merc. 40 4hp GNAT

[ready4itall]

New here, and new to boats. I received a Mercury 40 4hp. GNAT from a relative and its in need of some tender loving care.
So far it needs:
2 new spark plugs
One new Clamp Screw
One boot assembly for the shutoff switch on the handle

Here are some questions I think you guys can help me with. Thanks in advance!

1) the closest marine store is an hour away and ive looked on napa auto parts and found some spark plugs labeled br6hs-10. the motor however uses br6hs. What is the difference? if there is not a difference ill go to napa and get the br6hs-10 and save me the drive+gas. If there is a difference, then ill make the trip.

2) how can I remove the clamp screw? the one that is on my motor is not spinning, so likely stripped, and there is no thumb to turn the screw as it seems to have been broken off.

3) from the looks of it and on youtube of other GNAT motors, the boot assembly (#1 on diagram) on the handle for the shutoff switch is just a button I presume. So would I need it? cant I just press the part where the boot connects too and the motor would still shutoff (#7 on diagram)?

Here is a diagram of the handle.
(http://www.*****************/parts/me...andle-assembly)

 

[ready4itall]

Update:

I added a new carburetor, changed out fuel lines, got new spark plugs.
I'm getting spark on both plugs and fuel is making its way into the carburetor.

However the motor isn't starting still. It turns over though. What to do next?

 

[MTboatguy]

What is the serial number on the motor? you link is not readable as Iboats won't allow competitor websites be posted.

 

[ready4itall]

What is the serial number on the motor? you link is not readable as Iboats won't allow competitor websites be posted.

9121089

 

[MTboatguy]

9121089

Well it looks like we have a 1976, so I can do some looking now.

 

[ready4itall]

Well it looks like we have a 1976, so I can do some looking now.

Thanks!

 

[MTboatguy]

As far as your thumb screw, if it is stripped out, you are probably going to need to replace that part of the bracket the part number on those two are as follows:

Bracket: 1478-5553A
Screw : 10-70183A 1

The bracket is listed as no longer available, you will probably be able to find one on ebay.

As far as the kill button, you should have something hooked up

Here is what ebay has listed for that motor right now:


http://www.ebay.com/sch/i.html?_fro...+hp+gnat.TRS0&_nkw=Mercury+4+hp+gnat&_sacat=0

 

[ready4itall]

As far as your thumb screw, if it is stripped out, you are probably going to need to replace that part of the bracket the part number on those two are as follows:

Bracket: 1478-5553A
Screw : 10-70183A 1

The bracket is listed as no longer available, you will probably be able to find one on ebay.

As far as the kill button, you should have something hooked up

Here is what ebay has listed for that motor right now:


http://www.ebay.com/sch/i.html?_fro...+hp+gnat.TRS0&_nkw=Mercury+4+hp+gnat&_sacat=0

Yeah I got the thumb screw custom made by a machine shop already, so that's taken cared of, just gotta go get it at the machine shop.

I believe the kill button is just a wire under the button to connect the circuit to shut off. I can see what I'll do about that.

Any ideas on how to get it to start up?

 

[MTboatguy]

Well if it has spark, fuel and air, it should run, do you have the ability to check the compression on this motor?

 

[ready4itall]

Well if it has spark, fuel and air, it should run, do you have the ability to check the compression on this motor?

Oh man how can I forget compression test. I'll be right on it. What numbers should I expect?

And what if they are bad? Does that mean the motor is done for?

 

[MTboatguy]

Oh man how can I forget compression test. I'll be right on it. What numbers should I expect?

And what if they are bad? Does that mean the motor is done for?

Mainly what you are looking for is even number between the cylinders and of course you don't want some thing down in the 20's or 30's, needs to but up around a hundred or more, but it is kinda by the engine. If they are bad, the motor is not shot, but it will need to be re-built.

 

[ready4itall]

Got 86 and 83 on the cylinder 1 and 2.

Got the motor to start with the help of 4 friends. Started on the 14th pull. Took too long in my opinion.
So now the problem is 2 things:

1) takes too many pulls to start up, has to be continuous strong pulls too

2) doesn't idle well, must have throttle open to some degree for it to not die out. Sucks idling at high rpms. Tried adjusting knobs with same outcome.

 

[MTboatguy]

You said you put a new carb on it, was it new, rebuilt or just off another motor?

 

[ready4itall]

You said you put a new carb on it, was it new, rebuilt or just off another motor?

New

 

[MTboatguy]

Sounds like the low idle system is not adjusted correctly. I have not worked on that particular carb, so perhaps someone who is familiar with that particular carb will chime in.

 

[ready4itall]

It's fine, I think adjusting the carb is pretty straight forward.
Now it's a matter of getting it to start in 2-5 pulls.

I tried starting it this morning to adjust the carb. But the only way I can get it to start is to loosen the flywheel nut. However now the flywheel is not strapped down tight enough and scares me.

Is there a way to get the flywheel to spin more freely or faster?

 

[ready4itall]

I get it to start in 2 pulls with a loosened flywheel nut.

Ps.
I know it's not safe

 

[MTboatguy]

I have always found that outboard carbs are not quite so straight forward, and no it is not safe if you have to loosen the flywheel, I might suspect there is a spacer missing somewhere, you probably need to call and talk to a Mercury Tech to see what is going on.