Mercury outboard fuel help!!!

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Tenner
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Joined: 10 Nov 2017, 15:18

Mercury outboard fuel help!!!

Post by Tenner » 18 Jul 2018, 23:12

Alright here is the dilemma. I am pretty sure I’m running out of fuel at WOT.

Here is the info I have and what I have done. 1991 Mercury 90/75 Jet. 3 cylinder. This motor ran great all waterfowl season. Since this spring I have bee. Fighting a fuel issue. At first I figured it was just cold blooded as I would leave the dock and it would bog down at wot. I could come off the throttle and it would idle. After a few minutes it would run fine.

The next outing it would run bad again. Primer bulb would feel normal. I could squeeze it and feel fuel. It was not sucking flat. Sometimes pumping it would help. I could put the boat in neutral and idle it high and it would be fine but in forward gear it would give me fits for 15-20 min at wot. So I changed plugs and cleaned the cards.

Next outing the boat would feel better on the bottom. And run wot fir 1/2 then bog down. And do it for 15-20 min the. Run fine. It would continue to do this the next few outings.

I rebuilt the fuel pump and replaced all the fuel lines on the motor. I also replaced the lines from the oil pump to fuel pump. It would run good for a few miles then bog down. I ripped the fuel pump off on the water and double checked everything. Ran good fir 4 straight miles to the dock at wot.

I thought I had fixed it...went out the other morning and immediately it would not run wot. I’d squeeze the primer bulb and it would change anything. So fur the next hour I’d move short distances at 1/4-1/2 throttle. Then o decided to run upriver. It ran wot for 6 miles up then 3 miles back down then bogged down!!!! I put it at 1/4 throttle and was pumping the primer bulb and then after a few min it ran the other 2 miles back to the dock fine.

What is going on?!? I am out of ideas!!! The only thing fuel wise I haven’t changed is the hose and bulb from tank to motor. I just can’t figure out why it’s so hit and miss. Help please.


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richg99
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Mercury outboard fuel help!!!

Post by richg99 » 18 Jul 2018, 23:25

"I haven’t changed is the hose and bulb from tank to motor"

Well, that change fixed my fuel issues. EPA approved ethanol rotted out the inside of my fuel line. New lines and bulb worked for me. rich

Striper57
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Mercury outboard fuel help!!!

Post by Striper57 » 19 Jul 2018, 00:28

I agree with Rich. Replace the fuel line and possibly any fittings as well. I know that the fitting on the fuel tank can also go out and cause problems. A lot of tanks have one way fittings that can have issues and need to be replaced, but that is less common. Process of elimination. It sucks but it eventually works.

Also, have you checked your electical connections under the cowling? I have had a faulty rev limiter that caused issues in a jet outboard years ago. Not the same issues as you, but just a thought to at least eyeball the electrical stuff.

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Tenner
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Mercury outboard fuel help!!!

Post by Tenner » 19 Jul 2018, 00:31

richg99 wrote:"I haven’t changed is the hose and bulb from tank to motor"

Well, that change fixed my fuel issues. EPA approved ethanol rotted out the inside of my fuel line. New lines and bulb worked for me. rich
Ok I will switch it out. I figured one the fuel was primed then vacuum just would draw fuel they that line. It makes sense that the inside could be rotted.


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Tenner
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Mercury outboard fuel help!!!

Post by Tenner » 19 Jul 2018, 00:32

Striper57 wrote:I agree with Rich. Replace the fuel line and possibly any fittings as well. I know that the fitting on the fuel tank can also go out and cause problems. A lot of tanks have one way fittings that can have issues and need to be replaced, but that is less common. Process of elimination. It sucks but it eventually works.

Also, have you checked your electical connections under the cowling? I have had a faulty rev limiter that caused issues in a jet outboard years ago. Not the same issues as you, but just a thought to at least eyeball the electrical stuff.

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I’ll look at the fitting on the tank too. As far as electrical. Yes I was forced to check all of those when my rectifier went bad and burned up so I replaced it and checked all electrical.


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richg99
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Mercury outboard fuel help!!!

Post by richg99 » 19 Jul 2018, 08:36

You don't, by any chance, have one of those new EPA tanks that doesn't vent, do you? The one where you have to add a Fuel Demand Valve (LINK below)?

Those things have been crapping out and are mentioned weekly on some of the fishing/boating sites that I frequent. If so, check the FDV for leaks. I had to replace one on one boat.

I've read that some guys removed it completely and put an old-fashioned vented cap on their tank.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

Tenner
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Mercury outboard fuel help!!!

Post by Tenner » 19 Jul 2018, 11:58

richg99 wrote:You don't, by any chance, have one of those new EPA tanks that doesn't vent, do you? The one where you have to add a Fuel Demand Valve (LINK below)?

Those things have been crapping out and are mentioned weekly on some of the fishing/boating sites that I frequent. If so, check the FDV for leaks. I had to replace one on one boat.

I've read that some guys removed it completely and put an old-fashioned vented cap on their tank.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1
No my tank is a 12 gallon potable with a vent cap. My cap does not vent thru the vent screw though. I just don’t tighten it all the way and leave a little loose so it can vent. If I tighten all the way it will suck the bulb flat. Think this could be a problem leaving it loose? I’ve done it for a year.


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handyandy
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Mercury outboard fuel help!!!

Post by handyandy » 19 Jul 2018, 13:07

Honestly don't buy the new low permeation fuel line it's got a lining that tends to separate from the outside rubber fiber reinforced line and the inside line then collapses. Just use good old regular fuel line. Napa usually carries the good USA made regular old black fuel hose. Use that and a genuine evinrude primer bulb. I just keep rolls of the good fuel line as it seems I always need some for some car, tractor, mower, small engine, outboard, or boat I'm working on. Ebay has 25' rolls pretty cheap of decent fuel hose this is what I've bought before to have a good selection of line for anything I need. If you don't want a whole roll just buy whatever you need at a parts store just make sure it's not the garbage china rubber that stuff dry rots and deteriorates a lot quicker I have found. The ebay line I have so far all of it I have used on various things is holding up well.

https://www.ebay.com/itm/1-4-5-16-3-8-x ... m570.l1313

I have been running a evinrude primer bulb the last 3 years it's the only one I've had last this long with no issues.

https://www.ebay.com/itm/NEW-OEM-Johnso ... m570.l1313

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richg99
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Mercury outboard fuel help!!!

Post by richg99 » 19 Jul 2018, 13:09

Some people use these caps successfully.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

Striper57
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Mercury outboard fuel help!!!

Post by Striper57 » 19 Jul 2018, 16:53

richg99 wrote:Some people use these caps successfully.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1
I'm one of those people. Every one of my portable tanks has one of those caps on it. The EPA caps reside in a drawer hopefully to never see the light of day again. I couldn't stand the fact that the screw vent on the EPA caps seemed to be just for show because they sure didn't vent the tanks.

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Tenner
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Mercury outboard fuel help!!!

Post by Tenner » 19 Jul 2018, 18:16

Thanks guys. I’ll order that stuff and give it s try and yes my can is exactly as the epa caps are. A little vent that screws and doesn’t do anything. I eve. Took it out to see if it was broken or needed cleaned and I don’t even see how it would vent. Lol.


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richg99
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Mercury outboard fuel help!!!

Post by richg99 » 19 Jul 2018, 19:34

My understanding is that those caps do eventually vent.

The pressure has to reach a very high level; the plastic tanks blow up like balloons; fuel is driven into your engine unless you have an FDV valve that is functioning.

Wow, what a plan. Thanks, EPA!

CedarRiverScooter
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Mercury outboard fuel help!!!

Post by CedarRiverScooter » 19 Jul 2018, 22:07

There is a saying - half of all fuel issues are caused by ignition & vice versa!

Tenner
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Mercury outboard fuel help!!!

Post by Tenner » 03 Aug 2018, 13:30

I just wanted to follow up and say I believe switching out he primer bulb fixed the problem. I ran the boat for 15 miles last week and had zero issues. The old bulb looked like the drain stop ball had come loose and was rattling around inside the bulb

Thanks everyone.


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richg99
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Mercury outboard fuel help!!!

Post by richg99 » 03 Aug 2018, 13:37

Glad that your problem appears to be solved.

Thanks for posting back here. That will help the next guy who does a search with similar issues.
rich

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