Bang pop pop bang pop how do I stop

Coverfire

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Hello all, I'm hoping you guys can send me in the right direction. I'm popping non stop on deceleration. I'm running a predator 212 non hemi with mods on a Murray Explorer with a 10 tooth gear on the jack shaft and a 60 tooth on the axle. Here is a list of mods: billet flywheel, billet rod, mod2 cam, 18 lb valve springs, header pipe, 22mm mikuni, AR 3910X spark plug and a juggernaut 30 series torque converter. So, I tried all the fuel settings on the mikuni from leanest to most rich and messed with the air / idle screw to try dialing it in and nothing seems to stop it from popping profusely. It's got the bigger 140 jets in it from gopowersports vs the 100 that also came with the mikuni. I understand that I'm probably going to always have some popping but it seems like too much popping at this point. Am I running too rich? Too lean? Should I put in the smaller jets? Here is some photos of the spark plug with minimal use. Any help will be much appreciated.
 

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JTSpeedDemon

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You’re running too rich according to that spark plug. But before you think it’s the fuel system, it’s it’s as likely to be weak spark which will give the same symptoms. Try a standard spark plug, those fancy “racing” ones don’t really do anything, it’s better to invest in a reliable long lasting one.
Other than that, there’s also different float clip settings on Mikunis, it’s not just the needles. I would start by trying a different, known good spark plug, then try throwing in the 100 jets. A lot of people think because they’re upgrading their engine, the HAVE to richen it a bunch, but that’s frequently not the case.
 

Coverfire

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Hey
You’re running too rich according to that spark plug. But before you think it’s the fuel system, it’s it’s as likely to be weak spark which will give the same symptoms. Try a standard spark plug, those fancy “racing” ones don’t really do anything, it’s better to invest in a reliable long lasting one.
Other than that, there’s also different float clip settings on Mikunis, it’s not just the needles. I would start by trying a different, known good spark plug, then try throwing in the 100 jets. A lot of people think because they’re upgrading their engine, the HAVE to richen it a bunch, but that’s frequently not the case.
Hey, thanks for the feedback, I appreciate your input. So, after I read your comment I through the ol' trusty plug in there and took it for a spin and it's still popping and crackling like a mofo. So it seems like my next option is to try and use the smaller jets. I have a feeling that they may not provide enough fuel but I'll definitely give it a try tomorrow and see how she runs.
 

JTSpeedDemon

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If it turns out too lean with the 100 jets the worst that happens is you can drill it out a little bit. It sounds like it's running way too rich right now anyways so I get the feeling it'll be a lot better with the 100s.
 

Coverfire

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If it turns out too lean with the 100 jets the worst that happens is you can drill it out a little bit. It sounds like it's running way too rich right now anyways so I get the feeling it'll be a lot better with the 100s.
Awesome, thank you. I really appreciate the help. This is my first engine build and I'm having a blast and learning a lot from people like you. I'll swap the jets tomorrow and post the results in this thread. I'm guessing I should start with the richest setting on the mikuni once I swap to the smaller jets and work my way down if I don't think its dialed in correctly?
 

JTSpeedDemon

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Start rich and work it leaner, better too rich than too lean, as a rich engine will still run, and as the engine gets leaner the power drops much more sharply than if it's too rich.
 

Karts of Kaos

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I have always understood the backfiers to be the compression release engaging when you rapidly drop your rpms, but I could be very much mistaken.
 

Coverfire

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Check for unburned fuel igniting in the exhaust system.

So, it seems like that is the general consensus . . . that I'm running rich and burning fuel in the header pipe. How do I check for unburned fuel being ignited? Just fire it up at night and look for flames? I also told everyone that the mikuni had the bigger jets in it but turns out I had the smaller (100) jets in there this whole time. So sounds like the 140 jets would be way too big, huh?
 

Karttekk

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You'll have to experiment with different jets, different carbs possibly, float settings if applicable. Definitely a fuel issue it seems, you'll just have to keep at it until you find what works best. Sometimes there's no magic answer.
 

Coverfire

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Agreed, first chance I get I'll switch the jets and go through the tuning process aging and see what happens.
 

madprofessor

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JT's dead right on that black soot plug showing too rich a mix, and also on running the stock plug if you're not doing racing only. Those other plugs foul quickly when putt-putting around some.
Unfamiliar with the Mikunis, but my Predator 212's get not only a .036" main jet, but a .022" low jet as well. Unsure how the draw on the low jet when slowing down would affect what's going thru the Mikuni, just know my stuff never pops.
 

I74

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This condition ''can'' also be caused by to big ''& or'' short of a pipe,, especially if letting off after high revs.
Harley's are notorious for this if running to big of pipes & not having enough back press. ect.
Basically letting cold air into the up stream part of the pipe & exhaust chamber of the head..
Also can lead to crystalized exhaust valves....
 
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