Leaky needle and seat

David G

Well-known Member
I put a new needle and seat in a carburetor.

The float is not heavy.

I cannot find any obstructions, but it leaks when sitting.

What else can I do other than trying another one?
 
Just today I was working on a riding mower with a similar issue. After taking it off several times, I got the Dremel tool out and selected a pointed stone tip that fit approximately right. Then I twisted it back and forth by hand in the seat of the carburetor. Inspected it with a magnifying glass to be sure all was smooth and put it back together. Success! Good luck.
 
I've sharpened a pencil sized dowel, applied a dab of fine valve grinding compound and down basically the same thing. It works good if the needle's okay. gm
 
Yes, it flooded over, when sitting. I don't know where the vent hole was. Sent it off to be repaired. What kind of tractor are you working on?
 
One of a couple thing can be your problem.

#1 seat is not tight enough or you forgot the gasket under it

#2 the float is not set as it should be or it sticks as in hits the float bowl sides.

#3 the needle is one of the new rubber tipped ones and if it is you need to put a set in it by putting the needle in the seat and then tap on the needle a few times. Then pull it out and you should see a ring in the rubber tip and that is what is called a set
 
Put the needle in a cordless drill chuck just enough to grip it. Then run it in the seat with toothpaste. If it is a rubber tip, Old has the answer.
 

I, as well as others that I know of, have had success with the procedure that "young fella" Old describes for the neoprene tipped needles.
 
I solved my problem with leaky carbs on Jubilee, Farmall and briggs engines on mowers with leaky prone carbs by installing a solenoid shutoff.

My Terramites came from the factory with fuel solenoid shutoffs. Not to be confused with solenoids in carb.

The price of a solenoid is cheaper than a tank of gas that ran out of the Jubilee.

The way I see it, if carb works fine when running, just shut off the gas when it's not running. Soleniods always work, manually shutting off the fuel requires a good memory, not to mention remembering to turn it on again.
geo
 

The needle and seat BOTH need to be cleaned with aerosol carb cleaner, and then blown dry before installing. If the needle is not clean, it will leak.

Seat it with a hammer only if you have a strong desire to buy another needle and seat.
 
So which is it? Set it or don't set it?

I've had grizzled old timer experts tell me that setting the needle is the only way to do it, and grizzled old timer experts tell me that setting the needle ruins it.

In my experience it doesn't really matter. They all leak to some extent no matter what you do. I've cleaned, I've polished, I've cleaned again, I've set, I've cleaned one more time, I've not set... Drip drip drip...
 
(quoted from post at 06:30:58 04/18/17) So which is it? Set it or don't set it?

I've had grizzled old timer experts tell me that setting the needle is the only way to do it, and grizzled old timer experts tell me that setting the needle ruins it.

In my experience it doesn't really matter. They all leak to some extent no matter what you do. I've cleaned, I've polished, I've cleaned again, I've set, I've cleaned one more time, I've not set... Drip drip drip...

I have rebuilt countless Farmall H and M carburetors. It was my profession for awhile. I never had any issues with sticking or leaking needle valves AFTER I learned to thoroughly clean and dry them before installing. Seating the needle creates a ring. That ring is why the old needle was leaking. That ring occurs naturally over time. Why would put a wear ring on a brand new needle?
 
You can test the seal one of 2 ways,

The easy way, if you don't mind doing it... Turn the top upside down with the float installed, suck on the fuel fitting, put your tongue over the hole, see if it will hold vacuum.

The other way is to connect a temporary fuel line, hold the top upside down, watch for leaks with fuel gravity pressure on it. That will also check for leaks around the gasket, crack or pin hole in the casting.
 
It depends on why it leaks . If due to a poorly mfg seat it needs to be coined. I never use the needle to form a good seat. I use a needle from a injection nozzle and tap the seat with that to shape seat. Some are so bad you can see it with the naked eye.

Then I do the mouth suction test to confirm results. Also have done the temporary hook up to a supply of gas.
 
(quoted from post at 06:21:38 04/18/17)
The needle and seat BOTH need to be cleaned with aerosol carb cleaner, and then blown dry before installing. If the needle is not clean, it will leak.

Seat it with a hammer only if you have a strong desire to buy another needle and seat.

Seating with a hammer would require a whole new carburetor! Not only would it not flow gas it would not flow air either, LOL.
 
Also, as for "seating" a new needle, I have never done it.

In fact, some rebuild kits caution you not to exert pressure on the new needle while adjusting the float.
 
What do you "thoroughly clean and dry" them with?

Obviously carburetor cleaner and a shop rag is not the correct method to use. I've cleaned, cleaned, cleaned, can't detect any sort of residue on the needle or seat. Needle feels like rubber. Seat feels like brass. Still leaking. Drip drip drip... %$#@!
 

Over the years, I 've had it become automatic to check the crankcase oil, check for nuetral and turn on the gas before I get in the seat where I then push in the clutch(especially when it's cold out), turn on the ignition, then give her a bit of choke, check that the hand throttle is closed and hit the starter. In using the petcock when parked I guess I am just 'covering up' a leaking needle and seat but as long as the tractor runs good I'll just 'keep on keepin' on'. :)
 
you know the three sides of the needle are the wear points,polish them with emery cloth. the made in china parts seen to be just a little rough/too big. i have been doing this for 20 years.
 
Make sure your seat is tight. I had a 77 leak and couldn't stop it until I made a tool to tighten the seat better.

Usually those seats slots are narrow and the seat wide and most wide screw drivers are thick. I milled a piece of flat iron to fit into the 0.050 slot and wide enough to span it. The seat 'popped' twice tighter and worked pretty well ever since. It was a M&S carb.

RT ( my 2?)
 
(quoted from post at 13:03:33 04/18/17) What do you "thoroughly clean and dry" them with?

Obviously carburetor cleaner and a shop rag is not the correct method to use. I've cleaned, cleaned, cleaned, can't detect any sort of residue on the needle or seat. Needle feels like rubber. Seat feels like brass. Still leaking. Drip drip drip... %$#@!

Aerosol (spray can) carburetor and choke cleaner and compressed air. Brake cleaner in a spray can will also do the job and might be easier to find.
 
(quoted from post at 21:10:10 04/17/17) One of a couple thing can be your problem.

#1 seat is not tight enough or you forgot the gasket under it

#2 the float is not set as it should be or it sticks as in hits the float bowl sides.

#3 the needle is one of the new rubber tipped ones and if it is you need to put a set in it by putting the needle in the seat and then tap on the needle a few times. Then pull it out and you should see a ring in the rubber tip and that is what is called a set


All three points are valid!
 

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