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Old 23-03-2020, 17:21   #31
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Join Date: Oct 2018
Location: East coast US
Boat: Catalina 440 DS
Posts: 2
Re: Yamaha 8HP 2 stroke outboard

With the gas tank cap closed tightly and in the sun, my tank will puff up and eventually I will hear a high pitched hiss of pressure escaping. In these instances, I did a couple of things. I covered the tank with one of my life jackets (which of course are regulation) and cracked the cap (or pressure valve, whichever you may have). I leave the cap/valve a little loose at all times in case there is over pressure from the sun. The only time I close the cap/valve is at night or during passages. The cap/valve needs to be slightly cracked for proper operation. Always pump the bulb 3 times before starting, especially if the motor has been rotated to a tilt up position. If you pull it more than 3 times and the motor doesn't start, it is flooded. If flooded, I will never choke it but rather open the throttle handle to 3/4 to full wide open, make sure it is out of gear, then pull it once or twice. Be ready to rotate your throttle back down to normal as it will rev up quickly. These tips have worked for me, hope they help you out!! Good luck
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Old 26-03-2020, 21:16   #32
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Re: Yamaha 8HP 2 stroke outboard

Originally Posted by felizcortez View Post
I have an 8HP 2 stroke Yamaha that runs great when it is running, but when you leave it to sit in the sun for a period of time it doesn't want to start. I am not sure what is causing this.

It usually happens if we go snorkeling in the middle of the day and let it sit for an hour or so. Then I come back and it takes me 10 mins of pulling to get it to start. Or someone will give us a tow back to the boat and it takes me quite a number of pulls to start
Generally this is the result of vapour lock, the fuel in the carb or fuel line heats up to the point of vaporisation which cases pressure which has difficulty being bled out of the system. Ive not experienced it with boat engines, but i used to race cars and it occurs often when fuel lines aren't rerouted away from engine blocks or shut down in the middle of the day with no shade or same when they're painted black. Try taking the cover off the engine and throwing a t shirt over it instead as an experiment, same if you can insulate the fuel line even if its newspaper and stickytape.

I tested today. I started the motor just fine this morning and immediately shut it off. I let the motor sit for a few hours and went to start it today and had to pull and pull to get it started.
Could be the same gremlin of vapor lock. If you start it and run, stop and start it again then all good, but leave it and its not. also when its hot you may heat hear the engine surging or stalling at least eratic idle. but under power works well same like first thing in the morning.
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Old 04-04-2020, 11:39   #33
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Re: Yamaha 8HP 2 stroke outboard

I have a bit more data.

If I unplug the fuel connector at the outboard it starts every time no problem after sitting in the sun. However my female connector has a small tear in the seal and pumped a bunch of gas into the bottom of the dinghy the othe other day.

The fuel demand valve is definitely bad as well, I talked to West Marine where I bought it via chat and they are going to send a new one to me. Since I'm on Mexico and the current state of affairs with corona virus, this might take some time.

I also tried leaving just the hose attached to the outboard and unplugging the hose at the fuel tank. This also caused difficulty starting as I think pressurized fuel can still get to the carb when the hose beats up in the sun.
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2 stroke, outboard

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