Carb Question

So Im working on my Franken Bike, managed to get a few rides yesterday and today. The question I have is about the choke circuit. The bike is hard to start when stone cold. Yesterday it took multiple tries before if stumbled to life, meaning it was hardly running and it slowly built revs with full choke. I decided to turn in the air screw 1/4 turn in and today it started on the second try but still slowly built up revs with full choke. The carbs have been cleaned and the pickup tubes removed and cleaned inside. All passages have been checked with brake fluid and are clear. A little background on this bike. I purchased a 74 Z1900 and got another chopped up monstrosity with it. Basically I only kept the engine, carbs,and rear wheel. Every thing else was Harley and scrapped. The frame was raked and worthless although I cut off some of the tabs. So I located a 1980 Frame and mounted the engine in this frame. So the engine is KZ900 I believe, I used a KZ1000 crank because I had it and wanted to test it. The carbs are late / early 73/74, the airbox is a stock 1980 Kz1000 box with stock filter. The engine has stock pistons honed with new rings and the head has all new guides, valves with the proper machine work. So why does the bike barely start with full chock and once started takes about a minute before it build revs to only around 2000 with full choke. Carbs have all of the stock jets and new choke plungers and all are lifting off the seat to full height, also carbs have been synced and were almost perfect from bench setting. All the valves have been rechecked and at .005. This is not my first rodeo but Neve have had this issue so any insight will help. I have several sets of carbs and probably will put a set on and see how they react. Before I go to that trouble hopefully someone has an easy answer for me.

I should also add, once the bike warms up it runs and idles well. I can close the choke after a  several minutes before I can pull away. It takes about a mile or so before it settles down but coughs a bit during that time. It pulls good from idle and I have just the slightest bog around 4,000 rpm but pretty satisfied on how it runs. Once it is fully warmed up.

 

What is the cutaway on the slides?  What jetting?  And what advancer are you using?  The bike looks superb!

Std for the 73 VM28SC carb, PJ is 20, needle 5J9-3 position, main is 112.5.  Cutaway should be 2.5 but not sure I did not actually check those slides. idle mix 1 1/2 but im at 1 1/4. plan on checking with COLORTUNE. 

My first instinct is a lean condition due to the KZ1000 air box but not sure. Inout from others may suggest that condition lets see before I start down the rabbit hole of jet changes.

Ignition is Dyna s (maybe a knockoff cant remember at the moment will have to check) 5 ohm coils. Timing looks good with strobe.
 

Cra-z1 wrote:

Std for the 73 VM28SC carb, PJ is 20, needle 5J9-3 position, main is 112.5.  Cutaway should be 2.5 but not sure I did not actually check those slides. idle mix 1 1/2 but im at 1 1/4. plan on checking with COLORTUNE. 

My first instinct is a lean condition due to the KZ1000 air box but not sure. Inout from others may suggest that condition lets see before I start down the rabbit hole of jet changes.

Ignition is Dyna s (maybe a knockoff cant remember at the moment will have to check) 5 ohm coils. Timing looks good with strobe.

 

I would be surprised if a factory airbox (even from a different year) would make that much difference ? bike looks great . The carbs look immaculate but are the float bowl "vents" clear - no air in means no fuel out ?

0.05 is too tight minimum valve lash. 
original service manuals quoted that figure but quickly changed it too 0.10 -0.18 with a sevice bulletin. 
tight valve lash cuases hard starting. Always aim for the larger gap spec of 0.18, too big is better than too small.

Warren3200gt wrote:

0.05 is too tight minimum valve lash. 
original service manuals quoted that figure but quickly changed it too 0.10 -0.18 with a sevice bulletin. 
tight valve lash cuases hard starting. Always aim for the larger gap spec of 0.18, too big is better than too small.

I think the .005 is 5 thou and not 0.05mm , so ok at the 0.127mm equivalent but would have gone 6 thou ( 0.1524mm equiv ) myself when re shimming on stock cams..

Fantastic "left-over" assembly, looks Great! You mention you'd pulled the choke P/U tubes. They can be re-installed too deep if not careful. The casting hole where tube goes connects to a "slightly" angled carb galley. You'll note externally where the singular brass ball is pressed. This galley is longer then needed. From this galley is the hole is milled for choke plunger needle. Being the "angled" galley is longer then needed there remains a "pocket" towards that singular brass ball where DEBRIS can linger and hinder the siphoning from bowl choke jet. Another thing that can happen is when reinstalling the tube you can smash over the hole in insert of tube. Or if using a dirty drift/tool, you can jam crap in that little hole. Reducing flow or hindering it. It's small hole, fractional approx #70 bit size.If when warm, does choke operation affect operation? Because these carbs are the most funky to work on are you sure the slides are shut at idle? Slides initially set too high you won't create enough vacuum to pull from the choke circuitry. Your Colortune will also verify operation. You'll get it!! 

Yes, it sounds lean to me.  I remember reading somewhere they switched to 1.5 cutaway because the 2.5's caused issues at idle.  

I think the KZ1000 airbox would be more restrictive, hence not a cause of a lean condition.  On myy 1980 LTD I use a Z1 airbox, mostly because it's easier to remove/install the carbs.  That setup runs very rich, but I also have a set of '76 carbs on the bike.

I assume engine compression is OK?

Did that valve cover come with the engine?  It doesn't look like it's a KZ900 valve cover.  Not that it matters with respect to your starting problem.

HRM you are correct during the 1974 run they changed to 1.5 cutout slides.  My late 74 Z1 (march 74) came with the 1.5 cutout slides.  I remember my buddy Pete's early 74 Z1 had 2.5 cutout slides.  Tip from our mechanic buddy at the Kawasaki dealer service dept was to swap in the 1.5's. The reason was as you stated, idle quality and starting. 

Good points HRM and sf4 but you have to realize the other side of the slide isn't cut-out and it's initial adjusted position is the critical thing on starting. These series (early) ones had a unique #4 adjuster, cap nutted and special adjuster. The (nut) tightened down to the tip of the adjuster when assembled so was to serve as a "base" adjustment for the remaining 3. If anything is wanky then that slide is initially set too high and you won't get vacuum required for a crisp starting. They changed that on the late 1974 and 1975 Z1's to a conventional adjuster/locknut like the rest. I always change them out on all these ramp style 28's i do for full adjustability. Crazy here's that cast passage i was talking about with the small brass ball plugging it off. The bigger brass ball above it is for capping off passage of course to deliver fuel to the engine side of slide. Anyway, if you happened to of bead-blasted the bodies, media can get wedged in that area behind the little ball. It can fall back down into the P/U tube you pulled. This is why i always 3000psi all the bodies and gallies after blasting. You can witness output of fluid and rate. Hope it helps!!  Also if blasting was done, check for media in the upper portion. There's 2 cast holes in the roof of carb casting. One is open to vent at the TEE, other is a blind hole and goes up pretty far. Media can get wedged in the blind hole only to fall out later clogging up jetting.      

Thanks for all the info so I think I will get another carb bank set up before I pull these AGAIN to have a look at the pick up tubes and passages. It's got to be something simple. I use a wire with a dimension of .029 thou to set the height which gets me close to normal idle. The bodies don't look to be blasted but who knows. The bowls and other parts were chromed way back when it was cheap.  Bodies were cleaned in my ultrasonic cleaner with new fluid. Since to bike runs pretty well once warmed its got to be something to do with the starting circuit so I will concentrate on that. I always blast fluid and watch for flow so I will check those pick up tubes again along with the bowls themselves.
I have  several projects going so it would be nice to figure  this out quick.

Today I changed out the bodies since I had a set, but I don't think that was the issue . After all the work I Hate to admit it but I think It was the fingers lifting the choke plungers. Now I have done many of these carbs and i'm wondering how I may have missed that little detail. Anyway tomorrow I will finish up adjusting those fingers and try things out with the spare bodies. Hope it solves the issue because I hate installing those carbs on that bike. The early 900's were way easier. 

Took some time away from the Fraken bike project to test out the KZ1100A2 I picked up last fall with my friend and his 70 CB750. Lots of cleaning on this one, carbs were a mess along with everything else, I dont think it has run since the early 2000's. The bike has 28,761 miles on the odometer. Didn't take apart the engine, just removed it from the frame and cleaned it. The frame got powder coat along with other bits and a new paint job.  Pleased with the initial test run.