Major Mods to an Old Twin Carb!

Message

coffee_brake · Sat Dec 29, 2007 6:14 pm

A project bike fell into my lap--a much-unloved '82 Kawasaki KZ440. This is a parallel twin with 2 carbs, basically the predecessor to the Vulcan 500 and the Ninja 500. Parts are hard to find and/or expensive. The carbs are shot, I could put my pinkie through the diaphragm rips, and replacement slides are incredibly high-priced. So, why not run a single carb to both cylinders? I got this bike to learn some stuff, so I'm trying to learn what to do to get it running on one carb. I have a CV carb from a newer ATV, a single-cylinder 4-stroke 350cc. For now, I have a galvanized "T" piece of plumping pipe and two elbows of radiator hose to do a mock-up, because I don't even know if this engine will run yet. If this works, I will trade my local welder a case of adult beverages to make me up an intake.
My question is: I don't have any idea where to begin with jetting modifications. Is there a rule for this? What do I look for as indicators that this or that jet should be changed? If I do this mock-up and the engine actually begins to run, what do I look for?
Also--placement of the carb is an issue, the frame may get in the way (I'll be running a pod air filter). Does the carb need to be directly behind and on the same level with the cylinders, or can I move it up or down a bit? On the bikes I've seen, the carb is on the same level as the cylinders even if it's one carb for multiple cylinders.

Help is certainly appreciated, the poor machine deserves a chance to run after its decade of neglect!

Johnj · #2 Unread post by **Johnj** » Sat Dec 29, 2007 7:26 pm

I don't know the answer right off the top of my head, but Triumph used to offer single and double carburetored versions of both 500cc and 650cc models. Both used the same bodies but the single carbs used bigger jets and a different slide. It seems like it had a greater angle on the cutout on the slide. Try looking there.

coffee_brake · Sun Dec 30, 2007 8:45 am

Thanks, will do!

#4 Unread post by **dr_bar** » Sun Dec 30, 2007 9:22 am

Don't know if I'm right or wrong, but wouldn't the single carb have to be bigger than the twins to handle the increased air/fuel flow? Just makes sense to me, but what do I know???

Johnj · #5 Unread post by **Johnj** » Sun Dec 30, 2007 9:44 am

I broke out the old manuals. the twin carb has a 180 main jet, and the single uses a 230. They both used the same 0.106 needle jet and STD needle, but the twins needle position is 1 while the single drops the needle to position 2. There is also a different slide or throttle valve with the Bonnivilles using 3s while the Tiger used a 3½.

dablade · #6 Unread post by **dablade** » Sun Dec 30, 2007 11:43 am

What a cool project. You certainly are ambitious. Please let us know how this turns out, and post some pics if you can. I hope this works out for you.
Regards,
Perry

coffee_brake · Sun Dec 30, 2007 5:10 pm

Hey, thanks JohnJ! That gives me a starting place, if not for actual jet size, then at least a useful ratio!

The bike is at my buddy's shop. He does this stuff for a living so when he's not too busy at it, he'll at least answer a question or two. He's not working on my bike or anything, I'm determined to do all the work on it myself, he's just letting it stay in his back storage area.

You're right, I better take pictures because she is one ugly stocker right now...