primer bulb question...

AGUILERA2000

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Sep 15, 2008
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OK guys I have a question, how does one test a primer bulb?
I will tell you my problem. I own an 85hp mercury 2 stroke outboard, the motor stars and runs good it idles good but there is a problem when trying to go fast, the motor picks up speed and then it just drops to slow even with the speed control all the way up (fast) the I bring the control back down and cruise at slow speed, motor wouldn't die tho. So I decided I am not going to mess with the motor anymore so I bought and different boat (pontoon) the new boat has a 55hp Suzuki oil injected outboard, motor starts and runs good except when I try to go fast, it basically has the exact same problem as the mercury, now the one thing the two motor have in common is the primer bulb does not build pressure anymore, I can get lucky at starting to where the bulb gets hard but most of the time it does not so I have to hold the bulb up right certain ways to make it build up pressure...
Now does this sound like the primer bulb could be the issue??? On both outboards when I try to go fast it just feels as if they just not getting enough fuel... Any feedback is appreciated! Thank you
 

Mi duckdown

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How old is the line and bulb? two motors and same problem? portable tanks? built in tanks? More info. the primer bulb is only used to fill the carbs. You got other problems before the motor.
 
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MTboatguy

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Actually it sounds like the tank(s) are not venting correctly, one of the most common problems with high speed operation on all internal combustion engines. If the tank is never vented correctly, then the motor is not going to run correctly at WOT
 

henleyhale

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We call this a vapor lock where im from, at wot if your fuel hose or bulb sucks in then replace them the ones you buy from attwood last 2 seasons if your lucky for 40 bucks. If fuel tank isnt vented it would die at low speed when the suction for the tank was greater than the sucktion from your vacuum pump. And if none of those is the issue the fuel line in the fuel tank can soften and crimp up too.
 

Texasmark

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Couple of problems and the guys have addressed them. However I have a comment or two.

On the tank venting, one way to tell if it's not is to pull the cap off if a portable tank while running at WOT just to test it, or check your vent and vent hose if a permanently installed tank. Dirt dobbers just love to fill small holes with mud and an embryo. Most vents have screens but maybe yours doesn't. How would I do that? Well I thought about that and I think you need to remove the hose from either the tank or the vent fitting on the boat and see if you can blow through the hose. Realizing that if you blow into the inlet fitting end you are blowing into the tank, but if the hose is clogged you will know it as compared to being able to blow some air through it and into the tank till you get the tank pressurized to your breath's pressure!!!!!!! Since most hoses are reluctant to come off barbs after being clamped on for any length of time, I'd see if there was adequate length and just cut the hose off at the barb and when finished with your inspection push it back on and clamp it back as it was.

On the fuel line and bulb, if you are running the OEM gray hose and it's over 10 years old it may be like mine was. Tan flakes of material dislodge from the hose and follow the fuel flow through the line (with the fuel) to the bulb, to the pump, and ultimately into the fuel filter in the engine. These flakes will cause your problem also. Problem in chasing this problem is "where to open the line to see"? On my last engine, there was no removable connector between the fuel line and the engine at the engine entrance, just a double barreled union with a SS clamp on each end. I just cut off the hole beyond the barb on the union and had a look verifying my hunch.

If your squeeze bulb is aftermarket, then you should have two SS crimped clamps on each end and a plastic hose barb beyond that where you slide the fuel line over them and clamp with a SS screw clamp. That would be a point of access.....I'd take it loose on the engine side, get a suitable container, and use the bulb to pump some fuel into the container looking for contamination.

On bulbs, folks on here suggest that you replace with the Quicksilver/Mercury OEM bulb, not the aftermarket. I have used both over the years but usually used the OEM style on my Mercs which were my engines of choice the last 25 or so years. They sell them and hoses on this site.
 

AGUILERA2000

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Thanks guys... They are portable thanks and last year I did buy a new bulb but it didn't make much of a difference on the mercury.
As far as venting, I always have the venting "screw" open all the way on the tanks until I am done running the boat for the day, is that the right way to do it? Also I will try doing some of the testing suggested , one thing I do notice is that when pumping the bulb I can hear the fuel go right back into the gas tank, I mean it comes up to the bulb and on the next pump it flows right back into the tank instead of building pressure, yes I will buy a new bulb for sure, the reason I posted the topic was to see if my symptoms matched a defective bulb, also the comment that the bulbs last 2 seasons makes some sense they seem to be strong for like the first year and then they just don't work as well, anyhow I will install a new bulb and see, will do an update, thanks for the replies...
 
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AGUILERA2000

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Would it make sense to switch to a thank with a built in pump? I have an old thank that has a pump that you push up and down with your thumb seems a lot easier and perhaps more reliable, would that work? Or is it a bad idea?
 

Chris1956

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Do not add an additional fuel pump. Can you pump your primer bulb when running at high speed and keep the motor going at a constant high speed? If so, the issue is your fuel pump, or some kind of minor restriction in the fuel flow. If the bulb collapses, the restriction is between the bulb and the tank.
 

mr 88

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Having problems over the years with priming bulbs led me to EBay where I picked up a 3/8 ID one way check valve. I bought the one that was made for fuel and eliminated that issue.Installed it between bulb and engine.
 

MTboatguy

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Don't use the thumb pump in tank, they are a nightmare, I have one on a 2 year old generator I have to replace and it is not cheap, which really pisses me off on a 2 year old generator that has a little over 5 hours on it!
 

AGUILERA2000

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Thumb pump tank is out of the question as the fittings are different. I am almost sure it is the bulb, I didn't test anything today due to weather but what I did do was again turn the bulb different ways until it starts to "pick up" fuel and building pressure tomorrow I will buy a couple of new bulbs...
 

AGUILERA2000

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Having problems over the years with priming bulbs led me to EBay where I picked up a 3/8 ID one way check valve. I bought the one that was made for fuel and eliminated that issue.Installed it between bulb and engine.

Thanks very much I am my way to order a couple of them valves :)
 

AGUILERA2000

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Having problems over the years with priming bulbs led me to EBay where I picked up a 3/8 ID one way check valve. I bought the one that was made for fuel and eliminated that issue.Installed it between bulb and engine.

Thanks, wouldn't it make more sense to install between tank and bulb? Since the bulb itself tends to release fuel back into the tank? I am buying a valve either way. Thanks
 

AGUILERA2000

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Do not add an additional fuel pump. Can you pump your primer bulb when running at high speed and keep the motor going at a constant high speed? If so, the issue is your fuel pump, or some kind of minor restriction in the fuel flow. If the bulb collapses, the restriction is between the bulb and the tank.

I will test that it makes perfect sense, thank you very much...
 

Texasmark

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The bulb is supposed to have a check valve internally. What you said indicates a defective bulb. Leave the rest of the suggestions alone. Millions of boats are out there operating satisfactorily with a vented tank, fuel line, and properly operating squeeze bulb. On a fuel pump (electric) between the tank and the engine, forget it. BTDT and it doesn't do what you think it should.

Get a new bulb and check your lines for scale debris!
 

Silvertip

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Is the bulb installed with the arrow pointing at the engine? If this is a plastic tank check for bits of plastic clogging the pick tube. You do not need an anti siphon valve on a portable tank as it is not a fix for the problem you have. It is a bandaid at best.
 

AGUILERA2000

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Sep 15, 2008
Messages
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Do not add an additional fuel pump. Can you pump your primer bulb when running at high speed and keep the motor going at a constant high speed? If so, the issue is your fuel pump, or some kind of minor restriction in the fuel flow. If the bulb collapses, the restriction is between the bulb and the tank.

OK did the test, I am testing still using old bulb, first I took the fuel filter off and it was very clean except for a few big particles at the bottom, pumping pushes fuel with the filter on and off, now to the running part, I ran the motor and tried going fast, the motor never really picked up speed, it ran good up to 8mph and then dropped the power, at this point I check the bulb and the bulb is soft almost towards collapsing but not collapsed too bad just soft, I checked the air vent and that was fully opened I even opened up the gas cap bulb still on the soft side while running, doesn't this prove the blockage to be between tank and bulb or the bulb itself?... Thanks...
By the way I will be installing a brand new bulb but I had to order online since the store only had the smaller size and not the 5/16" I need...
 

Chris1956

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If the bulb is partially or fully collapsed, there is a restriction. Some fuel tanks have screens on the bottom of the pickup. Permanent fuel tanks have anti-siphon valves which can get clogged, My Searay had a fuel screen inside the fuel pickup tube. It clogged one day. The fuel pickup tube unscrewed to allow access to the filter.
 
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