# Briggs and Stratton V-twin Intek problem



## badger77

Help. I'm having issues with my Briggs and Stratton 20 hp V twin running rough under load. The details of the engine are as follows.

Purchased 2002 (Scotts mower)
150 hours
Model 406777
Type 0128 E1
Code 020409YG

This engine has been well maintained but has had a backfiring problem I since the first year I owned it. I never did anything to address the backfire, but now I wonder if it is related to the more severe issues I'm having now. The engine starts fine and runs well at high speed when just driving, but any time the mower deck is on, it runs rough (sounds like it misses). It also seems to have a slight and occasional miss at idle when it is cold. Things I have checked or changed are as follows.

New Air filter
New spark plugs (helped the problem, but didn't solve it)
Cleaned carb
Checked coils/wires with spark gap tester (spark jumps .250" gap)
Set valve clearance
Checked flywheel key (seemed straight, but I did not pull it)
check fuel delivery, everything seems good there.
Checked compression (126 psi one side, 140 on other), I thought this was okay.

After changing the spark plugs, the mower was usable again, missing only occasionally. I did notice that one of the plugs was full of soot and the other was not. I used the mower after changing the plugs and it got progressively worse, running rough under load, and belching black smoke under load. After using for only a few hours, the new plugs were black, with one full of soot again. I change the plugs again, and it runs a little better again. The cylinder with the excessive soot build up is the cylinder with the higher compression pressure. 

Thanks in advance for any help you can provide is solving this issue.


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## 30yearTech

May be time to check the valve lash, which is recommended every 100 hrs for your engine. I really think you may have an carburetor problem. From your description, it sounds like your getting too much fuel when the engine is under a load.


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## badger77

Thanks for the quick reply. I set the valve lash at .004" on all 4 valves and no change. I'm affraid it is a carburetor problem. Is there a way of confirming it?


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## 30yearTech

I would take the carburetor back off and check and make sure the jets are properly seated, and there are no leaks on the seals for the fuel transfer tubes. Pay close attention to the side that feeds the cylinder that's running rich.


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## badger77

While "looking" for the jets, I believe I have stumbled on the problem. I found a parts explosion of the carburetor (a Nikki) and noticed that they changed the carb design after mine was made. While reviewing the difference between the old and new design (thinking that Briggs and Nikki may have designed out the problem I'm having), I noticed that my old carb has a single jet and the new carb has 2 seperate jets for each venturi. The "jet," if you should even call it that, is at the bottom of the fuel bowl and positioned in the brass housing that the fuel shut off solenoid screws into. That brass housing seals to the fuel transfer tube. The two are sealed with an o-ring.....a rotten brittle o-ring that has lost all elasticity. When the engine is operating under load and drawing a lot of fuel, extra fuel is bypassing the jet and getting past the o-ring seal and flooding the cylinders. For some reason it seems to flood one side worse than the other (maybe because the intake manifold is not symetrical). The oring between these two parts soaks in gas all the time, even when the engine is not running. I don't know if it is the ethanol in the gas around here, or just the gas itself, but it seems like a pretty flawed design. If there is a rubber that can tolerate being submersed in gasoline/ethanol for years, Nikki/Briggs didn't use it.

At least this is what I think it happening. We will see after the $3 part arrives in the mail.


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## 30yearTech

Sounds to me like that could very will be your issue. Let us know how it turns out.

Best of Luck.... :thumbsup:


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## badger77

The o-ring was it. I assume the problem I had is what drove Briggs and Nikki to redesign this carb. I hope this post helps someone with the same problem.


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## nitrohauler

Badger77

Did you notice if gasoline was getting into your oil? I have the same carb that you have and I'm having problems with gasoline getting into my oil. I went to a repair shop and all they did was give me some vague answers. I do also think it is because of flooding.


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