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Briggs and Stratton 5 HP Horizontal - Runs good for 60 seconds, then down hill


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04-15-15, 06:25 AM   #1  
Briggs and Stratton 5 HP Horizontal - Runs good for 60 seconds, then down hill

I have a Briggs and Stratton 5 HP horizontal crankshaft engine with a Pulsa-jet small well carburetor.

The tank had bad rust on the inside so I replaced with a new B/S tank. I took the pump cover off the side of the carb and cleaned all the fuel passages and replaced the diaphragm with B/S genuine part. I put a wire into the short pickup tube all the way up through the main jet and also sprayed carb cleaner up through the jet. New spark plug, air filter installed.

The engine starts right up and sounds great for about 60 seconds at full throttle. Then it starts not sounding so great. It's hard to describe, but it sounds like it's moving in/out full throttle and almost sounds like it's misfiring because I hear kinda like a thumping or popping sound every few seconds which is not natural. I'm not describing this very good. When it starts up and is running good for the first 60 seconds, the choke lever hardly oscilates at all. When it goes into the bad running cycle, the choke lever is oscilating back and forth more than normal like it's struggling. Also, it never recovers and goes back to the initial 60 seconds of running good. It never dies, but it never goes back to running good.

No problems at idle, the engine sounds fine. I did not take the welch plug off the side to expose the idle fuel mixing well, but I'm thinking these orifices would not be the problem if it is idling fine, but I may be wrong?

Any help would be appreciated. Thanks.

 
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04-15-15, 06:34 AM   #2  
I meant to say the throttle lever is oscilating back and forth, not the choke lever.

 
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04-15-15, 10:36 AM   #3  
I would assume there is still something blocked inside the carburetor. One problem with rust and dirt is that carb cleaner can't dissolve it so you may have to try cleaning it again. Remove the carb from the engine and remove the jets so you have better access to the internal passages. Here is a link to some disassembly and cleaning instructions. The good thing is there is not much on that carburetor you can't clean or fix.

What is this engine on?

 
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04-15-15, 11:38 AM   #4  
The engine is on a 25" Tru-Cut reel mower.

Thanks for the link. I've cleaned out every orifice in the link diagrams except for the idle mixing behind the welch plug on the side. I spray the carb cleaner down the orifices and the cleaner comes out the other end where it is supposed to come out. Are you thinking even if that happens, there still may be a clog that doesn't show itself until the vacuum and pressure differentials start up with the engine running.

 
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04-15-15, 12:33 PM   #5  
How clean is the screen on the bottom of the longer pick-up tube, the one that supplies fuel from the larger gas tank to the shallow (little) tank ?

It almost sounds like you don't have a reliable source of fuel coming from the primary tank to the small sump; even with the new diaphragm.

 
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04-15-15, 12:38 PM   #6  
Did you go through the adjustment procedure for the idle mixture? Did you do it when the engine was good and hot?

 
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04-15-15, 01:09 PM   #7  
Vermont, screen is clean going down into main tank. I will fess up that I connected the plastic extension tube with the metal tub that goes into the carburetor with a short piece of plastic hose that is very snug on both sides. I also ensured the plastic piece didn't extend too far down into the tank (extends just off the bottom). I've ordered a new plastic extension with clip and will install when I get it.

Pilot Dane, I did not go through the adjustment procedure for the idle mix. I cleaned the Idle mixture needle and reseated it and backed it out 1-1/2 turns.

 
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04-15-15, 02:07 PM   #8  
Just a little after-thought regarding that tank . . . . I think all of the pulsa-jet tanks (that I've seen) were made of pressed aluminun, meaning they don't rust. That orange crusty material that you see deposited on the interior is a build up of gasoline additives that accumulate elsewhere throughout the fuel system.

I've dissolved some of it using propylene gylcol antifreeze; but not all. It seems to stay put in the tank, so I don't worry about it there very much . . . . deposited elsewhere, it's a serious problem.

 
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04-27-15, 04:13 AM   #9  
Update: I cleaned the carburetor again (including orifices in idle mixing well) and also replaced the idle needle and put it all back together. The engine now works well. I still get the muffled popping sound but that is something that is happening in the cylinder and/or muffler/exhaust. That doesn't seem to be impacting the performance of the engine.

Thanks for everyone's help. Paul

 
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05-26-15, 10:05 AM   #10  
That muffled popping is likely too much fuel. Try turning the adjusting in 1/4 turn or two. Or out if that doesn't work. Or back to where it runs best and leave alone.

 
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