Mikuni BS34 ?'s

Hey all,

Just put my BS' back together, and had a few questions:

1) Is it critical that there be no breaks or cracks in the enricher plunger boots (on the "choke" pistons)? I've attached a pic of the one on my left carb, not sure if it's a problem.


2) What is the screw on the right carb, located below and behind the float fill tube? (pic also attached) Doesn't seem to go anywhere, as I didn't note any channels or tubes from that area, but I didn't remove it, either.


5) Can one reliably measure the float level without using the clear-tubing method? One of the drain screws is totally buggered up (NOT BY ME! HONEST!), and I can't get it open. Better shut than leaking, I thought, so left it alone.

4) How many jet sizes should I go up if I'm still popping on deceleration at 5 turns out on the mix screws? I don't have the funds to buy a fistful of jets and just try them, in the off chance that one size will work.

5) There were no o-rings or steel washers on the mix screws, but the screws themselves had o-rings in a notch near the top of the screw head. Problem, or model change?

6) How does one remove the plastic needle retainer from the slide? Didn't necessarily want to change the needles, just trying to be fastidious in my cleaning. Do they pop out, unscrew, permanently attached, or what?

TIA,
Nick

Just a quick additional note:
I reassembled and reinstalled the carbs tonight, with the mix needles 5 turns out (they had been at 4.5 turns out). It ran, but badly, engulfing me and the shed in a cloud of blue smoke, so I need to address the idle circuit. I also barely needed choke to start, I was off choke and running un-enriched within seconds of starting, but the blue smoke continued, moreso from the right pipe than the left.
While tweaking the throttle, it stumbled off-idle, and once or twice I glimpsed a pop of flame out the right pipe as the throttle snapped shut. So, tuning is in order, but I ran out of daylight in which to do it. I need to fit the mufflers and tune the bike this week, as I hope to have it inspected this Friday so I can apply for title, reg, and plates.

The boot on the enricher shouldn't be a big problem. I've been running like that for years.
It sounds to me like you are running too rich in the idle circuit. The pilot screws are generally set between 1 1/2 to 2 1/12 turns out. Some popping during deceleration is quite normal as these bikes have a ''wasted spark'' which occurs during the exhaust stroke.

Hoyt Clagwell wrote: The boot on the enricher shouldn't be a big problem. I've been running like that for years.
It sounds to me like you are running too rich in the idle circuit. The pilot screws are generally set between 1 1/2 to 2 1/12 turns out. Some popping during deceleration is quite normal as these bikes have a ''wasted spark'' which occurs during the exhaust stroke.

Okay, won't worry about the enricher boot, although if I have cause to remove the carbs again, I may paint them with plasti-dip or similar, as some cracks are starting in addition to the hole.

Knew about the idle mix screws, but the PO had them set to 4.5 turns out, and it was popping on decel, so I upped it to 5. Now, the 'quite normal' part I have a problem with- who would buy one if they did that from the factory? ("Harley riders," quipped my wife- LOL!) I'd rather figure out how to fix it than just live with it- it's ANNOYING! Besides, many Hondas (my 350 and 550 in particular) also have wasted spark ignitions, and neither one pops on decel. The 550 used to, when I fitted pods and open mufflers, but a few turns in on the air screws took care of that pronto.

Is this the rubber part you need (see diagram below)? If so, Z1E has them. Ed

www.z1enterprises.com/ItemDetails.aspx?i...1100&item=16012-1010

Yep, that be it! Good to know, thanks!

I love this forum!

this link is great as I am looking for the same choke plunger cap as well. Also I am wondering about the turns out on the pilot screws I have a manual for a KZ750 that I picked up, not the same as my 84' KZ750 L4 but the same carbs and it says 2-1/2 turns out, and being new at this I am unsure as to weather that means two full rotations and a half rotation, or just two and a half turns back of your screwdriver? because my turn is about a half of a full rotation of the screwdriver.... and I hope it's okay to butt in on the conversation?

Hey, jump right in, the water's fine! :laugh: I've done it enough on other threads, I figure someone hijacking one of mine is no big deal.

When they say "2 turns", they mean two FULL turns, like 360* rotation of the screw. Since I, like you, typically turn the screws in half-turn increments, I count to myself, "half, one. half, two. half, three" and so on.

As for myself, I'm having the devil's own time tuning this bike! I can't keep it running long enough to address the idle adjustment. I gapped the plugs today, and the right one is badly fouled, although with oil or gas I can't tell. When I start it up, it blows white smoke like crazy, which makes me think it's oil... whoopee.

Also, the intake ducts are badly cracked... the PO tried to patch them with electrical tape, and failed at doing more than getting everything nice n gooey. Since the ducts are unavailable pretty much from anywhere, it's either repeat that epic fail or try to figure out some other form of ducting. I'd love to switch to pods, but I've heard these BS34s don't tune worth a tin $#!t if you do.

The pain in all this is that it RAN when I got it... really, it did! But it popped on deceleration, and wouldn't idle at less than half-choke. Thinking the problem was dirty carbs, I took them off and cleaned them... didn't change a single adjustment, just CLEANED them, and that opened this whole can of worms. Guess I have to go back to square one (valves, cam chain, carb sync, etc) and figure it out from there.

Here's something interesting...
While perusing MikesXS reading up about the Mikuni BS34, I noted this regarding the idle mix screws:
"O-Ring fits under metal washer at bottom of mixture screw hole and the engine will not idle properly if it
is not present - (O-ring is often disintegrated). These parts are not shown in service & parts listings as Yamaha did not want "emissions" related parts accessed, however adjustments were often necessary to get New bikes to run
properly."

When removing my idle mix screws, there was MOST DEFINITELY NOT an o-ring OR washer under the screw and spring! There was an o-ring at the TOP of the screw, above the threaded portion; on one screw, the o-ring was trashed, on the other it was still good.

I tried hooking around down there to fish out a washer and o-ring, and never came up with anything. Did the KZ750 BS34s not have these o-rings, or they should and mine are missing? That would explain why I can't get this thing to idle worth a hill of beans... that, in conjunction with all the other garbage going on, certainly can't help.

Pretty sure there should be both a washer and an O-ring on each pilot screw.

Okay, that's irritating, because I thought I was vindicated by this diagram:

www.kawasakiepc.com/SSIConverted/2760361_110611_113434_7075.png

This shows NO o-ring, NO washer. Just the spring, the screw, the top o-ring, and the screw plug.

Going back out with a flashlight and a wire hook to see if I can dislodge anything... maybe it's just stuck.

Nope! Just got back in from running out to the shed where the bike languishes. I removed the mix screw and spring, and shined a light down the bore. Absolutely, positively, without-a-doubt NO washer or o-ring down there. All that's down there is the tiny bore for the tip of the screw.

Given that the Kaw factory diagram for the BS34 as used on the M1 does not list an o-ring, I'm going to go with that. I do, however, still need to get a replacement o-ring for the TOP of the screw. While I don't need a rebuild kit, I may get one just to have all the tiny parts on hand.