# Primer Bulb Question



## salarmi (Jul 10, 2006)

Hello I have a question about a primer bulb, I have a tecunseh 5hp the carb is the type with no adjustments....anyways if the primer bulb is the non vented type, if there is a small leak ( due to a crack) will this cause the carb to flood? is there a vacuum created by the bulb in addition giving the carb some gas?

If so why? I was told that the bulb does two things prime the carb but also creats a vacuum for gas flow.


Thanks


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## paulr44 (Oct 14, 2008)

In short, no. A primer CAN cause fuel to overflow on a sealed system if the primer is the bowl vent (see following diatribe) and is clogged, but elsewise no, it can't. It can however, allow dirt in which is never a good thing in a carb.

There are different set-ups...Tecumseh made 3 different primer bulbs that mount directly on the carb. itself, and a couple mounted in the blower housing.

So a correct answer can't be given without knowing what you have...posting engine spec and a pic would help.

For instance, on snowblowers it doesn't matter as the carbs still have an atmospheric vent so the primer may have an intentional hole in the middle but it doesn't matter.

On some mower engines, the hole IS the atmospheric vent so it does matter.

Primer (wet, dry, or system air-purge type) bulbs do not EVER create a vacuum for fuel flow. Many hand-held machines have a primer that creates a partial vacuum, but only for purging the system of air. Calling it a primer is somewhat wrong, as back-in-the-day primers often forced fuel into the venturi by means of being a wet-bulb (B&S in the 80's) or using air-pressure (like Tecumseh Snow King engines) on top of the fuel in the bowl with the same effect. The hand-helds have check valves, so the bulb assy. is really a pump that pulls fuel from the tank through the carb and routes the return back to the tank (again, it's an air-purge which gets the metering chamber full to help in cold starts or ran-out-of-fuel re-starts).


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## salarmi (Jul 10, 2006)

*Carb Primer Bulb*

I have the carb number 640025C which replaces 640025 hopes this helps


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## paulr44 (Oct 14, 2008)

Again, a primer bulb that DOESN'T have a hole in it is not part of the vent system, so if there were a hole it in, NO, it could cause fuel to overflow.

FYI The carb. 640025C you have has a prime system that applies air pressure on top of the fuel in the bowl "forcing" fuel into the venturi. So a cracked bulb is irrelevant.

Either there's a fuel in the float, or there's an inlet needle and seat issue as the carb. you have is a bowl type. On a bowl type, even if the vent system were clogged the crack you have in the primer bulb would provide a vent so that's (the vent system) a non-issue.

Don't know where you got the idea a primer creates a PARTIAL vacuum for gas flow, but someone is misinforming you. I just deleted 2 paragraphs going further into primers. What you need to know about the system you have, I've stated.


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## salarmi (Jul 10, 2006)

*Primer bulb*

Ok thanks for all the info, guess I got bad info ...

I had replaced the needle and seat and float and the 
engine then would only stay running if I continued to press the
bulb and noticed the carb was flooding... if I did not continune to press the bulb it woud stall out. I replaced the bulb and it solved the problem, 

when I bought the bulb I was told it is a closed system......and it was not the pressing of the bulb that was keeping it going it was you blocked the leak with your finger, the pushing of the bulb (as I was doing was flooding) the carb. thats where I got the vacuum info.


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