Mikuni CV BS34 lean but rich?

I don't think these carbs are that unusual, but they DO NOT have float bowl vent tubes. The vents are internal. Also the idle jets just have a spring below the needle jet which has the o-ring "on" the top. (See diagram in 1st post)
The main jet needle is not adjustable PN 16009, I would like to replace them with the CAN version 16009A, which is adjustable. Trying to shim up (richen) the non adjustable ones because of the plastic disc that holds them in place may not work.

I can't believe the pilot ciruits are that hard to get clean, but that's what it's looking like is the problem with these carbs.
I'm going to blast them and try the #40 bleed pilots and see what happens.

jga2z wrote: I don't think these carbs are that unusual, but they DO NOT have float bowl vent tubes. The vents are internal. Also the idle jets just have a spring below the needle jet which has the o-ring "on" the top. (See diagram in 1st post)
The main jet needle is not adjustable PN 16009, I would like to replace them with the CAN version 16009A, which is adjustable. Trying to shim up (richen) the non adjustable ones because of the plastic disc that holds them in place may not work.

I can't believe the pilot ciruits are that hard to get clean, but that's what it's looking like is the problem with these carbs.
I'm going to blast them and try the #40 bleed pilots and see what happens.

You don't need adjustable needles for a street driven bike. You can go to Radio Shack and purchase a misc small washer kit. Use the 3mm washers in the kit under your OEM needles to richen your midrange. Is you bike stock or do you have mods ? Your OEM jetting should only require a slight richening of the jetting IMO

jga2z wrote:

jga2z wrote: I rechecked the coils, 2.6-2.7 ohms, batt voltage @coils, will jump 5/16-3/8 air gap on all 4.
Doesn't this seem like it should work?

Does anybody want to try answering this question?

If a stock bike with OE coils within spec won't run, nobody would be riding with stock coils.
Sure it would be nice to get higher performance coils, but it shouldn't be a necessity.

As far as a carb sync goes within the last 100 miles it would idle perfectly down to 6-700rpm when warmed up. I usually like it to idle around 8-900 though. I will eventually do the vac sync.

Finally a thought on multitasking with multiple systems. I want to go thru everything that could be an issue since it's still a mystery

For me working on a KZ is just a few steps up from working on a lawnmower compared to what I usually work on with cars, which includes anything and everything on any car or truck from bumper to bumper. If it's a part of a vehicle, I fix it for going on 35 years. My motto..."Got a problem? No problem."

:ohmy:

Kawasaki states that the operating idle should be set at 1050 RPM +/- 50. Setting too low of an idle speed could cause the oil pressure to be to low for engine safety.

jga2z wrote: Well it looks like I have been spinning my wheels here and not the wheels on the bike
All the carb work has changed nothing. While doing the rebuild I went ahead and put in the 127.5 main jets I had planned to put in before. Since it seemed rich I've waited til now thinking I've fixed the problem of leaky o-rings. I even changed plugs in case they got gas fouled one too many times.
It still is not even running on all 4. I am trying to run with tank off pouring gas into fuel line with a tiny funnel until it stops (bowls full, no overflow) then starting.
When I got it started I tried to determine which carb/cyl might be an issue. I shot a spurt of starter fluid in each carb, in 1,2 rpm down, 3,4 rpm up. After I shut it down exh pie on 1,2 were hot, 3,4 barely warm. Tried it with propane and couldn't tell any difference.
Put in the new plugs. No real difference from above except maybe #3 exh got a bit warmer.

It's still looking like a carb problem, but after totally going thru them this time I don't know. When I took the carbs apart AGAIN tonight I first checked fuel level and it looks like #1 might be a bit high, 3,4 ok #2 can't check because I can't get the drain screw out as it's stripped, but I dumped the bowl and it measured about the same as the others I drained into a cup. I noticed the the bearing grease I used to lube the orings on install in the pilot jet plugs looked like it might have "gelled" up, but I'm pretty sure that the grease will dissolve in the gas and not plug up anything.

I'm back to square one checking all the basics, compression, recheck ignition, wiring etc.
I did the coil rewire a long time ago, and checked original coils 2 days ago, 2.8 ohms on primary.
I've always thought that I might still have a weak spark even though it checks good. Used an inline spark tester light and it seemed fair on all cylinders. I need to check spark output by seeing how big a gap it will jump, but not sure how to do that.

I'm not a novice by any means having rebuilt 80-100 car carbs and did quite a few KZ carbs back in the 80's, but I'm about to throw up my hands for now on this bike. I don't have time to spend hours a day trying to get this figured out. My head is spinning, literally.

3 & 4 are on separate ignitions components so you can pretty much rule out ignition as the cause except for plug cap and wire issues. Often times the wires get green corrosion at the plug caps. Seeing as how those wires are removable from the coils, you can test each wire by itself as well.

If that's all in order,. Do a valve lash check, then compression check. If you have oddball readings with compression, it's time for a leak down test.

As for the carburetors, they really should have all the proper O Rings in place. Almost right fitting O Rings could cause problems. Be careful removing float pins. It's so easy to have a stuck pin result in breaking off leg it goes through. A spring loaded punch works great to get float pins out.

Fuel level is critical. Do a design fuel level check. Float height doesn't do justice to what's actually happening. Don't be fooled into thinking each carb wants the same pilot fuel screw setting either. It's a good ballpark thing to do but it doesn't always mean the engine likes them all the same. 2 full turns out from lightly seated on the pilot fuel screws will generally get you up and running if the rest of the carb circuits are working properly. Adjust from there after a good ride to fully warm the engine.

Set idle to a least 1000RPM as was suggested. It will help keep good oil flow to the valve train.

so have we got to the bottom of all this yet? Has anyone thought to check the diaphrams? I ecperienced the same problems only to find I had minute pin holes & the only way I spotted it was to hold the m up to sunlight and stretch (lightly) the rubber, Replaced the diaphrams and guess wat, easier to start, no more popping and it runs on all four cylinders. Just a thought.
1981 Z1100A Shaftie

Unfortunetly I don't know yet if I've got it fixed.
I tripled cleaned the pilot circuits and replaced the stock 37.5 "non-bleed" type pilots with #40 "bleed" type and the carbs have been setting for days now uninstalled. I still need to check the fuel level once they're on, and maybe I'll be good to go.
I looked pretty close at the diaphragms and they looked perfectly fine, but I didn't look as close as you. It's possible they could be a cause of the problem. I hope not as those things are NOT cheap.

I have been having acute back problems from my chronic condition, and things are on hold.
I will keep posting till I get it done, and running.

OK I got it running today.:woohoo:
Now using 127.5 mains, and #40 pilots. Installed carbs and did the clear line fuel level ck, all OK.
It started right up on full choke (97 degrees today) but was TOO much, switched to half choke immediately, and it ran great. Choke off after 30 sec and it still ran OK. Warmed up another min or so and it revved fined and idled well,no choke.
This is all fantastic. All my previous symptoms are gone, starts perfect, no dead spot idle to 2500, no popping in that range, and no signs of black smoke from running rich.

Now the new problem.
I tried to adjust the idle mixture screws and get no noticeable difference all the way in to 3 1/2 turns out except on #4 all in a tiny bit smoother and raises RPM's a tiny bit.
Set them all at 1 1/2 out which is where they were when I started it up at first.

Took it for a 1 mile ride 35-45 mph, gagged it to 5k+ a few times and it ran great.
What to do now? ?
I'll do a longer ride tomorrow and check the plugs for more info.

jga2z wrote: ...tried to adjust the idle mixture screws and get no noticeable difference...What to do now?....

If not already done, would assure valve clearances are within specs.

Good Fortune!

no dead spot idle to 2500

2500 rpm idle seems a bit high... on my KZ550 and KZ750 FSM they specify around 1000-1300 rpm on average maybe different for your bike but 2500 rpm... that would be new!

regards,
laurent

EDIT: Oops misread the reply .. my bad time for bed!

Here we are again, back to trying to resolve this issue. I have riden very little since the last post. The bike was at least rideable with the #40 pilots. I thought that maybe I had finally gotten the carbs cleaned and the #40 pilots were just too rich and that's why it needed little choke to start cold, and then run OK albeit a bit rich when warm.
I decide to change back to the 37.5 pilots yesterday, and it ran like it did with them before, popping sputtering, and poor throttle response below 2500. Fully warmed up it's better but not right. Seems lean with 37.5 "non-bleed", and rich with 40 "bleed" pilots???
Another new symptom is when parked it is slow to idle down after revving. I read something about this but can't remember what that means.
Could this problem really be valve clearance related given idle mixture adjustment screw changes have little to no affect on the idle cold or hot? Does valve clearance tend to get loose or tight with wear over time? What about syncing of carbs? Bench sync is fine. When it's fully warmed up it runs OK, but mostly seems rich. Maybe I should go back to the stock 122.5 mains instead of the 127.5's.
On a side note I am working on an '83 1100 LTD shafty and it has 117.5 mains stock which seems odd to have smaller mains in a bigger engine?