TOPIC:

I have a 9.8 HP 2016 Tohatsu (4stroke) that was running fine at the end of last season.   I brought the boat in for Maintenance and an issue with the Yamaha in Oct, and it ended up taking until two weeks ago to get it back due to parts availability.   During the shakedown run yesterday the kicker started but was running really rough for about a minute and then died and now it will not start.     The engine and lower unit oils were changed while it was in for maintenance and I put in new spark plugs last weekend.    Since I didnt winterize the engine last year I thought maybe it was a gummed up carb so I took the carb apart and cleaned it and all the jets but it was almost spotless before I did anything to it.   Put it back together and still same thing, so I checked the spark plug gaps and made sure I was getting spark (which I am).   So I pulled the fuel filter and that is fine and pulled the fuel line from the carb and cranked the engine to be sure the  fuel pump was working.    I tried giving it some instant start and it still didn't fire up.    At this point I am leaning towards a weak spark but I am not sure how to verify proper amount of spark.   Other thing I can think of off the top of my head is somehow the carb got knocked out of adjustment so not getting proper air/fuel mixture.    Any help would be greatly appreciated.   

A; the power needed to jump a gap with a spark plug under compressed air fuel mixture vs  in open air is 3/8"  not just a .030 spark gap 
  this is often the reason weak spark is not properly diagnosed   
 B; old crappy fuel from a fuel line that been sitting for months can foul a spark plug causing a hard start or not start at all  
 thy new spark plugs and flushing some fresh gas into the carb by opening the carb drain and squeezing the primer bulb until you get a fresh gas smell from the fuel draining from carb often this is all it takes to bring em back from the dead  just some things to try 



 

Non-existant user wrote:

A; the power needed to jump a gap with a spark plug under compressed air fuel mixture vs  in open air is 3/8"  not just a .030 spark gap 
  this is often the reason weak spark is not properly diagnosed   
 B; old crappy fuel from a fuel line that been sitting for months can foul a spark plug causing a hard start or not start at all  
 thy new spark plugs and flushing some fresh gas into the carb by opening the carb drain and squeezing the primer bulb until you get a fresh gas smell from the fuel draining from carb often this is all it takes to bring em back from the dead  just some things to try 

Fuel should be good since I did drain the fuel while doing the tests on each of the fuel segments.   I am taking the fuel from my main tank that the Yamaha is running from so I think the fuel itself is fine and by now all the old fuel that was in the lines should be clear.    When you say the gap under compression should be 3/8; the owners manual calls for a .31 to .35 so I put it about .33 - should that be good or do you suggest a full .037 gap? 




 

Is your spark yellow or blue ??yellow is bad blue is good.  Good luck

Spark was blue

take it in
never set any spark plugs to a 3/8" gap
set the spark tester to 3/8 of a inch this takes about same amount of energy it takes to fire a plug under compreshion in the cylider
sory for the confushion just trying to help
some times we can do more harm than good

Non-existant user wrote:

take it in
never set any spark plugs to a 3/8" gap
set the spark tester to 3/8 of a inch this takes about same amount of energy it takes to fire a plug under compreshion in the cylider
sory for the confushion just trying to help
some times we can do more harm than good

No problem at all - I didn't change anything so no issues.
 

I would focus on what was worked on. I changed a plug at the beginning of one season and didn't torque it enough. The loss of compression = no fuel pumping (compression escaping from the plug threads itself) It ran for a few minutes but must have backed off enough to not start again. I remembered I was going to get a torque wrench and forgot. It cost $50 in fuel trolling with the big motor.
if your spark tester has blue spark you're good to that point. Maybe bad out of box spark plug or oil on it?  I don't like to recommend using starting fluid to help distiguish between lack of or bad fuel or lack of or bad spark issue becuase people over do the the starting fluid by applying more than 0,25 second mist and cause bad issues. 



 

@HondaCat I sent you a PM on this.

If you are running ethanol fuel the white plastic floats swell on the pivot pin.  At first they stick intermittent and after a while it will not float up enough to close the needle / seat.  It seems like every 3-4 seasons it’s time for a new float.  Easy fix.  Not much to go wrong on a carb fed kicker.  If you have spark you eliminated one possibility.  Plug gap on my Merc kicker is .035”.  Honestly plugs work fine on a kicker right out of the box.  Gapping takes no time so may as well set it.  My vote is stuck float due to ethanol swell.