KZ900 carb help

[warren3200gt]

We're the inlet rubbers genuine or repop? The repop ones I tried are nice and soft but pretty rubbish quality. With unsupported cabs on one of my 650's they only lasted a few months before the split at the tube/mount plate seam. When cold it wasn't noticeable but once warm it ran like a dog because the softened rubber further made them sag under the carb weight and caused a vac leak.
I actually made support brackets to take the carb weight and used genuine rubbers. Never had an issue since.

Weak mixture causes backfire through the carbs not popping through the exhaust. That's down to unburnt fuel and airleaks in the exhaust system.

[1975-S1C]

They aren’t the genuine Kawasaki ones, but I bought them from Zpower and they seem pretty good quality.
In the first instance I’ll see if supporting the carbs solves it. I’m not going to get anywhere with trying to get it running right if I don’t fix this first

[Al]

Please feel free to disregard after my most recent 'bum steer' sent you down the rabbit hole. You mentioned that there were new pilot air screws. I dont knw how good these are as repros' they may be just fine, i cant say and that you have them at all 1.5 turns out. The only way to be really sure if this is correct or if you have air leaks is to use a colourtune on it. Its one of the cheapest diagnostic tools you could routinely buy and it gets used frequently as you go along to highlight any issues that crop up to give an indication of whats happening and what might be done about it.
Dont be surprised if not all the airscrews are set to the same amount when you do as each may have worn differently or be restricted to some small degree. Needless to say, if any are significantly different or wont 'tune' then there is something there for you to go after. Agree; idle hanging will usually be too weak a mixture in the pilot setting range if not air leaks. Matter of interest; do you or did you glue the rubbers to the head with high temp RTV or similar? It usually takes one un-certainty out of the equation particularly as the boots age and the base plates start to deform.
AL

[1975-S1C]

Hi Al,

Thanks for the response, I appreciate it.

I didn’t use any RTV on the rubbers to be honest. They seemed to fit up pretty snug so I decided against it, not to say that I won’t try that if I’m still getting the same symptoms after I’ve got the carbs properly supported and the air screws set correctly. I’ve been looking at Colourtunes and I think I’m definitively going to have to get one, that should at least get me in the right ballpark.

As for ‘disregarding your post’. Absolutely not. I do really appreciate all advice and support given.

[Al]

Up Front; i know nothing about Boyer ignitions but did look at the installation instructions today on the website to try to understand why you had no advancer springs, notwithstanding the fact that it is digitally advanced not mechanical, i still couldnt understand why someone would leave the bob weights hanging in the breeze. I found nothing but did read that the timing must be checked with a strobe at 5000 RPM and that as a consequence of this; ignition timing will be somewhat different to factory when at idle. It says: "The electronic advance can be seen by accelerating up from idle, this is operating from cranking speed and therefore will be more advanced at idle than standard".
This was for the MK3 (Kit 00073) which again, i have no idea what is meant by the numbers or models but may strike a note with you with what you found using the strobe on yours!!
AL

[Grog]

Hello mate; bit of a late reply, but re. your rev hang mentioned in post #75 - I had the same after a carb rebuild and that was down to a slightly weak mixture. All came good after tweaking the air mixture screws in a bit and the problem went away.

TTFN Grog

[1975-S1C]

Thanks Al.
I’ve downloaded the info sheet for the BB ignition system that’s fitted to my bike now, so I’ve got a bit more info on that.
I’m going to sort out a proper support for the carbs, get a Colourtune to hopefully get the air screws in the right ball park, and try to see if I can set the timing up accordingly to the BB leaflet.

I’m also going to try to speak to a local business that specialises in old Kawas and has a Dyna set up, to see what they’d charge to help me get it sorted if I fail to be able to do it.

[1975-S1C]

Thanks for the heads-up Grog. I’m going to see if I can lay my hands on a Colourtune and check out the air screw settings. Hopefully this will allow me to get them in the right range
Appreciate the info mate.

[1975-S1C]

Well folks, in the end I decided to concede defeat. Yes, I’d got it fairly close, but not nearly good enough !

I spoke to a local chap, Tim Blakemore (of Tim Blakemore Race & Classics). A very nice chap and very knowledgeable, and for a very reasonable amount of drinking vouchers he’s sorted my bike out for me in less than a day !

I rode the bike down to Tim’s garage yesterday morning. It ran OK’ish when I left home, but half way there, after it had been farting back through the carbs, it suddenly starting running really rough. I tried a little choke and this seemed to help, so I limped it slowly the rest of the way. When I arrived Tim immediately spotted that the rubber blanks were missing from the two outside carb / head rubbers vacuum off takes. They are a pretty sloppy fit, and maybe I should have just bought OEM instead of pattern. Anyways, the blanks are now held firmly in place with wire clips.

Tim treated the carbs to an ultrasonic bath, reset the fuel levels, set the air screws, balanced the carbs and adjusted the timing slightly. It now runs so much better, there’s no throttle stumble off idle, and it even ticks over nicely !

There is still exhaust popping, particularly on the overrun, but as Tim pointed there is an air leak where the headers join the 4-1 collector box, with sooty evidence around all 4 joints. It’s exactly as Warren said in his post. I shall be addressing this with some exhaust sealer over the weekend.

Took the bike for an hours ride this evening and really enjoyed it. It’s great to be back out on the Zed again.

A big thanks to everyone that took the time to post up all the helpful comments on this thread.

[Ultim8pc]

Well folks, in the end I decided to concede defeat. Yes, I’d got it fairly close, but not nearly good enough !

Glad you got sorted!

[Gray17]

I too am glad you got it sorted, No one enjoys riding a bike that doesnt respond well to throttle inputs! It ruins the experience.
You're symptoms mirror my own findings in as much got mine running but not particularly well, the inlet caps on mine kept blowing off too, yes mine were pattern also! And caused exactly the same problem as yours too in that in ran a lot rougher once they shot off, obv weak mixture. I bought some new ones which fit a lot tighter and rubber 3 times a thick so hopefully thats sorted that issue for us both. Also like you gave up in my attempts and entrusted setting it up to someone far more experienced then me.
As for exhaust popping mine was on 1 cylinder i removed copper sealing washer heated up on gas hob and replaced and tightened exhaust nuts again which seems to have worked. Perhaps you could try that yourself.
Happy riding!

[1975-S1C]

I too am glad you got it sorted, …………… !

Thanks Gray. Ye’h I could have persevered but in the end I just wanted my bike rideable again. It’s sooooo much better now.

My exhaust seems to be leaking from where the headers go into the collector. Hopefully get that sorted in the next couple of days, but for now, as the sun is out, it’s ride time

Enjoy your bike amigo

[Al]

Great news. It may well pay you later on, to make a formal and permanent note now, of the number of turns on each pilot screw. Any that are radically different from standard or from the others can be used to track any changes if you get drift and it starts misbehaving.
AL