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4hp Mercury 1988 4 hp wonbt start

packfan919

New member
"Hi,

Got a 1988/89 Mercury 2stroke 4hp (made in Japan) that won't start. I can squirt gas directly into the carb and it starts on the first pull. I rebuilt the fuel pump with all new gaskets/parts and still no luck.

Removed carb to clean bowl and check float and all is fine. However its not pulling fuel into the bowl, but I am 100% positive that the fuel pump is working (its part of the carb on this engine).

What am I missing? Why is the carb not causing the fuel pump to pull fuel into the bowl? - Again all new parts on the fuel pump (including the screws that hold it in place!).

thanks"
 
"Since you are not getting gas

"Since you are not getting gas to the carb and you have just redone the fuel pump I would suspect you have a blockage somewhere on the "other" side of the fuel pump.

That would be in the hose going over to the tank or any of the inline components - fuel filter, fuel cock or the little hoses in between. You may even have a clog in the tank itself.

I would disconnect the fuel line that is feeding the fuel pump and see if you have gas flowing. Since it's gravity feed to that point, you should get a decent flow - if not, start back tracking from there..."
 
Thanks for the advice!

I


Thanks for the advice!

I checked the fuel line going to the pump just before I rebuilt the fuel pump and it had very good gravity flow.

What bugs me is why the carb is not causing the fuel pump to pull the fuel into the bowl. Is there a vacuum problem of some sort that I'm missing?
 
Pump the fuel bulb and see if

Pump the fuel bulb and see if she runs.

Reeds could be stuck open and not causing vacuum to draw fuel in? Weird as she would not start if this was the case.

Good luck!
 
"Okay - new information.

So


"Okay - new information.

So, I went home at lunch and disconnected the hose from the tank (the tank is internal so I don't have a primer bulb). I pulled the starter rope while holding my finger over the hose that leads directly into the fuel pump. No suction. There is no pulse coming from the carb to cause the fuel pump diaphram to move and pump fuel into the bowl.

Now we are getting somewhere - except I have no idea what the issue might be in the carb.

Suggestions on where I am losing the suction?"
 
"Recheck the diaphram on the f

"Recheck the diaphram on the fuel pump (it may have got pinched, split or even have a bad gasket and also make sure that the little hole leading to the crankcase is not clogged up.

It's crankcase pressure that operates the fuel pump, so that's the number one suspect..."
 
"Well, I was ready to take it

"Well, I was ready to take it to the mechanic when I decided that a brand new complete carb shipped to my door was cheaper by far than paying a mechanic to rebuild it.

Less than 150 bucks for the carb with complete new fuel pump. It took 5 minutes to put on the new carb and it fired up on the first pull. My suspicion is that the old carb has some port blocked with grime or something.

I'll keep it around for spare parts anyway. Thanks for all of the help!"
 
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