Briggs and Statton Backfires through carb

[Southern Comfort]

I have a 445677 0476 E1 Briggs Eng on a Husqvarna lawn tractor. Ran fine shut it down and the next day when I tried to start it it backfires through the carburetor. I checked the coils for spark, checked flywheel key all ok. I took carburetor apart and cleaned it. Still backfires. My next thought is valves, but what has me baffled is it ran fine the day before. Anybody have any suggestions?

 

[i7win7]

checked flywheel key all ok

If you didn't pull the flywheel to check the key, then I'd replace the key. A slight bend will cause spark timing issues.

 

[Southern Comfort]

I pulled the fly wheel to check it. Thank you for your help

 

[RandyT]

I would remove the valve covers and check to make sure all the push rods are still in place, and also check valve clearances. If you find a bent push rod then look closely at the corresponding valve because the biggest cause of bent push rods on that style engine is overheating of the head due to debris buildup on the cooling fins and the valve guide will migrate outward the valve caps until the valve can't open causing push rod failure. And in the event of a missing push rod the rod had migrated through the oil passage hole in the head into the crankcase.

Also if you didn't properly torque the flywheel after removal while checking the flywheel key it could of sheared on start attempt.

 

[R134a]

I have a 445677 0476 E1 Briggs Eng on a Husqvarna lawn tractor. Ran fine shut it down and the next day when I tried to start it it backfires through the carburetor. I checked the coils for spark, checked flywheel key all ok. I took carburetor apart and cleaned it. Still backfires. My next thought is valves, but what has me baffled is it ran fine the day before. Anybody have any suggestions?

I have a stand-by briggs generator w/ a Vangard v twin did the same thing. Drove me crazy. Carefully...check valve adjustment. If OK then replace BOTH ignition coils. Yeah I know you checked. I did too and it ran like sh*t backfiring a million times. Changed out both coils and now runs like its brand new.

 

[Southern Comfort]

Thanks for your reply. This Eng is driving me crazy. I have spark on both ignition coils but on a 20k scale I get a reading of 4.90 going from the sparkplug wire and the ground terminal. I don't think I should have a reading. The coils might be the problem because the lawn tractor was working fine the day before and the next day is when I started having this problem.

 

[R134a]

I have a 445677 0476 E1 Briggs Eng on a Husqvarna lawn tractor. Ran fine shut it down and the next day when I tried to start it it backfires through the carburetor. I checked the coils for spark, checked flywheel key all ok. I took carburetor apart and cleaned it. Still backfires. My next thought is valves, but what has me baffled is it ran fine the day before. Anybody have any suggestions?

Mine is propane and started backfiring out of the blue also. Briggs answer to backfiring was to check / adj valves. I did that and fooled with the carb but I knew it had to be timing related. I had both sides showing spark but apparently when those coils get crusty, the don't fire like they should. Mine were original likely 15+ years which is way too old when it sits outside all day.

 

[Southern Comfort]

I guess my next step is to check the valves but what is so confusing is this happened suddenly overnight. Thats why I though it was fuel or electrical related

 

[Southern Comfort]

I should have a reading on my coil going from the spark plug wire to the ground.

 

[Southern Comfort]

Update. I found my problem Bent push rod. Thank you everybody for your suggestions. Now the fun begins

 

[RandyT]

Update. I found my problem Bent push rod. Thank you everybody for your suggestions. Now the fun begins

Now look very closely inside of that valve spring. Make sure the guide is the same height as the valve guide on the other valve. If the head overheats it will cause the valve guides to migrate toward the valve keepers which then get to a point that they will prevent the valve from opening which is the cause of the bent push rods most of the time.

 

[Southern Comfort]

Thank you. Do you think I should pull the head and make sure there isn't any damage to the valve or piston

 

[RandyT]

Thank you. Do you think I should pull the head and make sure there isn't any damage to the valve or piston

As long as the valve guides haven't moved toward the valve keeper where they will prevent the valves from fully opening and bending another push rod, the valve and piston and cylinder should be fine.

 

[Southern Comfort]

The valve guide has moved and there is no indication that there ever was a valve seal on that valve. On the parts supplier web sites I don't see a listing for the valve guides for my engine. Do you know if this guide is replaceable.

 

[RandyT]

The valve guide has moved and there is no indication that there ever was a valve seal on that valve. On the parts supplier web sites I don't see a listing for the valve guides for my engine. Do you know if this guide is replaceable.

Only the intake valve would have a valve seal. And the guides are not replaceable.

 

[arto98607]

Sorry for the trouble - I thought these were pretty good engines?

Your post caught my attention since I also have a Vanguard engine in a Vermeer SC362 stump cutter.

It's a 35 hp 993 cc engine with about 800 hours on, and as one would expect it's a pretty tough service in stump grinder!


Question: Does your engine have an oil cooler (see the red arrow)?

 

[Southern Comfort]

No, my Eng doesn't have an oil cooler. Mine is in a Husqvarna lawn Tractor 24hp. Trying to find a way to repair a valve guide that has moved. I was thinking of trying Loctite

 

[etpm]

No, my Eng doesn't have an oil cooler. Mine is in a Husqvarna lawn Tractor 24hp. Trying to find a way to repair a valve guide that has moved. I was thinking of trying Loctite

Loctite needs some space to work. If the guide fits the hole with with no space between the guide and the head when the guide is pressed in the Loctite will just be wiped off. You could file a groove for the Loctite in the guide and then press the guide in. The groove needs to be only a few thousandths deep. The green (#609? I forget) Loctite for cylindrical parts loses its hold completely at about 450 degrees F. It does start to weaken at about 400 degrees.
Eric

 

[RandyT]

Sorry for the trouble - I thought these were pretty good engines?

Your post caught my attention since I also have a Vanguard engine in a Vermeer SC362 stump cutter.

It's a 35 hp 993 cc engine with about 800 hours on, and as one would expect it's a pretty tough service in stump grinder!


Question: Does your engine have an oil cooler (see the red arrow)?

View attachment 879939

The Vanguard isn't the same engine as the OP which is the Intek series. The Intek is more of a 750-1000 hour homeowner engine where the Vanguard is a commercial rated 1500-2000 hour engine.

 

[RandyT]

No, my Eng doesn't have an oil cooler. Mine is in a Husqvarna lawn Tractor 24hp. Trying to find a way to repair a valve guide that has moved. I was thinking of trying Loctite

There are a few people out there that have pressed them back into place and found a way to lock them there. If the attempt fails the guide will migrate back out and cause another bent push rod or worse end up in the crankcase. If the repair fails you will know in about an hour of operation.