Bike is noisey below 1600 RPM

Hi all,
I just got a kz750ltd back on the road. It runs great at 1600 rpm all the way to redline. However, I can't get it to idle below 1600 rpm without a lot of engine noise. It will hold an idle at 1000 rpm but it is very noisey. It sounds as if it is coming from the transmission. Also, I have to turn the idle adjust up to get the choke to work in the mornings. I have checked adjusted the valves, cleaned and lubed the advancer, and cleaned the carbs, removed the cam chain tensioner and cleaned it, installed a new battery. My compression readings dry were 1-135, 2-140, 3-140, 4-145 . The carbs are Keihin CV carbs. The intake boots are not leaking. The 0-rings in the idle mixture holes are old and hard. So, I am going to replace the air/fuel o-rings tomorrow. Could the carbs just be out of sync? Or do you think I need to clean the pilot circuits one more time. The bike runs really strong. I have never synched a set of carbs before so any tips would be appreciated. I linked a pic of the bike below. Thanks
home.fuse.net/fishbone1/DSCF0278.JPG

fishbone1 wrote:

Hi all,
I just got a kz750ltd back on the road. It runs great at 1600 rpm all the way to redline. However, I can't get it to idle below 1600 rpm without a lot of engine noise. It will hold an idle at 1000 rpm but it is very noisey. It sounds as if it is coming from the transmission. Also, I have to turn the idle adjust up to get the choke to work in the mornings. I have checked adjusted the valves, cleaned and lubed the advancer, and cleaned the carbs, removed the cam chain tensioner and cleaned it, installed a new battery. My compression readings dry were 1-135, 2-140, 3-140, 4-145 . The carbs are Keihin CV carbs. The intake boots are not leaking. The 0-rings in the idle mixture holes are old and hard. So, I am going to replace the air/fuel o-rings tomorrow. Could the carbs just be out of sync? Or do you think I need to clean the pilot circuits one more time. The bike runs really strong. I have never synched a set of carbs before so any tips would be appreciated. I linked a pic of the bike below. Thanks
home.fuse.net/fishbone1/DSCF0278.JPG

yes...sync the carbs....heres a start for you....

www.motorcyclistonline.com/howto/motorcycle_carb_sync/

has cam chain ever been adjusted?

check out this...

www.carbtune.com/

Post edited by: firemun59, at: 2006/10/03 12:11

The cam chain has an auto adjuster but I guess it could be stuck. I will pull it and clean it again. I have a mercury type carb balancer. Just never worked up the courage to use it. Afraid I will mess something up. I will check out the links and give it a try. Thanks

Doubled somehow.

Post edited by: Mikes82KZ1100, at: 2006/10/03 13:15

What about the vaccum gauges? Maybe like the ones listed on ebay? Would they get you "close enough" for everyday riding? I'm sure the Morgan Carbtune is worth the $129.00, Just a little steep for a (hopefuly) one time use.Hmmm, maybe get it, use it and then E-BAY it.

Post edited by: Mikes82KZ1100, at: 2006/10/03 13:31

That 750 is going to sound terrible until you get the carbs synced

What you are hearing is more than likely the primary chain (that's the usual culprit).

It is a pretty nasty sound. I will try to synch them this weekend. Is there anyplace I should adjust my idle to for a starting point?

My 750 knocked like a bitch at idle till I synced the carbs. Now smooth as can be. Didn't have the proper tool, as you have , so I used a singe vacuum gauge adapted to fit one carb vacuum port at a time. Requires capping off the other three ports.

Set Idle low, say 1100 if it will stay running. It's not critical. As you change the settings, the idle will have to be re-adjusted using the knob underneath-center.
The knob does not affect the sync.

Since the throttle cable pulls on number 2 carb, set number 1 vacuum to match number 2 vacuum. Locknut and screw between 1 & 2 carbs.

Set number 3 to match number 4 or visa-versa. Locknut
and screw between 3 & 4 carbs.

Then set (3 & 4) to match (1 & 2). Locknut and screw between 2 & 3.

That's how I did it-not knowing-and it worked.

Don't forget the big fan to cool the engine, nor the 8' of 5/16 fuel line so you can elevate the tank. Set petcock on prime. An inline fuel filter can be installed between the tank and the carbs before ya buttin it up-cheap insurance.

Hope this helps ya.

DanAir,

Thanks for the help. I will give it a try this weekend.

www.powerchutes.com/manometer.asp

The link shows how to build a cheap manometer that works great. It is best on 2 cylinder machines, but I used it on my 4 cylinder.

I just synced 1-2, then 2-3, then 3-4. Then I checked all of them against #1 again.