Johnson AD10 WOT issues.. 1956 7.5

[johnboy65]

I have a 1956 Johnson AD10 on my 14' tracker topper jon boat.. The motor starts perfectly, idles fine, shifts great, and is as pretty as a Dolly Parton in a red halter top..
I'm having a problem with my advancing of the throttle.. The carbs have been professionally rebuilt and its been converted to an external fuel pump with preformed hoses that aren't kinked.. The motor almost acts like a spun prop situation.. Low RPM's and it pushes fine..
As soon as I hit 3/8 throttle the transom vibrates and acts like the prop is cavatating in air pockets..if I advance even more it acts like the packing on a hub would if it was spun out.. Yes..I'm a newbie here.. Any help or suggestions would be appreciated.. Thanks in advance!

 

[Chinewalker]

Sounds like it's running rich. REAL rich. Have the carb knobs been set? If turning the high speed (lower knob) inwards (clockwise) makes it run a bit better (in gear, at throttle) you're headed in the right direction. Loosen the knob from the shaft as needed and set it to center (vertical) once the sweet spot has been found.

Only other thing that comes to mine is the lower driveshaft has a slip clutch in it. The spring within it can break, binding things up.

 

[johnboy65]

The motor was tank tested after the carb was rebuilt and I haven't messed with the low and high idle screws.. Only seems to do it under a load.. Are you referring to the pinion shaft and shock absorber assembly Admiral Chinewalker? ..

 

[oldboat1]

sounds like rich-running to me too, either a carb setting or possibly too much oil in the fuel mix.

 

[Chinewalker]

Yes, the shock absorber was what I was referring to. Typically, if they break, they bind up under load, which was why I put less stock in that one. Get the needles set and see how it goes from there...

 

[F_R]

I also suspect carburetor adjustment. Those knobs are there for a purpose, not to be feared. Go ahead and try it anyhow. As for the shock absorber, they seem to be failing a lot lately. I suspect it is from metal fatigue over the years. But when they fail, it normally is felt as a binding up like the brakes are on. And very difficult to pull the recoil starter.