Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 12-03-2020, 17:12   #1
Registered User

Join Date: Mar 2017
Posts: 215
Yamaha 8HP 2 stroke outboard

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.
felizcortez is offline   Reply With Quote
Old 12-03-2020, 17:32   #2
Registered User

Join Date: Dec 2016
Location: Oregon
Boat: Santana 23D, 23ft
Posts: 13
Re: Yamaha 8HP 2 stroke outboard

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.
Vets sailing is offline   Reply With Quote
Old 12-03-2020, 17:38   #3
Registered User

Join Date: Mar 2017
Posts: 215
Re: Yamaha 8HP 2 stroke outboard

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.
felizcortez is offline   Reply With Quote
Old 12-03-2020, 18:15   #4
Registered User

Join Date: Oct 2015
Posts: 2,008
Re: Yamaha 8HP 2 stroke outboard

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.
billknny is offline   Reply With Quote
Old 12-03-2020, 18:22   #5
Registered User

Join Date: Nov 2019
Posts: 1,698
Re: Yamaha 8HP 2 stroke outboard

Quote:
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.

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
slug is offline   Reply With Quote
Old 12-03-2020, 18:29   #6
Registered User

Join Date: Mar 2017
Posts: 215
Re: Yamaha 8HP 2 stroke outboard

Quote:
Originally Posted by slug View Post
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.
felizcortez is offline   Reply With Quote
Old 12-03-2020, 18:34   #7
Registered User

Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 13,088
Re: Yamaha 8HP 2 stroke outboard

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.
belizesailor is offline   Reply With Quote
Old 12-03-2020, 19:30   #8
Registered User

Join Date: Jan 2020
Location: EC
Posts: 403
Re: Yamaha 8HP 2 stroke outboard

Potentially your spark plug is on its last legs. Try a new one, makes a big difference to 2 strokes.
Tin Tin is offline   Reply With Quote
Old 13-03-2020, 09:06   #9
Registered User

Join Date: Mar 2017
Posts: 215
Re: Yamaha 8HP 2 stroke outboard

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.
felizcortez is offline   Reply With Quote
Old 13-03-2020, 09:44   #10
Registered User
 
Sailmonkey's Avatar

Join Date: Sep 2009
Location: Houston
Boat: '76 Allied Seawind II, 32'
Posts: 9,060
Yamaha 8HP 2 stroke outboard

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.
Sailmonkey is online now   Reply With Quote
Old 13-03-2020, 11:20   #11
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,473
Re: Yamaha 8HP 2 stroke outboard

Quote:
Originally Posted by Sailmonkey View Post
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.
a64pilot is offline   Reply With Quote
Old 13-03-2020, 14:28   #12
Registered User
 
Madehn's Avatar

Join Date: Nov 2014
Location: Kemah Tx
Boat: Gulfstar 51
Posts: 309
Re: Yamaha 8HP 2 stroke outboard

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.
Madehn is offline   Reply With Quote
Old 13-03-2020, 15:55   #13
Registered User

Join Date: Apr 2016
Posts: 162
Re: Yamaha 8HP 2 stroke outboard

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.
skipper53 is offline   Reply With Quote
Old 13-03-2020, 16:04   #14
Registered User
 
Sailmonkey's Avatar

Join Date: Sep 2009
Location: Houston
Boat: '76 Allied Seawind II, 32'
Posts: 9,060
Re: Yamaha 8HP 2 stroke outboard

Quote:
Originally Posted by skipper53 View Post
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.
Sailmonkey is online now   Reply With Quote
Old 13-03-2020, 16:09   #15
Registered User
 
Cheechako's Avatar

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 23,920
Re: Yamaha 8HP 2 stroke outboard

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.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Reply

Tags
2 stroke, outboard

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Yamaha 6/8hp vs Tohatsu 9.8hp mikedefieslife Auxiliary Equipment & Dinghy 12 23-04-2020 01:03
For Sale: Yamaha 8hp 2 stroke outboard 15" short shaft Boatguy30 Classifieds Archive 1 06-08-2015 17:15
For Sale: Yamaha 8hp 2-Stroke 15" (Short) Shaft konakoma Classifieds Archive 6 14-10-2011 11:03
For Sale: Yamaha 8hp Two-Stroke Outboard - Still Under Warranty Critical Classifieds Archive 3 28-09-2010 13:58
For Sale: Yamaha 8hp, 2-Stroke - $550 - Stuart FL John Drake Classifieds Archive 1 25-07-2009 18:35

Advertise Here


All times are GMT -7. The time now is 07:04.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.