Briggs....Carb gaskets


Old 01-07-01, 07:40 AM
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I have a minor question...

Neighbor brought over there old lawn mower because they bought a new one, and thought I may be able to tinker with it.

Briggs & stratton...It has spark after I gapped the mag/coil off the flywheel. The bolts to the coil where loose and the coil was riding on the flywheel.

Gave it a prime(has a primer bulb) and she fired right up...Yea! Then it died.. Not getting fuel flow...

Pulled the gas tank(metal) and carb(plastic) Took the carb off the tank, Talk about crud! Cleaned everything up, and blew the passages out by mouth and the WD-40 can.
The gasket was and still is questionable. It has 2 gaskets. One fiber thicker gasket and one thin rubbery gasket. I didn't tear it when I removed the carb, but it has 2 places in the rubbery gasket that act like reeds. It looks like they have been sucked into the holes they covered, and are formed to the holes sort of. I reused it anyway, because there was no place open yesterday to even look for the gaskets.

Now it won't even suck to prime from the bulb. Just sucks and blows air. Tried everything to get the primer primed. One of the reed petals on the gasket covers one of the holes air is spewing, and it isn't getting a good seal. So I thought oh well I'll choke it with my hand over the carb throat. That didn't work either. Its sucking air from what looks like the cranckcase breather tube. OK, plugged it and tried again. No go. I can dump some gas into the carb and she will run like a champ for 10 seconds, and while it is running I put my hand over the carb to get it to suck, and it refuses to. All the screens and passages are free of trash.

It won't suck fuel from the tank?????

My question... The gasket...... Will it cause it not to flow fuel.

Stumpped, but not quitting!

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Old 01-07-01, 11:06 AM
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Lightbulb Diaphragm Carb?


Based on the carb discription you posted, I would venture to say your referring to a diaphragm carb. <A carb without a fuel bowl.>

If that is the case, that thin flexable rubbery one isn't actually a gasket. <It should have a metal piece in the center of it.> If so, it's the diaphragm plunger.

That diaphragm part actually fluctuates from the postive and negetive pressures in the crackcase, as the piston moves up and down. It's movements open and close a center pin which allows fuel to move into and thru the carb.

Double check and verify you didn't accidentally invert the round but opened center gasket with the diaphragm one. If it's not reversed installed <A common error by the way> then you may just get lucky if it can be reassembled once more without damage.

Personally, it isn't often I ever had any luck attempting to get an engine equipped with this type of carb to run correctly once the diaphragm was remove and the same one reinstalled. Time wise, in a shop for profit business, a new one was installed from a kit.

In summation, your correct and on the right trail. It's that *%@#!#$* part that's most likely causing you the GRIEF...LOL

However, it's a great learning experience if you have never done this before. If you hang in there and succeed, you'll have a low compression four wheeled weed wacker...haha

Last edited by Sharp Advice; 05-07-04 at 09:10 PM.
Old 01-07-01, 06:15 PM
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No it is definitely not a diaphragm carb. I'm use to diaphragm carbs on jetskis. Like the Mikuni SBN type. Wish it was a Mikuni.

This carb is basically just a jet and a primer bulb. All the circuits and bowls are made into the top of the gas tank, with the gaskets, one on top of the other sandwiched together.

I'm pretty sure it's just the gasket has become old and comformed to the small holes they are suppose to cover/float over. The little reed like pieces of gasket kind of float over the holes, in two of the chambers between the carb and gas tank. They are not sandwiched between the metal tank and plastic carb. Just little tabs that stick out from the sealing surface. I'm guessing it acts like a needle/seat.
Old 01-08-01, 04:59 AM
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Carpets Done Wright, Replace the diaphragm as Tom says and I bet your mower will run.....Mike
Old 01-09-01, 10:58 AM
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Thanks Tom and Mike!

Have not tore it back down yet, but when I went to get the gasket, the guy behind the counter said...Oh, you want the diaphragm.... LOL. It was the gasket/diaphragm I needed.

I'll let you know how she purrs.

Old 01-09-01, 02:51 PM
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Well....It ran!
But not without problems.

Got it back together and it took forever to get a prime. It would run and then die. Same as before only now I had a primer again. Well for a little while I had a primer??

Blew into the gas tank and pushed gas thru the carb. Fired right up ran decent, putting my had over the throat of the carb to get it to suck gas, which it did. Ran it for about 5 minutes. Ok, put the Flame arrestor on and started to mow and put a load on it and she did alreight for about 10', then sputtered and died.

Messed with the spring on the butterfly and the air flap/accelerator and got it to stay running!!!!!
Topped off the gas and mowed the yard! Only hiccuped once. Started to surge and then it died. Was going to try the primer now and noticed it was sucked all the way in. Blew in the gas tank again and she fired right up and finished mowing the yard??

Oh well, It runs better then it did, which was not at all!!!!

Thanks Again!

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