Popping sound after I accelerate and let off?(79 KZ750 Twin)

Illuminaughty · 05-17-2009

Just curious, I'm very new to bikes and barely do any of the work myself yet, but I'm learning. I just took my '79 KZ-750 Twin out from storage for the winter and I notice when I'm riding it after I accelerate it'll have a popping sound coming from the mufflers, or when I'm at low speeds not accelerating, just maintaining speed. Doesn't happen all the time, but happens sometimes.

Any KZ/ bike experts in here to give me some tips?

Thanks!

ETA:

I've owned this bike for a few years now, it has 6,400 original miles on it currently. Last year I had the carbs professionally cleaned, oil changed, and new chain installed.

I've only ridden about 15 miles so far, plan on riding more in the next few days, or as soon as it warms up a little. I'm guessing I just need to ride it a bit and get all the remaining old fuel out of it (already filled up with new fuel 89 grade). I bought some dry gas to put into it thinking that'd help, haven't added it yet though, will before I go out next time though.

So far I've not done anything to fix this problem. I'm also having stalling at stops sometimes. Again I'm guessing I just need to ride it a bit, my truck will do similar things after it sits all winter (it's a show truck type I only drive in the summer on nice days).

Nate · 05-18-2009

If yours has the air injection system intact, popping on deceleration is a sign that one of the reed valves in the valve cover is hanging open or the vacuum switch isn't working properly.

coverdog · 05-18-2009

Running too lean.

Illuminaughty · 05-18-2009

Quote:

Originally Posted by coverdog

Running too lean.

What does this mean, and how can I fix it? I apologize but I'm not mechanically inclined but I'm try to learn how to do this stuff for myself.

thehumble1 · 05-19-2009

It means that the air mix has too much air and not enough fuel. Lean=too little gas. Rich= too much gas. One way to check is to run the bike for a while, maybe 20 minutes at least to warm it up completely. Then stop and pull the spark plugs out. You can find plenty of posts on this site or others showing you how to read a spark plug (meaning that you look at the condition of the spark end to give you an indication of what kind of combustion is happening in the cylinder). Most likely yours will be white or light brown. They may not be too noticeable if they have been changed recently.

The fix for it is probably more complicated than my small amount of technical information is able to properly understand, so I'll leave that to someone else. But I have no problems blathering about what I conjecture might be wrong:

1) poor seating on the carb boots (the rubber connectors between the carburetor and the air box and cylinder)

2) cracks in the carb boots

3) improperly set jets after rebuilding the carb

4) air filter out of place, allowing too much air into the carb.

5) valve timing (but this is getting outside my little area of knowledge as yet).

6) demonic possession. (Unlikely, but most difficult to repair) Usually requires a lot of starter fluid and a holy hand grenade.

05-17-2009	#1 (permalink)
Illuminaughty Newbie Join Date: Mar 2006 Posts: 20	Popping sound after I accelerate and let off?(79 KZ750 Twin) Just curious, I'm very new to bikes and barely do any of the work myself yet, but I'm learning. I just took my '79 KZ-750 Twin out from storage for the winter and I notice when I'm riding it after I accelerate it'll have a popping sound coming from the mufflers, or when I'm at low speeds not accelerating, just maintaining speed. Doesn't happen all the time, but happens sometimes. Any KZ/ bike experts in here to give me some tips? Thanks! ETA: I've owned this bike for a few years now, it has 6,400 original miles on it currently. Last year I had the carbs professionally cleaned, oil changed, and new chain installed. I've only ridden about 15 miles so far, plan on riding more in the next few days, or as soon as it warms up a little. I'm guessing I just need to ride it a bit and get all the remaining old fuel out of it (already filled up with new fuel 89 grade). I bought some dry gas to put into it thinking that'd help, haven't added it yet though, will before I go out next time though. So far I've not done anything to fix this problem. I'm also having stalling at stops sometimes. Again I'm guessing I just need to ride it a bit, my truck will do similar things after it sits all winter (it's a show truck type I only drive in the summer on nice days). Last edited by Illuminaughty : 05-17-2009 at 06:50 PM.

05-18-2009	#2 (permalink)
Nate KZ Kool! Forum Supporter Join Date: Oct 2004 Location: Marysville, KS Posts: 2,652	If yours has the air injection system intact, popping on deceleration is a sign that one of the reed valves in the valve cover is hanging open or the vacuum switch isn't working properly. __________________ "Riding is the reward for time spent wrenching." "Wrenching is the result of time spent riding!" KZ650 SR

05-18-2009	#3 (permalink)
coverdog retired guy Join Date: Apr 2009 Posts: 7	Running too lean.

05-19-2009	#5 (permalink)
thehumble1 mechranically declined Join Date: May 2009 Location: Philly Posts: 32	It means that the air mix has too much air and not enough fuel. Lean=too little gas. Rich= too much gas. One way to check is to run the bike for a while, maybe 20 minutes at least to warm it up completely. Then stop and pull the spark plugs out. You can find plenty of posts on this site or others showing you how to read a spark plug (meaning that you look at the condition of the spark end to give you an indication of what kind of combustion is happening in the cylinder). Most likely yours will be white or light brown. They may not be too noticeable if they have been changed recently. The fix for it is probably more complicated than my small amount of technical information is able to properly understand, so I'll leave that to someone else. But I have no problems blathering about what I conjecture might be wrong: 1) poor seating on the carb boots (the rubber connectors between the carburetor and the air box and cylinder) 2) cracks in the carb boots 3) improperly set jets after rebuilding the carb 4) air filter out of place, allowing too much air into the carb. 5) valve timing (but this is getting outside my little area of knowledge as yet). 6) demonic possession. (Unlikely, but most difficult to repair) Usually requires a lot of starter fluid and a holy hand grenade.

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