Yamaha F70 Hard Start

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El Rollo
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Yamaha F70 Hard Start

Postby El Rollo » Mon Feb 25, 2019 11:19 am

I took out my 1988 15 Boston Whaler powered by a 2015 Yamaha F70 for the first time in a couple months. I had my friend drive the boat, as I launched him into the water. The motor would not start, and he was helped over to the dock by a fellow boater.

After parking the truck and trailer, I walked down the dock to find out the motor was turning over but would not fire.

I checked the fuel primer bulb and gave it a few pumps, and it felt full.

I checked the kill switch, and shifted the gear lever in and out of gear. Still nothing.

I shut off the power to the motor and turned it back on, and still no fire. The battery is newer, of good quality and fully charged.

I loosened the drain at the bottom of the Racor filter and dumped the fuel in the bowl. There was no contaminants that I could see. I re-filled the bowl with the primer bulb, and the motor would still not fire.

We pulled the boat out of the water and put it on the wash rack. I attached the ear-muff style flushing attachment to the outboard and connected the hose to the hose bib. With the water turned on, I turned the key and the motor fired right up. We let the motor run for 10 minutes, and then we shut it off. I turned the key and the motor fired right up again. So we let it run for an additional 5 minutes, before we launched again and went out fishing for the day. The motor ran flawlessly all day, the battery seemed to come right back up to full charge, and we never had a problem.

I'm just curious as to what may have caused the hard star and would appreciate people’s thoughts.

Just for more information about the engine. There are only 204 total hours on the engine. I have always kept up on the service schedule using only Yamaha parts only. The boat is stored on a trailer, never in the water. I use what I believe is quality gassoline fuel all the time, and add a proper amount of fuel stabilizer if the boat is to be stored. I live in California and non-ethanol gasoline is not available here.

Someone had mentioned the way I had stored the boat this time, may have contributed to the hard start. We have had a lot of rain here this season. I had the bow of the boat tilted up, so the rain water would roll off the boat cover. With the tongue of the trailer raised up, I have to tilt the motor up as well to keep the lower unit from hitting the ground. The boat was probably in this position for two months. Could this storage position have created a problem in the fuel system that resulted in the hard start?

Thanks in advance for any thoughts.

flymo
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Re: Yamaha F70 Hard Start

Postby flymo » Tue Feb 26, 2019 7:38 am

I have had my F70 since 2010, and only had one time where it was difficult to start - that was in the spring of around 2013 after it had been winterized and stored for about 6 months. It cranked and and fired a couple of times, but would not catch. I ended up changing the plugs and after that it was fine. My interpretation is that the old plugs were soaked with fogging oil—I must have been overaggressive with the winterizing. Since then, it has always started just fine, even after being stored for the winter. I typically first start it with the oily plugs, let it burn the oil off, then replace with new, clean plugs. That's probably excessive, but cheap insurance.

I think your instinct that the hard startin was fuel related is probably correct: when was the last time you changed the fuel filter?

Or you may have had some type of siphon or air lock.

In any case, after the boat has been sitting for a couple of months, I would recommend always starting it on the muffs before launching.

My F70 does have one quirk: it always starts very quickly, but if it's cold, it will stall if I try to advance the throttle right away. It then restarts and runs perfectly thereafter. I've gotten used to it, but it is a bit odd.

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Phil T
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Re: Yamaha F70 Hard Start

Postby Phil T » Tue Feb 26, 2019 7:55 am

Always wise to run the engine on the muffs, check steering, and check all electrical systems prior to launching after a long layup.
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jimh
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Re: Yamaha F70 Hard Start

Postby jimh » Tue Feb 26, 2019 8:46 am

Is the F70 engine fuel injection or carburetors?

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Phil T
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Re: Yamaha F70 Hard Start

Postby Phil T » Tue Feb 26, 2019 8:58 am

That model year of the F70 was fuel injected.
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Jefecinco
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Re: Yamaha F70 Hard Start

Postby Jefecinco » Tue Feb 26, 2019 9:47 am

I use Sta-Bil fuel stabilizer regularly and it seems to work well. I've never had a hard start after several weeks of non-use. I have not tried other brands but they probably work as well.
Butch

El Rollo
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Re: Yamaha F70 Hard Start

Postby El Rollo » Tue Feb 26, 2019 11:11 am

Thank you for the replies. I will replace all the fuel filters and perform a complete service on the motor.
I should have started the motor on the ear muffs prior to going out after the long period of non-use.
This was the longest stretch of time I have not used the boat. I have grown so accustomed to the reliability of the Yamaha F70, it didn't occur to me to run a system check prior to launch.

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Phil T
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Re: Yamaha F70 Hard Start

Postby Phil T » Tue Feb 26, 2019 11:22 am

I would not go overboard with diagnostics since it was a one time thing and happened to a different operator.

The clean start on the muffs tells me it may have been operator error.
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jimh
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Re: Yamaha F70 Hard Start

Postby jimh » Tue Feb 26, 2019 6:45 pm

For an engine with fuel injection, one would expect that the fuel system would not be sensitive to the engine being left in a tilted-up orientation, even for several months, although perhaps the fuel-air separator might have been oriented in a way that allowed the fuel in the reservoir to evaporate to the atmosphere.

If the fuel-air separator did become empty of fuel due to evaporation, I would expect that a float switch in the reservoir would have signaled an electric pump to refill the fuel system and in the process expel all the air.

In a small engine like a 70-HP, perhaps there is no second fuel pump to maintain the fuel-air separator at full, and the fuel lift pump, often operated from vacuum pulses from a cylinder, is relied on solely to deliver fuel.

If that were true, the engine would have to be cranked over for a long time to get fuel back into the system, or the fuel line primer bulb would have to be used to push fuel into the engine and fill the fuel system.

In the situation under discussion was the fuel primer bulb squeezed repeatedly until it presented resistance, indicating the fuel system was full?

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Re: Yamaha F70 Hard Start

Postby jimh » Tue Feb 26, 2019 6:55 pm

El Rollo wrote:I checked the fuel primer bulb and gave it a few pumps, and it felt full...
...I loosened the drain at the bottom of the Racor filter and dumped the fuel [from] the bowl. There were no contaminants that I could see. I re-filled the bowl with the primer bulb, and the motor would still not fire.


If the fuel system were low on fuel due to evaporation, you might have to pump the primer until you replaced all the lost fuel. It might take 8-ounces or more to refill the system. A few pumps would not do it.

After opening the RACOR filter, you would have introduced more air into the fuel system, possibly making the problem worse.

After you pushed fuel into the filter bowl, you likely pushed air into the downstream fuel system. That air would have to be expelled before the fuel injectors would be able to deliver fuel to the cylinders.

El Rollo
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Re: Yamaha F70 Hard Start

Postby El Rollo » Wed Feb 27, 2019 11:57 am

Hello Jim, thank you for your thoughts. I am inclined to think you are correct.
I also don't think pulling the boat out of the water and putting it on the ear muffs had anything to do with it starting.
I think it was just coincidence, and the fuel system was charging or filling up, it just happened to be back on the trailer when it finally fired.

Just for reference, once the motor did fire it ran just as normal as it ever has. There was no unusual smoke out of the exhaust, the motor didn't sputter or hesitate at all. I put it in neutral and gave it a few small revs, and again no hesitation, excess smoke, etc.

If this happens again, i will report back. It's a great little motor and I have zero reservations about it.

Thanks again for all the input.