# Briggs cutting out



## Munkey (Jun 12, 2006)

Hi all, I've got a problem with an old vertical shaft Briggs. I'll get the number tomorrow, but its one of the old vertical starters with an exposed crankshaft grill.

Anyway, i pulled it (attached to a deck) out of a garden where it had sat for 10 years or so, cleaned the carby and changed the oil and air filter and it started up second pull  . Bore is virtually perfect, it must have been barely used. It idles great, but when you give it more throttle it runs rough and will either cut out or carry on running rough for 20 secs or so before going smooth.

I thought it was running too lean, so it was richened by a good couple turns, which made no difference at all... Then I thought it was over-fueling so it was weakened back past original, but it still behaves funny. After that, I stripped down the carb again and cleaned all the jets and choke diaphragm. Guess what? It still cuts out.

Then, I blamed the governer for shutting it off when it starts to rev. But the governer (its one of the in-crankcase ones) is working fine it turns out.

Damn, this thing is annoying me. Anyone got any ideas? Thanks


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## tom tilson (May 1, 2006)

What type of application is it in? If it is a mower, after it cranks, gently increase the speed to wot and see if it responds ok. If so. one of the idle progression holes may be plugged and you will either need to resoak it and blow out the passages or use it like it is. On something like a go-kart then it has to accelerate with quick response. You say that it is old. If it is a bowl type carb, the accel nozzle may be clogged and will require cleaning out. This nozzle is located on the casting that sticks down into the bowl and is about 2 1/4 " long. It. is screwed in at about a thirty degree angle with the vertical casting that the bowl high peed jet screws into and also holds the bowl on. Make sure that all of the holes in the bowl screw ( hi sp jet) and possibly with some idle drillings as well are cleaned out. If you have to remove the nozzle, it is usually tight fom being there so many years and can be easily ruined with the wrong screw driver. To remove, select a screw driver with a bit that fits the full width of the screw and which is thick enough to fit snug. Spray PB Blaster on the nozzle. hold the screw driver straight in the nozzle slot and give it a sharp rap. If you attempt this and bugger the screw slot, there is a way to still get it out,but lets not go there yet.


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## Munkey (Jun 12, 2006)

Its on a rotary mower, and even gently increasing speed causes it to cut out. It isn't one of the older bowl-carb types, its one of the half-in-fuel tank ones which have two pick-up tubes, both of which are unblocked. (the type made just before the fixed-mixture carbs came in) The carb only has a single jet and one adjuster screw. 
Thanks for the help.


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## nitrojeff (Jul 23, 2005)

my old toro had a bad peckok on the gas tank that did not allow enough fuel at full throttle, it also sat awhile.?!.


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## tom tilson (May 1, 2006)

The choke on that carb has a metal butterfly in the carb throat, not a diaphram. The thin diaphram that you see is the fuel pump membrane. I have a 3hp tiller that is like your carb but has only one pick up. Mine is in need of a repair kit, but I do not have time to fix it with the garden in full production. I place the throttle in the wide open position and choke full on. When it fires, I jockey the choke lever, that is, I move the choke to off and right back onabout 90% of the travel. I have to do this for sometimes 2 min until the engine warms up, then she is ready. Before you try this, turn the adjustment needlesin until it just touches the seat, DON'T FORCE IT, then preset it by opening it about 1 1/2 turns. The main jet is probably fixed and the needle then would be your idle fuel mixture. If that doesn't work for you, then let's move along.
The long tube in the tank picks fuel up from the lower part of the tank and discharges it into a reserve well where the short tube picks it up and feeds fuel into the carb. I don't remember what you have done already, but I would definitely replace the diaphram, all of the gaskets and put the little red tube on the carb cleaner can and blow through every passage. I you have an air compressor. blow the jets out with the idle needle removed from the carb. If it does not run get back with me. make sure that when it starts, that the choke will come all the way off. That is, no restriction to air flow,


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## Munkey (Jun 12, 2006)

Hmm. It doesn't start when the throttle's in full position, but it starts fine when it's on idle or about 1/4 speed. The diaphragm on mine is directly connected to the butterfly by a short length of wire, so when it starts the engine's vacuum pulls the diaphragm down and opens up the choke (a plastic valve with a bypass vacuum valve). It doesn't appear to have a fuel pump membrane, as the only diaphragm there operates the choke.

When its running, the choke is open fully so I guess this is working ok. I've already tried opening the set screw 1 1/2 turns, and right now it's on that setting. Richening or weakening it appears to make little difference, which is a bit weird.

I'll run down to the local mower shop and get a new gasket/diaphragm. Its all combined into one rubber sheet with the spring and brass fixing riveted into it. Thanks again for the help.


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## tom tilson (May 1, 2006)

One look is worth a thousand words and unfortunately, I don't have an exploded view of the carb. I did not realize that it had an automatic choke and they do have plastic butterflys and a vacuum operated dahpot just as you described. Although I do not have the diagram, the way it acts suggests to me, that you still have dirty passages in the carb body.A trick that I use. one can of carb cleaner from Walmart @ $1.14 Put the little red nozzle on it and with your hand over the mouth of say a pickle jar to prevent splatter, empty the contents in the jar. You now have a nice carb dip that will not hurt gaskets etc, I soak overnight and then blow out jets with compressed air. Blow in every hole that you see and with the needle removed. I feel that dirt or rust since the machine sat idle so long is the issue. Poke a small piece of tag wire in each hole before blowing it out. Good luck. Please keep us informed. If the filter has a long bolt that goes through it and you are trying it out with the filter off, stick the bolt back in the hole as that open threaded hole can seriously affect carb functions if not installed.


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## tom tilson (May 1, 2006)

One look is worth a thousand words and unfortunately, I don't have an exploded view of the carb. I did not realize that it had an automatic choke and they do have plastic butterflys and a vacuum operated dahpot just as you described. Although I do not have the diagram, the way it acts suggests to me, that you still have dirty passages in the carb body.A trick that I use. one can of carb cleaner from Walmart @ $1.14 Put the little red nozzle on it and with your hand over the mouth of say a pickle jar to prevent splatter, empty the contents in the jar. You now have a nice carb dip that will not hyrt gaskets etc, I soak overnight and then blow out jets with compressed air. Blow in every hole that you see and with the needle removed. I feel that dirt or rust since the machine sat idle so long is the issue. Poke a small piece of tag wire in each hole before blowing it out. Good luck. Please keep us informed.


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## Munkey (Jun 12, 2006)

Thanks, I'll try that. Time to get some more carb cleaner...


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