# 2019 Tohatsu 50hp “misfire?”



## Smackdaddy53 (Dec 31, 2012)

Take it to get scanned and see what pops up on the diagnostics


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## Sublime (Oct 9, 2015)

Agree with Smack and it is always interesting to see all the data on the report. I was amazed at how many times I tried to start my motor in gear.


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## georgiadrifter (Jan 14, 2009)

I’ve scheduled a diagnostic scan but they are “extremely backed up.” In the meantime my Tohatsu mechanic tells me to change out the spark plugs. What he said, if accurate, makes sense. He said the greatest load on a spark plug is around 2000rpms….just above idle but before I get on plane. …which is where the misfire occurs. He said to let him know if that resolves the issue. Of course no one in the area stocks the Iridium spark plug I need. So I ordered from Amazon with a delivery date sometime next week.

Thanks for the advice….I’ll post my findings.


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## Smackdaddy53 (Dec 31, 2012)

Boats.net doesn’t have plugs for it?


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## georgiadrifter (Jan 14, 2009)

Smackdaddy53 said:


> Boats.net doesn’t have plugs for it?


I’ll check….thx.


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## LowReynolds# (Mar 23, 2021)

I did a bunch of looking around and the cheapest price I found for those NGK Iridium plugs for my Tohatsu was RockAuto.com.


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## southernbassangler (Apr 27, 2021)

georgiadrifter said:


> My 2019 50hp MFS 4-stroke is misfiring between 1400 and 1800 rpms. The engine never dies but it skips a beat so-to-speak…like maybe one cylinder is misfiring. Outside that range it runs like a sewing machine. I thought it might be contaminated fuel….but it idles perfectly and runs at 5000rpm great.
> 
> I run only non-ethanol…but do not have a fuel/water separator. I know…I know… it’s next on the list.
> 
> So….any thoughts on what might be the culprit? Virtual beers for folks with pertinent advice. To quote Captain Bob, “Ain’t boats fun?”



My 2018 50hp had an issue with bogging / misfiring randomly a year ago. Ended up being a faulty wiring harness. Basically one of the plugs was rattling loose from the cylinder and would cause it to only fire 2 of 3 cylinders. Certified shop ordered a new wiring harness in Feb of 2021 and it didn't come in until a day before Halloween. Thankfully Tohatsu warranty gave the shop a green light to silicone the old wiring harness in place until the new harness came in. Hopefully it's just the spark plug in your case.


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## firecat1981 (Nov 27, 2007)

Are you sure it's a misfire, and not just vibration. My 60hp does kinda the same. Smooth idle, runs great at speed, but in a slow speed zone she isn't happy. It's not missing, just a characteristic of the model I think on mine. At 1500-1900rpm she is a bit louder and vibrates more. My Yamaha did something similar.


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## NealXB2003 (Jun 8, 2020)

firecat1981 said:


> Are you sure it's a misfire, and not just vibration. My 60hp does kinda the same. Smooth idle, runs great at speed, but in a slow speed zone she isn't happy. It's not missing, just a characteristic of the model I think on mine. At 1500-1900rpm she is a bit louder and vibrates more. My Yamaha did something similar.


I have seen some motors act similar when trimmed down at a fast idle pushed the exhaust snout under water. Trimmed up to let it breathe, the issue went away.


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## firecat1981 (Nov 27, 2007)

Trimmed up it gets a little better, but it's still there. I think it's a characteristic of some of these smaller 2 or 3 cylinder lightweight motors. They don't have the weight to keep them calm when at a light jog.


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## georgiadrifter (Jan 14, 2009)

NealXB2003 said:


> I have seen some motors act similar when trimmed down at a fast idle pushed the exhaust snout under water. Trimmed up to let it breathe, the issue went away.


This is an interesting possibility. I do trim the motor down before applying throttle to get out of the hole….while idling away from the ramp.

I replaced the plugs with the factory spec Iridiums. It briefly “coughed” once on the first day of two days of fishing. I’m gonna run it one more time before calling it “fixed.”


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## redfish5 (Jun 28, 2011)

Someone else posted about a similar issue. Claims it was a bad ignition coil on 1 cylinder. Hopefully your spark plugs have fixed the issue.


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