Re: What's Cruis Throttle?
It pretty much applys to most 2 stroke outboards. Take off the engine cowl and observe how the spark and throttle linkages move in relation to each other.
Starting at idle, as you advance the throttle the ignition timing advances while the carbs barely move off of the idle stop. Once the engine reaches full spark advance, about 3/4 of throttle lever travel, then the carbs start to open up. As mentioned earlier, pulling back on the throttle lever reverses the order. Carbs close 1st leaving the engine with full spark advance. Since boats need lots more power to go a little faster, to go a little slower takes a lot less power.
During the 70s, the carbs on a lot of outoards were redesigned to reduce the air pressure in the fuel bowl which resulted in leaner air/fuel ratio at part throttle. This was done by applying manifold vacumn to the float chamber. An air bleed regulated the amount of pressure reduction. At full throttle where manifold vaccumn is low, the air bleed allowed full atmospheric pressure in the carb. At high rpm with full spark advance and closed carbs, manifold vaccumn would be high, Applying this vaccumn to the float chamber would result in less than atmospheric pressure inside and a leaner mix.
Unfortunately, what worked well in the 70s with 70s gas does not always work with todays crappy gas. Now the engine is too lean under part throttle condintions and a meltdown often occures. Adding ethanol to the gas doesn't help matters either.
I've taken five adults around twice each and I'm at around a half a tank. Thanks for the tip.