Mid to high speed miss.

[Greenhumber]

Hi all. I've got a 1972 Johnson 50 hp. Model# 50ESL72C.
Last year it had a very intermittent miss at full throttle. Didnt think much of it.
This year its a constant miss from 1\2 to full throttle.
I have cleaned and rebuilt the carbs.
Installed a new fuel line.
New spark plugs.
I had to install a new ignition switch this year as well.
Top cylinder has 148 psi
Bottom has 145 psi
It wont idle properly either. Ill set the idle and itll be good until I back it down from running on plane and itll idle down so low it stalls.
For the motor to run smooth at an idle the top slow speed needle is turned out a half turn and the bottom is turned out one full turn. I know this isnt right either.
Also, if the motor sits for a few days it is really hard to start. But once it is started it has no problem starting.
I am lost as to what to check or do next.
Any tips would be appreciated.
Thanks!

 

[racerone]

Checked fuel pump diaphragm ?----Does spark jump a gap of 3/8" or more , when cranking it over with the sparkplugs in the cylinder head ?

 

[oldboat1]

If the motor idles smoothly with the needle settings you describe, I would use those settings. Does it also run smoothly at speed with those settings?

 

[oldboat1]

By the book, the high speed needle should be set first at or near WOT on the lake. Then the l.s. needle is set/reset.

 

[racerone]

Once again----There are no high speed mixture needles on a 1972 model 50 HP.---Johnson / Evinrude used FIXED high speed jets on most big outboards starting in about 1962 !!!!

 

[oldboat1]

^^Well, carb for the mod. number has a low speed needle. Perhaps he has different carbs, or a different model. Initial settings given are generic for older models so equipped.

Maybe you can make it all clear.... We see through a glass, darkly.

 

[racerone]

On the idle are both throttle plates CLOSED at idle ?-----They must be CLOSED.-----On the hard starting , is the choke properly adjusted ?---Check diaphragm on fuel pump.------In order for this motor to start properly you need the following.----A good starter motor , so take your starter apart for inspection.---Test ohms on armature / commutator.----Perhaps new brushes.----Have battery load tested.---Check battery cables and connections.

 

[Greenhumber]

Hi all,
So the carbs are both identical.
Both throttle plates are closed at idle. The motor runs smooth but after running at full throttle for a while and bringing it back to idle it slows down so much it stalls. Even though i had the idle adjusted high enough to stay smooth and running.
As for the hard starting, the choke operates properly. The starter is brand new and works properly. The battery is good as well and cranks the engine over fast. Ill have to check the fuel pump.
Somebody suggested that the power pack could be failing. Causing the hard starting and the miss from mid to full throttle.
Or even the coils could be going bad.
I will check the spark with a spark tester and the fuel pump. Any other suggestions are welcome.
Thank you all!

 

[racerone]

On a good ignition system the spark can jump a gap of up to 1/2 " ( 12 mm ) so do that test.-----Checked the flywheel key ?

 

[Greenhumber]

On a good ignition system the spark can jump a gap of up to 1/2 " ( 12 mm ) so do that test.-----Checked the flywheel key ?

No i havent checked flywheel key. Will do that as well.

 

[Greenhumber]

Hi all, so I just got back to checking the spark after not using the boat since Saturday. I have no spark. It takes a lot of turning the motor over to get a spark and one thats strong enough to fire the motor. Once it starts though it has no issues starting up. Can this issue also be causing the miss from mid to full throttle? What should i check?
Thanks

 

[racerone]

Charge battery.----Load test battery.----Take starter apart for cleaning.-----Ohm check on armature commutator to ground.-----Possibly new brushes.

 

[Greenhumber]

Charge battery.----Load test battery.----Take starter apart for cleaning.-----Ohm check on armature commutator to ground.-----Possibly new brushes.

The starter is brand new, I have charged the battery and load tested it. The starter spins the motor faster than the old starter did last year. I replaced the starter because the gear on it broke. It was the original starter.