Reply To: ’67 80 HP, seems to starve out with throttle advance, plus rope start link

[Don]

Bill’s technique is tried and true, and easy enough to do on this engine, no funky air box/hardware to remove. That being said, safey is key here. You will need an assistant to drive the boat and you must be securely “perched” close enough to the engine so you can spray the carb throats easily. Just put some 50:1 mix in an oil squirt can and spray the throats one at a time at the problem throttle position. Like Bill says, one of three things will happen when each throat is sprayed:
RPM will decrease indicating the fuel system/carb is functioning OK
RPM will pick up indicating something is restricting the fuel supply in either the delivery or carb
RPM will not change indicating those cylinders aren’t firing for some reason
I think it is safe to say that option three isn’t occurring, but who knows. Keep in mind that you can get different results on both throats. RPM might pick up when spraying one throat, while it might decrease in the other throat. If this occurs, there is some sort of fuel restriction in the carb barrel that increases RPM when sprayed.

Needless to say, do not perform this operation if you don’t feel relatively safe doing it, perhaps the transom restricts easy access to the carb throats. Have a fire extinguisher ready, although there is no big fire risk here. Backfiring is extremely unlikely.
I am not that familiar with the sync process on the older V4s like yours, but Frank sure is. I’m pretty sure that the carb has a stop on the throttle shaft that prevents it from going past fully open position but it is worth a look…Perhaps the roll pin is out of the shaft, or the stop boss is broken off the carb body. The symptom you describe sounds like what happens on the newer engines when the sync is off and the carb butterflies can go past the full open position….But again, I’m pretty sure your carb has a stop on the throttle shaft that prevents going past the full open position.
The only other thing I can think of is that perhaps incoming air is restricted to the engine, or perhaps there is an exhaust leak under the cover. But, I’m pretty sure you have run it with the cover off with the same results….