# 70 HP motor seems underpowered. How do I troubleshoot.



## acolic (Oct 13, 2016)

Hi,

I finally put my 16' fishing boat back together and took it for a test drive last week. The boat is your basic 16' Alumacraft fishing boat with a 1977 7077S3 70HP 2 stroke motor and remote steering.

With 2 small kids up front and at full throttle I couldn't get the boat to go faster then 7 mph/6 knots. 

I think the weight of the boat is pretty low. While there is a front and rear casting platform the casting structure was built using square hollow aluminum tubing and the platform is 3/4 plywood.

Should the boat be able to go faster then 7mph?

If so what's the best way to troubleshoot this?

thanks

Alex


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## DaleH (Oct 13, 2016)

Prop spinning? Engine revving up OK? I get almost 40mph out of my 16' rig with a 60hp ...


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## acolic (Oct 13, 2016)

The prop seems to be spinning fine.

Motor doesn't seem to be revving up as much as I would have expected. I say that because the largest motor I have owned to date has been a 15hp motor.

I guess I will need to install a tachometer to verify if the motor is revving up correctly?


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## DaleH (Oct 13, 2016)

You can also use an in-line 'visible' spark jump tester thingie (forget the proper name, but usually available on loan from some auto parts store) to check the viability of the coil/plug wires too.

Get some plastic spark plug boot 'pullers' ... put OB to a fast idle - remove OB cowling - and remove plug wires one at a time. The RPMs should drop whenever a plug boot is pulled. If it doesn't, the coil/plus wire could be dead (see above) or the cylinder could have such low compression that it doesn't add to the RPMs, although it is firing. Sometimes swapping wires (BOTH ends!) from cylinder to cylinder can help you diagnose where the problem lies.

NOTE to make this easier, _BEFORE_ testing, w/ OB off of course, I apply dielectric grease liberally to the plug & boot.

*CAUTION *... moving parts - be careful! Do not use your hand or metal tool ... you WILL get shocked!


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## Crazyboat (Oct 13, 2016)

Does she rev freely when not under load? If so you could have many issues starting with gears/oil compression and so forth.


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## DaleH (Oct 13, 2016)

> Does she rev freely when not under load?


*WATCH that ...* as rev'ing too high in neutral can easily blow a bearing or wrist pin or other part ... 

I'd personally try to never go above ~1600 RPMs in neutral unless by accident or momentary (a second or two or less), like if/when starting ... but there's NO WAY I'd ever intentionally put her over ~2K or so RPMs in neutral! 

_But your mileage may vary ... _


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## Pappy (Oct 13, 2016)

How bout we start with propeller pitch? If it is the correct propeller then we can start troubleshooting the engine.


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## acolic (Oct 14, 2016)

Hi,

the propeller says Evinrude 18.75 x 13.

Any concerns with that?

Alex



Pappy said:


> How bout we start with propeller pitch? If it is the correct propeller then we can start troubleshooting the engine.


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## Crazyboat (Oct 14, 2016)

DaleH said:


> > Does she rev freely when not under load?
> 
> 
> *WATCH that ...* as rev'ing too high in neutral can easily blow a bearing or wrist pin or other part ...
> ...


I don't know if your wrong or right, I don't expect someone to run an engine in neutral for more then a second, just wanting to see if the RPM's go up or stay below an operating norm.

I've seen many a dirt bike throttle up with the clutch not engaged and nothing bad ever happened. How many times do I see some dummy trying to warm up a cold engine in winter by revving her while cold, not a good idea but done often and by many. With that it's the cold part not the revving that's the problem (I think).


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## Pappy (Oct 14, 2016)

Yes....the numbers you gave me are not correct. An 18.75" diameter will not physically fit that engine. Even the V8 engines did not have diameters like that. The first number will always be the diameter. Second should be the pitch. I realize that after almost 40 years the numbers may be a bit difficult to read but try again.


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## acolic (Oct 17, 2016)

I'm away for a for a few weeks. I'll see if the wife can find other numbers on the propeller.


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## acolic (Oct 21, 2016)

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Hi

I made a mistake it's 13.75 x 13. 

It's an Evinrude 3 bladed aluminum propeller. 

The. manual says the out of the box propeller should have been a 13.25 by 17. 

Is this much of a difference? 

Picture is below.


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## Pappy (Oct 21, 2016)

With that prop the engine should get the boat on plane. 
Thinking that the engine is not trimmed in or not running on all three cylinders at this point. Check and see if you can trim the engine in more if you think it is running on all three. If you think it may be the engine then you should start with a compression check and spark check.


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## Reelized (Oct 22, 2016)

First place I would start is with the throttle linkage.Make sure you have full throttle movement . I have owned a a lot of johnson outboards. One common problem is the timing linkage sticks. When you apply throttle the linkage opens the carbs but there is a secondary linkage that follows the throttle linkage when when moved. It has a rod that goes up under the flywheel to adjust the stator to advance the timing. If it does not advance you get no power and low rpm. 
With the engine have some one move the throttle forward and make sure the part I circled in yellow move forward also. That will show if your timing is advancing as it should.


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## acolic (Oct 22, 2016)

Hi
‎
Not sure if the test can be done with the engine off but if it can this is what happened. 

In neutral the lower cable is out about 1.5" and the top cable is entirely in. 
‎
If I push the throttle forward the lower cable starts moving in (rearward) and stops when the throttle is 1/2 forward. 

If I continue moving beyond the 1/2 point the upper cable starts moving out (towards the bow) and stops when the throttle is all the way forward. ‎
‎
There is no movement near the flywheel as you've pointed out. ‎
‎
Make sense?

Thanks


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## Reelized (Oct 22, 2016)

If the picture I posted looks like your linkage,the part I circled should move forward after about half throttle. Do the same test again and see if you can push the arm connected to the bar i circled forward.It should move freely.If that arm that connects under the flywheel is in the same position from idle to full throttle position you are not advancing the timing. Yes you can do this with the engine off.
I would get a service manual and it should explain the sequence of the throttle and timing.


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## Pappy (Oct 22, 2016)

You said the upper cable starts moving toward the bow? The system is a push to open and pull to close. The long black part of the cable attached to the vertical arm should be the only part moving and it should move rearward forcing the upper part of the arm forward. Is it a small black part moving toward the bow and does that part have what looks like a serrated thumb wheel on it? If so it is called a trunion and should be captured by the stainless piece the same as the lower cable trunion is. Could be when you mounted and hooked up the engine this was not done properly?


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## acolic (Oct 24, 2016)

Thanks for all the help maybe these pictures can help.


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## acolic (Oct 24, 2016)

Hi

I forgot forgot mention in the above linkage picture you can see two channels in the aluminum. Should the linkage be going through there?


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## Pappy (Oct 24, 2016)

Your control cables are not connected! See my last post.
That's what I thought based on your last post. Get them adjusted then connect them. Pull the cover off of the trunion anchor bracket (stainless cover over the top of the "U" shaped openings just below your cables). 
Starting with the shift cable. 
Find the "slop center" of the neutral position on the engine shift lever. Then, by pulling and pushing the cable end, find the "slop center" of the cable with the control box in neutral.
With the two centers found, adjust the trunion on the cable until it slips into the trunion anchor without moving the cable one way or the other.
Throttle cable.
The throttle cable should be adjusted to where it holds the throttle arm closed with just a little tension. Just enough that it returns to the fully closed position every time the throttle handle is returned to idle. 
On the shift side the cable is always adjusted to the engine, not the other way around....ever.


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## acolic (Oct 24, 2016)

Thanks for the info. 

I have a service manual but it's a text based. 

I'll try try to find a YouTube video to explain the process.


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## nccatfisher (Oct 24, 2016)

Once he gets those cables adjusted he will be looking for a prop, that small prop will make that 70 scream on a 16' boat. LOL


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## acolic (Oct 24, 2016)

If anyone has a similar motor and can take a picture of how the linkages are routed it would be appreciated.


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## Pappy (Oct 24, 2016)

Photo of it back on page 1.


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## acolic (Oct 31, 2016)

Hi,

cables put back they way they are supposed to.

Just hoping for a somewhat warm day this week to take it out for a test drive.

Thanks for the help,

Alex


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## Pappy (Nov 1, 2016)

You're very welcome.


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## acolic (Nov 6, 2016)

I managed to get the boat out this afternoon. The water was a bit choppy but I managed to get it up to 35 MPH.

The ride was wild I thought the boat was about to tear itself a part.

There are five holes to set the tilt of the motor. Initially the motor was in the 4th hole away from the stern. I could not seem to get the boat to plane. The bow would not seem to go down at speed.

I then tilted the motor to the 3rd middle spot and things seemed to be better. It still took a bit of time for the bow to drop.

I think I will have to play around with it perhaps there is another configuration that will drop the bow down faster.

Thanks


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## Pappy (Nov 7, 2016)

The closer in, toward the transom, the faster the boat will plane. 
Always a trade-off as you will lose bow lift and speed if you go too far but you will figure this out pretty quickly.


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