Inconsistent Throttle

[jjt98]

I have a 2000 2096 VIP with a 5.0 Mercruiser. When I set the throttle level to one position say around 2-3K RPM to cruise around or pull tubers / skiers at a consistent speed most of the time that speed is maintained. But sometimes the engine will speed / rev up a little bit and I have to adjust the throttle level back a little to maintain the same speed.

I asked the local boat mechanic about this and he said that is common due to the cable that runs from the throttle level back to the carb. He said this cable can flex and cause the speed to not be consistent.

Is this true? Has anybody else experienced this?

 

[6meter]

Re: Inconsistent Throttle

Haven't experienced that yet. But I have experienced the boat slowing down or speeding up if you're right around the planning speed. This is where the trim button works well to control the speed and plane.

 

[security6]

Re: Inconsistent Throttle

Your mechanic's explanation seems a little goofy to me.

Short explanation:

Your boat is planing a little better, so the engine is able to speed up for the same amount of throttle. Other factors include more or less chop, how much resistance your skier/tuber is giving, and wind. When these factors change, your engine (and boat speed relative to water) will go up or down.

Long explanation:

You can control an engine one of two ways: throttle position or engine speed. You can control only one of them because your environment dictates the other.

Throttle position: On your boat you can control the throttle position. Your car does the same thing with the gas pedal. If you encounter less resistance (say going down a hill) then your car will speed up if you keep the throttle the same.

Engine speed: Engine speed can be controlled by using a "cruise control" system. Some boats (usually ski boats) have a similar system. On these systems, the engine speed is kept (roughly) constant, but the throttle position changes depending on whether you are going up or down a hill. A generator does the same thing (engine speed must be constant or the voltage of the powerhead will change).

 

[chaparall villain 2]

Re: Inconsistent Throttle

well something else to consider is you might have a plug wire or plug thats not firing all the time and when it kicks in the speed goes up dont know but its worth a check of plugs to see if any of them look wierd... good luck ... i thought mine was running wierd and i had 2 plugs fouled .. it ran ok but wow what a difference when i changed the plugs and wires

 

[jjt98]

Re: Inconsistent Throttle

I don't think it has anything to do with chop or pulling resistance. I have noticed this when the water is completely smooth and I'm not pulling anybody. The engine does have around 500 hours on it so maybe I just need to get a tune up and replace all the plugs and wires.

What does a shop normally do for a tune up on a 5.0 Mercruiser? What questions should I ask?

Thanks