slowly dies at idle, primer bulb goes soft

[pcrussell50]

1987 2.0L 150, oil system removed, premix only

Runs strong, idles well. LOVE this motor.

BUT

-If I idle or low power long enough, it stops drawing fuel, empties the line, and dies. If I pump the bulb back up, it fires right up and runs great.

-Above about 2500 rpm and planing, it stays full and runs great.

-The carb to carb and carb to pump fuel lines are fresh, tight, and leak free, and the bulb pumps up firm and does not force any leaks

-new diaphragm and gasket kit from promarine a year ago... no improvement

-Peter

[rgsauger]

If you have an old bulb and line, swap it for a new ethanol compliant one. Might pop in new gaskets in pulse pump. Lastly, might run some seafoam in fuel to clean fuel system.

[pcrussell50]

Bump...



1987 2.0L 150, oil system removed, premix only

Runs strong, idles well. LOVE this motor.

BUT

-If I idle or low power long enough, it stops drawing fuel, empties the line, and dies. If I pump the bulb back up, it fires right up and runs great.

-Above about 2500 rpm and planing, it stays full and runs great.

-The carb to carb and carb to pump fuel lines are fresh, tight, and leak free, and the bulb pumps up firm and does not force any leaks

--new diaphragm and gasket kit from promarine a year ago... no improvement

-Peter

[rock]

Check your tank vent or anti-siphon valve if present.

Rock

[Motv18]

Place a fuel pressure gauge on it and pump the bulb tight. Then listen and watch and see if it falls to 0 quickly.

Then repeat at idle.

That will sort seperate a general fuel system issue vs, something while running.

Does it idle rough.

[SS Minnow]

I check my lines between tank and pump with a vacuum pump/gauge. That part is not under pressure while in use.


https://shop.harborfreight.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/i/m/image_27888.jpg

[SS Minnow]

I have to add that I have found a couple few primer bulbs that would hold pressure, as in they would not leak gas, but would not hold vacuum. Disconnect line at tank and plug, disconnect line at pump and install vac pump.

ETA: If this were an issue for OP, I doubt it would be the only one. When I had this issue I was running out of fuel on the top end. It helped a little, but I needed a new fuel pump too. You say it runs good on the top end so......
And, when I found this on other peoples boats, they did not notice any issues, I was just doing routine maintenance.

[pcrussell50]

Thanks guys. It runs well at idle until it runs out of fuel. Then after I pump up the bulb, it runs well again... It does NOT run out of fuel on the top end... above about 3000rpm it just keeps going great.

I just took the pump off for inspection and I discovered something:

it's missing a couple of internal parts: that black plastic disc and spring :mad:

disc:
https://www.crowleymarine.com/parts/4948.cfm

spring goes under disc:
https://www.amazon.com/MERCURY-SPRING/dp/B00N6DAIVY

I made a separate post about it. Think that could be my problem for low signal at idle?

-Peter

[rock]

It's there to keep the diaphragm tight so it's possible.

[pcrussell50]

It's there to keep the diaphragm tight so it's possible.

I'll go get the spring and disc and try it out and report back. Thanks.

-Peter

[RSWORDS]

Fix that then hook a portable tank directly to the pump run. If it still acts up... it's the motor side... if its fine... it's the boat side.

[home made tunnel]

AH-HA!!! did you see my post in the General section about - fuel pump kits on amazon - buyer beware?
Get a sierra kit. Don't cheap out. The cheap kits don't have the rubber discs. Just the plastic ones.

[pcrussell50]

AH-HA!!! did you see my post in the General section about - fuel pump kits on amazon - buyer beware?
Get a sierra kit. Don't cheap out. The cheap kits don't have the rubber discs. Just the plastic ones.

For my motor, 1987 150hp 2.0L, none of the kits I have seen come with the spring and disc for tensioning the diaphragm. Yet for some reason, the ones for 90hp look exactly the same, and they DO come with the spring and disc. Weird, eh? Off to go read your thread. Thanks for pointing it out.

Anyhow, I ordered springs and discs from both Mercury and Quicksilver so I'm hoping those brands are trustworthy enough.

-Peter

[home made tunnel]

your missing spring and disc issue is like my missing diaphragms haha. Get her running again !

[Capt.Insane-o]

-.-

[RSWORDS]

AH-HA!!! did you see my post in the General section about - fuel pump kits on amazon - buyer beware?
Get a sierra kit. Don't cheap out. The cheap kits don't have the rubber discs. Just the plastic ones.

Your kit had exactly everything in it that it needed. The old rubber discs have been gone along time and the plastic discs updated.

[pcrussell50]

Anyway...

MY pump is supposed to have spring and disc and for the last four years I've been using it, it hasn't had them... A fact I didn't realize until shortly after I started this thread. I got some in there and took the boat out for a spin today, with disc and spring, tensioning the diaphragm. The lack of those things seem to have been the problem that was causing my motor to run out of fuel at low rpm. Putting them in seems to have fixed it. It never ran the fuel line dry at idle or low rpm like it has been or the last few years. Will report back if that changes.

Still a little miffed that none of the pump kits for my pump 1987 2.0L 150 with the "old style" pump, come with a spring and disc. I had to order each separately. WTF?

-Peter

[flabum1017]

Anyway...

MY pump is supposed to have spring and disc and for the last four years I've been using it, it hasn't had them... A fact I didn't realize until shortly after I started this thread. I got some in there and took the boat out for a spin today, with disc and spring, tensioning the diaphragm. The lack of those things seem to have been the problem that was causing my motor to run out of fuel at low rpm. Putting them in seems to have fixed it. It never ran the fuel line dry at idle or low rpm like it has been or the last few years. Will report back if that changes.

Still a little miffed that none of the pump kits for my pump 1987 2.0L 150 with the "old style" pump, come with a spring and disc. I had to order each separately. WTF?

-Peter

Two things here.... When ordering parts, they usually show a picture of what's included. and second, using the OEM service manual, you would have seen there needs to be a spring and disc J/S :D
T

[pcrussell50]

Two things here.... When ordering parts, they usually show a picture of what's included. and second, using the OEM service manual, you would have seen there needs to be a spring and disc J/S :D
T

Looking at the manual was how I discovered that those things were missing. I got the powerhead used, rebuilt the carbs, Chris Carson reeds, new bleed lines, new fuel pump kit (which did not come with spring and disc), dropped it on and it worked just fine except for slowly dying at low rpm. I was new enough to Merc that I had no idea that parts were missing... until I actually looked at the manual the other day. When I looked at pictures of the kits online, I had no idea that there was even supposed to be a spring and disc... until a couple of days ago... Because none of the pump kits I looked at had a spring and disc.

And I have not yet seen a kit with a photo that had the spring and disc. For some reason the kits for lower horsepower motors look exactly the same, and DO show the spring and disc in the kit. :confused:

Oh well, I ordered them separately now that I know about them.

-Peter

[bigboy]

I think I have the same problem. My engine stalls when trying to plane when its cold or when it sits for a short period. When I squeeze the bulb its fine. I rebuild the pump a year ago. Don't recall it had a spring. Engine runs fine once on plane...

[pcrussell50]

So the slowly dying at idle thing comes and goes. It might be related to the health of the fuel pump gasket and membrane stack. Maybe. I just put in a fresh gasket stack and did not suffer the problem today.

BUT STILL... re tank venting....

So, chasing down the venting scheme on my welded aluminum tanks...

As far as I can tell there is no vent... But yet there has to be, obviously. Can someone tell me what the venting scheme is for this kind of setup?

There are only three "opening" that I know of in a welded tank like this:

The sender:
507467

The withdrawal system:
507468

The flip top gas cap:
507469

Maybe the rubber flapper seal on the gas cap is purposely not air tight and acts as a vent? Otherwise I have no idea where a vent would be on a tank system like this?

-Peter

[David - WI]

I would guess it's the cap in your system... it would almost certainly vent "outside" the boat?

[pcrussell50]

I would guess it's the cap in your system... it would almost certainly vent "outside" the boat?

That's the only guess I have too. Since there has to be venting, and there is not another opening. :shrugs:

Surely there are dozens if not hundreds of boaters whose boats have welded aluminum tanks. The venting systems must surely be well understood. We (you and I ;) ) shouldn't have to be guessing.

-Peter

[David - WI]

My old aluminum (and new plastic) tanks have a separate vent outlet and a hose running to a vent on the side of the boat... that pukes gas & oil down the side of the boat if you overfill it. :rolleyes:

[pcrussell50]

My old aluminum (and new plastic) tanks have a separate vent outlet and a hose running to a vent on the side of the boat... that pukes gas & oil down the side of the boat if you overfill it. :rolleyes:

Got it. Thanks.

While looking for something else, I stumbled on a pic of one just like what you described. WhyTF does mine not have that? It's a full on USCG approved tank made by a well known fabricator in SoCal from the mid-80's.

Along with you, I'm back to guessing that the venting has something to do with the gas cap.

Oh well, all is running well right now so it's more of a curiosity than anything else right now. Thanks for your input. Feel free to jump back in if some eureka moment sheds more light.

-Peter

[David - WI]

"Cap is vented. Mount in a well ventilated area."

https://www.fillernecksupply.com/2-custom-hot-rod-boat-flip-top-fuel-filler-cap-166033-351800-617920/