KZ650 jetting woes

'79 KZ650 B3 (pumper carbs, non-adjustable jet needle,Dyna-S ignition)

Pods & MAC 4/1 with baffle

WiredGeorge recommended 17.5 pilots and 110 mains, which I did.

Have had black smoky exhaust (even at idle), crappy mileage, and constantly fouled plugs ever since. It fouls the plugs in just a few hundred miles.

From a 60 mph roll-off in 5th gear, the bike tops out at 80 mph. If I downshift to 4th and run it up to redline before going into 5th, I can get it up to around 105. To be fair, I'm 6'5"/290lb, and the gearing is 17/40, so the top speed issue may not be entirely carb-related.

Even on a cool day, the bike starts right up with no choke. On colder days, maybe just a touch of choke, and only for 30 seconds to a minute. Clearly the bike is rich.

What I don't get is, time after time, I see people with similar setups running that 17.5 pilot/110 main combination with great success. I wonder why it is so rich on my bike?

seanof30306 wrote:

'79 KZ650 B3 (pumper carbs, non-adjustable jet needle,Dyna-S ignition)

Pods & MAC 4/1 with baffle

WiredGeorge recommended 17.5 pilots and 110 mains, which I did.

Have had black smoky exhaust (even at idle), crappy mileage, and constantly fouled plugs ever since. It fouls the plugs in just a few hundred miles.

From a 60 mph roll-off in 5th gear, the bike tops out at 80 mph. If I downshift to 4th and run it up to redline before going into 5th, I can get it up to around 105. To be fair, I'm 6'5"/290lb, and the gearing is 17/40, so the top speed issue may not be entirely carb-related.

Even on a cool day, the bike starts right up with no choke. On colder days, maybe just a touch of choke, and only for 30 seconds to a minute. Clearly the bike is rich.

What I don't get is, time after time, I see people with similar setups running that 17.5 pilot/110 main combination with great success. I wonder why it is so rich on my bike?

Would assure correct fuel level in floatbowls by using the clear tube test. Too high fuel level results in excessively rich mixture.

Would also measure positive voltage at coil primary winding terminals to assure receiving full battery voltage at coils.

If original coils are still fitted, old hard plug wires or plug caps might be leaking voltage.

Would also check and assure valve clearances are correct.

Good Luck!

pods

650ed wrote:

pods

Hey, 650ed . . . no four-letter words allowed. :laugh:

Good Luck!

What plugs are you using? Maybe go to a hotter plug?

Like the guys said...
Fuel level
voltage measurment ... Coil mod candidate?
hotter plugs
Maybe use the stock jets and go from there.

Nothing worse that the low milage and constant plug changes due to running rich. The exhaust stinks of fuel as well.

The coil mod solved the problem for me. I have a box of fouled plugs to prove it. Since the mod I have run the same set of plugs.

"I see people with similar setups running that 17.5 pilot/110 main combination with great success"....

Keep in mind, what is successful for others doesn't constitute ideal operations for your KZ...

Too many variables involved... Example, exhaust system, pods, head porting, carb selection & operations, elevations, perfomrance builds, electrical power distribution etc... just to name a few...

What may have worked for someone else can and will be different on your engine...

As in learning the jetting of my new carbs... It's a PITA but a neccessary one to learn...

As in my case, mid and WOT have been sweet with no popping on deceleration/accelration, no flat on face performance or blurp but still a little on the carbon side on the plug base ring.

Regarding cold or hot start ups... Just a slight puff of smoke for the first 10-30 seconds then clears up.
In my case, Can't use the choke at all thus going the next size smaller (52) on the slow jets (Keihin for pilots).

I also ordered the next size larger (leaner) of the needle jet. First thing first, slow jets first, test run for awhile then and only if required, the needle jet will be the last....

Basically trial and error & tweaking to get totally dialed in... It's the name of the game for every engine, riding style, performance upgrades, exhaust modifications etc.... all come into play of what you're requiring..

Some will say, close enough, runs good versus others desiring tighter tolerences of 100% dialed in...

Keep at it for as mentioned, you have some confirming in coil voltages, fuel levels, jetting to accomplish yet...
Once you get it there, you'll definitely notice the difference...

OMR

Old Man Rock wrote:

"I see people with similar setups running that 17.5 pilot/110 main combination with great success"....

Keep in mind, what is successful for others doesn't constitute ideal operations for your KZ...

Too many variables involved... Example, exhaust system, pods, head porting, carb selection & operations, elevations, perfomrance builds, electrical power distribution etc... just to name a few...

What may have worked for someone else can and will be different on your engine...

As in learning the jetting of my new carbs... It's a PITA but a neccessary one to learn...

As in my case, mid and WOT have been sweet with no popping on deceleration/accelration, no flat on face performance or blurp but still a little on the carbon side on the plug base ring.

Regarding cold or hot start ups... Just a slight puff of smoke for the first 10-30 seconds then clears up.
In my case, Can't use the choke at all thus going the next size smaller (52) on the slow jets (Keihin for pilots).

I also ordered the next size larger (leaner) of the needle jet. First thing first, slow jets first, test run for awhile then and only if required, the needle jet will be the last....

Basically trial and error & tweaking to get totally dialed in... It's the name of the game for every engine, riding style, performance upgrades, exhaust modifications etc.... all come into play of what you're requiring..

Some will say, close enough, runs good versus others desiring tighter tolerences of 100% dialed in...

Keep at it for as mentioned, you have some confirming in coil voltages, fuel levels, jetting to accomplish yet...
Once you get it there, you'll definitely notice the difference...

OMR

Why can't you use your choke?

Thanks for the input guys.

Bike has the WG coil mod, new Dyna green coils, new Accel wires, new NGK plugs; not sure which ones, but they're the ones recommended to work with the Dyna S ignition. I'm sure the float levels were right; we checked them several times.

The carbs are off the bike right now for a thorough re-cleaning. I'm going to put the stock jetting back in the bike and work up from there (if necessary). The way it starts right up with little or no choke and belches black smoke at idle has me convinced the 17.5 pilots were too rich, and the only smaller choice there is back to the stock 15s.

We're also in the process of building a new wiring harness from two good ones I got from two awesome KZRider.com members. That @#$%!!! KZ650 has had major electrical problems since I bought it, but it has always gotten proper voltage to the coils. When it ran, the bike always ran perfectly, with no cutting out, skipping, etc.

Also, on the 4/1, I put a new baffle in it from MAC. It actually has the bike too quiet; it sounds like a salad shooter. I'm thinking that baffle is probably severly restricting the exhaust, too.

"Why can't you use your choke".... Too Rich!
If I lift the choke more than a mm or two, chokes it out...

Cold or hot, no chole what so ever it starts right up. I have spoken with others who have the keihin CR Specials.. same scenario for them....

Keihn pretty much builds and ships their carbs out (jets) on the rich side... Don't want anyone burning holes in their pistons :ohmy: I guess.... Or just to sell more jets dialing them in for your application...

I am running a very similiar setup with 17.5 pilots and 112.5 mains and my plug chops are great. Make sure you manually sync the carbs by dialing in the slide height. I am running mine at .035 since this was the only solid core welding wire I had. The book calls for .032 or .043 depending on air screw or pilot screw type carb.

I also agree on the no choke as I shot a fireball out of my tail pipe when trying to start the bike after jetting. Mine starts hot or cold wihout choke now.

Hope this helps...

Brian

vintagestyle7 wrote:

I am running a very similiar setup with 17.5 pilots and 112.5 mains and my plug chops are great. Make sure you manually sync the carbs by dialing in the slide height. I am running mine at .035 since this was the only solid core welding wire I had. The book calls for .032 or .043 depending on air screw or pilot screw type carb.

I also agree on the no choke as I shot a fireball out of my tail pipe when trying to start the bike after jetting. Mine starts hot or cold wihout choke now.

Hope this helps...

Brian

We've been starting with a manual sync, then dialing it in with a vacuum gauge set.

Can you post the vacum measurements?