Backfire is the name of the game

[JonahPro]

I have a Lawnboy SilverPro Series 10324 with the 6.5 hp Duraforce. I installed a new carburetor, checked the exhaust ports (which were surprisingly clean), installed a new NGK spark plug gapped at .035, air filter is clean and everything is in good order. Or so it seems. This thing starts up usually first or second pull and runs fairly good, with one exception - it backfires constantly. It has enough power that I could probably mow with it but the backfiring is a total nuisance. Not to mention it’s an indication that something is not right and there’s the chance I might do more harm by running it.

Does anyone know of something I can try? Thank you so much.

 

[Tiger Small Engine]

I have a Lawnboy SilverPro Series 10324 with the 6.5 hp Duraforce. I installed a new carburetor, checked the exhaust ports (which were surprisingly clean), installed a new NGK spark plug gapped at .035, air filter is clean and everything is in good order. Or so it seems. This thing starts up usually first or second pull and runs fairly good, with one exception - it backfires constantly. It has enough power that I could probably mow with it but the backfiring is a total nuisance. Not to mention it’s an indication that something is not right and there’s the chance I might do more harm by running it.

Does anyone know of something I can try? Thank you so much.

Why did you install a new carburetor? Do you still have the OEM carburetor? First thing I would do is open the valve cover and do visual inspection and check/set valves to spec.

 

[Douglas Lee]

I have an Old Blue Homelite XL chainsaw that was popping and carrying on one day,
turns out the solder joint that connects the condenser to the mounting clip had broken
and was making and breaking contact while the saw was in use. Re-soldered the clip
and good to go!
Don't forget the electronics!
Thanks,
Doug Lee
*

 

[sgkent]

there are two or three kinds of "backfires." Is it coming back out the carb? Is it an explosion in the muffler Is it fuel and air igniting outside the exhaust? Is it a random "misfire" that you are hearing? Each has a different cause. You need to do a better job of determining exactly what the symptoms are and what makes them better or worse - Meaning you can observe it in the dark and see if there are any halos or sparks where the ignition is grounding out. You can use the choke or your hands to enrich the mixture to see if that makes it better or worse, etc..

 

[JonahPro]

Thanks for the replies everyone. I checked the ignition module and everything is connected soundly. I do remember replacing that module many years ago but I don’t know if it could be the cause of backfiring or not. In fact at some time or another I’ve replaced a number of parts back when I was using it a lot but the 2001 mower has been sitting idle now for over 5 years due to health reasons and now I’m just attempting to resurrect it. I’m aware that like me, it’s getting old but heck, it’s a Lawnboy. My first one lasted over 20 years under very heavy use. They are great little mowers if you ask me.

A couple of you mentioned the backfiring or popping sounds being different sometimes and that’s interesting because I had even thought this backfire sounded ‘sharper’ or ‘poppier’ than a normal exhaust backfire, but its really hard to say. Someone suggested running it in the dark to see if any evidence and I’m going to do that when I can. I’ll try to establish where it’s coming from.

Thanks again for the suggestions and ideas so far, I plan to consider them all. I operate at a snails pace these days so it might take me awhile but I’ll report progress as I can.
Blessings to you all!

 

[slomo]

Flywheel key.

 

[JonahPro]

Flywheel key.

Yes. I had that off just yesterday and only minor cleaning was necessary. Thanks!

 

[Rocky J]

I think Douglass was real close. Maybe the off / on switch is coming apart inside and shorting out or the kill wire from the coil is rubbing a bare spot somewhere. When I was younger and we did not have all the exhaust of todays cars we use to run up the RPM's and turn off the key for a count of three and turn it back on so it would back fire , A good time was had by all

 

[JonahPro]

Flywheel key.

I think Douglass was real close. Maybe the off / on switch is coming apart inside and shorting out or the kill wire from the coil is rubbing a bare spot somewhere. When I was younger and we did not have all the exhaust of todays cars we use to run up the RPM's and turn off the key for a count of three and turn it back on so it would back fire , A good time was had by all

Haha! I’ve never pulled that stunt myself, but I knew a few guys that did.

Yeah, I pulled the shrouds and actually examined the wires closely and their connection and I couldn’t see even any nicks in the wire at all. Could something on the inside of that coil be causing it? Like I said before, I recall replacing that coil but it’s been many years. I always thought those coils were either good or faulty, meaning if they went bad they just quit totally. But I’m def no expert. Like sgKent said, I need to more closely identify the kind of backfire I’m hearing. I’m not positive yet exactly what kind it is.

 

[Rocky J]

I would unplug the kill wire and try again and if it still does it change the plug again and if it still does it then it is must be the coil . How much gap is on the coil to flywheel ? Myself I fold a piece of printer paper four thicknesses and let the magnet on the flywheel hold it tight for me and tighten , roll the flywheel while pulling on the paper to remove it .