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My 4-stroke had a similar problem:

If replacing a faulty fuel pump, remove the protective rupper caps from BOTH intake (done) and outflow nipples before attaching the fuel lines.


Don't ask.....

Last edited by las; 12/03/22.

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Originally Posted by las
My 4-stroke had a similar problem:

If replacing a faulty fuel pump, remove the protective rupper caps from BOTH intake and outflow nipples before attaching the fuel lines.


Don't ask.....

Doh!

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If the hose/bulb isn’t at fault the low speed jets mentioned by others is a good possibility. If you have any Kroil on hand saturate the carbs. Turn the motor a few cranks then spray it again. Let it sit a day then run. Cured a badly gunked merc V6.


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I am NOT an outboard motor guy, but see very good responses above:

dirt in idle circuit (maybe first try some Seafoam or other cleaner in fuel system before opening it)

if your fuel pump is vac operated (from crankcase?) and there is ANY leak in that area (bulb/hose?) or a check valve problem, the pump may not be getting enough vac at low rpms

pump may be wearing down enough to be weak at low rpm

best wishes


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I had the soft bulb issue last summer and running problems with a 50hp two stroke, problems as yours. I’d never had real solid bulbs on motors of which I’ve had plenty.

Took the motor in to a really super guy who tested inside and out then grabbed a new hose and bulb from the wall. He chewed my ass for buying hoses and bulbs from fleet farm, Cabelas etc.
His was nearly 80.00, really good quality. That did it. Issues solved.
That thing once pumped up stays as hard as a rock.
I know the new hose/bulb sounds expensive but compared to the other things mentioned here it’s not.

Osky


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I'd vac test the impulse line to the fuel pump. If that holds, I'd pop the bowl and check that pilot is clear....if all that (10 minutes time to do the above) passes, fuel line, bulb and any quick fittings get the peek.


Originally Posted by BrentD

I would not buy something that runs on any kind of primer given the possibility of primer shortages and even regulations. In fact, why not buy a flintlock? Really. Rocks aren't going away anytime soon.
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Best bet is to buy a service manual and go from there… usually the first thing I do when buying a new or used boat motor.

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Originally Posted by Salty303
put the 2 smoker ob in the back of your truck back up to the dump bin and deposit. Buy a 4 stroke. Sorry, that's all i got

This!!!

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Originally Posted by Osky
I had the soft bulb issue last summer and running problems with a 50hp two stroke, problems as yours. I’d never had real solid bulbs on motors of which I’ve had plenty.

Took the motor in to a really super guy who tested inside and out then grabbed a new hose and bulb from the wall. He chewed my ass for buying hoses and bulbs from fleet farm, Cabelas etc.
His was nearly 80.00, really good quality. That did it. Issues solved.
That thing once pumped up stays as hard as a rock.
I know the new hose/bulb sounds expensive but compared to the other things mentioned here it’s not.

Osky

Yep, same for the fuel line connector at the motor. Had an off-brand that would act like it was clipped on and open to the engine...but it wasn't. The schitty materials or specs were off just enough to give inconsistent attachment. Replaced the cheap connector with an OEM and solved the problem.


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2 strokes are incredibly simple. Pretty much if it has compression, spark and the seals are good.....it'll run.


Originally Posted by BrentD

I would not buy something that runs on any kind of primer given the possibility of primer shortages and even regulations. In fact, why not buy a flintlock? Really. Rocks aren't going away anytime soon.
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2004 is pre ethanol right? Any of your internal fuel lines could be suspect, in addition to fuel lines outside the motor. A little fuel line hardening quickly leads to high rpm air leaks. Also those "lined" fuel lines can cause all sorts of problems and likely were required by the epa as a way to frustrate people into buying new fourstrokes....


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Originally Posted by OldmanoftheSea
2004 is pre ethanol right? Any of your internal fuel lines could be suspect, in addition to fuel lines outside the motor. A little fuel line hardening quickly leads to high rpm air leaks. Also those "lined" fuel lines can cause all sorts of problems and likely were required by the epa as a way to frustrate people into buying new fourstrokes....


Did you read the guys issue, or just see "boat motor problems" and just give your diagnosis?

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Originally Posted by Crow hunter
Originally Posted by Salty303
put the 2 smoker ob in the back of your truck back up to the dump bin and deposit. Buy a 4 stroke. Sorry, that's all i got

This!!!

Obviously neither of you have ever had to push/drag an 18 foot john boat loaded with decoys, guns and gear through 6” of water/wet grass. I like my 2-strokes for a few reasons and have no interest in motors that are heavier, more complicated and higher maintenance than what I’ve got.



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Originally Posted by mirage243
Just put some Sea-Foam in it, that seems to be the consensus from all the Fire marine experts who don't know sheit. 😁😁😁

#2 consensus- Check the ground wire

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Check you fuel vent hose for muddobber stoppage. We have these little black bastids that will plug anything with a ⅛ to ⅜" hole in it.


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Originally Posted by mirage243
Originally Posted by 12344mag
If the fuel bulb is going soft in a short amount of time you probably have a bad check valve in the bulb and or the fuel pump on the engine is getting weak.



Here is your correct answer.
What the he'll do you know about outboards, especially a Yamaha.


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I'm gonna agree with CCCC about the idle air circuit being gummed or plugged. The fuel pump on that motor sucks from the tank with a single hose, there is no pressure in the primer bulb and it won't stay hard when running. There is a U-Tube video explaining the idle circuit, with a diagram of how the air in that circuit pushes fuel into the carb at low speed. The timing linkage needs to be set precisely, as well. I have a 2004 60 hp and a factory manual, which covers the 70 and 90 also.

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Originally Posted by TrueGrit
Originally Posted by mirage243
Originally Posted by 12344mag
If the fuel bulb is going soft in a short amount of time you probably have a bad check valve in the bulb and or the fuel pump on the engine is getting weak.



Here is your correct answer.
What the he'll do you know about outboards, especially a Yamaha.

😁😁😁

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I replaced the fuel pump diaphragms twice in 2000 hours of running on my Pro-V 150 due to ethanol laced fuel pinholing the diaphragms. Same symptoms, bulb would go soft, hard starting and poor throttle response. Pretty inexpensive and easy to do.


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Bad/weak spark plugs can also cause some funky issues.


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