Is my 85hp producing enough power?

[TWPilot]

Last fall, I bought an 89 Glastron 16ft, with an 85hp Force and a 21p prop. After changing plugs and rebuilding the carbs, she would only get to 4k rpms which was good for 21mph. Seems slow, but it was the end of the season, and I was going t rebuild the transom, stringers and floor. Additionally, the 17gal tank was only good for about 3hrs, so I figured while I was at it I'd install a larger tank- went with a 32gal. It's only the wife and I, so I figured the extra 90lbs of fuel wouldn't really affect anything.

Fast-forward through the build, which I pulled about 200lbs of water-logged foam out from under the floor, and she will still only get to 4k RPMs and 21mph. I changed to a 17p prop, and it did bump it up to 4200rpm and 28mph.

I haven't had a chance to really tear into the motor, but last year she was making about 100psi (cold) compression. I'm in the middle of re-sealing my drive-way, but as soon as I'm done (Thursday), I'll pull the boat out and check everything with the motor warm. Looking for ideas from the group here.

Is this thing not making enough power? What speeds should I be seeing on a 16ft boat with this motor? What RPMs should this thing be getting to? There doesn't seem to be any hesitation, and she fires right up every time. Idles fine, even under load and gets on plane fairly quickly without the whale-tail (I removed it thinking that was dragging and slowing her down).

 

[Nordin]

Your speed seams pretty normal with that set up.
The RPM range of that engine is about 4500-5200 RPM.
The factory service manual calls for 4500-5000 RPM and it is rated 85Hp at 5000 RPM.
General every inch decrease in prop pitch will rise the RPM with about 200.
You should set up the engine soo it top out at WOT at 4500-5000 RPM then you get the most power out of the engine.
Try with a 15 in prop if you are able to get one.
General you rise the speed with a lager pitch but loose in the hole shot.
I would set it up to reach the 4500-5000 RPM range at WOT and if water skiing use a lower pitch prop to get a better hole shot.

 

[jerryjerry05]

I drove a new 1988 17ft Bayliner with an 85hp.
It ran almost 37mph.

You have trim @ tilt? NO?
Then where's the motor tilted as you drive.

Do the compression test and do a spark test on all 3 cyl.
Post the results.

The 16ft. 85hp should be able to turn that 17p prop up to 5500+

 

[TWPilot]

Jerry- will post the results as soon as I get done with my driveway and can pull the boat out of the garage.

 

[Nordin]

Sorry did not notice it was mph, thought it was knots.
Looks a bit low speed then and as you has removed water logged foam do as jerryjerry suggested.
Check for spark at all plugs and check the compression .Also check the trim of the engine.

My youngest son has a Fletcher Arrow Sport 15ft with a 1988 85Hp Force.
It is runing about 35-37 knots with a 19 pitch prop and about 28-30 knots with a 17 pitch depending of load
The 17 pitch gives much better hole shot.
I do not know the RPM, we have not checked it.

 

[TWPilot]

Update- still haven't been able to pull her out of the garage and warm her up, but compression cold at WOT is 105psi on all three cylinders. Can't check timing yet, because all others in the house are working.

 

[TWPilot]

Second update- had the wife help me last night. Checked spark from all three plugs, blue and bright. Timing was dead-on at 28 degrees, but I bumped her to 30. We'll see what that does today out on the water.

 

[jerryjerry05]

Your compression at 105 shows the readings were done wrong or done with a faulty/cheap gauge??

The good: all 3 are at 105

When I stopped using my 88/85hp the compression was the same as when it was new.145-150#

Knots vs MPH at the slow speeds we travel it doesn't make much difference
1 mph =1.2knot

 

[Nordin]

Jerryjerry are you sure your conversion mph to knots is right?
In my mind 1mph is 0,87 knot.
10mph = 8,69 knots

As he hit 28mph with a 17 pitch prop and 4200 RPM, that is a bit low.
4500 RPM WOT he would be running 35-40mph with regular load.
35-40mph would be 30,4-34,8 knots and that is a more expected speed with a 85Hp on a 16 ft boat.

 

[TWPilot]

Took her out on Lake Winnipesaukee yesterday to test the changes:

Bumping timing to 30 degrees made it worse. I counted the turns when I bumped her, so I turned her back while at the dock. Not accurate, but it was enough to restore what power I had previously. I'll re-set with a light today.

Syncing the carbs did nothing as well. She still only runs around 25-28MPH while at 4100-4200rpm.

The compression tester I used- bought it from Harbor Freight, so yes, it's a cheap gauge. However, all cylinders are reading the same, so I'm guessing compression is not the issue here. The only thing I can think of at this point- reeds? I've not pulled the carbs since last fall when I rebuilt/deep-cleaned them, but when I did, I didn't look at the reeds.

 

[jerryjerry05]

Nordin, Your right Knot/.868 to 1 MPH.
I've been wrong all these years.(hate being wrong )

How are you doing the timing? You doing the "static timing" described in the sticky's?

Your getting 4200 your sure tach is right?
Speedo right?

Asked before? Trim@ Tilt??

ANY?? fuel coming from the front of the carbs?

Does it run better with the cover off?

Is the lower end original? If the lowers from a 125 it could make the difference?
Is it blue or white?

Check the fuel pump diaphragm?

Is the shifter and linkage opening the butterfly's far enough. Do the link and sinc?

 

[TWPilot]

Jerry-

Timing was done static. Neutral switch by-passed, plugs removed and grounded, WOT, at cranking speed. Timing was at 28 degrees.

Not sure if the tach is right, but all things equal from before I made changes (same prop, same speed), it read the same rpms. Speedo is about 2mph low from GPS (using GPS speed, verified using opposite direction runs).

Trim and tilt are hydraulic/remote. No gauge, but I'll start from all-stop in the lowest position, and once on plane, I'll raise to just before cavitation. That gives me about 1 more MPH.

No fuel coming OUT of the carbs- only into the motor.

Haven't tried with the cover off.

Not sure if it's the original lower. Paint looks to be about the same fade- and it's black. You're talking about the lower (transmission/gear housing), right?

I'll tear the fuel pump apart today and let you know.

I did the link and sync per the sticky. The butterflies have about another 10 degrees until horizontal when at WOT, if the pointer at idle is set correctly.

*another note- odd thing, not sure if this is normal (first boat), but the throttle control seems to have a very small range of motion. From neutral to fwd/reverse- good indent, and it shifts into gear. However, there's a lot of travel (almost to full deflection) until the motor begins increasing rpm. It's a very small window at the end of travel where I can adjust motor speed.

 

[Redbarron%%]

I had a heck of a problem meeting the 9 degree idle, 28 degree WOT setting and the throttle plates close and getting the carb throttle plated to 100%.
I found that there are at least two cams and the difference I have found is the ball is in different distances from the pivot. Of course my sport jet is different as well, but after finally getting the timing bias correct and meeting specs I took the #1 cam off (I had a #2 that was previously installed and even less throw) and drilled a new hole in the #2 lower than the ball on the #1 to get the throw on the carbs to open 100%.
Is there a # 0 to go with the 2 and 3? These motors have been rebuilt so many times and the rebuilders supply the cam (?) and not necessarily for the exact application the block is going into.
As far as I know there is no part numbers stamped on them to be able to check for the correct one installed on the motor.

 

[jerryjerry05]

#1,
Put it in the water, remove the cover.
Get to a safe area.
Then try running wide open.
Any difference?No, go to next step

#2
Then as your running, try having someone advance the throttle, trying to open the butterflies.

The butterflies can actually go past horizontal when under full throttle.

Might be something as simple as a cable/ shifter adjustment??
Or the cable in the wrong hole on the shifter?

 

[TWPilot]

Jerry- will do...

Can the cables be swapped???

 

[chris.olson]

It's a very small window at the end of travel where I can adjust motor speed.

This seems to indicate a problem with the cables or linkages, or the control.

But.....

She still only runs around 25-28MPH while at 4100-4200rpm.

Realistically, you're not too far off the maximum that engine can do hung on that boat. With the boat on plane if you can run WOT and it makes 4,200 rpm, but you can back off the throttle and it still stays at 4,200 and nothing changes except amount of noise coming from the carbs, it's got a power problem on the top end. Maybe a bad reed petal on one cylinder? Is all it takes.

On the other hand, if you back off the throttle and it looses rpm immediately and slows down, then that's all she's got.

Do the math on it. I don't remember what the gear ratio is in the lower unit, I think it's about 2:1. That being the case, with a 17" prop you're going to top out around that 28 mph mark. Maybe 30 mph if you have the boat rigged perfectly and get a little less prop slip. Or sometimes you can rig it so it will ventilate the prop and get more rpm and horsepower with more slip and maybe gain a mph or two.

Best is like Jerry said - take somebody for a ride that is experienced with tuning those engines, and give 'er a run with the cover off so he/she can look at the linkages and carbs under load to make sure everything is working right on the power head and control. It is possible you're doing something like over-camming the carbs and sending them over-center where you will never get full power with the control at WOT. And I've seen that situation more than once. And if you got a bad reed that acts up at full power, so one cylinder is low on output, your mechanic will also be able to tell which cylinder it is by the noise coming from the carbs.

 

[jerryjerry05]

"Can the cables be swapped??"​

They're the same cable but I doubt they need replacement.
Try the ride and the tests I suggested.

If it's set up right and the motors not sick then 53-5500 rpms is what you should shoot for.

 

[TWPilot]

"Can the cables be swapped??"​

They're the same cable but I doubt they need replacement.
Try the ride and the tests I suggested.

If it's set up right and the motors not sick then 53-5500 rpms is what you should shoot for.

I meant was- can they be swapped inside the motor? i.e.- throttle for shift. Perhaps I got them messed up? I doubt it, because the one that moved first when deflecting the throttle control, I assumed was the shift... I know, dumb question- but I'm new to boats and outboards.

 

[The Force power]

I meant was- can they be swapped inside the motor? i.e.- throttle for shift. Perhaps I got them messed up? I doubt it, because the one that moved first when deflecting the throttle control, I assumed was the shift... I know, dumb question- but I'm new to boats and outboards.

Yes you can mix it up, when in doubt; set control to warm-up/high idle and see if only the linkage to the carbs. move

 

[jerryjerry05]

You had them right.
Pretty hard to mix them up.
The connectors are different lengths and they won't fit if crossed.