Bravo III trim adjustment

I have a single 350 MAG MPI with a Bravo III drive. I recently learned of the adjustment you can make by flipping the trim limit pin to allow a more aggressive angle to help with your boats whole shot (if it is in the aft position). Well since my pin was in fact in the aft position I did the flip and now she takes off very well. However, I also messed with the setting on both port and starboard trim switches (aka "puck") on the drive and now she is running 400 RPMs over where she should be (should be 4800 - 5000 and now running at 5600 at WOT if I allow) and also dropped approx 11 MPH at WOT. Prior to any adjustments she was running 38 MPH @ 4800 RPM and now I am pressed to hit 27 MPH @ 5000 RPM.

My question is does anyone know the proper procedure for adjusting the pucks? I know the port side is the sending unit and probably the cause of my headaches. Do I adjust the puck counterclockwise or clockwise or is it different per application?

Thanks!

Re: Bravo III trim adjustment

Howdy,


I did exactly the same thing with my 1987 Four Winns after I installed the Bravo III.

There is a Mercury TSB http://www.crownline.net/limiterblocks/om94_1r.pdf that also speaks to that issue from a safety standpoint.

I found that mine did not go in far enough and I had to change the position of the pin too. Made a huge difference being able to trim further (or all the way) in for hole shot.

The pucks are another matter. One is for trim limit so you cannot run the drive out too far (to prevent damage).......

the other one is for the largely useless gage...... drive position while running at planing speeds is more by feel than by gage indication.

You can (or should be able to) tell when the hull is "mushing" (drive IN too far at a particular speed....) or if your "Porpoising" (drive OUT too far at higher speeds.......)

If you trim WAY too far out, you should be able to tell by the way it sounds that it is just too far out!! The most efficient trim setting at high speed is the setting that allows for maximum speed and no porpoising. You usually won't trim out (up) any further than that for any other speed.




Just set the limit "puck" so the drive cannot be trimmed out too far when you let someone else drive your boat!!! (you shouldn't let anyone else drive it anyway!!!)

It won't affect where the drive goes if you have a "trailering" switch. That switch bypasses the trim limit switch.

Re: Bravo III trim adjustment

Prior to haul and flipping the trim limit pin = 38 MPH @ 4800 RPM consistent readings per GPS and Tach.

After haul and flipping trim limit pin = 27 MPH @ 5000 RPM and RPM range up to 5600 which is too much for this engine and leads to overheating. Readings from same GPS and Tach with no changes other than trim limit pin and messing with the trim sending "pucks."

What could be the cause????

Re: Bravo III trim adjustment

Trim Limit Dimension 21-3/4 in.


puck should be adjusted so when you raise drive it stops with dimension as measured from mounting rod to rod on each end of lift cylinder (dead, mounted end to live, moving end)

Re: Bravo III trim adjustment

jaxnjil said:

Trim Limit Dimension 21-3/4 in.


puck should be adjusted so when you raise drive it stops with dimension as measured from mounting rod to rod on each end of lift cylinder (dead, mounted end to live, moving end)

Click to expand...

Ok thanks. Will check the measurement later on. If that adjustment is off, could that be the reason for the 11 MPH drop in WOT?? I pay good attention to the way she sounds when running and I really don't believe I am over trimming allowing the prop to travel to high to the water.

Re: Bravo III trim adjustment

Just for info,


Do you have 2.00:1 or 2.20:1 drives?


What is your prop pitch? (20, 22, 24?)


Have you have the boat on a trailer, ran both drives all the way IN (DOWN) , visually compared both, and set the trim gage senders so they indicate same relative gage "position"?


Then, have you set the trim at PARALLEL (cav-plates exactly parallel to the bottom of the hull) and noted the gage(s) indication? (so you can repeat it with the boat in the water)


What is the max RPM for your engines. (4800 or 5000?)


You want to "prop" your engines so that you get MAX RPM at WOT ........BUT the props should NOT be cavitating (like it appears they may be doing now)

The best trim setting for planing might be no more than a few degrees "above" (or "out" from) exactly parallel.


If you have adjustable TABS, Adjust them all the way UP so they're not in the picture......If you have spring loaded tabs, back them all the way off(or remove them) so they don't influence trim adjustments......

Re: Bravo III trim adjustment

ihave a single screw MAG 350 MPI with Bravo III drive. Like I said everything was running great before hauling out and flipping the trim limit pin. I am now considering a malfunction in the trim tab causing drag or perhaps a loose prop causing it to slip with the higher RPMs it is now putting out. Not sure of the drive gearing. I know normal RPM for the engine is 4800 ~ 5000 and the rev imiter is supposed to set at 5150.

Re: Bravo III trim adjustment

ZekeLI said:

Ok thanks. Will check the measurement later on. If that adjustment is off, could that be the reason for the 11 MPH drop in WOT?? I pay good attention to the way she sounds when running and I really don't believe I am over trimming allowing the prop to travel to high to the water.

Click to expand...

yes it could effect your top speed. you said you messed with the pucks. it needs checked and set any way. as you have already said

you could have set the trim stop to the point where you dont have any trim up.

there is more to adjusting than i stated but to be honest i have set mine on the trailer and had good luck.

on the trailer run the drive all the way down. raise till it stops. (make sure you dont use or bump the trailer up button.

mesure the cylinder at this point and fine tune till you get the proper dimension.

run it up and down and measure, repeating a few times to confirm you have it set
the idea here is to let you trim up to a safe level without stressing your u-joints or running the drive to high and out of the support area where it can open to a point beyond which there isnt any support at bottom.

if this is all you worked on, i think you are on the right track to getting back to where you started.
your not out much and can then move on up the ladder looking for problems

Re: Bravo III trim adjustment

may be a loose coupler or cone clutch (i doute that) but b3's run metal to metal on the prop drives and props. they either turn or not
you said you hauled it out. maybe stirred up some crap or water in fuel and need new fuel filter????

Re: Bravo III trim adjustment

OK...Single (I don't know why I thought it was a twin!!)

If your TACH is indicating 5600, I would hook up a different tach. That's an MPI engine. Unless you have a serious electronic problem with the ECM, the REV limiter will limit RPM to whatever it is set to....and it's completely independent of what the TACH indicates...

It's pretty unlikely you have "loose" props. Everything in a Bravo III is "metal-metal" with the props. (no rubber hubs etc)

The inner prop is locked in place with it's own nut torqued to around 100 ft-lbs. The outer prop is also locked in place at around 60 ft-lbs.


If they were "loose" it wouldn't be pretty.....

Re: Bravo III trim adjustment

After putting her back in I installed a new fuel water seperator as I was on the same thought level u are. I also did an oil change and even installed a new impeller. I am going to go to the boat in a little to mess with the trim tabs. I spoke w Lenco and I do have a fault with my port side trim tab. I'm also going to try adjusting the port puck to see if I can get the right measurement as stated. This may be a bit tough in the water but I am sure its been done before.

Re: Bravo III trim adjustment

It sound to me like you are trying to use the trim gauge to trim with. Forget the gauge.
When you take off with your trim down you will be plowing, then as you trim up, your speed and your rpm will be increasing. At some point, the speed will stop increasing and the rpm will not increase. When you trim up just a little more your speed will start to drop and the rpm will increase. That is when you have trimmed just a little too much. when your speed has dropped way down and your rpms have gotten well above 5000, then you are just flat trimmed out WAY TOO MUCH. Trim it down. until you get max speed and max rpm. That is where you get max WOT rpm from.

Re: Bravo III trim adjustment

Don S said:

It sound to me like you are trying to use the trim gauge to trim with. Forget the gauge.
When you take off with your trim down you will be plowing, then as you trim up, your speed and your rpm will be increasing. At some point, the speed will stop increasing and the rpm will not increase. When you trim up just a little more your speed will start to drop and the rpm will increase. That is when you have trimmed just a little too much. when your speed has dropped way down and your rpms have gotten well above 5000, then you are just flat trimmed out WAY TOO MUCH. Trim it down. until you get max speed and max rpm. That is where you get max WOT rpm from.

Click to expand...

You know you would think I would have that down since I have done it literally hundreds of times with this boat but perhaps with the trim limit pin flipped and an increase in hole shot "grip" I am not trimming it correctly. I thought I was but I will try tomorrow. Usually what I do is put the drive all the way down and trim tabs set for bow down. Give it full throttle then once the bow is down and the speed doesn't increase I use the trim tabs to bring the bow up then bring the drive up just a little so she doesn't porpoise but reaches WOT speed and RPMs. Like I said that's the usual.

Re: Bravo III trim adjustment

I use the trim tabs to bring the bow up then bring the drive up just a little so she doesn't porpoise

Click to expand...

If it starts to porpoise, you need to trim the drive down just a bit, not up. That would make it worse.
You should be using the trim tabs primarily for port & starboard trim, not bow up and down.
Granted, they help getting a big boat up on plane, but don't overuse them.

Re: Bravo III trim adjustment

Ok thanks. You are right. Since having issues getting on plane in June I have been relying strictly on the trim tabs to get up on plane. Thanks!