# 16' Lowe w/ 50hp Force won't plane



## meatdog (Apr 30, 2015)

Hello,

I have a '89 16ft Lowe with a '98 50hp Force. I just installed the motor and took it out for a run today. The boat also serves as a bow fishing boat. It has a deck on it but it really doesn't weigh that much. I have a 19 hp longtail that I have been running and getting up on plane with a bigger load (i.e. generators, buddies, gear) and have recently added this motor so that I can get places quicker.

Today on the water I tried all the positions for the tilt. With the motor furthest away from the boat it cavitated. With the motor closest to the boat it just plowed through the water. The motor starts quickly and runs strong. 

My thoughts are 1. wrong prop size, 2. motor sits too low, 3. throttle linkage is not set to get motor to full rpms (unlikely)

Any tips or troubleshooting steps?


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## Skiffing (Apr 30, 2015)

1 - Cav plate submerged? Too low
2 - Engine compression close to spec?
3 - RPM close to spec at WOT?
4 - What size/pitch prop? 

With this info you'll determine the problem


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## meatdog (Apr 30, 2015)

Thanks Skiffing. I'll take the list and go check it out.


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## Skiffing (Apr 30, 2015)

Engine looks low. Remember as water passes the stern is rises up - Rule of thumb is ca plate at keel height gets you close.

That's where mine was - but at speed it was buried. W/ a 6" jack plate I have it raised 3" from original and still needs to come up a little.


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## meatdog (May 6, 2015)

Raised the motor up a couple inches and it ran better but not great. If I throttled slowly it would come up on plane for the most part and not ventilate. If I turned too sharp the engine would ventilate. The compression on each was 123psi. I have ordered a tach to check rpms. I'll pull my prop to check pitch when I have time.

I have included a pic of my motor running at WOT at its current position. Is it too high now?


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## Johnny (May 6, 2015)

Dog, :WELCOME: to Water World !!

*#1 issue* - just yesterday, a young man fell off his boat and the boat turned
around and ran over him, killing him.
EVERYONE - PLEASE BE CAREFUL when taking pictures of your motor while under way.




> My thoughts are 1. wrong prop size, 2. motor sits too low, 3. throttle linkage is not set to get motor to full rpms


any of those can contribute to poor performance of your rig . . . been there - done that - and got the T Shirt !!
I had a 35 Force on my 1648 MV bass boat that would only do 18 mph .... it was 3" too low. It died.
I got a 50 hp Force to replace it. While the 35 was off, I remade the transom from wood to all aluminum
Jack Plate style to efficiently carry the 50hp.
At *31*mph, I backed off the throttle as it was scaring me !!!! (speed according to the Humminbird FF w/GPS)
No tach, so I have no idea what the RPMs actually were - but, it was FLYING !!!
This was heading into the slight wind with maybe a 2" chop. Perfect for a fast ride on plane.
So I am thinking that your boat should have comparable results.
yeah, something is not right.


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## SumDumGuy (May 6, 2015)

All cylinders firing?


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## Skiffing (May 6, 2015)

The engine is still too low - and since you cavitate on turns tells me the pitch and/or engine tilt is off. A tach will tell you about the pitch.

Is that picture WOT? Holy cow! Something's really wrong.

Take a look at my thread bottom of this page:

https://www.tinboats.net/forum/viewtopic.php?f=21&t=36735&start=15

In those pictures the engine is still an inch or so low after raising it 3 inches.







Looking at your prop it looks middle of the road pitch-wise - maybe 13 - 14?

You sure the hub isn't spun?


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## meatdog (May 7, 2015)

SumDumGuy said:


> All cylinders firing?



I am assuming all cylinders are firing. How can you tell if both cylinders are firing? I'll replace spark plugs and see.

Thanks Skiff, I'll check the hub first and prop size when my Tach gets here. I see what you mean about where the cav plate should ride in the water. I didn't put it together 'til now but I used your thread a lot in refurbing my boat. Thanks for posting up pics and details.


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## vahunter (May 7, 2015)

meatdog said:


> SumDumGuy said:
> 
> 
> > All cylinders firing?
> ...


The best way is probably a spark tester (it will show you how good of a spark). As a quick check I use a timing light which clips on the plug wire and flashes each time that cylinder fires. When you change the plugs you should be able to tell if a plug isn't getting juice or other issue by how the plugs look. Not a bad idea to check compression either while you do plugs.


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## Johnny (May 7, 2015)

Seven Bucks at Harbor Freight or Amazon.com
$10-15 at Auto Stores.

This tester will tell if you have spark voltage from your coil to the spark plug.
But, so will a spark plug that is in the plug wire and the body held against the motor (while cranking over)
to check for spark. Or, a wet finger standing barefoot on wet concrete.
it will _NOT_ tell you if your plugs are fouled or the gap is out of specs. (that is a visual inspection).
On those older outboards, you must be EXTREMELY careful as not to strip the threads.
If the threads are already stripped, then, there are threads on here on how to use the
Thread Restore Tools.
good luck


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## meatdog (May 7, 2015)

It looks like my prop is 10.5 X 14. Now to wait on the dang mail to bring my tach. Thanks again for the help.

Thanks vahunter & barefoot. I'll go grab a spark tester here at lunch.


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## richg99 (May 7, 2015)

My normal first approach any time an engine isn't running properly (low power, hard to start etc) is to put new and properly gapped plugs in. Worked enough times and plugs are cheap. 

If it doesn't help, at least you are starting out with that portion covered. 

Oh yes, and I change to new gas/oil too.

Many will say that those two items are often not the problem. Yet, many times, they ARE the problem.

richg99


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## Skiffing (May 7, 2015)

^^^^

Just for comparison I'm using a 14 X 13 prop on a Merc 40hp 4s - 16 foot V - and it's either real close or dead on to where it needs to be. I'll know this weekend now that I have my tach calibrated.

It will be interesting to finally figure out what is causing your problem.


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## Skiffing (May 10, 2015)

Any update?

Real curious to know what's causing this.


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## meatdog (May 18, 2015)

Sorry for the delay, got bogged down with work. 

I bought a spark gap tester per barefoot_johnny. From what I could tell everything was working fine. 

I am going to get new plugs and fuel like richg99 suggested. 

I bought a jack plate and installed it today. I started with a 2" lift. My tach came in but I have not had a chance to install it. Hopefully I can get on the water tomorrow and post up some results.

I tried to check my hub, not sure if I did it right but it I will check it after I'm on the water tomorrow.

Skiff, what'd you find out about your tach/prop?


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## Skiffing (May 18, 2015)

My last run I had the engine a little too high - so with a little wind chop it wouldn't get above 5400 rpm without ventilating. it was doing 28 mph upstream.

Earlier on a downstream run when river was glass got up to 5800+ and 31 mph.

I lowered the engine an inch and will test again this weekend. 

My tentative conclusion is the 14' x 13p prop is the right one for this set up.

Good luck with yours.


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