Reply To: Thrust, hp, and weight comparisons

[Don]

OK, well you might be onto something with the packing on the low speed needle.  Many of these carburetors have a pesky threaded sleeve that the low speed needle threads into.  This sleeve can just rotate in the carburetor casting when you turn the needle if the packing is not tight enough.  Perhaps the threads are messed up as well.  So, even though you are turning the needle, the needle may not actually be moving in and out due to the spinning sleeve.  I wish I knew why the carburetor was designed this way, it can be very frustrating indeed.   It is not abnormal to have the low speed running quality affected by making adjustments to the high speed needle.  Usually the high speed needle is dialed in first, then the low speed needle is adjusted.

OK, it sounds like you have the linkage set up pretty well, seems like the carburetor is opening all the way.  Good for you discovering that the throttle cable trunnion may not be allowing the throttle linkage to advance fully!

You still feel that performance is off/low.  Have you replaced the propeller lately?  If so, perhaps you have the wrong “pitch” prop.  A propeller with too much “pitch” won’t be able to develop full power, it may lug at full power and not perform well due to low full throttle RPM.  Think of propeller pitch as the various gears in a manual shift car.  Think of how your car would react if you pushed the accelerator to the floor at about 20MPH in high gear.  The engine would probably stumble, bog, ping/knock, and would be very slow to respond until the car got up to speed.    Now think of the other extreme, let’s just say your prop pitch is too low.  Think of how your car would respond if you just left it in second gear while accelerating onto the highway.   The engine would just scream/over rev and the car wouldn’t go very fast.

There is also a trim rod adjustment on your engine on the bottom of the stern brackets.  The boat will plow through the water at high speeds if the trim pin is in too far, and not perform well.  Trimmed out too far, the boat may be hard to plane off because the bow pops up during acceleration, the boat may “porpoise” up and down at high speeds as well.

Sorry, don’t know any members in your area, hoping someone will chime in for you….  Don