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I have a 2016 Yamaha F70 with 110 hours. It runs smooth and efficiently, but lately (since about 90 hours) it has trouble starting for the second or third run of the day.
It fires up immediately at the ramp, but after I have fished a spot for an hour or two, I’ll try to crank it and it will die after a couple of seconds. It might take one or two more cranks to get it to finally turn over and start. This will happen once or twice each outing. Funny it never happens on the last crank to load the boat back on the trailer.
I had all of the 100hr maintenance done in January and the problem still persists. I’m thinking fuel pressure? Spark plugs? Any insight?
 

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Zephyr Cove is on FIRE!
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My buddy had this issue and it was the fuel line under the deck getting pinched when turning the wheel. As stated, check the entire fuel line and system from tank to motor first.
 

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Let me know what you end up finding out. I am having a different issue but somewhat similar. After about 30 minutes of running my F70 bogs down... I prime the ball and good for another 30 minutes or so. I am going to start by changing the primer ball. 700 Hours on 2016 F70.
 

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I Love microskiff.com!
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Because of the fuel efficiency of F series Yamaha, the engine will operate for quite some time before fuel pump cavitation due to a fuel restriction or air leak. After changing a thread on 10 micron Yamaha filter between the tank and engine, I started the engine on hose flush and checked for leaks all ok. Trailered for six hours, launched and was half mile from ramp when engine stopped. Could not pump primer bulb tight, so ended up getting towed in. The threads on the Yamaha filter were defective not allowing the filter gasket to contact the filter manifold. Replaced with new filter and problem solved.
 
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