Carb needle adjustment

Hey guys,

I've done a lot of reading through the forums on carburetor cleaning, rebuilding, and jetting. I just have a few uncertainties. I'll begin with what I'm working with:

1978 KZ650 Custom
4>1 Exhaust w/baffled muffler
Stock Air Box w/K&N filter (cleaned)

What I've done:
Cleaned and replaced all hardware.
105 main jet (down from 118. not sure why it was so high)
15 air screw
Needle Jet @ 3rd.
Also checked for air leaks at connectors by spraying carb cleaner and looking for rpm increases... all good.

Result:
Bike starts up fine when cold with choke of course. Idles @ about 1-1200rpm.
BUT!!! She runs a little flat at the 4-6000rpm range. As if she's running too lean. Kinda feels like shes topping out but pulls through eventually. Thing is the mixture screws are only a turn out. That is 180 degree turn. From what I've read, the mixture screw should be out a whole turn (im ssuming this means 360 degrees out) and a 1/2 to start. This symptom only occurs for about two miles or so. She begins to run fine after that. :huh: All this happens when she sits overnight and I start her in the AM or after my 8 hr shift at work.

I've hit a bit of a slump. The next thing I was going to try was adjusting the needle but I'm a little unsure of which direction to go. Again, this is my first carb rebuild and first bike! I'm thinking I've gotta drop a groove on the needle to make the mixture richer. Am I on the right track with this? I really don't think I should be going too much higher than 105 main jets. My kits didn't come with larger air screws but I also don't think I should have to go up to 17.5 considering I still have the air box.

What do you guy's think? I really wish I had a go pro to record the bike's reactions at start-up and after a bit of riding.

*If I were to adjust the needle would I have to re-sync? I can access them by removing the tank and tops to the carbs. I'd love to avoid removing the carbs again and adjusting those lock-nuts and screws.

Thanks guys! I really appreciate any and all input.

Adjust your idle mixture screws out 1 1/4 turns out. Your just 1/2 turn out now.
Air cooled bikes are a little cold blooded at start up . But you being in Houston
that shouldn't be much of a problem. When rejetting I've learned to go a little
farther to the other end of the jetting spectrum and go back to a happy medium.



.

Nebr_Rex wrote: Adjust your idle mixture screws out 1 1/4 turns out. Your just 1/2 turn out now.
Air cooled bikes are a little cold blooded at start up . But you being in Houston
that shouldn't be much of a problem. When rejetting I've learned to go a little
farther to the other end of the jetting spectrum and go back to a happy medium.
.

The startup isn't much of a problem. She starts right up and idles well. The problem occurs when I get in gear and take off, but only for about a couple miles. I know the mixture screws should be out further but I can't otherwise she'll bog down. She won't except any throttle with the screws out more than 3/4 turns. She like's the half turn out but I know that's not ideal. I'm thinking that by dropping the clip on the needle I'll get a richer mixture and will allow for the correct air mixture screw settings? Or maybe it's the opposite? Ha, that's where I'm a little confused.

Yes, raising the needle will richen the mixture.
I would run a can of Berrymans B12 in a tank of fuel to clean out the system.
Sounds like the idle circuit is partially clogged. The idle mixture screw allows
air into the engine. By only opening up the adjustment screw 1/2 to 3/4 of a turn
you are restricting the air into the circuit making the engine draw in more fuel.
If the fuel passage in the idle circuit is restricted ( partially blocked ), less air is needed.
Meaning the air passage ( idle mixture screw ), has to be closed down to adjust for
a proper air fuel mixture.

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Since you have a 650 C1 - I assume you have the stock vm24ss carbs on it. You have a 4 into 1 exhaust and the stock air box with a K & N less restrictive (than stock) air filter.

You say are running 105 mains and a 15 air screw. From this I assume you mean you are running a 15 pilot jet. You indicate the needle is set on the 3rd clip - which IIRC is one slot leaner than the stock setting was. I am pretty sure the stock settings were a 102.5 main, a 15 pilot, a 5DL3 jet needle set to the 4 slot, an O-8 needle jet (that is an OH not a zero) and a 1.5 cutaway on the slide. So it sounds like you have increased the main one size and leaned the needle setting one slot.

Which type of pilot adjustment screw do the carbs have. an air screw on the side of each carb or a pilot screw on the bottom of each carb, or do they have both?

gd4now wrote: Since you have a 650 C1 - I assume you have the stock vm24ss carbs on it. You have a 4 into 1 exhaust and the stock air box with a K & N less restrictive (than stock) air filter.

You say are running 105 mains and a 15 air screw. From this I assume you mean you are running a 15 pilot jet. You indicate the needle is set on the 3rd clip - which IIRC is one slot leaner than the stock setting was. I am pretty sure the stock settings were a 102.5 main, a 15 pilot, a 5DL3 jet needle set to the 4 slot, an O-8 needle jet (that is an OH not a zero) and a 1.5 cutaway on the slide. So it sounds like you have increased the main one size and leaned the needle setting one slot.

Which type of pilot adjustment screw do the carbs have. an air screw on the side of each carb or a pilot screw on the bottom of each carb, or do they have both?

Thanks a bunch gd4now. You have no idea how much I've searched online for the info you provided. I had already begun to work on that needle and moving the clip down one groove to the 4th has made a world of difference.

To answer your questions:
My carbs have the the air screws on the sides of the carbs. With the needle adjustment, the air screws are now at about a whole turn and a 1/4 out She started just fine as usual but I definitely got that power back in the 4-6000rpm range in all gears. I'll have to ride her a little more of course to ensure it's all fine but man am I excited! :laugh:

Thanks a bunch guys for all the input!