75 9.9 rough idel and stalling help

[twindad01]

I just got a1975 9.9 with a 15 hp carb runs pretty good wide open and accelerating but stalls at idel and when you give it a lil throttle to keep it ideling its shacking and running rough. Some one mentioned a few years back about plate under fly wheel having movement. Mine does any one know the fix for it? Also what should plugs be gapped at

 

[dfrants]

the plugs should be gapped at .030

 

[flyingscott]

Did you adjust the carb should be around 1.5 turns out from lightly seated may need to rebuild the carb. Do a compression test if that turns out good I would usually say check the points but on that motor replace them with factory points and condensors do not buy aftermarket. If the carb has the cork float in it buy the factory carb kit has a new style float in it. I have no idea what shacking is.

 

[oldboat1]

throttle plate is under flywheel, and that moves by design. Rough running and shaking sounds like ignition issues, offhand. Need a compression test with a screw-in style gauge. You will also need an adjustable spark tester. If compression is good, and you want to work on the motor, change out the impeller as the motor is new to you. A lot depends on how comfortable you are (or want to be) in working on it. Get a manual.

If you know the history of the motor, that can potentially help with decisions on what to do first. Maybe the recent owner replaced ignition coils, for example. Best to just figure on rebuilding the carburetor with an appropriate kit -- new float is good, but not absolutely necessary. You may need new ignition coils, with new points and condensers -- depends a little on what the history is. You may need the driver coil that is under the flywheel.

Post a model number for the motor.