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30 hp 1956 Johnson....Won't rev out past 2000ish rpm on the lake

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cjbrill715

Regular Contributor
My motor when on the water, won't rev out past maybe 2000 rpm at best. The Carb is rebuilt, the ignition system gone through (coils and condesors replaced, and points cleaned and set) New plug wires. The carb butterfly is full open and the base/timing plate is fully advanced. It acts kind of rough and "bucky" almost like it's fighting itself once it gets to that 2000ish rpm mark. The motor has 120 psi compression on both cylinders, the spark effortlessly jumps a 5/16" gap...The motor starts and idles great. If it's worth noting, the previous owner hit something at speed, and sheared the flywheel key, which I've since replaced. I'm thoroughly out of ideas, please help!
 
Have you adjusted the bottom ( high speed ) mixture needle while at full throttle out on the water , yes or no ?
 
racerone said:
Have you adjusted the bottom ( high speed ) mixture needle while at full throttle out on the water , yes or no ?
Click to expand...

Yes, it seems to run the best around 3/4 turn out....I pulled the side exhaust cover, and discovered that the separation plate that the water is supposed to flow behind didn't have a gasket between it and the block. It had 2 gaskets stacked between the plate and outer cover....Either it was a Monday at the Johnson factory, or the previous owner didn't know that one gasket was supposed to go on each side of the plate. It was getting water in the exhaust ports, especially the bottom one. I think this explains why the bottom plug was so clean, and if it's getting water in the bottom cylinder, it would explain why the engine acted like it was fighting itself when trying to throttle up. I think it was dropping that cylinder, when throttling up, and the live one up top was just dragging it. Fixing the spark issue as you prescribed did help it immensely( I changed the plug wires), and it idles down greatly now. I'm in the process of making new gaskets for it, Im thinking that the faster it tried to go, the more water was getting in there, and at a certain point, it could no longer ignite on that cylinder...Probably explains the unspent fuel I was seeing it the water when throttling down....We'll see I suppose
 
Last edited:
cjbrill715 said:
Yes, it seems to run the best around 3/4 turn out....I pulled the side exhaust cover, and discovered that the separation plate that the water is supposed to flow behind didn't have a gasket between it and the block. It had 2 gaskets stacked between the plate and outer cover....Either it was a Monday at the Johnson factory, or the previous owner didn't know that one gasket was supposed to go on each side of the plate. It was getting water in the exhaust ports, especially the bottom one. I think this explains why the bottom plug was so clean, and if it's getting water in the bottom cylinder, it would explain why the engine acted like it was fighting itself when trying to throttle up. I think it was dropping that cylinder, when throttling up, and the live one up top was just dragging it. Fixing the spark issue as you prescribed did help it immensely( I changed the plug wires), and it idles down greatly now. I'm in the process of making new gaskets for it, Im thinking that the faster it tried to go, the more water was getting in there, and at a certain point, it could no longer ignite on that cylinder...Probably explains the unspent fuel I was seeing it the water when throttling down....We'll see I suppose
Click to expand...

Got the gaskets on, fixed the leak, but I'm still having the same problem....Completely stumped
 
racerone said:
Reed valves checked ?------Run with a timing light and see if you have a loss of spark on one cylinder.
Click to expand...

Either the packing nut on the high speed needle was too tight, or it is slightly bent, I'll check it out some other time...It gave me a false seating, as I try to be gentle with them. I found out it was out further than I thought. I closed it down some more, and it revs out nicely now....Evidently it was getting too much gas. Thanks for your help!
 
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