I'm assuming this is the same problem from your previous post, so to repeat;
"Did the
engine sit up for a long time in it's recent life?
If you're sure that there are no vacuum
leaks in the suction side of the fuel system (fuel wouldn't be obviously leaking except possibly when the
engine is off), then the problem sounds more like an injection
pump or governor issue.
For the injection
pump; either internal sealing issues or sticking p&b(s), on the governor/governor linkage; a missing, broken or stretched spring or corroded governor bearings. Either of these conditions would be best diagnosed by an experienced on-site
mechanic.
As an aside to the previously mentioned 'specified' idle speed, I still think 700-800
rpm is the appropriate idle for a small engine, and know that shifting at 1200 is detrimental for the
gearbox, so an easy workaround would be to set the idle at the lower speed, shift at that speed and then immediately run up to the appropriate speed to avoid chatter. And then of course remember not to run the engine in
gear at less than the 1000-1200 speced by Universal..."
The inconsistency described thusly, from your previous post,
'The new fuel injectors are giving me a little problem. The
motor now has a really rough idle. I suspect that the idle speed is low, but it kind of burps along and every so often will rev up 50 or so RPMs and then cool down again. I haven't been able to get it to run consistently clean without burps of white
exhaust.'
seems to describe erratic fueling, which could be caused by internal failure of a rubber fuel line as described above, but if the problem predates the changing of the fuel lines, probably not.
Another thing that hasn't been mentioned (though it wouldn't explain white smoke, which is usually indicative of over-fueling [if
compression is good]), is a blocked
fuel tank pickup or a blocked tank vent.
The blocked vent fix is easy and self explanatory.
Not so easy for the blocked fuel pickup. For some unfathomable reason,
fuel tank manufacturers often install a fuel
screen on the lower end of the fuel pickup. This usually winds up getting clogged, restricting flow. To solve this problem the tube has to be taken out, which can be difficult (or impossible) in the (usually) confined spaces in a
small boat, and the
screen cleaned, or better yet, removed. A shot of compressed air will probably blow the clog off the screen as a test to see if this is your problem before trying to remove the tube, but the problem will eventually return as the sludge
washing around in the tank gradually re-collects on the screen.
The previous suggestions are all good, a simple test is to disconnect the throttle cable and stop cable and see what max
rpm is, out of gear, with the throttle lever operated by hand at the engine...