TOPIC:

Hi everyone,

I have KZ700 that has been troublesome for some years now. When it runs right, it's great. But it often doesn't.

Everytime it gets out out winter storage, it runs like it's been at the bottom of a lake and i'd be busy for a while getting it back again.
I've had the carbs off too much times to count.
Back then i was a student, so some choices were made on a budget (starting with buying a bike that someone did a lot of half-assed work on). Nowadays i'm fixing a lot of cheap choices from then. I just want it done properly now.
But i'm a but stuck on how to attack this.

Some background on the bike:
Originally it's a KZ700, the bottom end still is. But along the way, someone fitted a KZ750 cilinder on it (738cc stamped in the cilinders and bore size to match). The carbs are Keihin with black plastic tops, they state "1526 ua13" on the body . Presumably from a KZ750N Spectre. The barrels may be from that as well.
No idea if the head is original 700 or 750. Are there differences and how to identify? There is a different valve clearance specification for the 700.

Earlier work

• I've had the head rebuild about 2 years ago. New valves and recut the seats. Guides were fine, seals were replaced.
• Extremely loud and rusting exhaust was replaced by a Kerker megaphone system (new reproduction system).
• Intake boots were replaced a some time, but can't remember when.

After the last storage period it came out bad again, And i'm done with that. It shouldn't need weeks of TLC everytime it sits idle for a couple months (no ethanol gas).

Recent work:

• Took out the wiring loom for a full inspection. Removed all tape, found some damaged wires and replaced or repaired all of them. Also removed the reserve lighting device and hazards light relay as both systems were out of order.
• Replaced the starter as one of the bearings started to whine. I may rebuild the old one later on, but replaced with a used one for now.
• Replaced the coils with Dynatek coils. The existing ignition has been troublesome from time to time and one of them seems to be dying (out of spec). I didn't want to go back to another set of 40 year old unknowns. So bought these new ones. Original igniter still in place.
• Removed the emission system between the airbox and the head (put a hose between the 2 covers on the head, may want to find another valve cover in the future.

Current status (and the reason for this topic):
She runs bad. 
Started with unsteady idle, misfires, unable to run without choke, slow rundown after closing the throttle.

• Checked fuel level in the bowls. All even and a couple of millimeters below the line as specified.
• Checked the valves. All are within 0.13 and 0.18mm. This yields issue 1: Which clearances to use? KZ700 specifies 0.13-0.23 while KZ750/4 in general requires 0.08/0.18mm. I was under the impression that the heads were the same, but apparently the spec is different. Which to follow for this combination of hardware?
• Reset mixture screws to factory spec
• Synchronized the carburettors.

Synchronization helped the most. Bike runs a bit more steady now, back/misfiring is mostly gone. Still comes back slow from revs and seems to be inconsistent in idle level. Synchronizing had to be done at approx 1500 rpm. The stated 1050 rpm was not stable enough to work on. 
Did notice that the carb sync tool (carbtune) only shows about 12in/Hg of intake vaccuum where the manual expects about 20. Maybe the tool is inaccurate, but maybe you recognize it. The synchronization also seems to vary a bit between tries. I've done multiple rounds of adjustment back of forth in the hopes it would lead me to victory, but i don't know.

There seems to be little response from changing the mixture screws. Gone half a turn both ways (from 2 turns out), but little effect on idle or the rundown speed. Tried if choke helped the rundown (could indicate a lean condition) but that didn't seem to help. 

Spraying brake cleaner around the intake boots sometimes has an effect, but only after a while. Other times i can douse everyting in brake cleaner and nothing happens. 

I was thinking about replacing the boots and all jets and needles to originals, just to have a baseline. Also because all the years of working on those carbs have made my memory fuzzy on what is actually in them now. And as the carbs seem to be wrong for the bike, maybe i followed the wrong jet spec in the past. But before firing the parts cannon again, i'm wondering if i'm not missing something else.

Maybe the carb to engine combination isn't that good to begin with? (although i'd expect that 50cc not the be that big of an influence).
In that case, i would rather spend my time and money on tracking down a better set.
I've also contemplated buying a second (similar) carb set, maybe something is just wrong with these.

Or are my symptoms caused by something else entirely?

I know it's a lot of text, but i hope it explains the process a bit.

Thanks for any help

Tim

I would first suspect that the carb holders are the main culprit. Unable to get idle low enough, uneven idle speed, slow to return to idle all point to a very lean mixture, often caused by hard, leaking carb holders. Incorrect jetting may be adding to the problem.

You could set the valves between .015 and .018 until you are sure which to use.

Might be a good idea to lube the throttle cables and insure they move smoothly.

I took it for a short drive just now, to get it good and warm for a change and let some fuel go through the carbs.

Idle is still a bit vague. It seems to run a bit better now, but also backfires more on idle.
On acceleration it seems to slightly hesitate initially and has a power dip somewhere around 40-50% of the rev range. After that it pulls away cleanly.
I'd say main jetting seems (roughly) ok at least. So then we're back to air leaks and pilot screw+jet.

I seem to have KZ750N carbs, they look exactly like these:

from here: kzrider.com/forum/3-carburetor/604254-je...e-h-spectre-keihin-s

Anybody tried the difference in the listed jettings for these keihins?
KZ750H & -N has 65 primary and 90 secondary with a N10A needle
KZ750E has 62 primary and 125 secondary with a N01A needle

Current jetting matches the -H and -N variant (65/60/N10A).

The kz700 originaly came with mikuni BS34 with a slight decrease in main jet (105) compared to the KZ750L (110).

When I was getting my 750LTD on the road I bought carb holders from eBay.  Even though they were new they leaked vacuum.....the hotter the engine was, the more they leaked and the idle would increase.  If I set the idle when warm it would not idle at all cold..  You could try getting some hi temp sealer between the holders and head.  .II that helps I'd synch
 them again..  I don't think you could get a proper synch if you're leaking vacuum. I ended up getting OEM carb holders AND used a little hi temp sealer.  That was the last piece of my puzzle.  It's running perfectly now.

I have a parts bike 1984 KZ700. I think it kind of ran when I got it. It had no title so the guy gave it to me.

"Always start with the freshest fuel you can find." --Kevin Cameron