Tach reading on 85hp Force

[geeco1]

I finally got my tach installed and I have some numbers.

Idle with muffs......1000 rpm
Idle on water ........750 rpm
WOT with 5 people..... 3900 rpm
WOT with 2 people..... 4200 rpm with trim adjusted to acheive max
RPM range from sticker 4500 - 5500 rpm (85 hp rated at 5000 rpm)

Prop .... Michigan #071037 from what I can find its a 13 x 19 pitch.

When pulling tubers, I tend to bog down in the turns. Not really able to "whip" them on the turns like I should.

What can I do to hit the sweet spot on the Tach (5000 rpm's ). I know that going down a step in pitch will buy me about 300 rpm, but that still falls short.

Is it possible that my throttle cable needs adjusting. I have to move the throttle almost 80 degrees forward to get throttle and 90 degrees is Max.

One other item is when I push the center button and move the throttle forward (when starting), I can not rev the engine.

HELP!!!!!

[jerryjerry05]

Put it in the water and remove the cover.Run it like you normally do.Then push the throttle all the way forward at the motor and see if it changes.
With the motor trimmed up in a turn you have to lower the drive to power through the turns.No difference? Then do a compression/spark test.
If all checks out then work on the prop/pitches.
WOT with 5 people is asking a lot from a 85hp.People and fuel and junk don't forget food,towels,dogs,beer. .Sounds like your way overloaded.
Do these test with a normal load.2 adults 1-2 small kids,small cooler and the tank almost full.Then post your results.
As far as the shifter/neutral you need to unhook it and start again.J

[geeco1]

I'll try to manually increase the throttle as indicated.

The 3900 rpm was with 2 adults and 3 kids, 12 gal fuel. No food, soda, etc. Boat is rated for 7 or 1050lbs. Granted, I was probably pushing 900 lbs. That's why I did the second RPM test with just myself, 1 kid, 6gals fuel (4200 rpm).

Compression test was done about 3 weeks ago.... 120's in all 3 cyl's.

When tubing, I generally have the motor trimmed down. It is not cavitating, it's just slows down in the turns. As you mentioned, it may be just too much drag with the tube and slowing it down. Once I complete the turn the boat accelerates back up to normal speed.

When you say I need to unhook the shifter then start again...explain please. I am not sure that I understand what you mean.

thanks.

[geeco1]

This past weekend, I was able to do a little more to the engine to get a little extra throttle out of it. It didn't look like the throttle linkage was getting full travel when I pushed the handle to WOT. I loosened and extended the throttle cable where it attaches to the throttle linkage, that gained me about 200 rpm.

I also had my son drive the boat while I sat in the back. When he was at WOT I reached back and was able to push the throttle open just a little bit more. That gained about another 200 which was putting me at 4400 rpm (1 adult, 2 teens, 2 kids, 3 gals fuel). Getting closer to that magical 5000 mark.

My question is, if I downsize props to a 17 inch, I know that it will get approx another 300 rpm, but will that gain me any speed or the ability to pull through turns better. I realize that 4700 rpm is better than 4400, but the smaller pitch prop is pushing less water.

Should I just be happy with RPM's in the lower end of the range?

[my1stboat1]

17 pitch prop... ill give you mine if youd like to try it out... Im in need to go to a 16 stainless..

[Frank Acampora]

Search for and read my post on synchronizing carbs and timing. See what that does for your RPM, then decide whether or not you need another prop. If you are flush with money, Stainless will give 200 RPM more than the equivalent aluminum prop.

[geeco1]

Thanks Frank, the link and sync was going to be my next step. Unfortunately, I have no money so I will have to stick with my alum prop. I might get to the link and sync this weekend, if so I'll try to post the results.