Backfiring through the exhaust

[PTmowerMech]

Stop it with the inferior spark tools LOL.

Taryl made a video "showing" all us how a coil can show "visible sparking" with the inline Christmas light types. Would blink at low, med and high revs with the bulb type. Gap type showed spark at low revs, nothing at mid and high revs at all. Weak coil all the way.

Here is Taryl's video on spark testers. Explanation starts at 4:04 through 7:07. Fast forward to get to the point.

Thank you. Also @Auto Doc's @Forest#2 and the others for this imput. That explains what I'm missing.

Tester ordered.

 

[PTmowerMech]

Here is Taryl's video on spark testers. Explanation starts at 4:04 through 7:07. Fast forward to get to the point.

One thing I noticed about this engine with the bad coil....... It didn't backfire.

 

[wekjo]

Blow shop air backwards thru fuel line to clear any obstructions. Costs nothing. Fuel starvation can cause intermittent back fire

 

[slomo]

One thing I noticed about this engine with the bad coil....... It didn't backfire.

Didn't expect it to, myself.

Hope everyone got the idea about poor coil/spark testers. Don't use the inline Christmas bulb type testers. They do not tell the whole story of coil performance.

 

[Savage3]

Assuming you checked timing, spark plugs, and all the other ideas posted above and all is well:

If it has the little anti backfire solenoid on the bowl of the carb, test the voltage and current coming to the solenoid. Check resistance as well.

Sometimes that solenoid goes bad, not all the way at once. The wire coating melts and it still works, but, not like it should. It will cause a lean condition.

Pull the spark plugs first, look at them. See if they are running lean.

 

[Gord Baker]

407777 0188 B1

On a service call, started out, this thing ran like crap. Lot's of back firing through the exhaust. After about 10 minutes of it running & mowing, it seemed to clear up. It was still backfiring, but in spurts, it would completely clear up for several seconds. Maybe even a couple of minutes.

So I thought maybe it was just some junk in the carb that made it's way through. A couple of weeks later, customer calls and says it still running bad and that it wouldn't even stay running. So I picked it up and brought it home. (like a dummy, I didn't even try to crank it there)

At home, I crank it, and it's still got a little back fire issue. But nothing major, like it was the first time I cranked it. I throw on a set of new plugs (RC12YC). Of course that didn't change anything. But it eliminated the possibility of a bad plug. I ran it for about 10 minutes and the plugs were spotless.

So I guess the question is what could make it run like crap one minute. I don't want to do nothing to it, return it to the customer, only for to start doing it again.
Like I said the only real symptoms now is the slight exhaust backfire. I remover the air filter so I could see down in there, and didn't see any carburetor back fire.

I suggest a fuel diagnosis. Sounds like it is running Lean. The usual suspects, carb/filters. Check Valve Lash.

 

[Ed5060]

The carb is clean as a whistle. Even the bowl had almost nothing in it. The valves were at about .06. So I didn't mess with them.

So you cleaned out the jets and passageways, not just looked?

 

[90210]

Had the same issue with a craftsman lt1000 i went On Amazon bought aftermarket carb coils and oil change kit all For about 30 bucks it’s been running great all summer my guess is it was the coils ..mine is over 20 years old so Oem parts wasn’t going to happen at 3 times the price…

 

[Aquadisiac]

407777 0188 B1

On a service call, started out, this thing ran like crap. Lot's of back firing through the exhaust. After about 10 minutes of it running & mowing, it seemed to clear up. It was still backfiring, but in spurts, it would completely clear up for several seconds. Maybe even a couple of minutes.

So I thought maybe it was just some junk in the carb that made it's way through. A couple of weeks later, customer calls and says it still running bad and that it wouldn't even stay running. So I picked it up and brought it home. (like a dummy, I didn't even try to crank it there)

At home, I crank it, and it's still got a little back fire issue. But nothing major, like it was the first time I cranked it. I throw on a set of new plugs (RC12YC). Of course that didn't change anything. But it eliminated the possibility of a bad plug. I ran it for about 10 minutes and the plugs were spotless.

So I guess the question is what could make it run like crap one minute. I don't want to do nothing to it, return it to the customer, only for to start doing it again.
Like I said the only real symptoms now is the slight exhaust backfire. I remover the air filter so I could see down in there, and didn't see any carburetor back fire.

We have a brand new John Deere Z950M Zero Turn at the park where I work since retiring! With only 50.4 hours on it, it started backfiring through the exhaust. Long story short, It turned out to be Water in the fuel. Since it was brand new, we took it back to the dealership to let them work on it. They drained all of the gas, blew out or replaced the fuel lines and put on a new fuel filter, fuel pump and replaced the spark plugs. Today it has 75 hours on it and it is running flawlessly again!! So, check closely for water in the fuel system!!
Good Luck.

 

[hlw49]

I would do a cylinder leak down test and a compression test.