Backfiring through the exhaust

[PTmowerMech]

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

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

 

[RevB]

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.

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.

 

[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.

 

[Forest#2]

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.

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

 

[hlmorrison]

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?

Running out of gas because you shut off the power to the fuel solenoid

 

[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.

 

[hlmorrison]

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.

Pliers with really thick rubber handle or just tie a zip tie to it and pull the zip tie

 

[justin@justintime]

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

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

 

[woodstover]

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

Is that .06mm or .06"? .06mm = .0023"
Intake should be .004" Exhaust should be .006" Engine must be cold for setting valves