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Backfiring through the exhaust

#1

PTmowerMech

PTmowerMech

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.


#2

A

Auto Doc's

Disconnect the shut off wire on both coils and see how it runs. The coil shut off wire has tiny diodes that will go bad and create cross firing issues with the coils.

They make several coil harnesses for these so be careful to match the correct one to the date code.

www.partstree.com

PartsTree - Home of OEM Parts for Outdoor Power Equipment

Parts lookup and repair parts diagrams for outdoor equipment like Toro mowers, Cub Cadet tractors, Husqvarna chainsaws, Echo trimmers, Briggs engines, etc.
www.partstree.com www.partstree.com


#3

S

slomo

Flywheel key or new cam time.


#4

Tiger Small Engine

Tiger Small Engine

PTmowerMech said:
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.
Click to expand...
First thing I would do is clean carburetor, run and test under load. That doesn’t do it, check/adjust valves.


#5

PTmowerMech

PTmowerMech

slomo said:
Flywheel key or new cam time.
Click to expand...

Oh lord. I hope not.


#6

PTmowerMech

PTmowerMech

Auto Doc's said:
Disconnect the shut off wire on both coils and see how it runs. The coil shut off wire has tiny diodes that will go bad and create cross firing issues with the coils.

They make several coil harnesses for these so be careful to match the correct one to the date code.

www.partstree.com

PartsTree - Home of OEM Parts for Outdoor Power Equipment

Parts lookup and repair parts diagrams for outdoor equipment like Toro mowers, Cub Cadet tractors, Husqvarna chainsaws, Echo trimmers, Briggs engines, etc.
www.partstree.com www.partstree.com
Click to expand...

Tried your suggestion but, nothing changed. But I have a side question about what happened when I tried this.
With the wires disconnected from the coils, then turning the key off, 3 seconds later, the engine dies on it's own.
Reconnected the coil wires, then turn the key off, it dies right away. So how is the engine dying with the wires disconnected, 3 seconds later? It shouldn't die at all from turning off the key. Should it?


#7

A

Auto Doc's

Hello PTmowermec,

Even though you disconnected the coil kill wires, the anti-backfire still has the ability to shut off the fuel in the carburetor when the key is turned off. That creates a slight delay before the engine winds down.


#8

PTmowerMech

PTmowerMech

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.


#9

S

slomo

Any back-firing through carb or muffler is either cam or ignition timing out of whack.


#10

sgkent

sgkent

or mixture problem. Unburned gas can ignite when exposed to additional oxygen, and a lean mixture can burn so slowly due to distance between the molecules that it can extend into the next exhaust stroke when combined with lean-misfire. I would use the choke if it has a manual choke to see if it improves with a little choke. That will tell if lean or not.


#11

PTmowerMech

PTmowerMech

Here's the video. I'm not touching the throttle. The RPM's went down on their own. A few seconds later, they came back up.



#12

A

Auto Doc's

Hello PTmowerMec,

In the video, that sounds like a coil breaking down issue. You would need 2 adjustable air gap spark testers between the plug tips and the coil plug wires. Run the engine while watching the spark jump the gap on each tester.

One coil will spark continuously while the other breaks down and comes and goes intermittently.

The V-twin engines don't shake and rock as people would expect because they are mounted solid.


#13

PTmowerMech

PTmowerMech

Auto Doc's said:
Hello PTmowerMec,

In the video, that sounds like a coil breaking down issue. You would need 2 adjustable air gap spark testers between the plug tips and the coil plug wires. Run the engine while watching the spark jump the gap on each tester.

One coil will spark continuously while the other breaks down and comes and goes intermittently.

The V-twin engines don't shake and rock as people would expect because they are mounted solid.
Click to expand...

With the spark testers I have, I see no formidable differences between either side.
Note: They're not adjustable air gap spark testers. But I they do show when exactly the voltage comes through. Both sides glow bright.


#14

A

Auto Doc's

Sorry, you are using junk spark testers.


#15

PTmowerMech

PTmowerMech

Auto Doc's said:
Sorry, you are using junk spark testers.
Click to expand...

True that. But what I'm supposed to be looking at is gaps between sparks, instead of a constant blinking, correct? Even with the junk ones like I have, these gaps are visible.
I did notice some gaps in the spark. But they didn't coincide with the backfiring. As in many times there was several back fires in a row, when the sparks were constant.

Maybe there's more to those that are adjustable than I'm aware of. Above my pay grade, sort of speak.


#16

Hammermechanicman

Hammermechanicman

Have you done a compression or leakdown test on the engine?
Disconnect one plug and start the engine. How does it run? Reconnect the first plug and Disconnect the other plug and start the engine. How does it run?


#17

F

Forest#2

Here is the good inline spark tester.
OREGON SPARK TESTER Repl Briggs 19051 19368

Pull a plug wire one at a time and listed, compare one cylinder to the other.
Appears it's back fires out the EX maybe. Removing spark might give you a clue, no spark=no backfire
I suspect a valve not seating erratically.
If you find the suspect cylinder, pull the valve cover and closely inspect.
BUT:

I've also seen carb do such (spitting and sputtering) on a Briggs twin OHV, especially the Dual throat 2 barrel Nikki's. Each throat and the intake runner are separated from each other, one side of the carb foul and upset just one cylinder. I've even seen one cylinder completely dead due to the carb.
Is your carb the dual or the single throat? (that model engine used both types carbs, just required a different intake manifold is why I ask)


#18

S

slomo

You can hear one good cyl and one trying at times. Might have a valve nearly closed, that is stuck open.

Definitely look at ignition and valves/cams. Pop the valve covers and see what you got.


#19

S

slomo

PTmowerMech said:
Note: They're not adjustable air gap spark testers. But I they do show when exactly the voltage comes through. Both sides glow bright.
Click to expand...
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.


#20

S

slomo

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



#21

PTmowerMech

PTmowerMech

slomo said:
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.
Click to expand...


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

Click to expand...


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

Tester ordered.


#22

PTmowerMech

PTmowerMech

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

Click to expand...

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


#23

W

wekjo

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


#24

S

slomo

PTmowerMech said:
One thing I noticed about this engine with the bad coil....... It didn't backfire.
Click to expand...
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.


#25

S

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.


#26

G

Gord Baker

PTmowerMech said:
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.
Click to expand...
I suggest a fuel diagnosis. Sounds like it is running Lean. The usual suspects, carb/filters. Check Valve Lash.


#27

E

Ed5060

PTmowerMech said:
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.
Click to expand...
So you cleaned out the jets and passageways, not just looked?


#28

9

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…


#29

A

Aquadisiac

PTmowerMech said:
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.
Click to expand...
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.


#30

H

hlw49

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


#31

D

Dpmulvan

How many hours on the mower, what year is it? Is it parked outdoors, any sign of vermin? Sounds like an mis to me not a backfire. Does it get worse when it’s warmed up? If so probably a coil. Start easy,
obvious, before chasing your tail. I’d type more but the pop ups on this site make it ridiculous sometimes.
very annoying.


#32

P

pull-do

My 407777 was doing the same symptoms, took the Nikki off and cleaned it, still acted up,, (lean backfire) I thought. Took the carb back off and went through it again thoroughly with the new O-rings,,, runs good now.


#33

S

Stainless69

PTmowerMech said:
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.
Click to expand...
Mine did this before. I had to adjust the valves. It was pretty easy to do after watching a few youtube vids. The worst part was cleaning the old gasket off of the valve cover.


#34

PTmowerMech

PTmowerMech

Stainless69 said:
Mine did this before. I had to adjust the valves. It was pretty easy to do after watching a few youtube vids. The worst part was cleaning the old gasket off of the valve cover.
Click to expand...

I checked the valves, they were at .06. Close enough.


#35

PTmowerMech

PTmowerMech

Dpmulvan said:
How many hours on the mower, what year is it? Is it parked outdoors, any sign of vermin? Sounds like an mis to me not a backfire. Does it get worse when it’s warmed up? If so probably a coil. Start easy,
obvious, before chasing your tail. I’d type more but the pop ups on this site make it ridiculous sometimes.
very annoying.
Click to expand...

I got the new tester in (after I returned it). When I get back over there, I'll see what the spark looks like. Customer says it's funning fine now. But I'm thinking she just can't hear what I hear.


#36

PTmowerMech

PTmowerMech

Aquadisiac said:
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.
Click to expand...

There was no water in the carb. It's kept under a car port. But here in Arkansas, that doesn't mean much, as we have high humidity all year long


#37

PTmowerMech

PTmowerMech

Ed5060 said:
So you cleaned out the jets and passageways, not just looked?
Click to expand...

Yes, sprayed carb cleaner through every hole, keeping an eye on the stream that comes out the other end. Especially to two ports that come out into the venturi. Ran the guitar strings and probes through the holes and the jets. Replaced one intake mounting gasket. It was very clean.


#38

F

Forest#2

pull-do said:
My 407777 was doing the same symptoms, took the Nikki off and cleaned it, still acted up,, (lean backfire) I thought. Took the carb back off and went through it again thoroughly with the new O-rings,,, runs good now.
Click to expand...

Quite often with the dual throat Nikki's I can get a good run leaving the carb mounted to the engine and remove enough stuff that I can remove the 3 screws in the top plate, carefully remove the plate and then use low pressure air, about 20 to 30#'s and blow air across the top of the little channels. Do not direct inject air, keep the air nozzle back away from the channels. This is a jet area and the fixed jets are smaller than a tag wire.
Wear eye protection because the air will backflush fuel out of the carb bowl upwards also. Apply a lube to the flat gasket or remove the gasket and turn it upside down with lube for a seal. Start the engine and test.
If no go do as pull-do indicates.
Main thing is do not throw your NIKKI away expecting a China clone replacement to run ok. Try to repair your NIKKI.
These Nikkis'a have a learning curve and lots of info on-line about proper ways to repair them.


#39

PTmowerMech

PTmowerMech

Forest#2 said:
Quite often with the dual throat Nikki's I can get a good run leaving the carb mounted to the engine and remove enough stuff that I can remove the 3 screws in the top plate, carefully remove the plate and then use low pressure air, about 20 to 30#'s and blow air across the top of the little channels. Do not direct inject air, keep the air nozzle back away from the channels. This is a jet area and the fixed jets are smaller than a tag wire.
Wear eye protection because the air will backflush fuel out of the carb bowl upwards also. Apply a lube to the flat gasket or remove the gasket and turn it upside down with lube for a seal. Start the engine and test.
If no go do as pull-do indicates.
Main thing is do not throw your NIKKI away expecting a China clone replacement to run ok. Try to repair your NIKKI.
These Nikkis'a have a learning curve and lots of info on-line about proper ways to repair them.
Click to expand...

I didn't mess with that part of the carb. As I didn't have replacement gaskets. And mainly because the rest of the carb was just too clean to think there was any need to get into that far.


#40

justin@justintime

justin@justintime

PTmowerMech said:
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.
Click to expand...
Check your valve adjustments. sounds like they are tight zero clearance and probably hard to start both hot and cold due to mavrick air being sucked in making it super lean. as the engine warms up cleances tend to open a bit and valves wil seat. belive clearances should be .004" on all four valves do cylinder one first spin it by hand check agian then do cylinder 2. Theres also a part number change on the main jet and a slightly larger main jet in turn making it richer check your parts diagram


#41

PTmowerMech

PTmowerMech

justin@justintime said:
Check your valve adjustments. sounds like they are tight zero clearance and probably hard to start both hot and cold due to mavrick air being sucked in making it super lean. as the engine warms up cleances tend to open a bit and valves wil seat. belive clearances should be .004" on all four valves do cylinder one first spin it by hand check agian then do cylinder 2. Theres also a part number change on the main jet and a slightly larger main jet in turn making it richer check your parts diagram
Click to expand...

I checked them. They're fine. .06.


#42

R

RevB

PTmowerMech said:
With the spark testers I have, I see no formidable differences between either side.
Note: They're not adjustable air gap spark testers. But I they do show when exactly the voltage comes through. Both sides glow bright.
Click to expand...
Ignore the bad spark tester, good spark tester argument for the moment. While running pull the plug cap off one plug and note how it runs. Replace it and pull the other one. If there is a coil failing one of the two will cause a really rough running, skipping engine and the other might not (rare for both to fail at exactly the same time) and just run smoothly. Just ran thru this with Kawasaki....one side ran smooth the other side didn't but if this were the case just replace both coils. The coils these days have two transistors in each coil, one that charges the primary winding field and another that controls the dumping of that field into the secondary to cause the spark. Not sure about other makes but the Kawasaki requires two different coils that are specific to each cylinder...they're not interchangeable.


#43

PTmowerMech

PTmowerMech

Any tips on removing a plug wire while the engine is running.

I know that sounds like a rookie question. But the first and only time I've done it (decades ago), I got the fire knocked out of me, and never tried it again.


#44

F

Forest#2

PTmowerMech said:
I didn't mess with that part of the carb. As I didn't have replacement gaskets. And mainly because the rest of the carb was just too clean to think there was any need to get into that far.
Click to expand...
That is just a simple flat gasket with 3 holes for the screws.
Easy made if damaged.

I was like you at first, reluctant to go there, but after I noticed it's a important jet area access and I found that the slits for fuel flow can be stopped up/clogged by a nat's bristle or hair I've been their several times.
The slit ports are so small and in the bottom of the channels that you cannot check visually for restrictions.
Don't be scared, take the top off while still on the engines. Can even make the gasket from a Post Toasties/Cheeriors box.
If nothing else makes it fly give this a shot.

see pg 12 at this link. note the slits in red.

Disassembly, Cleaning and Repair of Briggs Intek V-twin Two-Barrel Nikki Carburetor - Part 2

outdoorpowerinfo.com outdoorpowerinfo.com


#45

H

hlmorrison

PTmowerMech said:
Tried your suggestion but, nothing changed. But I have a side question about what happened when I tried this.
With the wires disconnected from the coils, then turning the key off, 3 seconds later, the engine dies on it's own.
Reconnected the coil wires, then turn the key off, it dies right away. So how is the engine dying with the wires disconnected, 3 seconds later? It shouldn't die at all from turning off the key. Should it?
Click to expand...
Running out of gas because you shut off the power to the fuel solenoid


#46

R

rperk

All good info here. I had a similar problem on my Scag TT 35hp Briggs. Sent it to 2 different shops and it
got better each time but still backfired through the exhaust. I was messing with it one night in the shop
and didn't have all the lights on when I found the problem.

Spark plug boot had a crack in it and it was shorting the spark plug out. I just taped it up with electrical
tape for the time being and no more backfiring.


#47

H

hlmorrison

PTmowerMech said:
Any tips on removing a plug wire while the engine is running.

I know that sounds like a rookie question. But the first and only time I've done it (decades ago), I got the fire knocked out of me, and never tried it again.
Click to expand...
Pliers with really thick rubber handle or just tie a zip tie to it and pull the zip tie


#48

justin@justintime

justin@justintime

PTmowerMech said:
I checked them. They're fine. .06.
Click to expand...
put them to .004 and verify the correct main jets. you have a left and a right and wouldnt be th first time ive seen high altitude jets put in. you also have 2 diodes that can cause issues like that between the coills unplug them and see how it runs


#49

woodstover

woodstover

PTmowerMech said:
I checked the valves, they were at .06. Close enough.
Click to expand...
Is that .06mm or .06"? .06mm = .0023"
Intake should be .004" Exhaust should be .006" Engine must be cold for setting valves


#50

A

Auto Doc's

PTmowerMech said:
I checked them. They're fine. .06.
Click to expand...
They should be .006-inch feeler, not .060-inch feeler. The manual gives variables, but I usually go .005" on both valves.
I've never liked using metric measurements on anything, it's the way I was raised


#51

A

Auto Doc's

Dpmulvan said:
How many hours on the mower, what year is it? Is it parked outdoors, any sign of vermin? Sounds like an mis to me not a backfire. Does it get worse when it’s warmed up? If so probably a coil. Start easy,
obvious, before chasing your tail. I’d type more but the pop ups on this site make it ridiculous sometimes.
very annoying.
Click to expand...
Hello Dpmulvan,

Here is how to control the pop-up issue:

On the top right corner of the window, you will see 3 dots. Click there and go to more tools on the drop-down menu.

Pick internet options, a block with internet properties will open, On the top tabs will be a privacy tab, click on that and another box will appear.

At the bottom is pop up blocker. Click on that and it will resolve your issue.


#52

O

outdoorpowermike

A backfire is a pop sound coming out of the carb bore, not really the muffler. What you have going on is either a problem with the muffler coming apart internally or a exhaust valve or seat problem. If you do a good clean carb like you said I would check for these issues.


#53

A

Auto Doc's

According to the engine number, this is around 25 years old I'm guessing.

The one thing I notice that has not been mentioned is the exhaust. The muffler can usually be unbolted from the bottom of the chassis and slipped off the 2 exhaust tubes.

Try that and see if the engine sounds louder, but the odd miss/ backfire is gone. The muffler could have a rotted out internal baffle.

The other possibility is the exhaust pipe flange gaskets on the head are rotted and burned-out allowing air to be sucked into the hot exhaust flow. I've only had it happen once over many years. The engine seems to run normal, except it has an annoying exhaust note.

The exhaust flange nuts on the heads are nearly impossible to get to without loosening and blocking the engine up slightly for clearance.


#54

L

Lostviking

Check and see
PTmowerMech said:
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.
Click to expand...
if you have a burnt Exhaust Valve or possible Lazy Valve spring!!


#55

G

golfergordy

I had some backfiring (years back) with a Honda walk behind mower. Checked the valve clearances and found them out of spec. Re-adjusted the valves and no more backfiring.


#56

F

Forest#2

PTmowerMech said:
Any tips on removing a plug wire while the engine is running.

I know that sounds like a rookie question. But the first and only time I've done it (decades ago), I got the fire knocked out of me, and never tried it again.
Click to expand...
I prefer to ground the tip of the spark plug by sliding back the insulator rather than pull the wire
but if I need to pull I use

I use the scissor type ideal fuse pullers 34-002 that are about 7 inches long.
You can see them on flea bay


#57

R

RevB

PTmowerMech said:
Any tips on removing a plug wire while the engine is running.

I know that sounds like a rookie question. But the first and only time I've done it (decades ago), I got the fire knocked out of me, and never tried it again.
Click to expand...
Grab the cap and pull it off...won't get shocked unless you want to stick your finger in the end...🤔 The voltage isn't enough to each around the insulated cap. Many of the really old cables just had a bare metal clip that attached to the plug. If you have that I'd be surprised.

However, in retrospect Forest#2 says he prefers to ground the plug tip....that may not be possible, some connectors like the NGK are are solid plastic affairs. But his advice does bear scrutiny and made me reconsider just pulling the cap off as this may damage the coil transistors since the High Voltage has to dump somewhere.....better to pull the cap while not running and use an old spark plug that is grounded to dump the energy into a spark as was intended as the engine is started again...or just pull the existing plug and ground it. The engine would start more easily than having to fight a dead cylinder's compression.


#58

R

RevB

Forest#2 said:
I prefer to ground the tip of the spark plug by sliding back the insulator rather than pull the wire
but if I need to pull I use

I use the scissor type ideal fuse pullers 34-002 that are about 7 inches long.
You can see them on flea bay
Click to expand...
You made me question my advice to just pull the cap....see post #57. Thanks!


#59

PTmowerMech

PTmowerMech

woodstover said:
Is that .06mm or .06"? .06mm = .0023"
Intake should be .004" Exhaust should be .006" Engine must be cold for setting valves
Click to expand...

.02 isn't exactly right. But it's not enough to really be concerned about. It' wasn't a sloppy .06.


#60

F

Forest#2

RevB said:
Grab the cap and pull it off...won't get shocked unless you want to stick your finger in the end...🤔 The voltage isn't enough to each around the insulated cap. Many of the really old cables just had a bare metal clip that attached to the plug. If you have that I'd be surprised.

However, in retrospect Forest#2 says he prefers to ground the plug tip....that may not be possible, some connectors like the NGK are are solid plastic affairs. But his advice does bear scrutiny and made me reconsider just pulling the cap off as this may damage the coil transistors since the High Voltage has to dump somewhere.....better to pull the cap while not running and use an old spark plug that is grounded to dump the energy into a spark as was intended as the engine is started again...or just pull the existing plug and ground it. The engine would start more easily than having to fight a dead cylinder's compression.
Click to expand...
this may damage the coil transistors since the High Voltage has to dump somewhere.

Correct not a good thing to pull a plug wire on some ignition systems.
Also
If you have one of these inline spark testers it will also allow grounding the the ignition while the engine is running if the spark plug boot is the molded type and cannot be slide back on the ignition wire for access to the tip of the spark plug.
OREGON SPARK TESTER Repl Briggs 19051 19368


#61

PTmowerMech

PTmowerMech

Forest#2 said:
this may damage the coil transistors since the High Voltage has to dump somewhere.

Correct not a good thing to pull a plug wire on some ignition systems.
Also
If you have one of these inline spark testers it will also allow grounding the the ignition while the engine is running if the spark plug boot is the molded type and cannot be slide back on the ignition wire for access to the tip of the spark plug.
OREGON SPARK TESTER Repl Briggs 19051 19368
Click to expand...

Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?


#62

Hammermechanicman

Hammermechanicman

Screenshot_20250818_174351_Chrome.jpg
Look at this wiring diagram from an onan engine. What happens when you disconnect a plug wire to try and run on one cylinder?


#63

A

Auto Doc's

PTmowerMech said:
Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?
Click to expand...
Hello PTmowerMech:

An adjustable spark tester is recommended so the coil electric energy will be dissipated. If a plug wire is just left off loose even briefly the coil will overheat and fuse the internal windings.


#64

R

RevB

PTmowerMech said:
Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?
Click to expand...
As was stated earlier, better to remove plug, insert into plug cap, and ground the plug to discharge energy via spark.


#65

F

Forest#2

Hammermechanicman said:
View attachment 71570
Look at this wiring diagram from an onan engine. What happens when you disconnect a plug wire to try and run on one cylinder?
Click to expand...

this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.


#66

A

Auto Doc's

Hi Forest#2,

The OP is working on a B&S twin not an Onan, but it is good information to know. I occasionally see Onan generators in RV's. Thanks


#67

Hammermechanicman

Hammermechanicman

Forest#2 said:
this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.
Click to expand...
Exactly. Lots of folks assume onan engines are like most other engines.


#68

R

RevB

Forest#2 said:
this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.
Click to expand...
So...on an Onan two cylinder opposed, is there but one coil for both since both would fire at the same time. The only way for plugs to be in series would be on the opposed cylinder models.

But looking at the diagram from post 62 shows the outputs to be in parallel, not series.

Any V configuration would require two coils to service it's particular cylinder but you still get wasted spark there, too.


#69

F

Forest#2

RevB said:
So...on an Onan two cylinder opposed, is there but one coil for both since both would fire at the same time. The only way for plugs to be in series would be on the opposed cylinder models.

But looking at the diagram from post 62 shows the outputs to be in parallel, not series.

Any V configuration would require two coils to service it's particular cylinder but you still get wasted spark there, too.
Click to expand...

Lots of info on-line about waste spark ignition systems
AND
Onan's waste spark ignition system


#70

Hammermechanicman

Hammermechanicman

The onan engines are opposed twins


#71

R

RevB

Forest#2 said:
Lots of info on-line about waste spark ignition systems
AND
Onan's waste spark ignition system
Click to expand...
Boy...that really cleared that up....so is a Kawasaki and tons of other two cylinder engines. Nothing special.🙄


#72

R

RevB

Hammermechanicman said:
The onan engines are opposed twins
Click to expand...
Some but not all...


#73

F

Forest#2

I have replaced the twin tower ignition coils on some emergency generators during a emergency and the gen needed immediately by using two automotive coils by connecting the primary windings in series. (have to keep a heads up about correct polarity primaries when connecting in series)

Few years ago the Onan dual tower ignition coils were costly, not readily available and only available from Onan at prices higher than todays clones and long waiting period for a replacement.


#74

R

RevB

Forest#2 said:
I have replaced the twin tower ignition coils on some emergency generators during a emergency and the gen needed immediately by using two automotive coils by connecting the primary windings in series. (have to keep a heads up about correct polarity primaries when connecting in series)

Few years ago the Onan dual tower ignition coils were costly, not readily available and only available from Onan at prices higher than todays clones and long waiting period for a replacement.
Click to expand...
All you did was supply 12V and ground to each of the coil's terminals. Series, parallel, whatever.....makes no difference as far as I know. Each gets 12V and ground on the correct terminal. The reluctor wheel's magnet on the crankshaft triggers a Hall effect transistor in the "ignition module" which dumps the primary and induces the secondary to collapse its field and that is dumped to ground thru the spark plug. If there were no module it would be points doing the work. Same thing for the dual tower. There is no magnet passing by a trigger coil to collapse the field induced in the primary by the magnet. So, yes, + is + and - is -....or bad things happen.


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