Fuel supply problems

gpfishingdude

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Had the boat on the water Wednesday and it lost power and died about 2-3 minutes into wot. The primer bulb collapsed and stayed that way until after I loaded the boat on the trailer by hand. Yes! I loosened the gas cap when it first happened.
I just went out and pulled the- nearly new- Mercury fuel line off of the tank and did an autopsy on it expecting to find the inner liner of the hose had blocked the flow of fuel.
The hose line was clear and the bulb held pressure until I removed the Mercury fitting that snaps onto the motor. Then it pumped fuel out like it should when the bulb is squeezed.
I am thinking that I have a problem with getting fuel from the tank, maybe an anti- siphon valve or something. The tank is a 12 gallon Attwood low profile tank.
Does that tank have a built in anti siphon valve?
I am going to leave the Mercury fitting off the end and see if I can pump some fuel through to another gas can. Maybe set the can down low enough that I can see if it will siphon into the empty can. Then try pumping the fuel back into the boat tank and see if it acts any differently.
Any ideas on how to test the tank?
 

gpfishingdude

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I stuck the line back on the fuel tank and pumped the primer bulb It siphoned fuel until I raised the line up higher than the tank. I had to stick the mercury fitting back on the end of the line to keep fuel from running out whenever the line was lower than the tank.
That proves that the line is not obstructed and that the pickup supplies fuel to the line.
Before I had the problem on the water I had added a couple of feet of fuel line on the tank side of the bulb so that I could reach the bulb from the deck of the pontoon boat. Maybe that added distance from the bulb made a difference in the way the line supplied fuel.
Time to take the boat to a ramp and try running it on the trailer to see if shortening that line will make a difference.
Two more hot days here and then the weekend crowd should thin out at the ramps.
 

dingbat

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Nov 20, 2001
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Before I had the problem on the water I had added a couple of feet of fuel line on the tank side of the bulb so that I could reach the bulb from the deck of the pontoon boat. Maybe that added distance from the bulb made a difference in the way the line supplied fuel.
Pressure drop in hose in given per 100’ if that tells you anything about increasing the hose length. ;)

If a couple feet of hose makes the difference I would start by looking for a vacuum leak between the tank and the fuel pump. If nothing there, a compromised fuel pump would be my next suspect
 

gpfishingdude

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Pressure drop in hose in given per 100’ if that tells you anything about increasing the hose length. ;)

If a couple feet of hose makes the difference I would start by looking for a vacuum leak between the tank and the fuel pump. If nothing there, a compromised fuel pump would be my next suspect
I think that it tried to pump hard enough because it collapsed the primer bulb. So I'm thinking that the problem must be on the tank side of the bulb.
Does that make sense? At any rate I plan on taking the boat to a ramp on a week day and try running it for a while again to see if I can recreate the same conditions.
 

dingbat

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Nov 20, 2001
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I think that it tried to pump hard enough because it collapsed the primer bulb. So I'm thinking that the problem must be on the tank side of the bulb.
Does that make sense?
That would certainly make sense.
Your tank is CARB and EPA compliant. Also has a “built in vacuum valve so no need for manual venting” ….good luck, lol

Sounds like you may have an issue with the “vacuum valve”
 

Texasmark

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Dec 20, 2005
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How about the check valve on the inlet line to the primer bulb. If it malfunctioned such that it didn't open it could collapse the bulb with the fuel pump sucking on the line.

Have you tried putting things back together and see if it all magically works now. If so, with the troubleshooting that you performed, I'd think that the check valve is intermittently sticking. Never heard of that but I think you have eliminated everything else.

I remember comments on here years ago when the Mercury diamond shaped bulb was preferred to the oval that seems to be the norm today. Big guns recommended it be in a certain position, I think vertical with the output to the engine on top....why I don't know.
 

gpfishingdude

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I ran the motor with the boat on the trailer at the state line swamp. It started and ran good so I increased the throttle to about 1/4 and let it run for a few minutes and then half way for a while and then throttled back. When I throttled back the cooling water stream decreased by about half and a little steam came off of the cooling stream. I laid my hand on the engine cover and it was warm but I didn't feel a ton of heat coming from the motor.
Then I increased the speed to wot. and the prop wash started sucking logs over from the swamp and the moss and duckweed was getting thick behind the boat. WHEW! does that stuff stink.
I squeezed the primer bulb and it pumped fuel and the RPMs picked up for a second or two.
The primer bulb got soft but it didn't try to collapse as far as I could tell.
I really don't know if I can trust the motor on open water yet or not?
Seems like it would have got me there and back today.
 

gpfishingdude

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May 1, 2012
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538
How about the check valve on the inlet line to the primer bulb. If it malfunctioned such that it didn't open it could collapse the bulb with the fuel pump sucking on the line.

Have you tried putting things back together and see if it all magically works now. If so, with the troubleshooting that you performed, I'd think that the check valve is intermittently sticking. Never heard of that but I think you have eliminated everything else.

I remember comments on here years ago when the Mercury diamond shaped bulb was preferred to the oval that seems to be the norm today. Big guns recommended it be in a certain position, I think vertical with the output to the engine on top....why I don't know.
I read somewhere that you have less problems if the primer bulb is vertical like that. I can try to tie that end of the fuel line up higher and see if that helps.
 

gpfishingdude

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I think the next step is to run the boat around on a lake but to try to stay upwind of the boat ramp for a while.
 

gpfishingdude

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May 1, 2012
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I just watched a great youtube video from -Born Again Boating- called "Follow these steps-Why outboards run out of fuel. I really like how he shows how to check for air leaks in the system. I will try to find more of videos from this source and maybe subscribe.
 

gpfishingdude

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May 1, 2012
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The boat ran good today on a lake I made several trips into the west wind and back to the dock before I loaded onto the trailer in the cross wind. I don't know if I ran it at wot or not but it was moving along at a good pace and really purred along nicely. I think that the boat is dependable enough now but I am going to take a spare fuel line and a few tools along just in case I have any more problems. Time to move on to another problem. Heard a loud pop inside the console when I turned the wheel to the right a couple of times.
 
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