AR15.Com Archives
 Small engine guys, how the heck does this work?
Specop_007  [Team Member]
5/5/2010 9:06:57 PM
So I have a Troybuilt with a Briggs and Stratton 6.5 HP or some such engine. I know it has spark and I know its getting gas because if I pull'n pull'n pull I can get it started and it will fire up and run fine.

What doesnt work is the primer bulb. SO I cant prime the engine, hence having to pull my arse off to get it to start. I've taken the air filter cover off (Which is where the bulb is on) but frankly I cant figure out hoe the hell the thing works. Theres no tubes, no moving parts.....Its just a damn rubber push button.

How the heck does a primer bulb work, and how can I tell if its not working and proceed to fix it??
Paid Advertisement
--
Oakley  [Team Member]
5/5/2010 9:08:35 PM
Is the rubber bulb dry rotted? Maybe a crack, not allowing it to suck gas?
Specop_007  [Team Member]
5/5/2010 9:10:53 PM
Originally Posted By Oakley:
Is the rubber bulb dry rotted? Maybe a crack, not allowing it to suck gas?


The bulb doesnt seem to be compromised in any way except for the little nipple on the end of the bulb. I *think* that is not sealed but allows air to pass. My belief is that its supposed to get covered by your finger to maintain a good seal, although there could be a hairline crack at the base which I wouldnt be able to see.
VaFarmBoy  [Member]
5/5/2010 9:12:36 PM
I have had those little primer bulbs go bad when they appear fine. Replaced the bulb, and I was back in business.
Oakley  [Team Member]
5/5/2010 9:12:59 PM
need some of this then...





Jeffreysox  [Team Member]
5/5/2010 9:13:56 PM
It creates vacuum in the carb, to suck gas from the tank and pulls gas into the bowl of the carb to ensure its full. For some reason there is not enough vacuum the pull the gas.

Does the bulb release quickly after you push it? If so, there is a crack some where. If it is very slow and still not pulling gas, there is a clog in the line or a filter is clogged.
Specop_007  [Team Member]
5/5/2010 9:17:49 PM
Originally Posted By Jeffreysox:
It creates vacuum in the carb, to suck gas from the tank and pulls gas into the bowl of the carb to ensure its full. For some reason there is not enough vacuum the pull the gas.

Does the bulb release quickly after you push it? If so, there is a crack some where. If it is very slow and still not pulling gas, there is a clog in the line or a filter is clogged.


Yep releases quickly. That explains it, thanks guys. I was thinking the operation was to push gas into the cylinder and the air would pull gas in. I was also thinking that didnt seem right as that little bulb wouldnt move enough air to create the pressure needed to draw gas into the cylinder.

Bulb time I figure.
Specop_007  [Team Member]
5/5/2010 9:18:23 PM
Originally Posted By Oakley:
need some of this then...


http://i81.photobucket.com/albums/j236/Muhkanik65/Funnies/StartYaBastard.jpg




Dont laugh, that might the fix. Damn mower is 5 years old or more, if it grenades I wont feel out much.
Mosspointers  [Team Member]
5/5/2010 9:21:18 PM
Replaceable. Get a kit at a Briggs dealer. Simple fix. Kit comes with a bulb and a star type washer. Take model and serial# with you.
ScrubJ  [Team Member]
5/5/2010 9:26:36 PM
Originally Posted By Jeffreysox:
It creates vacuum in the carb, to suck gas from the tank and pulls gas into the bowl of the carb to ensure its full. For some reason there is not enough vacuum the pull the gas.

Does the bulb release quickly after you push it? If so, there is a crack some where. If it is very slow and still not pulling gas, there is a clog in the line or a filter is clogged.


WRONG! On a Briggs and Stratton the primer pressurizes the bowl of a float type of carburetor pushing the fuel up into the throat of the carb. Without knowing the specific model I can't give any really good suggestions. It is not uncommon for those types that are mounted on the air box to not work right due to warping of the plastic air filter back plate. If it is one of these types, the least most expensive repair is to remove the back plate and reinstall it with two gaskets.
rapracing  [Team Member]
5/5/2010 9:29:07 PM
Put the palm of your hand over the air intake and pull the cord. That will prime it for you
Specop_007  [Team Member]
5/5/2010 9:37:05 PM
Originally Posted By ScrubJ:
Originally Posted By Jeffreysox:
It creates vacuum in the carb, to suck gas from the tank and pulls gas into the bowl of the carb to ensure its full. For some reason there is not enough vacuum the pull the gas.

Does the bulb release quickly after you push it? If so, there is a crack some where. If it is very slow and still not pulling gas, there is a clog in the line or a filter is clogged.


WRONG! On a Briggs and Stratton the primer pressurizes the bowl of a float type of carburetor pushing the fuel up into the throat of the carb. Without knowing the specific model I can't give any really good suggestions. It is not uncommon for those types that are mounted on the air box to not work right due to warping of the plastic air filter back plate. If it is one of these types, the least most expensive repair is to remove the back plate and reinstall it with two gaskets.




Burley  [Member]
5/5/2010 9:42:31 PM
I would wager that diaphragm gasket is bad. I had a 5 HP B&S exhibiting the same symptoms (mower was five or six years old at the time). Took the carb off, the flapper on the gasket was partially torn, not allowing the primer system to pump. Replaced the $1 gasket and all is well.
vpost35  [Member]
5/5/2010 9:48:21 PM
Originally Posted By Burley:
I would wager that diaphragm gasket is bad. I had a 5 HP B&S exhibiting the same symptoms (mower was five or six years old at the time). Took the carb off, the flapper on the gasket was partially torn, not allowing the primer system to pump. Replaced the $1 gasket and all is well.


This
ScrubJ  [Team Member]
5/5/2010 9:48:51 PM
Originally Posted By Specop_007:
Originally Posted By ScrubJ:
Originally Posted By Jeffreysox:
It creates vacuum in the carb, to suck gas from the tank and pulls gas into the bowl of the carb to ensure its full. For some reason there is not enough vacuum the pull the gas.

Does the bulb release quickly after you push it? If so, there is a crack some where. If it is very slow and still not pulling gas, there is a clog in the line or a filter is clogged.


WRONG! On a Briggs and Stratton the primer pressurizes the bowl of a float type of carburetor pushing the fuel up into the throat of the carb. Without knowing the specific model I can't give any really good suggestions. It is not uncommon for those types that are mounted on the air box to not work right due to warping of the plastic air filter back plate. If it is one of these types, the least most expensive repair is to remove the back plate and reinstall it with two gaskets.


http://i546.photobucket.com/albums/hh408/Specop_007/P1010493.jpg

http://i546.photobucket.com/albums/hh408/Specop_007/P1010494.jpg


Need model, type, and code. More than likely stamped into the heat shield above the muffler OR in the blower housing right above the spark plug. If you have the square air filter mounted to the carb on the side of the engine, you can check the function of the primer by removing the filter, look down the throat of the carb and press the primer. If gas doesn't kind of bubble up through the emulsion tube, you have a problem. Wet the area between the backing plate and the carb with fuel or some light liquid and press the primer. See bubbles between the plate and the carb? If so, go to your local small engine place armed with the numbers I mentioned and get TWO gaskets. Pro tip would be to use some blue locktite on the mounting screws.

The common rebuild kit (498260S) comes with one gasket and no primer should you decide you want to go that way.
ScrubJ  [Team Member]
5/5/2010 9:50:54 PM
Originally Posted By vpost35:
Originally Posted By Burley:
I would wager that diaphragm gasket is bad. I had a 5 HP B&S exhibiting the same symptoms (mower was five or six years old at the time). Took the carb off, the flapper on the gasket was partially torn, not allowing the primer system to pump. Replaced the $1 gasket and all is well.


This


As best as I can tell he has a float type of carb, not the tank mounted fuel pump type.
Keith_J  [Team Member]
5/5/2010 9:53:45 PM
For the primer bulb to work, two things are required, proper seal on the carb bowl and sufficient elasticity in the bulb. After several years, the bulbs get hard, then they won't make the seal when you press on them and as such, it won't prime the carb. Likewise with the bowl gasket.

Replace both and you should be fine. Jacks Small Engines is a good online source. The bulb is retained by a toothed ring, an awl can be used to bend the teeth in to remove the ring, the bulb then pops off. Use a socket wrench of correct diameter to force the new ring and bulb onto the carb.

ScrubJ  [Team Member]
5/5/2010 10:00:26 PM
Originally Posted By Keith_J:
For the primer bulb to work, two things are required, proper seal on the carb bowl and sufficient elasticity in the bulb. After several years, the bulbs get hard, then they won't make the seal when you press on them and as such, it won't prime the carb. Likewise with the bowl gasket.

Replace both and you should be fine. Jacks Small Engines is a good online source. The bulb is retained by a toothed ring, an awl can be used to bend the teeth in to remove the ring, the bulb then pops off. Use a socket wrench of correct diameter to force the new ring and bulb onto the carb.



Come on guys, your killing me. The primer on a Briggs and Stratton is held in by a plastic ring with two ears that either engage the air box or the carb. You remove the ring by depressing the ears and pushing the ring out of its place with a flat bladed screwdriver or the factory tool that looks like a pair of pliers.
Lootie23  [Team Member]
5/5/2010 10:23:51 PM
This is an interesting thread. My weedeater bulb broke and I just ripped off the remaining rubber, been running it for two years that way. I read somewhere that the bulb on the weedeater I own (Featherlight) that the bulb's purpose was simply to cycle fuel through and ensure fresh gas was available for the carb. It is a little harder to start now, I have to pull it 5 or 6 times with the choke on, but it operates fine.

I wonder how a mower differs from this?

ETA: Okay, I understand now, just makes it easier to start.
THEBAUMER  [Team Member]
5/5/2010 10:25:43 PM
Originally Posted By ScrubJ:
Originally Posted By Keith_J:
For the primer bulb to work, two things are required, proper seal on the carb bowl and sufficient elasticity in the bulb. After several years, the bulbs get hard, then they won't make the seal when you press on them and as such, it won't prime the carb. Likewise with the bowl gasket.

Replace both and you should be fine. Jacks Small Engines is a good online source. The bulb is retained by a toothed ring, an awl can be used to bend the teeth in to remove the ring, the bulb then pops off. Use a socket wrench of correct diameter to force the new ring and bulb onto the carb.



Come on guys, your killing me. The primer on a Briggs and Stratton is held in by a plastic ring with two ears that either engage the air box or the carb. You remove the ring by depressing the ears and pushing the ring out of its place with a flat bladed screwdriver or the factory tool that looks like a pair of pliers.


Go get them tiger.
Paid Advertisement
--