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post #1 of 19 Old 07-18-2019, 06:23 PM Thread Starter
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Briggs Twin Diaphragm Fuel Pump Problem

I have a 1995 Murray Mower with an 18 HP Briggs Twin L-head that I cannot get to pump fuel. Engine Model 422707 Type 1263-01. I changed out the fuel pump gasket, diaphragms, and springs 4 years ago when it became harder to start, and I had no problems. Afterwards it ran fine for several years until lately it became harder to start sometimes. I have done 3 things: 1) I removed the vacuum hose and added clamps to both ends. It had none prior. You can feel vacuum at the hose end when you crank the engine. 2) I sprayed the carb with cleaner 3) I changed every thing in the fuel pump to new OEM Briggs parts. It was at least running before, just hard to start sometimes. Now you can look down inside the carb and no fuel is being pumped. The engine will run if you pour fuel directly in the carb throat until that runs out. I am running out of ideas, but am thinking about getting another fuel pump kit and trying again.

Any help would be appreciated. I'm pretty sure I got all the gaskets and springs in the right place.
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post #2 of 19 Old 07-18-2019, 10:06 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Have you confirmed that pump is not filling the bowl? Checked fuel cap for venting? You may have clogged passages in carb requiring disassembly to clean properly. Maybe float needle is stuck closed. Has mower sat for long periods with ethanol gas in it?
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post #3 of 19 Old 07-19-2019, 09:50 AM Thread Starter
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Re: Briggs Twin Diaphragm Fuel Pump Problem

I may have clogged something, but I did remove the 4 screws and took the top off the carb. The float and needle move freely. I sprayed one of the small holes in front of the fuel pump area, and with the fuel pump removed, I saw spray coming out of the fuel pump plate where it mounts. I had thought that the hole between the fuel pump and carb was clogged, but evidently not. I have retried the old set of diaphragms and it still will not spray fuel into the carb.

The mower had been running prior to this, it was just getting hard to re-crank sometimes, and so naturally I was just trying to improve this. I should have just left it alone, but I had re-done the fuel pump 4 years ago and had no problem.

Fuel gets to the pump, because when I disconnect the line, fuel runs out of the fuel line.
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post #4 of 19 Old 07-19-2019, 10:11 AM
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When i ran into such problems, I'd take of the carb and take it to the local hardware store for cleaning. Even when I'd take the whole carb apart and clean it up it still often would not work right. They had a guy that had a special carb cleaner. He'd clean it for us and we'd be good as new. Often times it may be easier to replace the whole carb altogether. They should be fairly priced on ebay.

You mentioned pouring fuel into carb and it running till that ran out...exactly the symptoms i had when the carb needed replacing. Don't know if it will help. Just a thought...

Last edited by Andrew2; 07-19-2019 at 10:25 AM.
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post #5 of 19 Old 07-19-2019, 11:22 AM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

probably no adjustable main jrt. Not sure if you can unscrew it from side and make sure it's not plugged. Ditto for idle jet.
Have you seen this
Disassembly, Cleaning and Repair of Briggs and Stratton Opposed Twin-Cylinder Carburetor - Part 1
also a part 2 for that carb
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post #6 of 19 Old 07-19-2019, 01:48 PM Thread Starter
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Thanks, I'll watch the videos.

I was messing with it this morning and I'm returning to the idea that the passage from the fuel pump to the carb throat is blocked. There is only 1 hole on the fuel pump mounting surface that goes into the carb. I tried carb cleaner and then using air pressure applied to the hole and it doesn't seem like it's getting through to the carb.
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post #7 of 19 Old 07-19-2019, 02:30 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Quote:
Originally Posted by wayne50 View Post
Thanks, I'll watch the videos.

I was messing with it this morning and I'm returning to the idea that the passage from the fuel pump to the carb throat is blocked. There is only 1 hole on the fuel pump mounting surface that goes into the carb. I tried carb cleaner and then using air pressure applied to the hole and it doesn't seem like it's getting through to the carb.
You might consider trying couple of these tests. Take about 2 feet of 1/4 inch fuel line hose and connect it too the existing fuel pump INPUT with the hose upright, fill the hose with gas using a small funnel and crank the engine and see if the gas level drops in the fuel hose. You can leave the top off the carb and see if fuel squirts out of the inlet hole on the carb body while the engine is cranking. Pull both plug wires so the engine does not try to fire and run or ground the kill switch wire.

Also if you had one of these vacuum type fuel pumps you could plumb it in before the existing pump on the carb and see if it will pump fuel through to the carb.
https://www.ebay.com/itm/Gas-Vacuum-...ffbe0f564d6a6c

If you are using gobs of grease to hold the gaskets in place sometimes the grease will not melt and will gob up a vacuum pump.

Make sure you are using BOTH of the 2 small springs on the flapper valves and correct orentation of the diaphragms.
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post #8 of 19 Old 07-20-2019, 10:53 AM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Given that the pump is mounted to the carburetor, it's hard to connect fuel line to the carb inlet, and to check pump output.
As I remember, it is easy to get the pump parts installed sort of backwards. The image I have in my mind from Jacks SME parts, or another site, showed the arrangement of the 'plates', gaskets, valve block, and cover in a way that allowed for confusion if you don't happen to remember how you took it apart. AND spring(s).
The pumps are simple, but you have to pay attention to the assembly. Sounds like a scold, but not meant that way. I've done more than that in my past.
Have you checked that the filler and vent are working properly? The 'vacuum'{actually pulses of vacuum/pressure} pulses need the crankcase to be tight or there's not enough to work the diaphragm. If the filler tube base O-ring/gasket is leaky, or the dipstick tube cap seal is bad, you won't get good pulses. If the crankcase vent flapper is full of oil(flipped upside down and doesn't drain?) it won't work properly.
The twin should develop real STRONG pulses as both pistons stroke to oppose vibration, and both will move to the crankshaft and away at the same time, which will exaggerate pressure difference more than a single piston design.
You might attach a balloon or rubber glove or ?? to the filler neck, and crank it over to see how good the pulses are. If the check/flapper valves are good, it should work. Be sure there's nothing behind the diaphragm and the spring is not 'cocked' or it won't pump.
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post #9 of 19 Old 07-20-2019, 12:02 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Here is a link to your carb and fuel pump, how to re-build and repair.

Outdoor Power Equipment Information

select repairs index, then scroll down to Briggs and Stratton carbs then

Briggs and Stratton opposed twin, PART 1

and maybe end up at this link for part one.
of repairs

Disassembly, Cleaning and Repair of Briggs and Stratton Opposed Twin-Cylinder Carburetor - Part 1

Part 2 is the carb.

You can remove the top of the carb and watch for fuel to pump out of the lower section of the carb fuel inlet while the engine is cranking

Last edited by Forest Gump; 07-20-2019 at 12:20 PM.
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post #10 of 19 Old 07-20-2019, 03:47 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Mistake a lot of people make is getting vacuum and gas line connected backwards. I can send you a Service Manual for your engine IF you like, address below put in proper format and remind me model number and what you want.

Walt Conner
wconner5 at frontier dot com
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post #11 of 19 Old 07-20-2019, 06:22 PM Thread Starter
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Re: Briggs Twin Diaphragm Fuel Pump Problem

I appreciate all the help and ideas. From reading other posts, I was sure to watch and keep the vacuum hose on the bottom. I watched one of Taryl's videos, and I see you can take the top of the carb off and you will see if the fuel pump is working correctly because it will spurt up gas when you crank on the engine. At least this should tell me for sure if the problem is with the pump or the carbureter. I feel good about the way I install the springs and gaskets in the pump body because I've done it about 10 times now looking for errors. It was running pretty well before I tried rebuilding the pump and it's probably something simple I'm missing. It seems like I should have followed the saying "if it ain't broke, don't fix it". I was just trying to make it perfect.

Last edited by wayne50; 07-20-2019 at 07:55 PM.
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post #12 of 19 Old 07-20-2019, 09:26 PM Thread Starter
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Mr. Walt, thanks for the kind offer, but I do have a printed service manual.

I hope I get the opportunity on Sunday to try out some of these ideas y'all have presented.

Thanks
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post #13 of 19 Old 07-21-2019, 06:12 PM Thread Starter
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Update:

I took off the top of the carburetor. Now if you turn the key switch, the fuel pump pumps fuel like the "Old Faithful" geyser. Plenty of fuel is being pumped. So my problem is in the carb, not the fuel pump. I put a wire thru all the holes, sprayed with carb cleaner, and blew out with air. Everything seems open. I even removed the pilot jet screw, cleaned and replaced it to 1 and 1/4 turns out where it was. I removed the main jet cover screw, cleaned and replaced the screw. I blew air thru both of the screw openings and everything seemed clear. I put on a new gasket, put the carb top back on, and now it will half-way run if I keep it on full choke. I did notice that the float is not quite level. When I first replaced the fuel pump diaphragms, I shot carb cleaner thru the hole that goes into the carb float needle hole. That was the only thing I did to the carb at that time. Could the carb cleaner have swelled the rubber tip enough to cause this problem?
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post #14 of 19 Old 07-22-2019, 12:42 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Make sure that the carb welch plug is still in the front of the carb by the idle jet. Sometimes air pressure will send it into orbit.

Also make sure you have good gas. If little bit of water or contiminated gas them twins will run very rough and need a choke.

Also try 2 1/2 turns on the idle jet.

Kinda sounds like maybe a could be a air leak. Check the 4 torx head manifold bolts on each side and the two carb base bolts.

Just make sure all bolts in the manifold and carb are snug.

I do not remember if the top carb gasket at the float area can be turned upside down, check it and the carb has a breather hole in the top between the carb and the breather. Make sure the gasket between the carb and the breather is correctly positioned so the carbs vent hole is open.
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post #15 of 19 Old 07-22-2019, 01:49 PM
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Re: Briggs Twin Diaphragm Fuel Pump Problem

Will it stay running if you continously spray carb cleaner into the air intake?
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