Jetting +Needle + Maybe Breather problems

First off, I have a 1982 KZ750 csr-m1 (the twin)

with about 20k miles on the odometer and a slight oil leak out of one of the gaskets (very slight, maybe 1 litre per 400 miles)It always ran pretty well (maybe a little warm blooded, but it could easily accelerate fast enough and only topped out at what I would expect of a bike that age, maybe a slight hesitation around the 5k rpm range, but nothing major)

about two weeks ago, I got bored, ripped the stock airbox out (replaced it with two slightly used Standard (brand) Pod airfilters..) first off, I reconnected all of the breathing apparatus exactly as it was orig connected inside of the airbox (with the one open breathing port as well) and replaced one of the rubber tubes. (the one that connects to the top of the engine)


Once I did this, the bike still idled fine (with the stock 115 main jets) but wouldn't rev about 5 k in neutral and if I tried to ride it bogged, (not due to too much fuel) but kind of stutters and stalls if the rpms goes above 3000. I tried to adjust the needle but realized that there is only one position for the clip.(so I would have to shim it?)

I checked the plugs and they looked black(and error in judgement on my part, they were black I suppose from stalling it) , so I went to a 105, which turned them white.


I then tried a 132.5, which made it a little better, which would let me rev to maybe 7k, and ride it to maybe 3500.

I went back to the store( north american warhorse) and they suggested that I try a smaller so I tried a 97.5 which made it worse, they also suggested that I try adjusting the clip (n/a) and the fuel / air mixture (is that the screw/ jet on the top of the carb?)

I am thinking of trying a 150 tomorrow (going out and buying another) and seeing if that makes it better/ worse.

I suppose my actual question is,

is there anything special I should do when I remove the airbox in regards to the breathing apparatus, and is there anyone with previous experience...

I have tried searching, but I don't know the names of many parts/ techniques so I find it hard to find the right terms.


Thanks for your thoughts / help.

-Kieran


EDIT: I have the mikuni bs-34

www.wgcarbs.com/index2.php?option=com_content&do_pdf=1&id=27

specs on page 9 of this

Kieran...did you post this same question on George's site? You are likely to get a quick answer on his site.

You might also post this question on this site...

kz750twins.com/

It is run by a fellow named Biquetoast (who used to frequent this site but then started his own).

george as in wired george? I will do so...

same with the kz750 twins.

Thanks, I will update later after I install the new jets.

Hi gang! Popping in to pitch in... thanks McDroid for the mention. I thought this might be a bit too much to respond to on my blog (due to format), so I'll give it a try here...

Yial wrote:

First off, I have a 1982 KZ750 csr-m1 (the twin)

with about 20k miles on the odometer and a slight oil leak out of one of the gaskets (very slight, maybe 1 litre per 400 miles)It always ran pretty well (maybe a little warm blooded, but it could easily accelerate fast enough and only topped out at what I would expect of a bike that age, maybe a slight hesitation around the 5k rpm range, but nothing major)

Okay... a minor oil leak, no biggie, it happens... But, slight hesitation at around 5000? Hmm. At that point, you should be well into full advance (the auto-advancer fuly extends around 3k or so), and well into the "main" system of the carb... But the inability to achieve full acceleration like that on your BS-34's immediately makes a torn diaphragm come to mind...


Yial wrote:

about two weeks ago, I got bored, ripped the stock airbox out (replaced it with two slightly used Standard (brand) Pod airfilters..) first off, I reconnected all of the breathing apparatus exactly as it was orig connected inside of the airbox (with the one open breathing port as well) and replaced one of the rubber tubes. (the one that connects to the top of the engine)

Oh. Ugh. Ick. Yep, I'm "that guy" that advocates the stock airbox... I would never, ever, replace the stock airbox unless parts were just simply unavailable (like the 74/75 KZ400D)....


Yial wrote:

Once I did this, the bike still idled fine (with the stock 115 main jets) but wouldn't rev about 5 k in neutral and if I tried to ride it bogged, (not due to too much fuel) but kind of stutters and stalls if the rpms goes above 3000. I tried to adjust the needle but realized that there is only one position for the clip.(so I would have to shim it?)

Okay, hold everything. There is a certain condition that can be *caused* by pods... Some pod filters have a heavy rubber lip at the mating point with the carb, and they have been known in the past to *block* the small air inlets around the inner lip of the mouth of the carb. Step one, I think, would be to remove the pods and re-test. Of course, it will be running lean (more on that in a bit), but the passages won't be blocked and it should at least run.. Remember, 3000RPM is that magic number where these bikes are just entering full advance, but *also* transitioning off the "pilot" system of the carb to the "main" system... and when one part works but the other doesn't you can just narrow it down a bit... like the fact that the mains have a dependency on the rubber diaphragms, and that the transition to mains requires the needle position to be correct for the fuel/air balance, etc....

Yial wrote:

I checked the plugs and they looked black(and error in judgement on my part, they were black I suppose from stalling it) , so I went to a 105, which turned them white.

Whoa! Sooty. Pods. Does not compute. Blocked iar passage (I mention again for effect). White, as you know, equals bad. But you didn't mention which rpm range turned them white...?


Yial wrote:

I then tried a 132.5, which made it a little better, which would let me rev to maybe 7k, and ride it to maybe 3500.

Hmm.. Still not good.

Yial wrote:

I went back to the store( north american warhorse) and they suggested that I try a smaller so I tried a 97.5 which made it worse, they also suggested that I try adjusting the clip (n/a) and the fuel / air mixture (is that the screw/ jet on the top of the carb?)

Well I don't blame them for their anecdotal advice.. but let's step back a tad. Have you validated your float levels?!?! This is *mandatory*. Have you done Wired George's "Coil Power Mod"? This helps alot in being able to trust the plug readings you get. And here's the deal; it does not make sense that you would need to go to a leaner jet after moving to pods from stock. So *something else* is amiss...

Yial wrote:

I am thinking of trying a 150 tomorrow (going out and buying another) and seeing if that makes it better/ worse.

......

I suppose my actual question is,

is there anything special I should do when I remove the airbox in regards to the breathing apparatus, and is there anyone with previous experience... .....

[/quote]
Hmm. Are you running stock exhaust? If all you changed is the airbox, I'd suspect that all you'd ever have to do (if your float levels are correct, strong spark, good coil, etc.) is bump your mains up by one or two sizes, and *maybe* move one clip position on the main jet needle. But above you wrote "n/a"... forgive my ignorance, since I don't have BS-34's, but don't they have adjustable circlips on the main needle jet?

There's alot there... I hope that helps get you started....

Okay... a minor oil leak, no biggie, it happens... But, slight hesitation at around 5000? Hmm. At that point, you should be well into full advance (the auto-advancer fuly extends around 3k or so), and well into the "main" system of the carb... But the inability to achieve full acceleration like that on your BS-34's immediately makes a torn diaphragm come to mind...

The diaphragm is the rubber casing that is around/ near the needle? When I opened them up, they appeared fine, I made sure not to pinch them when I re-assembled them.

Okay, hold everything. There is a certain condition that can be *caused* by pods... Some pod filters have a heavy rubber lip at the mating point with the carb, and they have been known in the past to *block* the small air inlets around the inner lip of the mouth of the carb. Step one, I think, would be to remove the pods and re-test. Of course, it will be running lean (more on that in a bit), but the passages won't be blocked and it should at least run.. Remember, 3000RPM is that magic number where these bikes are just entering full advance, but *also* transitioning off the "pilot" system of the carb to the "main" system... and when one part works but the other doesn't you can just narrow it down a bit... like the fact that the mains have a dependency on the rubber diaphragms, and that the transition to mains requires the needle position to be correct for the fuel/air balance, etc....

It has the same running problem with or without pods (ie. running with pods or running without filters at all, same with the rev limitation)

Whoa! Sooty. Pods. Does not compute. Blocked iar passage (I mention again for effect). White, as you know, equals bad. But you didn't mention which rpm range turned them white...?

I don't know exactly, because when I have had each of the jets in, I have done basically the same thing, start it with full choke, rev it a little, let it warm up, slowly work the choke in, and then see where I can rev it too (where usually it sorta dies out) and then try riding it (with the same rpm range dying)

Well I don't blame them for their anecdotal advice.. but let's step back a tad. Have you validated your float levels?!?! This is *mandatory*. Have you done Wired George's "Coil Power Mod"? This helps alot in being able to trust the plug readings you get. And here's the deal; it does not make sense that you would need to go to a leaner jet after moving to pods from stock. So *something else* is amiss...

I haven't tried his coil power mod, but I looked it up and I will do it in the near future.

As naive as this may sound I'm not sure how to validate the float levels, so I will read the manual and see what else I can find.... the bike did run near perfectly before I did all this.

Hmm. Are you running stock exhaust? If all you changed is the airbox, I'd suspect that all you'd ever have to do (if your float levels are correct, strong spark, good coil, etc.) is bump your mains up by one or two sizes, and *maybe* move one clip position on the main jet needle. But above you wrote "n/a"... forgive my ignorance, since I don't have BS-34's, but don't they have adjustable circlips on the main needle jet?

Before I did this, I had experimented with no baffles, no mufflers, etc.... with stock jetting, found that no mufflers made it accelerate much better in the high rpms.... (I know, stupid thing to do...) but it continued to run great.

Currently the mufflers and exhaust are stock, I recently changed the exhaust gaskets (no leaks at the headers) but there may be a little loss where the headers connect to the mufflers. (not much though, I'll try butting some soap around them later, or something similar and seeing if there's a leak)


The main needle isn't adjustable on these (the manual says it should have 5, but the ones in the carbs do not, in fact, the whole needle system looks radically different from the ones described in the manual.

from speaking to a guy who changed his to straight pipes and a brand of pod filters, he *thinks* that he had to increase his jet size about 30% over stock...

so that would be *around* 150 ish.


I guess what do I have to lose by popping them in but ten minutes and $6 bucks....

I'm at the point where I might just pop in 200 size jets and start running Nos (a joke.)


Thanks for your help, I really do appreciate it, and I will be checking the float levels as soon as I get home and then I will pick up the materials for the coil mod.


EDIT: I will check the floats using this

www.gstwin.com/float_height_check.htm

method.

-Kieran

Hi Yial,
Check out this thread, I may be the only guy that has got his 750 M1 twin working correctly using pods.
kzrider.com/index.php?option=com_kunena&...d=3&id=173606#173805
Good Luck

Hey Toast, long time no hear.

Ron

Ron, thanks, I will read it over and use it for further tuning.


I actually have it running now, where I can drive it normally. Not quite as peppy as I would like but I will try tuning it better.

I adjusted the airscrews (the ones right over the top of the carbs where they inter the cylinder) about 2.5-3 turns out.

then I put the 132.5 main jets back in,

and then I shimmed the needles with 5, 4mm washers on each.

I I put the carbs on, it revved perfectly and then took it for a spin. great.

I will update with further tuning info as I do it.

-Kieran


EDIT: runs great in neutral and in first, similar in second.

when I get in higher gears (3rd, etc) there is delay. I guess from lack of fuel, but I have yet to pull a plug and see, if it is lack of fuel I will pick up a 140 and see if that will fix it.

The hesitation in the higher gears is mainly 2k-5/6k rpm. it's not a jerky or sputter, it's simply a slower acceleration.

besides one back fire during deceleration after heavy acceleration, the deceleration is actually quieter then it was before.

Yial wrote:

....The diaphragm is the rubber casing that is around/ near the needle? When I opened them up, they appeared fine, I made sure not to pinch them when I re-assembled them....

Okay good. Yeah, you have to check them very carefully. If they are not seated correctly or have even a pin hole, they can start to make the bike accelerate poorly...

It has the same running problem with or without pods (ie. running with pods or running without filters at all, same with the rev limitation)

Interesting...

I don't know exactly, because when I have had each of the jets in, I have done basically the same thing, start it with full choke, rev it a little, let it warm up, slowly work the choke in, and then see where I can rev it too (where usually it sorta dies out) and then try riding it (with the same rpm range dying)

So when you told me the plugs were sooty then, it must have been from running with the choke on. Roger. This is why a plug chop is so essential. You need to know the color of the plugs in each major RPM range (preferably while in use), so you know what to troubleshoot.

I haven't tried his coil power mod, but I looked it up and I will do it in the near future.

As naive as this may sound I'm not sure how to validate the float levels, so I will read the manual and see what else I can find.... the bike did run near perfectly before I did all this. ...

Yeah, definitely. It wouldn't help this problem at all, but it just helps diagnose properly. But you'll not regret it... you'll need a coil someday too... but that's for later... And float levels are critical. Absolutely critical.

Before I did this, I had experimented with no baffles, no mufflers, etc.... with stock jetting, found that no mufflers made it accelerate much better in the high rpms.... (I know, stupid thing to do...) but it continued to run great.

But you said you've always had a hesitation at 5000, and it was worse now? And if it ran better (not just guessing, but check with a plug chop) without mufflers, then you must've been overly rich to start with...?

Currently the mufflers and exhaust are stock, I recently changed the exhaust gaskets (no leaks at the headers) but there may be a little loss where the headers connect to the mufflers. (not much though, I'll try butting some soap around them later, or something similar and seeing if there's a leak)

Doesn't sound like any real problem there...

The main needle isn't adjustable on these (the manual says it should have 5, but the ones in the carbs do not, in fact, the whole needle system looks radically different from the ones described in the manual.

Really? Interesting. Could they be the wrong carbs? I'd look into this....

from speaking to a guy who changed his to straight pipes and a brand of pod filters, he *thinks* that he had to increase his jet size about 30% over stock...

so that would be *around* 150 ish.


I guess what do I have to lose by popping them in but ten minutes and $6 bucks....

I'm at the point where I might just pop in 200 size jets and start running Nos (a joke.)

Yeah, that sounds about right... Of course you'll prolly be changing pilot jets too... open pipes and no filters or just pods will require alot more fuel. More fuel and reduced performance...

EDIT: I will check the floats using this

www.gstwin.com/float_height_check.htm

method.

-Kieran

That *method* looks good, but the specs are wrong for you of course. Make sure to reference the manual for specs... if those *are* the correct carbs...

And following up what you mentioned about the pilot screws... The pilot circuit doesn't affect the cars around 5000 RPM, just idle up to about 1/4 throttle really, as it transitions to the mains... but your item about shimming the needle probably did the trick... I'm still suprised that you don't have cirlips, but like I said I'm not certain about the later carbs. Just make sure the main jet needle is still able to move around a tad so that it doesn't bind in the main jet.

And the fact that backing out the pilot screw is normal too, for having that much flow. That, and having your floats at the top of spec range, bumping up your mains, and shimming the needle should just about do it. Now you get to decide if you need to bump up the pilots too... time to fine-tune...

ronjones wrote:

Hi Yial,
Check out this thread, I may be the only guy that has got his 750 M1 twin working correctly using pods.
kzrider.com/index.php?option=com_kunena&...d=3&id=173606#173805
Good Luck

Hey Toast, long time no hear.

Ron

That's right! Ron! You're the guy I was thinking of... Yeah, you're a case study in this adventure...

It sounds as if you're having problems w/the transition between pilot and main jets, which is controled by the jet needle. IMO ya ain't never gonna git 'er runnin right w/that fat baseball bat of a Jimmy Carter, detuned needle jet in there. JMO

Yial wrote:

Ron, thanks, I will read it over and use it for further tuning.


I actually have it running now, where I can drive it normally. Not quite as peppy as I would like but I will try tuning it better.

I adjusted the airscrews (the ones right over the top of the carbs where they inter the cylinder) about 2.5-3 turns out.

then I put the 132.5 main jets back in,

and then I shimmed the needles with 5, 4mm washers on each.

I I put the carbs on, it revved perfectly and then took it for a spin. great.

I will update with further tuning info as I do it.

-Kieran


EDIT: runs great in neutral and in first, similar in second.

when I get in higher gears (3rd, etc) there is delay. I guess from lack of fuel, but I have yet to pull a plug and see, if it is lack of fuel I will pick up a 140 and see if that will fix it.

The hesitation in the higher gears is mainly 2k-5/6k rpm. it's not a jerky or sputter, it's simply a slower acceleration.

besides one back fire during deceleration after heavy acceleration, the deceleration is actually quieter then it was before.