# F70 just dies like it’s being keyed off



## Eirus (Dec 15, 2021)

I had a similar issue. I found corroded power and ground wires to the engine, replaced them completely and then replaced the fuel line and it ran perfectly. But my 115 was not shutting off suddenly, but rather depowering and going into limp mode. Yours is shutting off suddenly and that is quite different, but have you inspected those power wires for corrosion, and inspected the terminal bus connections for corrosion as well? Its worth replacing them and replacing the fuel line if you suspect anything.


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## BrownDog (Jun 22, 2019)

Check for loose or corroded connections and inspect the cut off system


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## bluechipfish (Jul 8, 2020)

Thanks for the tips so far I will certainly check the connections. Brown dog, what’s the cutoff system?


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## BrownDog (Jun 22, 2019)

keyswitch/lanyard


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## bluechipfish (Jul 8, 2020)

BrownDog said:


> keyswitch/lanyard


Roger that


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## scissorhands (Apr 8, 2012)

What kind of battery and how old?


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## Fishshoot (Oct 26, 2017)

Voltage spikes will cause that on a f70. If you have a lithium starting battery, that is your problem


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## TXJM (Aug 14, 2020)

I had this problem on my f70 recently except mine seemed to only happen at fairly high rpm’s. I found both main lugs at the battery were very corroded. I cleaned and have not seen the issue since.


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## Joe in Hudson (Feb 9, 2017)

2nd on the Key switch. I have had the same problem on a Ranger Phantom with an F60. New switch solved it, along with checking the power / ground leads.

Good luck, Joe in Hudson


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## bluechipfish (Jul 8, 2020)

scissorhands said:


> What kind of battery and how old?


The battery is an Odyssey extreme AGM, about 4 years old with very little use (29 engine hours in that time). One thing I'm thinking I can do is move the leads from the starting to one of the trolling motor batts which are the same battery, just a bit larger in size. I'll also try to get my hands on a new ignition system to switch that out and see if that's my issue, along with checking all the leads and wiring (it was rewired 4 years ago so, I'm doubting that's the issue, but you never know).

Thanks for the recommendations guys. Hoping I can figure this out without throwing a ton of parts at it, which should be doable since it seems electrical at this point.


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## afernandez (Aug 28, 2013)

This sounds like the same issue I have on occasion with my F70. Engine starts up fine and soon after you are on plane at higher RPM, out of nowhere the RPMs drop out from under you. I think it is vapor lock issue with the fuel system. You can immediately confirm this is the issue by reaching back and pumping your fuel ball as soon as it starts happening. You'll find that the fuel ball is pretty much empty and once you start pumping and refill the ball, the issue goes away and everything runs fine. I know of two well known fly fishing guides out of the everglades/keys that have had the same issue with their F70s. We came to the conclusion that this issue typically occurs when the engine is trimmed up for longer periods of time (while poling) causing some kind back flow somewhere in the fuel system within the engine. We have also found that pumping the ball a couple times after trimming the engine down to make sure there is fuel in there prevents this happening (if you can remember to do it). I would say that this issue pops up on me every 15-20 or so times i have the engine trimmed up then trim down to restart. I've had two different certified Yamaha techs look over my engine and confirm there is nothing wrong with it. It's just a weird tick on an otherwise awesome engine. Hope this helps.

EDIT: i just re-read your initial post and you said you confirmed the fuel ball was full. my bad. either way be aware of the issue I brought up above in case it happens to you.


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## Mav17T (Mar 9, 2020)

Yamaha doesn’t endorse Lithium Ion batteries at all.


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## permitchaser (Aug 26, 2013)

I had the issue with mine last year. I replace the ignition switch. Good to go


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