throttle plates (it would appear). Next I take Windex and spray the dickens out of it at any joint or hose coupling that I can think of. Really, just sprayed the heck out of the whole outside of crankcase. My hope was that I would get a stall or hesitation when the Windex found it's way into the assumed air leaking area. No such luck. Samey same.
Putting my thinking cap back on, my current theory is that the lower crankcase seal must be leaking. Of course this will require pulling the power head. Doesn't look like a big deal on this 2 cylinder motor but I have several questions I'd like to pose to the community before I proceed.
Is there anything else you can think of that I might need to check before pulling the power head? I can't imagine that I have a head gasket leak but if I pull the power head, should I just go ahead while it's on the bench and replace the head gasket, exhaust cover gasket and etc.?
Any suggestions will be appreciated. I'll eventually give you feedback as to how they came out. I can only work on this problem in spurts so please be patient for your feedback. Thanks for reading this long winded crying towel.
As for the ignition system, I'm tentatively ruling that out at present. The spark is hotter than a firecracker on both cylinders, is in perfect specified time, and is steady as a rock under the timing light. As a dumb check, I've also pulled the plug wires on each cylinders while running and the darn thing continues to run at an elevated idle on one cylinder. Also have checked cylinder two under the timing light and it's perfect also. Don't suspect power pack. I won't rule ignition out, but I'm presently looking elsewhere.
BTW, compression is 140 psi both cylinders cold which is a big part of why I bought this motor where-is-as-is.
So, suspecting an air leak or severe carb malfunction, I did the following. Replaced the upper crankshaft oil seal. BTW, no sheared key or other anomaly with the flywheel. Removed and disassemble carbs. Ah ha. Obviously had been recently gone through. Clean as a whistle and everything in order to my eyes. No doubt previous owner looking for same source of problem as I am. Removed intake manifold and reed valve assemblies. All in order and in good condition including gasket. No visible disorder in bottom end of crankcase. Replaced intake manifold gasket with a new one, but used a thin coat of Blue Halomar gasket sealer just to be double sure. Also replaced carb-to-manifold gaskets using gasket sealer. While at it, removed and carefully inspected VRO and hoses. Re-clamped hoses. BTW, oil intake on VRO has been blanked off so the unit is just functioning as a fuel pump.
Following the above work, I double checked synchronization and upon start-up, samey same. Checked ignition timing with light again. Samey same - perfect. So now I go old school approach. Alternately blocked carb intakes with rag. Not the severe impact you would expect. Definitely getting air somewhere downstream of throttle plates (it would appear). Next I take Windex and spray the dickens out of it at any joint or hose coupling that I can think of. Really, just sprayed the heck out of the whole outside of crankcase. My hope was that I would get a stall or hesitation when the Windex found it's way into the assumed air leaking area. No such luck. Samey same.
Putting my thinking cap back on, my current theory is that the lower crankcase seal must be leaking. Of course this will require pulling the power head. Doesn't look like a big deal on this 2 cylinder motor but I have several questions I'd like to pose to the community before I proceed.
Is there anything else you can think of that I might need to check before pulling the power head? I can't imagine that I have a head gasket leak but if I pull the power head, should I just go ahead while it's on the bench and replace the head gasket, exhaust cover gasket and etc.?
Any suggestions will be appreciated. I'll eventually give you feedback as to how they came out. I can only work on this problem in spurts so please be patient for your feedback. Thanks for reading this long winded crying towel.
