2005G3 w/ 02 174 Vmax

Just got the boat and had a cchance to really let the ponies run. Have a couple questions
1) 25 ft tritoon what prop should be on boat?
2)Tach "jumps", and its not cavitation causing it.
3)Tach seems to read high
4)what should rpm be at idle.
5)where is pitot tube for speedometer- it seems erratic also.

Thanks in advance- i'm brand new here!

Re: 2005G3 w/ 02 174 Vmax

1) Dont know since you've given us nothing to work with. (Like what prop -diameter and pitch is on it now. What rpm are you "observing" with what you consider an average load. Seems to read high??? Hi High. Tach jumps???? Under what conditions?? Loose connections perhaps. Reading high may be because the calibration dial is set wrong. Note the current setting, then turn it back and forth several times and reset to original setting. Pitot tube is built into the lower unit of the motor. Follow the tube. Idle rpm should be indicated on the engine info tag under the cowl. Probably in the 650 - 700 rpm range.

The technical answer to your question about the prop goes like this: The best prop is one that allows the engine to operated at or very near the upper end of the engine manufacturers wide open throttle rpm band with what YOU consider an average load. That is why we need the information asked for above. There is no such thing as a standard prop. In fact engines are shipped without one since the manufacturer has no idea what type of boat the engine is being installed on. A work barge, pontoon, go fast boat, cruiser, all take a very different prop.

Re: 2005G3 w/ 02 174 Vmax

you could look up a setup like yours on this web site and see what prop they used
http://www.yamahaoutboards.com/owner-resources/performance-bulletins

Re: 2005G3 w/ 02 174 Vmax

The boat is a 25 foot tritoon made by G3. Average load would be the boat with a cooler, towels, & 8 passengers. G3 is a Yamaha company so I'd think they would know how to prop it. The tach seemed to read high with boat less than wide open, the tach wwould jump up to 7K rpm. Also, when running across the water, at approx 6,000 RPM, I observed the tach "jumping" with no change in engine RPm. It even jumped up and pegged high a time or two. The one thing I do know it was not cavitation.

Thanks for info on pitot- was able to find it and discover tube had small split causing speed to work but not accurately.

I have owned multiple out bds (both OMC & Merc) but this is my first Yamaha. I have never owned a tritoon either. Not sure if its the difference in boat or motor but this thing is like a rocket from dead stop! I cannot believe how quick it raps-out. This is why the tach is important to make sure we stay within operating specs. It could be that we had such a small load yesterday (3 people, no cooler or supplies) was why it seemed to be too easy to over range the RPM's. I've owned ski boats, 2 pontoons, and 2 deck boats. This tritoon feels different than any of the others. Really expected it to feel same as a pontoon only faster. I failed to mention it has 3" lifting stakes also.

My idle is at least 1300 RPM so i will need to figure out how to adjust that. Motor is 02 but very low hours (<100, original owner estimated in the 50 yr range).

Thanks for all the advice/replies!

Re: 2005G3 w/ 02 174 Vmax

Sorry for the typo's in my posts, doing this on a tablet computer using my "fat fingers"! The outboard is a Yamaha 175HP Max, not 174.

Re: 2005G3 w/ 02 174 Vmax

You should not have to throttle back to keep it withing RPM range.
You need to have the tach checked out and fixed, find out what prop you have on the motor, and see if it is different to what that site I gave you was running.

Maybe it is under propped or tach is just off