kz-550 Decently Extreme Backfiring

The clean air system will also cause huge backfires on decel when it is not functioning properly.  To disable it, use a hose to connect the two big ports on top of the valve cover, and plug any vacuum lines going to the vacuum switch unit under the tank.

Like Nessism said, you have the wrong coils for points.  Points uses 4 ohm coils.  Every other Kz550 uses 2 ohm coils because they came with the factory electronic ignition.  The 1980 Kz550A1 came with points.  Using the 2 ohm coils will only shorten the life of the points, but won't cause the backfires.

As others have said, the backfires most likely are caused by underjetting for the pods and exhaust.

If you follow the links in my signature there is a website dedicated to your Tk22 carbs with hints on rebuilding and jetting.

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The clean air system will also cause huge backfires on decel when it is not functioning properly.  To disable it, use a hose to connect the two big ports on top of the valve cover, and plug any vacuum lines going to the vacuum switch unit under the tank.

Like Nessism said, you have the wrong coils for points.  Points uses 4 ohm coils.  Every other Kz550 uses 2 ohm coils because they came with the factory electronic ignition.  The 1980 Kz550A1 came with points.  Using the 2 ohm coils will only shorten the life of the points, but won't cause the backfires.

As others have said, the backfires most likely are caused by underjetting for the pods and exhaust.

If you follow the links in my signature there is a website dedicated to your Tk22 carbs with hints on rebuilding and jetting.

Still going through some of the ideas, and I think I def need some richer jetting, but the main tube for the clean air system was open, I closed it, and its perfect. Nearly zero backfiring and such. Out of curiosity, why does this work that way?

Edit- By plugging the hole I think I no longer have vacuum to my tank, therefore needing to to be on prime for the bike to run. Still falls flat on face above 5k due to jetting. But Im also experiencing some choppiness and sputtering on my 5 or 10 minute ride today. Any possible relations to the clean air or any other predictions?
 

The clean air system allows fresh air into the exhaust system.  It doesn't really affect the engine performance because the air is only in the exhaust, outside of the cylinder.  But it does promote combustion outside of the cylinder, hence the backfires.  Normally, there is enough fuel in the exhaust to burn after it exits the cylinder.  But on decel, the mixture is very lean so the combustion in the exhaust won't sustain.  Any small amount of fuel in the exhaust then starts to accumulate, and as long as a large amount of fresh air is let in via the clean-air-system, and the fuel is allowed to accumulate, periodic backfires will happen.  So during decel, which is when intake tract vacuum is very high, the air cutoff valve uses intake vacuum to close the valve and cutoff the air supply to the exhaust.  This prevents the big decel backfires.

The system can fail multiple ways.  If the tubing to the valve cover breaks, air gets in all the time.  If there is a vacuum leak in one of the vacuum lines to the valve, the valve might not close so fresh air gets into the exhaust all the time.  If the valve gets stuck open, air gets in all the time.  Any of these will cause the backfires.

Similarly, too lean of a mixture causes the decel mixture to be so lean that you get popping on decel for the same reason as when the clean air system fails.  But it's not as severe.  It's usually light popping.

The vacuum lines for the clean air system are attached to the rubber carb holders on cylinders 1 and 4.  The vacuum for the petcock is taken from a dedicated pipe on the #4 carb body.  So if you have a leak on that clear air system vacuum line, it will also be a vacuum leak on the petcock vacuum. 

The ports on the carb holders should be capped off.  Don't use generic vacuum caps. They tend to degrade within a few months and crack open.  I use fuel line plugged with a smooth bolt shaft or ball bearing (too big to get sucked in).  The fuel line lasts for years.  Cylinders 2 and 3 are capped using really good caps from the factory.  If you find a part number and can get them, they would be a good choice as well.

For testing, you can just put the vacuum petcock on prime and run it that way.  Then there is no question of vacuum interfering with fuel flow. 

I think I got it patched up. I linked the two valve cover ports and closed off the vacuum ports on the carb boots. Now very minimal backfiring that will most likely just stay unless I richen up the idle. Its not bad so I think ill let it be for now. If you don't mind me picking your brain though. Ive been messing around with my main jets for far too long now because the bike absolutely dies after 5k rpm. It was recommended in one of your posts to use a number 60 or 59 drill bit. 60 is a 1.01 ish mm drill bit. I bought one that calipered out to be right around 1 mm even though it said it was a 1.2. (china stuff). Now it won't even rev past 5k under load. Any ideas on course of action. Or where to get a decent set of drill bits to compliment my current one that goes up to 61 (the one you recommended in one of your posts about drilling jets). Thanks!

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I think I got it patched up. I linked the two valve cover ports and closed off the vacuum ports on the carb boots. Now very minimal backfiring that will most likely just stay unless I richen up the idle. Its not bad so I think ill let it be for now. If you don't mind me picking your brain though. Ive been messing around with my main jets for far too long now because the bike absolutely dies after 5k rpm. It was recommended in one of your posts to use a number 60 or 59 drill bit. 60 is a 1.01 ish mm drill bit. I bought one that calipered out to be right around 1 mm even though it said it was a 1.2. (china stuff). Now it won't even rev past 5k under load. Any ideas on course of action. Or where to get a decent set of drill bits to compliment my current one that goes up to 61 (the one you recommended in one of your posts about drilling jets). Thanks!

Did we cover the advancer mechanism?  That's would be the first thing to check.  If it's stuck retarded, the bike will never rev up past a certain RPM.

If the advancer is working and the ignition timing is correct, the next question is, did the bike ever run correctly while you had it?  Or did you buy it without ever hearing it rev up?
If the latter, then we can't rule out a cam-timing issue.  But for now, let's assume the cam timing is correct and the valves are within spec.  If it's idling nicely, then the valves are close enough that it should run ok.

So then the first real test is to try revving it with the choke about half way on and see if that makes it better or worse.  To see the choke plates you can look into the intakes and see the plate.  Whatever you find with the choke will determine what to do with the main size. 

What jet needles are you using and what are they set at?

My buddy's Kz550A jetted up nicely with just a bit of needle shimming using factory needles and factory jets (no jet kits or aftermarket jets used).  He's running pods and a Mac 4-into-1 exhaust.

Your exhaust looks chopped.  That will require some up-jetting for sure.

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I think I got it patched up. I linked the two valve cover ports and closed off the vacuum ports on the carb boots. Now very minimal backfiring that will most likely just stay unless I richen up the idle. Its not bad so I think ill let it be for now. If you don't mind me picking your brain though. Ive been messing around with my main jets for far too long now because the bike absolutely dies after 5k rpm. It was recommended in one of your posts to use a number 60 or 59 drill bit. 60 is a 1.01 ish mm drill bit. I bought one that calipered out to be right around 1 mm even though it said it was a 1.2. (china stuff). Now it won't even rev past 5k under load. Any ideas on course of action. Or where to get a decent set of drill bits to compliment my current one that goes up to 61 (the one you recommended in one of your posts about drilling jets). Thanks!

Did we cover the advancer mechanism?  That's would be the first thing to check.  If it's stuck retarded, the bike will never rev up past a certain RPM.

If the advancer is working and the ignition timing is correct, the next question is, did the bike ever run correctly while you had it?  Or did you buy it without ever hearing it rev up?
If the latter, then we can't rule out a cam-timing issue.  But for now, let's assume the cam timing is correct and the valves are within spec.  If it's idling nicely, then the valves are close enough that it should run ok.

So then the first real test is to try revving it with the choke about half way on and see if that makes it better or worse.  To see the choke plates you can look into the intakes and see the plate.  Whatever you find with the choke will determine what to do with the main size. 

What jet needles are you using and what are they set at?

My buddy's Kz550A jetted up nicely with just a bit of needle shimming using factory needles and factory jets (no jet kits or aftermarket jets used).  He's running pods and a Mac 4-into-1 exhaust.

Your exhaust looks chopped.  That will require some up-jetting for sure.

The bike did run properly at some point while Ive had it. There is just a little bit of valve clatter, but I have adjusted the valves approx 11 test miles ago. Timing is correct according to the service manual. Ive been able to get the bike up to the red line 9.5k sitting before but it wouldn't go under load. I just jetted up to the 1mm but you do bring up a good point. The bike now won't rev past 6 or 7 k regardless of what I do. Before it was just low on power but would go past 6k. Im assuming advancer but I am entirely unfamiliar with this system. Any tests I should run or methods to fix would be greatly appreciated. I stuck my phone in my pocket and took a short video on my last test ride and uploaded. ill attach a link 

Uuuuupdatesss. Im continuing in this thread for the sake of not making another one and crowding the forums. If I should please give me a heads up and id be happy to do so. I monkeyed with the advance after doing a few hours of research and looking through manuals, the advance plate was all rusted up and the shaft did not move freely as the book said It should. After cleaning and re lubing it lead me to retiming the bike as well with the static timing method, Runs like a dang top all the way up to around 7 or 8k ash on the tac, then it sputters, I took another video and will attach. Any ideas? My only thoughts are either still timing, still jetting, or fuel starvation from bowls? I have the floats set to the website spec although I haven't used the tube test yet. That or carb sync but I feel like that would be less likely. Any input is appreciated. Thanks a ton!

Have you timed it with a timing light?  So you can see what RPM the advance starts and is all in by.  

Also, what did the choke test do?  Rev better or worse?

I have not timed it with a timing light but I’m gonna borrow one today and take a look at the system. The choke test did very little. It may have made it worse at the very top end but it was almost un noticeable.  

I would get the timing light on the advancer.  It will show more than just timing errors.  It will show if spark is dropping out at higher RPMs, which is very possible if the points are worn or not set properly.  I wouldn't spend too much time jetting until you know the ignition is rock solid.

Timing light did indicate My timing is early and I’m losing spark. Im at the end of my adjustment on the plate (all the way to the clockwise stop). 

The contact of the points do have a small divit or pinhole in them. Maybe it is time for replacement. 
edit- timing light video
youtube.com/shorts/mW0kKrQIyuw?feature=share

Yes.  If you use a feeler to measure the point gap, and there is a bump with a matching divot, the points end up too far apart.  The feeler gauge rides the bump, but does not conform to the divot, so the overall gap ends up wider than the gauge.  This cause the dwell to be shorter than it should be and could affect timing to be out of range.

Since you already have 4-ohm coils, you could always go to a Dyna S ignition if you don't want to mess with points.  Some folks like setting points though.  Make sure to get decent quality ones if you do  Some points from China are terrible and there's a lot of counterfeit branding out there.  Make sure the pivot holes are round and not oval.  I've found many an oval pivot...not good for consistency at all.