Briggs and Stratton Intek v-twin 20hp

C

CLStout

Well-Known Member
I have an intermittent misfire with this engine. Serial number is 406777, type is 0442 B1. I have replaced the spark plugs after setting the correct gap. I have checked the valve lash. The intake on the left cylinder needed a slight adjustment. The others were all at .05. I cleaned the valve covers and put on new valve cover gaskets. I made sure there were no vacuum leaks. I even replaced the fuel filter.
This started as a slight backfire, but now has become more frequent. This engine has a lot of hours, but I can't give an exact number because there's no hour meter. I've had this mower since 2008, and it's been relatively trouble free.
Am I now having carb trouble? I'm stumped.
 
New spark plug wires?
Did you replace the coil and wires?
What is your compression on each cylinder?
I’ve had to remove the spark plug boot then clip a bit of wire off then reinstall the spark plug boot to the clean wire. Misfiring went away.
 
andrewslarge said:
New spark plug wires?
Did you replace the coil and wires?
What is your compression on each cylinder?
I’ve had to remove the spark plug boot then clip a bit of wire off then reinstall the spark plug boot to the clean wire. Misfiring went away.
Click to expand...
The coils are 2 years old, along with the wires. I haven't done a compression test yet. It's not using any oil and it's not building any pressure in the crankcase.
 
Is it possible you have a failing coil?
They can fail in under a year.
Can you swap the coils to see if misfiring follows the coil?

I’d love to see the compression numbers.
I read you listed backfire?
What causes a backfire? Exhaust valve not closing correctly? Fuel not burning from lack of spark at the correct time?
What other engine parts have been replaced since 2008?
 
Last edited:
andrewslarge said:
Is it possible you have a failing coil?
They can fail in under a year.
Can you swap the coils to see if misfiring follows the coil?

I’d love to see the compression numbers.
I read you listed backfire?
What causes a backfire? Exhaust valve not closing correctly? Fuel not burning from lack of spark at the correct time?
What other engine parts have been replaced since 2008?
Click to expand...
On the engine, just the coils and spark plugs. I'm not sure which side is backfiring. How can I test for this?
I'm sure I have a compression tester. Gonna have to dig it up.
 
New fuel filter. Fresh tank of gas. It's what I've been running since I bought the mower new back in 2008. The fuel pump is 2 years old. I will remove the fuel line after the pump and check it.
I haven't removed the engine cover yet to check the coils and the gap for the coils. I will do that tomorrow. I'm glad the compression numbers were good.
 
Hello C.,

One problem that is possible is the ignition coils kill wire because an inline diode is failing. The harness diodes fail with age. Usually, one of the cylinders will lose spark/fire intermittently. Eventually the problem becomes chronic.
 
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