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1981 25hp - Spark Plug issue

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stonec88

New member
Long story short. I’ve got a 25hp Johnson I’m trying to fix up. I tested compression 120 in each cylinder. ( I was bogging down at full throttle) I rebuilt carb , replaced fuel pump and lines. Etc etc . I also replaced spark plug (stripped the second cylinders threads on accident)

Current situation is the motor will start but die immediately (5seconds) . Would a spark plug that isn’t fully torqued “seated tight” cause this issue ?? Would it cause low fuel pressure? Trying to understand if I’m on the right track
 
I do not believe the sparkplug is the issue here.-----Not sure why you would ask about " low fuel pressure " when talking about a loose sparkplug.
 
racerone said:
I do not believe the sparkplug is the issue here.-----Not sure why you would ask about " low fuel pressure " when talking about a loose sparkplug.
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I’m asking if having a stripped spark plug that isn’t torqued could cause low compression. And since the mechanical fuel pump is “powered” by the compression the motor creates I’m trying to make sure my thought process is correct.
 
Your thouht process is admirable, but the resullt is incorrect. The fuel pump is "powered" by pressure pulses in the crankcase as the piston moves up and down. Those pulses would exist in the crankcase even if you totally left the spark plug out.

Not only that, it would continue to run on one cylinder if the plug was left out. You are telling us that it dies within 5 seconds.
 
Thanks for the reply and education. So if I have spark , compression , fuel getting to carb. Any ideas on things to check that aren’t carb related ? I feel I’ve got the carb good to go. (May revisit but need to eliminate anything else).

Unrelated (maybe) . My neutral switch is a little touchy . Won’t start unless I fiddle with the gear shifter in neutral . I almost have to push it a little forward to get it to start
 
Adjust the neutral switch on the motor.-----Perhaps that wee switch needs to be cleaned internally.----Easy to do.-----Agreed the neutral switch has nothing to do with bogging.----With a FULL carburetor the motor should run for more than 5 seconds.-----Find the high speed jet that screws horizontally into the carburetor float bowl.----Make sure it is clean.
 
As far as the spark plug situation, any auto parts store will sell a repair kit that includes inserts as well as the proper tap. They work well.
 
racerone said:
Adjust the neutral switch on the motor.-----Perhaps that wee switch needs to be cleaned internally.----Easy to do.-----Agreed the neutral switch has nothing to do with bogging.----With a FULL carburetor the motor should run for more than 5 seconds.-----Find the high speed jet that screws horizontally into the carburetor float bowl.----Make sure it is clean.
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I did clean the jet out . Also verified liquid could pass by spraying carb cleaner through the jet and out the post holes.
 
The high speed jet is about 5/8" long and screwed into the float bowl.----Did you find / clean that item.----Called an ---ORIFICE PLUG-----On the parts diagram.
 
Bad Al said:
Does the engine run at full throttle for any length of time... then dies out?
OR
Does the engine bog down and dies out immediately as throttle is applied?
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the first symptom was bog down after full throttle . Now that I’ve fixed some things it won’t run longer than 5 seconds
 
stonec88 said:
the first symptom was bog down after full throttle . Now that I’ve fixed some things it won’t run longer than 5 seconds
Click to expand...

Okay... Not the precise answer I was looking for but from it....................

I'll have to assume that the engine, when running, allows you time to get it in gear, and accepts full throttle normally, runs full throttle normally for 5 seconds... then dies out and stops running.

Is this about the gist of it? If so... have someone pump the fuel primer bulb constantly, steady to force the fuel mixture through the fuel pump and into the carburetor. Does this action have any effect, and if so, what?
 
Bad Al said:
Okay... Not the precise answer I was looking for but from it....................

I'll have to assume that the engine, when running, allows you time to get it in gear, and accepts full throttle normally, runs full throttle normally for 5 seconds... then dies out and stops running.

Is this about the gist of it? If so... have someone pump the fuel primer bulb constantly, steady to force the fuel mixture through the fuel pump and into the carburetor. Does this action have any effect, and if so, what?
Click to expand...

Forcing fuel mixture doesnt help it. Still doesnt want to start strongly. Like i said it will start (seems lean) then just dies within seconds.
 
Have you done a spark test? Should have a 7/16" white/blue spark.....In Joe's words: "a real snap". Perform the test with both plugs out and good cranking speed.
 
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