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gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 11:32 #787570

  • khungerf
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I have a another thread regarding the choke detent.  I have temporarily resolved that issue with a zip-tie while I search for parts (how did people keep vehicles running before zipties??)

I have two issues.
1) after revving the motor from idle it is slow to get all the way back down to idle.   I am guessing this is a float level issue that I will need to check.

2) the pulls reasonable from 3-6k rpm.   stutters really bad from around 6.2k to 8K   then pulls really good up to the 10.5k redline.  I shift, it drops back down in the 'stutter' area of 6-8k.     I don't think my float level is affecting things up there.   

Thoughts on what to look for for issue #2  ?

Also, what are your fuel/air screws set at(on top of the carbs)?   I think some have a cap there but mine are open.


Thanks for any help,
Lee 
-Lee
'84 GPZ550

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gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 14:00 #787578

  • gordone
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What I have learn, slow down to idle is often airleak. Can also be carb out of sync if its only close to idle its slow to come down.
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 14:08 #787579

  • SWest
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What type of carbs?
Steve

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gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 14:32 #787581

  • Scirocco
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Please upload a pic of your spark plugs. The spark plug color can indicate a lean or fat fuel/air ratio or a bad ignition timing to the late or too advance direction.

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gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 15:46 #787592

  • loudhvx
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He has TK27 CV carbs.  They are an upgrade from the Tk26 CV.

I agree, as Gordone said,  with no other evidence, slow to return to idle is most likely air leak.    A really bad sync can cause it too.
(Leaky choke can cause that too but you've addressed that.)

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Last edit: by loudhvx.

gpz550 carb questions - stutter at 6k rpm 24 Jul 2018 15:49 #787593

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Slides may be sticking. Bad diaphragms. 
Steve

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gpz550 carb questions - stutter at 6k rpm 25 Jul 2018 07:13 #787630

  • khungerf
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Thanks for all the input.

the air leak comment has wondering.   in the tk26/27 carbs the choke rod goes all the way through the carbs.   Shouldn't there be a plug on end of carb #4 where the choke rod ends?    seems having that open, as it is on mine, would not be good.

Also,
I will pull the plugs and post pics
-Lee
'84 GPZ550

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gpz550 carb questions - stutter at 6k rpm 25 Jul 2018 13:04 #787640

  • loudhvx
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The choke rod bore is vented to the underside of the diaphragm which is vented to atmospheric air anyway, so it shouldn't matter.  That area is open to air already.

The choke rod bore is not connected to the actual enricher circuit plumbing.

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gpz550 carb questions - stutter at 6k rpm 01 Sep 2018 18:15 #790120

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finally... plug pics. I am not good at reading these but they look OK to me.
After more riding - I get an undulating idle once it warms up. when I rev it to keep it running at when that happens it will backfire.
rich? bad float level setting?

-Lee
'84 GPZ550
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gpz550 carb questions - stutter at 6k rpm 02 Sep 2018 09:02 #790144

  • loudhvx
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The problem with plug photos online is that the lighting and camera setting can influence how things look, as long as the plug colors are reasonably close to being normal. I can take a couple photos of the same plug and one will look rich while another will look lean if I change the lighting/settings.

If the plug is way off, like totally black or white, then it's easy, but when you are close it becomes increasingly difficult to say.
Another major issue is that one part of the carburetion can be lean while another is rich. So then how you drive it can influence how it look. If it's rich at idle, but you spend all your time on the highway, the plug may end up looking lean. Again, this is if things are close to being correct. If something is way off, then it becomes easier to see something is wrong.

To me, your plugs look pretty good, but some of the photos seem darker than others.

So this means you will likely have to do other things to diagnose your specific problems. Without an AFR gauge, you will need to use seat of pants.

The first thing is the idle. If you have an oscillating idle when the bike is fully warmed up, this still could be an air leak or choke issue. I know you don't want to hear that.

Another possibility is that for some reason you are idling a bit on the main circuits. This means the throttle is open just enough to start actuating the slides. As the slides go up and down, the mixture goes rich and lean. Since the slides are slow to react, this causes an oscillation.

I don't remember if you have pods or airbox. If you have pod filters, you can pull them and use a camera phone to see if the slides move during idle. They should not. Check all four. Do not try to look directly, up close, into the carbs while running. Make sure your face is not in the path of a backfire fuel/flame spray. I've seen 3-foot fuel/flame spray come out of carbs many times.

If the slides are moving at idle, then it could be the pilot circuits are plugged forcing you to use a bit of the main/intermediate circuits to idle. It could also be the pilots are too rich or too lean. If you idle for a while with no riding, the plugs might show you something. If they are wet with fuel, then it means the pilots are too rich or the choke is again not sealing off completely. There's probably many other possibilities I'm not thinking of, so hopefully some others will have some ideas.

You should have a system setup that allows you to see fuel level while idling on a perfectly level surface with the center-stand. You want to be able to verify fuel level quickly and easily, and get a lot of practice at it... eliminating bubbles etc. to get you a true reading. Its not as simple as the manual would have you believe. A hidden, trapped air bubble can throw your reading way off.

A really good thing to have is a stand with an auxiliary fuel can so you can run with the tank off. The aux can should not be higher than the fuel tank would be, but just high enough to gravity-feed the carbs. You will eventually need it for syncing anyway, so you might as well make it now and use it. It makes life much easier. There's probably a few threads with ideas on how to make them cheaply.

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Last edit: by loudhvx.

gpz550 carb questions - stutter at 6k rpm 06 Sep 2018 11:16 #790401

  • khungerf
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loudhvx wrote: The problem with plug photos online is that the lighting and camera setting can influence how things look, as long as the plug colors are reasonably close to being normal. I can take a couple photos of the same plug and one will look rich while another will look lean if I change the lighting/settings.


I agree - it was hard to get them consistent but the 'looked' OK from a non-expert who is color blind : )

loudhvx wrote: If the plug is way off, like totally black or white, then it's easy, but when you are close it becomes increasingly difficult to say.
Another major issue is that one part of the carburetion can be lean while another is rich. So then how you drive it can influence how it look. If it's rich at idle, but you spend all your time on the highway, the plug may end up looking lean. Again, this is if things are close to being correct. If something is way off, then it becomes easier to see something is wrong.
To me, your plugs look pretty good, but some of the photos seem darker than others.
So this means you will likely have to do other things to diagnose your specific problems. Without an AFR gauge, you will need to use seat of pants.

The first thing is the idle. If you have an oscillating idle when the bike is fully warmed up, this still could be an air leak or choke issue. I know you don't want to hear that.


Wanting hear it has nothing to do with it - I am trying to chase down all the possobilities - so I will look at that one again

loudhvx wrote: Another possibility is that for some reason you are idling a bit on the main circuits. This means the throttle is open just enough to start actuating the slides. As the slides go up and down, the mixture goes rich and lean. Since the slides are slow to react, this causes an oscillation.

I don't remember if you have pods or airbox. If you have pod filters, you can pull them and use a camera phone to see if the slides move during idle. They should not. Check all four. Do not try to look directly, up close, into the carbs while running. Make sure your face is not in the path of a backfire fuel/flame spray. I've seen 3-foot fuel/flame spray come out of carbs many times.

If the slides are moving at idle, then it could be the pilot circuits are plugged forcing you to use a bit of the main/intermediate circuits to idle. It could also be the pilots are too rich or too lean. If you idle for a while with no riding, the plugs might show you something. If they are wet with fuel, then it means the pilots are too rich or the choke is again not sealing off completely. There's probably many other possibilities I'm not thinking of, so hopefully some others will have some ideas.


I have the stock airbox (supposedly to simplify the carb tuning!)
I will look into this idle for a while and check the plugs as well as making sure I don't have my throttle cable to tight.
I think I will also double check the float level the shop said they set it...but it never hurts to check!

loudhvx wrote: You should have a system setup that allows you to see fuel level while idling on a perfectly level surface with the center-stand. You want to be able to verify fuel level quickly and easily, and get a lot of practice at it... eliminating bubbles etc. to get you a true reading. Its not as simple as the manual would have you believe. A hidden, trapped air bubble can throw your reading way off.

loudhvx wrote:
Not sure what you mean hear - and AFR gauge?

A really good thing to have is a stand with an auxiliary fuel can so you can run with the tank off. The aux can should not be higher than the fuel tank would be, but just high enough to gravity-feed the carbs. You will eventually need it for syncing anyway, so you might as well make it now and use it. It makes life much easier. There's probably a few threads with ideas on how to make them cheaply.


Carbs SHOULD be synced - I paid a shop to do it since I did not have the equipment.

as Always, I appreciate the input and suggestions!

Thanks,
Lee
-Lee
'84 GPZ550

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Last edit: by khungerf.

gpz550 carb questions - stutter at 6k rpm 06 Sep 2018 12:09 #790402

  • 650ed
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khungerf wrote: .........................

Carbs SHOULD be synced - I paid a shop to do it since I did not have the equipment..........


Just curious; how much did the shop charge to sync the carbs? Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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