kz-550 Decently Extreme Backfiring

Hola folks. I threw this in the carb category mostly because I think it could be either engine or carb but ill roll with it for now.
To sum up the build so far, ive put pod filters on, cleaned up the engine, checked valve clearances, got proper 2 ohm coils (points ignition), got a 4 into 1 header with a little straight through glass pack (for now). Bike has some really really mean backfiring after letting off throttle. Foot and a half fireballs. Im assuming this isn't normal. Ill list my carb specs below just in case anyone has any recommendations regarding that. Any input is appreciated and I will be actively checking in and updating with any answers that may assist in finding the problem. Thanks a ton!

Pilot Jet - 37 (I think)
Main Jet - 97ish (#61 drill bit)
Needle - 3rd groove up

Just guessing but it sounds like a lean condition brought on by pods and a straight thru exhaust. What do the plugs look like? 

Apply some choke or enricher when decelerating. Does it help or hurt?
Turn pilot screws to maximum richness.
Raise needles to highest clip position.
Increase pilot jet size.
You may have to richen your idle circuit more than you like to ge rid of the decel pop.
Of course, foot and one half fire balls are kind of cool too.

Messed up jetting brought on by the mods.  And points will burn with 2 ohm coils, although this is unlikely to cause fireballs out the exhaust.

Stupid question, have you checked to make sure all your header pipes are getting warm when you start it?

( In response to plug question) Plugs look decently black after pulling them
 

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Apply some choke or enricher when decelerating. Does it help or hurt?
Turn pilot screws to maximum richness.
Raise needles to highest clip position.
Increase pilot jet size.
You may have to richen your idle circuit more than you like to ge rid of the decel pop.
Of course, foot and one half fire balls are kind of cool too.
 

Foot and a half fireballs are super sick. The bike also seems to Peter out around 5k rpm on the main jet im guessing. Do you think richening that would have an effect?

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Stupid question, have you checked to make sure all your header pipes are getting warm when you start it?

I didn't use that method, but if the goal is to find out if all cylinders are firing, I had a problem with one not firing, so I pulled one spark plug at a time and checked for engine noise changes. If thats not the goal, ill throw a thermometer on it and try that out

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Messed up jetting brought on by the mods.  And points will burn with 2 ohm coils, although this is unlikely to cause fireballs out the exhaust.

I tried my best to follow jetting protocol from another forum post on here, my main jet is a little lean from what they call for though but I wasn't sure if that would affect it. Also I lied, I used to have 2 ohm coils and recently got 4 ohms because of the points

 

 

Foot and a half fireballs are super sick. The bike also seems to Peter out around 5k rpm on the main jet im guessing. Do you think richening that would have an effect?
 

I once had a CL response to a bike I was selling, saying the bike looked sick. I was offended, but my son assured me it was a compliment.
With your mods, I would expect several trial and error carb adjustments. Yes, see if larger jets help or hurt.
I like figuring these things out with plug chops. 10 minuets at idle. 10 minuets at steady 60mph. A few minuets at the highest speed you dare.
To reduce popping, you may need to go a little rich at idle. dark brown is OK, but not sooty black.

wrote:

wrote:

Stupid question, have you checked to make sure all your header pipes are getting warm when you start it?

I didn't use that method, but if the goal is to find out if all cylinders are firing, I had a problem with one not firing, so I pulled one spark plug at a time and checked for engine noise changes. If thats not the goal, ill throw a thermometer on it and try that out



 

I'm not suggesting that you grab hold of a hot pipe but when you first start the bike up you can lightly hand tap each header pipe very quickly to see if they are all warming up.
If you have a infrared thermometer even better.
Be careful!

wrote:

wrote:

wrote:

Stupid question, have you checked to make sure all your header pipes are getting warm when you start it?

I didn't use that method, but if the goal is to find out if all cylinders are firing, I had a problem with one not firing, so I pulled one spark plug at a time and checked for engine noise changes. If thats not the goal, ill throw a thermometer on it and try that out




 

I'm not suggesting that you grab hold of a hot pipe but when you first start the bike up you can lightly hand tap each header pipe very quickly to see if they are all warming up.
If you have a infrared thermometer even better.
Be careful!

you can also spray a fine mist of water on each pipe and note how quickly it evaporates. Much less painful than touching the pipes.