Re: Johnsnon 25r70 speed issues
your motor is a 1970, the legs were longer back then do to the placement of the water pump. you could slip a 1x2 under the transom mount, that will bring it up 3/4 of an inch. which will improve performance. like the pic below.
it sounds like who ever did you carb rebuild did not remove the high speed jet, and clean it, or it has become clogged again. ( don't run it like that, lack of lubricant).
in this link you will see the necessary tools and steps to remove the high speed jet, and clean it.
http://forums.iboats.com/showthread.php?t=244013
you can adjust the low speed jet, with out the linkage to the knob, buy turning the stem, once adjusted it rarely needs attention.
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.
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.
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.
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.
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.
any question just ask. good luck.