Running on One Cylinder

[engrkenr]

[FONT=&quot]After wasting countless hours focusing on fuel issues and replacing/rebuilding everything in the fuel system in my 1968 Mdl 60 6 hp 2 stroke/2 cyl Merc to fix a chronic lack of power at WOT, all of which failed, thanks to Racerone, I think I am finally pointed in the right direction. However, I still don?t know exactly what is wrong. [/FONT]
[FONT=&quot]I have spark at the plugs and to the plugs but, I?m not sure how robust the spark is in the upper plug; I have compression in both cylinders. [/FONT]
[FONT=&quot]I ran it at about 1K rpm in my tank and pulled the top plug wire, nothing happened. I reinstalled top plug wire and pulled the lower wire, it stalled instantly. I repeated process, same result. Then, I switched the spark plugs. I repeated the process and got the same results which means that it appears to be running only on the lower cylinder just as Racerone suggested. This would indicate that the root cause could be the top plug wire, the top cylinder coil, or its condenser. [/FONT]
[FONT=&quot]On the other hand, could a malfunctioning reed valve produce this same effect? In other words, could a defective reed valve prevent the air fuel mixture reaching the upper cylinder but work properly for the lower? [/FONT]

 

[racerone]

You need to answer this question.-----Does spark jump a gap of 1/4" or more with a snap you can hear, yes or no ?-----And yes a broken reed valve to the top crankcase can prevent the top cylinder from running !!!------The bottom crankcase is totally seperate from the top with it's own set of reeds.

 

[tommarvin]

Don't over think this, does spark jump 1/4 "inch or more, like racerone asked you?
If not replace the top plug wire, coil,condenser and anything else im forgetting.
If that doesnt fix the problem its very easy to check the reed valves.

 

[engrkenr]

In answer to Racerone and tommarvin's expert input above, ​

​we appear to be very close to the root cause of my lack of power at WOT under load. I have finally been able to positively test the robustness of the spark in the upper cylinder. There is a very weak light blue spark with the upper plug which does not bridge the 1/4 inch gap in contrast to a very bright blue spark with the lower plug which does. The good news is that it would point to a bad plug wire, a weak coil, a weak condenser, or points out of adjustment and not a malfunctioning reed valve. My only regret is having squandered all this time and effort on the fuel system which was apparently fine all along. If there are some specific test protocols for these individual components to avoid unnecessary replacement you can suggest, that would be most appreciated.

 

[racerone]

Not sure what tools are in your workshop.-----I use a MERC-O-TRONIC magneto analyzer.------A unit that is not from Mercury factory.-----And perhaps the points for the top cylinder need cleaning.----A no money fix to try first !!!

 

[engrkenr]

The Merc manual talks about pulling out and tying off the starter rope but, that may only apply if you were going to actually change the rope so as to keep the spring in tension. For just removing the rope starter assembly to get to the flywheel and points, is tying off the rope necessary?

 

[RCO]

You can just unbolt the recoil assembly, no need to do anything with the rope.

 

[Texas Prowler]

I vote for points being out of adjustment/ in need of cleaning. Don't rule that out...