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Discussion Starter · #1 ·
I recenty bought 2 beat up 1982 KZ440's. Both are in bad shape but I've got enough parts between the two of 'em to get one running bike. I only have one set of carbs. One carb looks great and the float was free and clean. But the other carb was stuck so bad, it took an hour and a lot of heavy duty tools and fluids to get it unstuck. Now I've got the carbs on one of the bikes and I finally got it started but the bike backfires REAL bad. The backfiring is coming from the back of the carbs through the airbox, not the exhaust.

I've got a few contributing factors that may be causing the backfire...
- The carbs were completely taken apart (every screw) and cleaned out, but I probably did not leave the screws in the same position as before.
- I don't have the air filter in the air box, I'm using a piece of foam to cover the back of the air box.
- I have not tightened the brackets very tight on the boots connecting the carbs to the motor. (I have felt and seen bursts of white smoke escaping this connection when backfiring)
- I have nothing to tighten the connecting boots between the air box and the back of the carbs. Do I need to?
- I don't have the gas tank connected, I'm simply pouring gas into a funnel connected to the main fuel line into the T-valve between the carbs.
- I had to spray WD-40 into the valves to free up the pistons to get the motor to turn completely. (But, I've had the bike running for over 10 minutes... the WD-40 should be burned off by now)

Given all of these conditions, what do you guys think I need to adjust to help with the backfiring? I'd like to leave the carbs in there, but if I need to pull 'em out to fix this problem, I certainly will. A friend of mine recommended adjustments to the timing chain, but I really doubt anything is wrong with that if all I've really had to work on is the carbs. Let me know what you guys think. Thank you!

PS: Do you guys think it will help if I post a YouTube vid of the bike running so you can see what it looks and sounds like??
 

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I recenty bought 2 beat up 1982 KZ440's. Both are in bad shape but I've got enough parts between the two of 'em to get one running bike. I only have one set of carbs. One carb looks great and the float was free and clean. But the other carb was stuck so bad, it took an hour and a lot of heavy duty tools and fluids to get it unstuck. Now I've got the carbs on one of the bikes and I finally got it started but the bike backfires REAL bad. The backfiring is coming from the back of the carbs through the airbox, not the exhaust.

I've got a few contributing factors that may be causing the backfire...
- The carbs were completely taken apart (every screw) and cleaned out, but I probably did not leave the screws in the same position as before.
- I don't have the air filter in the air box, I'm using a piece of foam to cover the back of the air box.
- I have not tightened the brackets very tight on the boots connecting the carbs to the motor. (I have felt and seen bursts of white smoke escaping this connection when backfiring)
- I have nothing to tighten the connecting boots between the air box and the back of the carbs. Do I need to?
- I don't have the gas tank connected, I'm simply pouring gas into a funnel connected to the main fuel line into the T-valve between the carbs.
- I had to spray WD-40 into the valves to free up the pistons to get the motor to turn completely. (But, I've had the bike running for over 10 minutes... the WD-40 should be burned off by now)

Given all of these conditions, what do you guys think I need to adjust to help with the backfiring? I'd like to leave the carbs in there, but if I need to pull 'em out to fix this problem, I certainly will. A friend of mine recommended adjustments to the timing chain, but I really doubt anything is wrong with that if all I've really had to work on is the carbs. Let me know what you guys think. Thank you!

PS: Do you guys think it will help if I post a YouTube vid of the bike running so you can see what it looks and sounds like??
Either you have a dirty carb(s) or you have a tight intake valve. Really need more details. Does the engine rev up ? Do you have a compression guage ?
 

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Navy Vet Search & Rescue
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Running lean will cause it to backfire through the carb. You obviously have air leaks (that will cause it to run lean) since you can see the white smoke blowing out at the manifold. Tighten the clamps on the manifolds and try to get something for the airbox boot. That may solve your backfiring.
 

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Discussion Starter · #5 ·
Well, the airbox had a nice hinge on top to access the battery. But I bent it up and down a few too many times and it snapped off. So I need to fasten that down some way. The triangle shaped metal frame for the air filter is still in tact, but the foam filter is old and deteriorating. I need to replace the actual filter before I put the whole airbox back together. I will tighten the clamps and try to prevent any extra air leaks and hopefully that will help. Thank you guys. I'll try posting a YouTube video of the sights and sounds when the bike is running and see if it helps you guys get a clear picture of what's going on. But I'll fix the simple stuff first. Thanks!
 
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