25 HP 1976 Johnson dies after start

[andreipou]

Hello,

One of my 25R76E starts only with choke nub pulled (closed throttle).
It starts very strong but dies after 2-3 sec.
I put new plugs and spark is very good.
Fuel is pumping and carb bowl was full of gas.
I disassemble carb and soaked it for over night. Tomorrow I will blow it with compressor and try again.

But if this does not help, what else can it be?

FYI:
I just fixed one spark thread with HeliCoil insert following exactly all the instructions. It was diying the same way before that, so i do not think it was it.

Thanks.

 

[tashasdaddy]

Re: 25 HP 1976 Johnson dies after start

start with compression and spark test, it is a simple magneto motor. alcohol resistant fuel lines are necessary with ethanol in todays fuel.

great info here >>http://forums.iboats.com/showthread.php?t=299680

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

Compression is 104 and 105.
Spark tester with 7/16'' gap shows good spark.
Carburator cleanup helped: It does not die in 2-3 sec anymore. It runs with higher rpms for 5 sometime 10 min, but then sneezes and dies.
Also I can not adjust it to low rpm idle. It dies when I put throttle to SLOW.

What else can it be?

Thanks.

 

[bonz_d]

Re: 25 HP 1976 Johnson dies after start

Sounds very simular to a problem I was having.

1st check the fuel pump. Even though it is getting gas it may not be holding pressure as mine was. If that is OK then sense you had the carb apart take it off and check the float.

While I was trying to fix mine during one of the times I had the carb apart I inadvertantly reinstalled the float upside down and it acted they same way you desribe.

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

The float is installed correctly since there is a gap on one side of it to match the "bump" of the high-speed valve on the bottom of the bowl.
Also the float is parallel to the bowl edge as it says in the manual.

What is the right way to check fule pump? I disconnected hose from carb and see fules coming out when I crank.

Thanks.

 

[crxess]

Re: 25 HP 1976 Johnson dies after start

Soaking it may not have gotten everything out. Small hard particles can still be in the passages abd moving to block them.
Only way to know for sure is Kit the carb and don't skip anything. Remove soft plugs and clean with small wire or welders files(my choice). Also run files through the orifice plugs.

 

[bonz_d]

Re: 25 HP 1976 Johnson dies after start

If you still have the carb off you can put a pcs of hose on the carb and try and blow through it. With it in the normal position you should be able to blow air through it. With it upside down you should not be able to blow air. If you can't blow air in either position then something is wrong.

Fuel pump test same way. The feed side of the pump should pass air but you shouldn't be able to draw air on that side. Just the opposite for the carb side of the pump.

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

After I soaked I blew it with compressor air gun.
It was very strong.

I have 3 of this motors.
I took carburator from the one that runs fine and put it on the trouble one.
It did not help, so it is not a carb.

What else can it be?

 

[bonz_d]

Re: 25 HP 1976 Johnson dies after start

Next I would look at the fuel pump. Mine was worn out and would not close and seal properly. Yes it would pump gas the way it was but when tested as I described both sides would pass air in both directions and should only pass air in one direction.

As for the idle. Try turning the idle stop screw in some. The new replacement screws are plastic and I have already replaced 2 as the tips were braking off.

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

I ordered new parts for fuel pump so it will be the next step.

The low speed needle is new and metal so it should be good.

Thanks.

 

[bonz_d]

Re: 25 HP 1976 Johnson dies after start

How's it coming?

The idle stop screw and the low speed idle are not the same thing. The stop screw is located down on the side were the remote throttle cable attaches.

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

I wish I saw this post before this weekend because i was playng with motors all Sunday.
What is this "stop screw".
As you said, I thought you were talking about low speed needle.
What does it do? How to set it properly if it has to be done?
I do not remember any thing about it in the manual.

I need to figure this because two out of my three 25R76E have the same problem:

1. They have good compression
2. They have good spark
3. They have new fuel pump membrane
4. Washed and blown carburators

They start strong and run strong on HIGH speed level.
When I turn handle to SLOW speed they die.

As manual says, I turn low speed adjustment needle all way in and then open it one full turn.

With this settings as soon as I go to SLOW it starts "sneezing" (I think it is called "backfire") and eventually dies on "sneeze".

One of the reason for "sneezing" according to manual is lean mix.

Only if I open low speed needle 1 & 3/4 turn sneezing goes away (almost).
But it runs on high rpms this way.
And still as soon as I turn tiller handle to pass SLOW mark it still dies.

What else can I do?


Thanks.

 

[bonz_d]

Re: 25 HP 1976 Johnson dies after start

The idle screw is on the right side. Straight back from the tiller, look about in the middle of the cover and under the lower part of the cover.

You should see it move when you turn the throttle. Looks like a small gear with a large screw and a spring in it. Screwing it in will raise your idle speed.

 

[andreipou]

Re: 25 HP 1976 Johnson dies after start

Now I know what you are talking about.
I did not touch it because I assumed it is correct.

What is the right RPM for idle for this motor?