carbs: jets

Hey everyone,

2 questions.

1) I am wondering if the air pilot screws need to be turned out by the SAME amount on all four carb boots? I am new to this, and right now the idle didn't last long, i disassembled the carbs (got 118 mains, 17.5 pilots); the air pilot screws right now are turned out 4 turns, the other 3 turns.

2) Should I turn those in, mount them, start the bike, then turn out gradually?

thanks!

hey wired george you better take this one.well anywho they should be 1 1\2 turns give or take a 1\4 turn and yes they should all be the same

Post edited by: gorack, at: 2008/01/29 03:20

thanks gorack!

so 3 turns is too much?

i have pods and x-pipe. engine has no mods and the carbs are clean.

They will generally be close but not exactly the same in number of turns out. 3-4 turns is too much, you're too rich, maybe try some 15 pilots and check the float heights. Not sure what carbs you have but 118 mains seem a little big for a stock 650 engine with X-pipe (newer style?) and pods.

What do the plugs look like after a few minutes of idle?

Did you set the bike up or was it like that when you got it?

Me, I'd put the jets back stock or use 15's and 112.5's in it to start with and if it has adjustable clips on the needles I'd put them in the middle and go from there as to what jets are needed. A lot of times jets are "opinion spec'd" before the bike is tried with the stock setup after exhaust and pod mods.

Post edited by: KZ_Rage, at: 2008/01/29 18:43

ZeeEuro wrote:

...wondering if the air pilot screws need to be turned out by the SAME amount on all four carb boots?...air pilot screws right now are turned out 4 turns, the other 3 turns....

If carbs are oem for 1979 KZ 650-C3, am thinking side-located pilot air screws which govern the amount of air being allowed to mix with fuel in the pilot jet. (The pointed tip restricts size of the air passageway by gradually closing it off).

Screwed all the way in (to lightly seated) would be the richest pilot circuit fuel mixture as little or no air is being allowed. Conversely, screwing out leans the mixture by gradually allowing more and more air into the mixture.

Usually, the pilot air screws are a final step in carb adjusting -- use pilot air screw to attain highest idle rpm, reduce idle positon thumbscrew, repeat for successive carbs. Results in best performing idle mixture for each carb, and not necessarily the exact same number of turns for each carb, although usually winds up being pretty close to the same adjustment (same number of turns) for each carb.

If turning the pilot air screw has no effect on the low rpm (idle speed), there is likely something wrong with the pilot circuit inside the carb (provided everything else is okay).

Good Luck!

KZ Rage and Patton, thank you very much,

Unfortunately I currently don't have any other jets. When this one mechanic failed to tweak theaftermarket jets right (to accomodate the stupid x-pipe), he took out the stock airbox and put cheap pods in. That worked, but he said not 100%, like 80%. Then the bike sat for 5 months. Started it, ran for 5 mins (choke closed), then it started to die off when i opened the throttle to 1/2.

Therefore, I assumed it was the carbs, and disassembled them (yes, Patton, OEM); they turned out to be clean (except for minor salt-like white stuff in one of the carb boots).

I cannot open the needle cover, need a thinner screwdriver.
So, given that i have no idea where the needles are, the floats are normal (26mm), without messing with the mains and pilots (i don't have other sizes in possession), is 3 turns too much? should I turn the air pilot screws IN more, to let's say 1.5 turns? Then if that doesnt help, start messing with the needles, then jets...?

I'd like to keep 118 and 17.5 jets (im currently broke) just in case i want to get a wiseco big bore kit, K&N filters, and other modifications i've heard guys here talk about as mods.

Do as Patton says, try to use a hand held tach as the bike tach is not accurate at idle. Use a fan in front of motor to keep from over heating and turn one air screw in or out to get the highest idle, adjust idle and then move to next carb (giving motor a couple rev's in between adjustments) finish all 4 and maybe go back and repeat.

ZeeEuro wrote:

So, given that i have no idea where the needles are, the floats are normal (26mm), without messing with the mains and pilots (i don't have other sizes in possession), is 3 turns too much? should I turn the air pilot screws IN more, to let's say 1.5 turns? Then if that doesnt help, start messing with the needles, then jets...?

I'd like to keep 118 and 17.5 jets (im currently broke) just in case i want to get a wiseco big bore kit, K&N filters, and other modifications i've heard guys here talk about as mods.

What I have learned from boards is that pods are the spawn of Satan, and generally make things run too lean and usually can't be dialed in just right.

That said, what I learned about carbs and found to be true from tuning experts:

1) Dial in the main jet first. If the bike runs strong at full throttle from about 4k RPM to redline, that is the test of the right main jet.

2) next screw with the needles. They tend to control 1/4 to 3/4 throttle opening at mid RPM band.

3) Fuel level in carbs if the engine stumbles when the throttle is opened quickly.

4) Then screw with the pilot jets, which set idle and very light throttle/low RPM operation.



Of course, the various systems also overlap some.

Here arte the experts:

www.factorypro.com/tech/carbtun.html

Post edited by: bountyhunter, at: 2008/01/29 17:47

Post edited by: bountyhunter, at: 2008/01/29 17:50

ZeeEuro wrote:

...don't have any other jets...carbs...disassembled...turned out to be clean...cannot open the needle cover, need a thinner screwdriver...have no idea where the needles are, the floats are normal (26mm), without messing with the mains and pilots (i don't have other sizes in possession), is 3 turns too much? should I turn the air pilot screws IN more, to let's say 1.5 turns? Then if that doesnt help, start messing with the needles, then jets...like to keep 118 and 17.5 jets....

Usually, the beginning final tuning position for side-located pilot air screws is set by turning in clockwise to lightly seated, then turn all four of them out counter-clockwise an equal number of turns (see FSM -- "Factory Service Manual") which is generally somewhere about 1 and 1/4 or 1 and 3/8 or 1 and 1/2 turns out from lightly seated. This default beginning position is supposed to be and is often near the final adjustment position after fine tuning them individually in conjunction with the thumbscrew to attain the best idle performance.

For the time being, would just leave the primary jets and main jets as is, and not change the jet needle clip position. Could double-check all four float bowl fuel levels to see if the fuel levels are 2-4 mm below tops of float bowls by performing the quick easy clear plastic tube test on each carb, which involves no disassembly besides removing the float bowl drain plug on the particular carb being checked.

Good luck!

Bluemeanie, bountyhunter, and Patton,

thanks for the tips, they really helped.

on a different note, i put the carbs back together but the accelerator pump gasket is leaking gas and the bike wouldn't start. going to order stuff from Z1 right now, then back to the jetting in a week. I'll keep you posted.

thanks again!