Primer Bulb on M2500

hrdman2luv

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These Murray M2500's are junk. I get that. But this one is almost brand new. I back blew the fuel filter, replaced the fuel lines (which weren't bad). When you try to prime it, the bulb works fine until fuel starts going through into the carb. Then once it's full, the bulb won't come back out.
Something is clogged in there, I just can't see where.

Any help would be great. I've got a few of these like this.
 

primerbulb120

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Take off the fuel pump cover on the carb (held on with 1 screw) and replace the filter screen. It could be clogged, or it could just be malfunctioning and refusing to let gas through.
 

primerbulb120

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The cover should say "Walbro" on it and have one Phillips screw in the center.
 

hrdman2luv

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The cover should say "Walbro" on it and have one Phillips screw in the center.

This one must have a different carb. Has two screws holding the primer. Those two are long enough to secure the fuel pump. I'm not sure what I cleaned out or blew out, but it's working now.

Just wished I knew what I did, so I could do it again without having to go through it all. You know what I mean?
 

primerbulb120

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Oh I'm sorry, I forgot you have the primer on the carb. The two screws holding the primer on are the ones you need to remove. Then remove the primer base and you'll be able to access the screen. On carbs that are set up for remote primer, there's only one screw.
 

hrdman2luv

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Oh I'm sorry, I forgot you have the primer on the carb. The two screws holding the primer on are the ones you need to remove. Then remove the primer base and you'll be able to access the screen. On carbs that are set up for remote primer, there's only one screw.

I got another identical to the one about (on a weed eater brand) that's doing the same thing. I got the screen out, There doesn't seem to be anything on it. But I can't see through it. Should I be able to see through it.

Also, just for the fun of it, I poked a small hole in the screen, put it back together and the primer still stays in once fuel starts coming up the line.
 

bertsmobile1

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You really need to go to the Walbro web site download the carb manuals then READ them.
For those with limited reading skill or language problems there are also some videos.
The primer , which is not a primer by the way, has a one way valve on it.
When you press the bulb you expel what is inside the bulb.
When you take your finger off, the springyness of the plastic causes the bulb to return to its original size.
Because of the one way valve, this creates a low pressure zone inside the bulb so it draws whatever is in the carb metering chamber , be it air or fuel, into the primer bulb.
That is not much in the way of pumping pressure.
As the metering chamber pressure falls it will draw whatever is in the pumping chamber into it.
Some times there is a check valve, other than the pump diaphragm which has to be working.
Between the pump and the metering valve is generally a screen which also has to be clean.
The resultant low pressure in the pumping chamber then draws fuel from the fuel line into the pump

So sorry, you have to check the fuel filter, fuel lines, pump diaphragm, filter screen, metering valve & primer bulb check valve to find where the blockage is .

To diagnose these cube carbs properly you really need to have a low pressure pump & vacuum pump otherwise you are just pissing into the wind, wasting time & money.
Every time a cover comes off a cube carb the gaskets should be replaced or any fix done will be temporary and if you are doing this for money you will then have a warranty job in a short while or get a reputation of being a useless clot or perhaps both.
Joe Public have no understanding of how cube carbs work & how difficult they are to diagnose & fix, in fact in the age of information overload Joe Public seems to be getting substantially more ignorant by the second.
 
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