# Pulsa jet carb leaking gas



## exfarmer (Apr 25, 2015)

Hi I'm new to the form and have a problem that has stumped me. I have an old B&S 5hp L head on a roto tiller.It hasn't been used for 10+ yrs. Before attempting to start it I cleaned the points, replaced the spark plug and cleaned the carb using carb cleaner, a fine wire and compressed air. New carb diaphram and gasket were installed also. The engine will start and run for a while but excess gas seems to be entering the carb flooding the engine. When it stalls the excess fuel runs out of the choke. This is a late seventies early eighties engine with gas tank beneath the carb. I think this is what B&S called a pulsa jet but this one has a pull out choke. I cannot think of any reason why or how excess fuel would build up in the carb's throat and run out the choke. Any ideas??


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## Sir Thomas (Dec 7, 2013)

Sounds like the same engine that's on my Till Smith Tiller. For some reason the carb is flooding. Have you adjusted the jet screw? It may be too far out.

Initial Adjustment
1. Turn needle valve clockwise until it makes light contact with the seat. DO NOT FORCE.
2. The initial setting of needle valve is made by turning out (counterclockwise) 1-1/2 turn. Final adjustment is made
with engine running.
3. Install complete air cleaner assembly.

Final Adjustment
1. Start and run engine at half throttle for five minutes
to bring engine up to operating temperature.
2. Place governor speed control lever in “FAST”
position.
3. Turn needle valve in until engine misses
(clockwise – lean mixture) then turn it out past
smooth operation point until engine runs unevenly
(counterclockwise – rich mixture).
4. Turn needle valve to midpoint between rich and
lean so engine runs smoothly.


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## exfarmer (Apr 25, 2015)

I adjusted the mixture screw just the way you said. It is as if the fuel pump is pumping gas directly into the carb instead of into the fuel bowl in the gas tank.


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## Sir Thomas (Dec 7, 2013)

I know this carb is a pain to remove but you may have too. Pull the carb and disassemble it completely. Remember to take the idle screw out before removing the needle valve nut and seat. On the bottom of the carb there is a long tube with a screen and a short one. While you are at it, make sure they are clean. When you see the pump area after taking the diaphragm off there are two small holes. I don't remember which one goes to which but take some carb cleaner with a spray tube on it and shoot it into each hole. One should come out of the long tube and one should come out of the bottom of the carb.
Also spray some into the needle valve hole and check the valve seat and the needle.


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## exfarmer (Apr 25, 2015)

Thanks Sir Thomas but that has already been done. 
I know these carbs have a fixed high speed jet but I'm not sure where it is located. Does anyone here know?


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## Sir Thomas (Dec 7, 2013)

See is this will help
http://outdoorpowerinfo.com/repairs/briggs_pulsa-jet_horiz_fixed.asp


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## exfarmer (Apr 25, 2015)

Thanks for the link. My carb is an older version that has a slide type choke under the air cleaner as well as a short plastic tube instead of the cast tube. The engine model is 130202 and it was built in 1980.
I had it running this morning. It ran good for about 30 sec then stalled. As soon as it stalled I could see the gas building up in the carb bore, there was probably 2/3 of a teaspoon of it. I don't know how that would even be possible, but it happens!


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## 30yearTech (Sep 14, 2006)

Pretty much the only way fuel is going to bypass the adjustment screw is through the fuel pump diaphragm. did you get the cap on the spring under the diaphragm. If not, the spring can poke through the diaphragm and cause it to leak. 

There is also no real low speed circuit on this carburetor, the brass seat under the adjustment screw feeds the main jet and the adjustment is for both top end and low speed performance on this carburetor.

Also make sure the fuel cap is venting the tank, or you can have issues with fuel being forced up the pick up tube.


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## Sir Thomas (Dec 7, 2013)

What brand is the rototiller? Mind is a Till Smith with the exact same model Briggs and Stratton. I rebuilt it from the ground up. I could not find any info on the tiller itself and parts were missing like the bar between the link to the belt tensioner and the lever linkage. I had to make one by trial and error.

https://www.dropbox.com/sh/fibb7lnqt98tpw7/AAD8BidTsyXy3ehDlUIs8UhMa?dl=0


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## exfarmer (Apr 25, 2015)

30yearTech said:


> Pretty much the only way fuel is going to bypass the adjustment screw is through the fuel pump diaphragm. did you get the cap on the spring under the diaphragm. If not, the spring can poke through the diaphragm and cause it to leak.
> 
> There is also no real low speed circuit on this carburetor, the brass seat under the adjustment screw feeds the main jet and the adjustment is for both top end and low speed performance on this carburetor.
> 
> Also make sure the fuel cap is venting the tank, or you can have issues with fuel being forced up the pick up tube.


The cap is on the spring and it's a new diaphragm. The gas cap wasn't on. I'm baffled!


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## Sir Thomas (Dec 7, 2013)

If there is no hole or tear in the diaphragm and the cap is on the diaphragm side of the spring there is no way excess fuel can enter the Carb throat and flood the carb. Besides the chamber on the spring side of the diaphragm does not enter the carb throat. There is a wall separating it from the other which ends at the intake port of the head.
The choke, and yours is like mine, cuts off the air flow from the air intake creating a vacuum which sucks fuel into the carburetor pass the idle screw. The idle screw restricts the flow of fuel as set. There must be something going on with the jet or needle screw and seat allowing TOO MUCH fuel to enter the carburetor. Did you get a new seat, nut and screw with washers?


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## Sir Thomas (Dec 7, 2013)

Fuel is in the tank but for the vacuum in the carburetor would not be strong enough to pull it into the carb throat. That is what the diaphragm is for. The vacuum created by the down stroke of the piston overpowers the spring drawing fuel from the bottom of the tank pass the check valve into the chamber between the diaphragm and the diaphragm cover. When the valve close and the vacuum is gone, the spring forces the diaphragm to pump the fuel into the reservoir. Then the vacuum in the carb throat created by the piston down stroke and the choke being closed pulls extra fuel from the reservoir pass the jet screw or idle screw into the carb throat and enters the combustion chamber. Once the engine fires the choke is no longer needed since the down stroke action of the piston is sufficient enough to keep the fuel flowing into the carb throat from the reservoir.


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## 30yearTech (Sep 14, 2006)

What part number diaphragm did you use? There are a couple of different ones available and if it's the wrong one, it could leak...


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## Sir Thomas (Dec 7, 2013)

I still can't see how fuel can get through the diaphragm into the carb by going around the split wall that ends at the intake mount.
https://www.dropbox.com/sh/r55kz2zmger6an7/AABJ63ZnPkzN_6SLjOLmeG-Ma?dl=0


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## 30yearTech (Sep 14, 2006)

Sir Thomas said:


> I still can't see how fuel can get through the diaphragm into the carb by going around the split wall that ends at the intake mount.
> https://www.dropbox.com/sh/r55kz2zmger6an7/AABJ63ZnPkzN_6SLjOLmeG-Ma?dl=0


Next time you have your carburetor off and your looking at that "split wall" pour some fluid in there and see where it comes out!

If it wasn't open to the throat of the carburetor how would the vacuum pulses of the engine operate the diaphragm?

Believe me, it's open all the way through, that's just a baffle you looking at. In fact you can see it if you look at the picture you posted. When your looking straight down the throat of the carburetor you can see all the way to the pulse port! If fuel leaks around the diaphragm, there is no way it's not going to enter the carburetor throat.


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## Sir Thomas (Dec 7, 2013)

OK...My bad. Please accept my humblest apology. Exfarmer, let us know what shape your diaphragm is in.


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