Yamaha 8HP 2 stroke outboard

[felizcortez]

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.

I have one of those sealed gas cans from West Marine that had the hose with the pressure valve in it.

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

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.

Any advice on what I should try or do to debug the issue?
Is it potentially flooded? Ie pressure from the heat build up of the sun is causing it to flood the engine?

I was going to try keeping the fuel hose unplugged and see if that makes a difference.

[Vets sailing]

Flooding due to heat building pressure is a likely cause. Had that same thing happen on same motor. Problem solved by leaving vent on tank open or if worried about moisture getting into take try unplugging the fuel line.

[felizcortez]

If it's flooding shouldn't the float and needle valve stop this from happening?

I will try unplugging the fuel line and see if that helps.

[billknny]

A simple test would prove/disprove Vets hypothesis: Leave the engine in the sun, and move the fuel tank to the shade, or leave the fuel cap loose on the tank to prevent pressure buildup. if it works, you know the problem.

Yes, the float/needle valve SHOULD prevent the problem, but it is only good up to a certain pressure it can be overwhelmed even if it is in good shape.

The other possibility-- exactly the opposite of flooding--is that the gasoline in the carburetor bowl all evaporates in the sun... have you tried pumping the primer bulb?

To clear a flooded engine, you need to move as much air though it as possible. Open the choke (put it in the normal "Run" position), and open the throttle all the way, and give a few pulls.

[slug]

Originally Posted by felizcortez

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.

I have one of those sealed gas cans from West Marine that had the hose with the pressure valve in it.

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

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.

Any advice on what I should try or do to debug the issue?
Is it potentially flooded? Ie pressure from the heat build up of the sun is causing it to flood the engine?

I was going to try keeping the fuel hose unplugged and see if that makes a difference.

Since new my Yamaha 8 two stroke will not start unless you pull the choke

[felizcortez]

Originally Posted by slug

Since new my Yamaha 8 two stroke will not start unless you pull the choke

Yes. I've tried it with and without choke. Neither works. Usually I have to use the choke when it is cold and that starts it up.

With regards to he fuel pressure. The fuel hose has a pressure valve in it. I'm wondering if that is starting to go bad. When I connect the hose to the engine fuel sprays out.

[belizesailor]

Or...ditch that stoopid fuel tank & hose, set engine in sun, stick the end of a simple fuel hose (minus tank end fitting) in a container of fuel and see if it cranks.

[Tin Tin]

Potentially your spark plug is on its last legs. Try a new one, makes a big difference to 2 strokes.

[felizcortez]

Is the fuel demand valve supposed to prevent fuel spraying when I connect the hose to the outboard? If I don't release pressure from the tank it sprays out when connected.

[Sailmonkey]

My solution to this sort of problem was to “modify” the stupid little vent valve on the tank so that it acts as a vent instead of a fuel bomb in the dinghy.

[a64pilot]

Originally Posted by Sailmonkey

My solution to this sort of problem was to “modify” the stupid little vent valve on the tank so that it acts as a vent instead of a fuel bomb in the dinghy.

Amazon sells an “illegal” fuel tank with a plain vent that vents both ways.
It’s the exact same tank if you buy a Yamaha two stroke in the Bahamas.
I got rid of my CARB compliant dinghy tank last year as it was giving me issues, and that’s on a fuel injected engine.
Amazon also sells fuel tank vents that you drill a hole in your CARB compliant Jerry can and now you have a real vent that allows the fuel flow without spilling.
The whole CARB compliant fuel cans are a perfect example of well meaning fools, they cause more fuel spillage and that and fumes are what they are supposed to prevent.

This tank has the old fashioned “illegal” vent like was used before the CARB days, look at the fuel cap.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

This is the Jerry can vents, but when you drill the hole you can’t use a regular bit, it will put a twist in the hole. You need a step drill, it will drill a hole that’s not bent by the twist drill.
https://www.amazon.com/JSP-Manufactu...4123445&sr=8-5

I’m still looking for a good old fashioned spout, Amazon sells some, but the ones I bought were junk, too thin to seal well. I have some old ones I keep and take to new cans, but that’s not going to last forever. So if anyone has a source of a good spout I’d appreciate it.

[Madehn]

spark fuel air-- 3 things needed to fire the engine- put a new plug in and check to make sure you are getting fire from it by grounding the body of the plug to the motor while the sparkplug is out of the cyclinder and pulling slowly to see if it sparks. put it back in the engine and see if it starts-- if it does not then pull it out look to see if it is wet- if it is you are getting fuel maybe too much-- if it is dry then you have a fuel delivery issue- replace hose and filter(including the ones on the engine)-- simple low cost trouble elimination. Once ( and this is like a pink polka dot unicorn it is so rare) I had an engine doing what you described and it was the coil which was almost gone and would break down when it got hot and not function-- that is a very remote possibility. the fuel hose can sometimes break down internally and cause intermittent issues.

[skipper53]

Don't know there are new regulation's on the design of fuel tank vents, but my newest vented tank cap doesn't really vent much at all. If the tank is in the sun for even a little while, the tanks swells up a lot.
Probaby is keeping some emissions from entering the atmosphere, but it sure isn't venting properly.

[Sailmonkey]

Originally Posted by skipper53

Don't know there are new regulation's on the design of fuel tank vents, but my newest vented tank cap doesn't really vent much at all. If the tank is in the sun for even a little while, the tanks swells up a lot.
Probaby is keeping some emissions from entering the atmosphere, but it sure isn't venting properly.

It’s venting properly according to the carb regulations.

Basically it allows air in, but no vapors out. It alarming to see the fuel tank in the dinghy puffed up like a blowfish.

[Cheechako]

Get a regular fuel tank I would guess. My 15 hp 2 stroke Yam was similar I think and always ran 1-2 pulls even if sitting in the tropic sun all day.