Bike lunging and studdering KZ 400

Picked up a bike that hadn't ran in a few years. Cleaned the carbs thoroughly. and did all proper maintenance. I cant seem to get the carbs dialed in though. The manual says the jets should be 135 (main) and 40 (pilot) but actually installed are 35 (pilot) and 130 (main). The manual says the pilot screw should be 7/8 turns out and when I got the bike, they were at 3.25 turns out. When I give the bike 3 turns out, it runs but lunges randomly, like its getting a bust of energy, if I give it around 1-2 turns out, it idles good, but dies instantly when any throttle is applied. I do have a vacuum balancing kit but I had to order the 6mm adapters (I only have 5mm) so I can't balance them just yet. Is the lunging related to the fuel air mixture being wrong?

Side notes:
The right exhaust gives significantly more pressure than the left although I checked valves and they are perfect and compression on both cylinders is around 180PSI.
The right chrome exhaust is blue at the head of the right cylinder, and it is burning.
The spark plugs are both fouled (brand new) black and wet.

Does the bike have the stock air box and filter in place? Ed

When I got the bike it had the original filter in it, but the woman I bought it from gave me a box of parts/goodies from a bike shop she went to asking how to restore the bike. So they obviously sold her everything in the book, so I got one of those foam air filters that you spray the sticky filtering spray on. And yes, original airbox.

Bump for any help?

I'm not familiar with the kz400 but it sounds like you may have a couple of issues. I wonder if the number of turns out on the pilot /air mix screw was an attempt to compensate for the smaller than stock jets ? I would try to get the recommended jet sizes and stock air filter if available and return to stock settings

Side notes:
The right exhaust gives significantly more pressure than the left although I checked valves and they are perfect and compression on both cylinders is around 180PSI.

Which makes me wonder if the left hand cylinder is firing or if you have intermittent firing on that cylinder.

The right chrome exhaust is blue at the head of the right cylinder, and it is burning.
The spark plugs are both fouled (brand new) black and wet

Get a spray bottle with water and spray or spit on the exhaust header as it exits the cylinder head. If that cylinder is firing then water will sizzle right off and if not firing then it will just evaporate .

Blue exhaust usually means running lean but black plugs usually mean running rich ???? Wet (with gas) plugs usually mean cylinder is getting gas but not firing. Fouled plugs dont fire or dont fire well
I would get brand new plugs and check that you have good spark at each and try to make sure that the ignition system is all in order before tackling the carbs
Good luck

Both exhausts get hot at the same rate, I know this because when I start i feel both exhausts and they heat up equally. I put in brand new plugs when I put the carbs back on after cleaning and then they turned black and wet looking. I could be the valve stem seals are leaking, hence the black smoke out of the right exhaust pipe, but I'm not sure why that would cause such bad performance. Maybe the burning oil is that much hotter causing the pipes turning blue?

Feeling the exhaust heat up is not a great test of a cylinder firing unless you burn your hand. :laugh: Spray water or spit is much better.
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Black smoke out the right exhaust...... would be more an indication of running rich. Perhaps as a result of mix screws so many turns out But then I am not familiar with the kz400 carbs so this may not be correct. Blue smoke more like burning oil. Blue exhaust is usually associated with running lean .Perhaps your plugs are black from an overly rich mixture ???? But then this does not square with blue exhaust. :

Regardless, If you are satisfied that the valve clearances are in spec then I would suggest making sure the ignition timing, points and plugs are in good order and then revisit the carbs and air filter

If you dont have a manual then check out www.kz400.com

Just food for thought, I'm pretty sure the kz400s are waste spark ignition systems. Meaning that if its running at all both plugs are sparking to some extent. I would imagine your problems are either in the carb or the points. Have you cleaned and adjusted the point gap?

Squirrel, I actually never did. I'm not entirely sure what that does/changes. Could that cause one cylinder to run different than the other? When I bought the bike, the PO gave me a bunch of parts still in box (bought it as a project and never started it) and in there is a brand new ignition system. Looks just like THIS

What exactly will this change? Make a larger spark? Thanks for all the help guys! I really appreciate it. Saving me form trailering the bike 300 miles to my girlfriends dad's house to have him fix it for me.

Hey guys, quick question. Everytime I think about getting this bike synced properly, I keep coming back to the carbs not being right. Since they are old (CVB 36) has anyone switched, or know someone who has switched to the later KZ400 carbs (CV 32). I found a set on ebay and am tempted to just get them instead. Since the engines from 76 and 77 are the same, wont these just pop right on and work? Thanks!

Another bump for more help!?!

FIXED IT!!!!

So I took the bike to my girlfriends uncle, hes a mechanic and drags old 80's bikes (mostly CB 1000's). It was this single stupid o-ring on the main jet. Now it starts up fine, but we're still trying to fiddle with the air mixture screws because I'm putting in an after market filter.

[img size=The O-ring] i.imgur.com/BqMsHw3.png [/img]

I have one last question! When we mess with the idle, we can turn it up and it sits at 900 rpm, keep turning it up, doesn't change, you finally get to a point where it just revs up to 3k rpm and stays there until you turn it down a bunch and then drops back down to 900 rpm. So It wont idle between 1-2.9k. Could that be air mixture ratio?

Thanks for all your help guys!