700 lx motor mount???

[Jeffrey Brown]

For anyone with a 700 lx, when looking at the mount position of the motor on the transom, how high is the motor mounted? Mine is mounted through the middle bolt holes. wondering if it is too high.

 

[MrFishFinder]

my mount has 5 holes x 2 on each side , the bolt is in the third hole on each.

 

[92 Nitro 190dc Owner]

Height of the outboard is based on the relative position between the anti-cavitation plate and the bottom of the hull. Can you tell me what causes you to suspect the need to adjust the height of the outboard? Does it seem that the boat is too slow/sluggish, porpoising, prop not running fully in the water at high speed (prop blowout), etc?

 

[Jeffrey Brown]

Height of the outboard is based on the relative position between the anti-cavitation plate and the bottom of the hull. Can you tell me what causes you to suspect the need to adjust the height of the outboard? Does it seem that the boat is too slow/sluggish, porpoising, prop not running fully in the water at high speed (prop blowout), etc?

It porpoising horribly. When its trimmed down enough to minimize the porpoising it torque steers horrible to the right. When I trim up to eliminate the torque steer it starts porpoising again. seems no even balance. Had wondered if the hydrofoil on the motor was amplifying the problem, but its supposed to help stop it. Really has me confused...

 

[byron cooley]

I have a 640LX, same boat like 6" different.
No porpoises issues. Just leaving work, will see what hole bolts are in.
You could just have a crappy prop that can't keep the bow up, not enough lift.
What motor do you have?

 

[byron cooley]

Hydrofoil is just a bandaid for a poor setup

 

[92 Nitro 190dc Owner]

There are at least 3 things that affect porpoising... Weight distribution (too much weight at the bow or too much weight at the stern) , motor height, and how the motor is trimmed under power. Setting your motor height: Your cavitation plate should be approximately an inch below the hull. This measurement will vary depending on your particular boat setup, but it is a good starting point. When you are on plane, the cavitation plate should run almost even with the lake surface. If you raise your engine too high, the prop will "blow out". Too low and the boat is sluggish under power and doesn't maneuver like it should. 1) I assume you have 5 holes for height adjustment, since that seems to be most common. If not, how many holes? 2) What hole are you using? 3) Where is the cavitation plate in relation to the hull? Higher/lower/or even with the hull? 4) If higher or lower, how many inches?

Motor height is usually the culprit. Assuming weight is distributed evenly, my first guess is the motor is set too low. However, your answers may show another issue instead or could be a combination of issues.

 

[Jeffrey Brown]

I have a 640LX, same boat like 6" different.
No porpoises issues. Just leaving work, will see what hole bolts are in.
You could just have a crappy prop that can't keep the bow up, not enough lift.
What motor do you have?

I changed my prop 3 years ago. The new one has less speed but pull stronger from a dead stop.

 

[Jeffrey Brown]

There are at least 3 things that affect porpoising... Weight distribution (too much weight at the bow or too much weight at the stern) , motor height, and how the motor is trimmed under power. Setting your motor height: Your cavitation plate should be approximately an inch below the hull. This measurement will vary depending on your particular boat setup, but it is a good starting point. When you are on plane, the cavitation plate should run almost even with the lake surface. If you raise your engine too high, the prop will "blow out". Too low and the boat is sluggish under power and doesn't maneuver like it should. 1) I assume you have 5 holes for height adjustment, since that seems to be most common. If not, how many holes? 2) What hole are you using? 3) Where is the cavitation plate in relation to the hull? Higher/lower/or even with the hull? 4) If higher or lower, how many inches?

Motor height is usually the culprit. Assuming weight is distributed evenly, my first guess is the motor is set too low. However, your answers may show another issue instead or could be a combination of issues.

Ill check next time i see it, its at the lake storage place. Im thinking its in the 3 hole down on the mount.

 

[Jeffrey Brown]

There are at least 3 things that affect porpoising... Weight distribution (too much weight at the bow or too much weight at the stern) , motor height, and how the motor is trimmed under power. Setting your motor height: Your cavitation plate should be approximately an inch below the hull. This measurement will vary depending on your particular boat setup, but it is a good starting point. When you are on plane, the cavitation plate should run almost even with the lake surface. If you raise your engine too high, the prop will "blow out". Too low and the boat is sluggish under power and doesn't maneuver like it should. 1) I assume you have 5 holes for height adjustment, since that seems to be most common. If not, how many holes? 2) What hole are you using? 3) Where is the cavitation plate in relation to the hull? Higher/lower/or even with the hull? 4) If higher or lower, how many inches?

Motor height is usually the culprit. Assuming weight is distributed evenly, my first guess is the motor is set too low. However, your answers may show another issue instead or could be a combination of issues.

I checked, I originally had a 12.5" x 23 pitch prop from the factory. It was damaged so I replaced it with a Black Max 13" x 19 pitch.

 

[byron cooley]

What motor

 

[Jeffrey Brown]

What motor

Im sorry, its the 90HP force

 

[92 Nitro 190dc Owner]

I checked, I originally had a 12.5" x 23 pitch prop from the factory. It was damaged so I replaced it with a Black Max 13" x 19 pitch.

First, I need to know cavitation plate measurement in relation to boat hull. We need to eliminate the porpoising issue before we move on to the correct prop pitch. Once the motor height is set properly with no more porpoising, then we need to know a few things about the motor to discuss the correct prop. Ideally, you'll want to select a prop pitch that allows you to run WOT within the RPM range of the outboard. To determine that, what year is the Force 90HP? That will help to determine the RPM range. The next step is to run your boat at WOT and read your tachometer. If the RPMs are too high, you'll need a prop with a higher pitch. If the RPMs are too low, you'll need a prop with lower pitch.

 

[Jeffrey Brown]

I had the motor dropped one notch down on the transom at tracker marine. Seemed before the plate was above the bottom line of the hull.
I have a 1998 Force 90Hp on it. I need to work on my gauges first, the rpm gauge is all over the place. One minute I am in a stretch of water doing 30mph at 4000 rpm, then 10 seconds later in same water conditions its 30mps at 5100 rpm. I can tap the gauge screen and it bounces around, so not real sure what the accurate rpm is.

Planning on installing a new fuse box and all new wiring to eliminate gauge errors.

 

[92 Nitro 190dc Owner]

OK. Let me know when you are able to answer the questions about cavitation plate vs. hull measurement before I can help you further. Regarding your outboard, the RPM range is 5000 - 5500.

 

[Jeffrey Brown]

Will get that measurement next time I'm at the lake, hopefully sunday.

Thanks for the help.

 

[Jeffrey Brown]

OK. Let me know when you are able to answer the questions about cavitation plate vs. hull measurement before I can help you further. Regarding your outboard, the RPM range is 5000 - 5500.

Hello,

Had the boat home this weekend, the cavitation plate is level with the bottom of the boat.

 

[92 Nitro 190dc Owner]

To start, I'd recommend raising the outboard one hole. Your anti-cavitation plate should then ride about 1" above the bottom of the hull. Take the boat out and see if that reduces the tendency to porpoise. It may not eliminate porpoising, but should reduce it. If there is a positive effect, then we're on the right track. If not, I'll want to discuss how you trim the outboard from the hole shot to the boat on plane.