Any advice appreciated Honda 20hp

[Clarky021]

I have a 2017 Honda BF 20 on my rib and had it serviced in Feb by main dealer.Took it on lake today for first outing since the service and filled the tank with E10 petrol.
Ran the boat for 15 mins no probs then pulled onto jetty for a walk round,when we came back an hour later it struggled to start but did eventually and all was good again for 30 minutes on the lake.
On way back in the engine started to bog and lose power and it dropped down to about a third power even though throttle was on full.
I’m not sure if it was running on one cylinder only but after a couple of minutes chugging along it seemed to clear and went back to full power again.
As I was going back in to slipway it cut out twice and wouldn’t Rev,took cowell off and nothing untoward to see.
Not sure if it’s a fuel blockage,poor fuel E10 or something else but before I get someone to look at it does anyone have any suggestions as to what it could be.
Engine had full service in Feb and still under warranty till July.
I’m no mechanic so any help appreciated.

[Fenlander]

Sounds like a fuel starvation problem but the other thing that's a known issue on this engine is the cam pulley working loose so the timing goes all over the place.

[jeffstevens763@g]

If it’s a twin cylinder might be a dodgy spark plug. Was the tank empty when filled or old fuel possible water contamination

[Orwell boy]

You wouldnt be the first person to forget to open the air inlet screw on the top of the fuel tank !

[Clarky021]

Thank you for your replies,I will look into the fuel issues and see if I can find the issue.It’s never missed a beat before so I can’t see it being anything major but need it sorting.

[Steve509926]

Originally Posted by Orwell boy

You wouldnt be the first person to forget to open the air inlet screw on the top of the fuel tank !

Been there, done that and it's the first thing I'd be looking at.

[GARYSHORT]

Also check the fuel squeeze bulb, cylinder compression, and a possible vacuum in your fuel line.

[Clarky021]

Thanks for suggestions,I did fill the tank from more or less empty and wondering if I have air lock.I ll have a look at fuel tank and bulb tomorrow but it does sound like it could be a vacuum issue reading on the symptoms.

[Highland Haggis]

Flying Dutchman had this problem with outboard it was contaminated fuel E10 only has a life span of about 4 to 6 weeks the Yamaha dealer told us then it’s ruined for outboard but will still run in your car

[CherMac]

Through a moronic miscommunication, I added a gallon of water to the roughly 4 gallons of gas already in my internal gas tank. Don't remember all the details as this was a while back, but the boat behavior sounded a lot like yours. We drained all the fuel out of the tank. Fuel separator was totally filled with water. Put in fresh fuel and Star Tron, and life was good.

[Steve509926]

Originally Posted by CherMac

Through a moronic miscommunication, I added a gallon of water to the roughly 4 gallons of gas already in my internal gas tank. Don't remember all the details as this was a while back, but the boat behavior sounded a lot like yours. We drained all the fuel out of the tank. Fuel separator was totally filled with water. Put in fresh fuel and Star Tron, and life was good.

With a 20% water/petrol mix I'm surprised your engine even started!

[CherMac]

What happens is the water sinks to the bottom of the tank, and the gas floats on top. They don't mix together. So, the boat will run for a while until you accelerate and get the bow up or encounter waves. Water then starts getting fed into the engine, and the engine starts sputtering. If you let the boat sit without running (like OP pulling into a jetty and walking around for an hour), the water has time to settle back down. The experience gave me a better appreciation of not hanging out too close to breakwall rocks on wavy days in case the engine fails for some crazy reason.