KZ900 carb help

[Grog]

Hello mate;

One more thought - the bike is now out at 1015, has been running a non-standard airbox and has a Delkevic fitted (all done prior to your ownership?). Have the carbs had an air corrector kit fitted to help deal with all the changes - if not that could be the cause of the rich running on/off idle. Easy way to check is to look down the airbox side of each carb mouth - if there are little brass inserts visible in the bottom (left? from memory) air bleed intake for the pilot system on each carb, then yes; if not, no. Means having the airbox off again but might be worth a look.

TTFN, Grog

[1975-S1C]

Hi Grog,

Thanks for the pointer.
The carbs had to come off again anyways, as I have new carb to head rubbers coming and I also need to set the float levels to get the correct fuel levels.
Just popped out to snap a picture, and doesn’t look like anything brass fitted to any of the apertures air box side.
Cheers
Paul

[zed1015]

Just popped out to snap a picture, and doesn’t look like anything brass fitted to any of the apertures air box side.

There's no air correctors fitted in those carbs and there never has been.

[Grog]

Hello mate;

As zed1015 says, no air correctors. For ref, mine's a Z1R so 1015cc, Delkevic 4-1 and K&Ns (so not a million miles from yours), and had correctors fitted since forever with various different 4-1 exhausts with good results. If you can get hold of some (there seem to be options in the usual places but can't vouch for quality - mine are the original Ledar supplied ones) then it might be worth a go. They won't break the bank and are easy enough to install as I recall.

TTFN Grog

[1975-S1C]

Thank you chaps.
I’ll see how we go, and correctors may well need to get added to the shopping list.

[zed9]

First thing i would do with any rough running is check/set points gap if it has any then strobe timing, its all quick and easy and should be done before messing with carbs.

Farting through carbs could be due to valve clearance. I had slight farting/sneezing issue with no. 4 carb and gap was .02mm instead of 0.1 to 0.15. Once shimmed to correct gap problem solved.

[zed1015]

Thank you chaps.
I’ll see how we go, and correctors may well need to get added to the shopping list.

I make and sell the air correctors and can provide all the jetting advice but you don't need them unless fitting pods or the airbox has been cut and offers virtually no restriction.

[1975-S1C]

Thanks Rob.

I’ve taken off the non-standard air box that was on there when I bought the bike and have replaced it with a new repro Z1 item fitted, along with a new filter. No alterations have been made to the new air box. I think on that basis from what you’re saying I probably don’t need the correctors.

Fingers crossed that by the time I get to the end of my ‘to do’ list all will be well.

I’m pretty sure the biggest culprit is the float heights. We’ll see I guess.

All the best

[1975-S1C]

First thing i would do with any rough running is check/set points gap if it has any then strobe timing, its all quick and easy and should be done before messing with carbs.

Farting through carbs could be due to valve clearance. I had slight farting/sneezing issue with no. 4 carb and gap was .02mm instead of 0.1 to 0.15. Once shimmed to correct gap problem solved.

Hi Zed9, it’s running a Boyer Bransden electronic ignition system. I do have new auto advance unit springs arriving tomorrow, and will check the timing with a strobe when I’m done.

Valve clearances were checked not so long ago. If symptoms persist after I’ve addressed everything I plan to do, I will go back and double check the clearances, but I’m fairly confident it’s not that.
Appreciate the thoughts / advice.

[1975-S1C]

After 2 1/2 unsuccessful hours, and no small amount of cussing, I’ve abandoned trying to set the fuel levels.
The first one was fine but the second one wouldn’t play nice and on closer inspection it looks like the needle is toast. No sense in wasting more time on it till this is sorted I guess.
Best get an order in !

[Gray17]

Hi, well reading your post sounds like dejavu in that its almost an exact duplicate of my issues on my Z900 A4 too.
Long post prior to yours on forum. Carbs overflowing then not, then
a diff carb overflowing? Very random. Carbs on and off checking floats etc.
Like you tried everything suggested to no avail the bike just ran crap, refused to idle properly, with sooty plugs and running rich on low speed, but ok on main jet, again like you started to replace parts, 4 full carb kits, all new jets, choke plunger seals, electronic ignition, relay mod to boost coil voltage, reset/ re checked valve timing, valve clearences etc.
Still no joy. Unlike yours mines on new standard 4 into 4, standard airbox and carb settings. Nothing seemed to work. After a fortune spent on restoration i was to say the least disapointed! Still am.
In my case ive ended up doing compression check which revealed low compression on 1 cylinder but not out of tollerence low, it did improve with oil down bore, know head and valves have all been done so def not that. Ended up having to re strip engine again and had full rebore all new pistons etc. Only thing not done previously.
Id like to say thats cured it but truth is its still ongoing, but thats partly down to me in so much as its nearly all back together again after re checking everything slowly and thoroughly.
Only thing left to do is refit the carbs and hope, it'll run as it should!
Hopefully youll have more success.
I thought old bikes were a lot less complicated then modern bikes with fuel injection and ECUs etc but turns out there equally complicated, just in diff ways, what makes it worst is a distinct lack of local knowledge where you can take it in to get fixed, as most dealers are clueless, makes the Forum.a valuable place for expertise and info source. Then the problem is your own abilities to do it properly (least in my case)
Please keep us all posted on your progress. Lets hope we both get the bikes sorted so we can actually enjoy riding them.

[Al]

Here is a fairly comprehensive treatment of the; fuel heights, float levels, carb settings, plug reading. etc for a 900A4 from the end of last year.
There is some really good background to the issues you raise and hopefully some fixes and key indicators as well.
It sounds like you are going through it the right way with an open mind and dealing with issues as they present themselves. Best of luck.

viewtopic.php?f=4&t=50630
AL

[1975-S1C]

Hi Gray17,
I’m hoping it won’t mean an engine strip. Too early to panic yet anyways. From what I’ve seen so far the bike was long overdue some attention anyways.
On the plus side, the compression readings all look really good.
I’ll continue to report progress as I work through the issues if it helps others.

Todays progress:
New carb to head rubbers fitted. The ones that were on the bike were rock hard and by the looks of it, not making a particularly satisfactory seal against the head. The offtake blanks were also hard and cracked, so definitely needed replacing.

[1975-S1C]

Al,

Thanks for the topic link. I will definitely have a read through that later with a beer in hand !

[Gray17]

The new carb rubbers look good, ot was one of the things i was advised to check too, mine were fairly supple so didnt replace them, but did remove them and use the silver bond on the surface to head to ensure an airtight seal just in case. However like yours my take off rubbers were perished, not even sure they were the correct ones, but these have now been replaced so thats another box ticked.
Im going to re attempt to aet up the float heights before re fitting carbs, now as reported this is harder then it looks as you set it correctly but it seems to change once on the bike as overflows, whilst you can get at the outer 2 the inner ones are not really accesible on the bike which means carbs on and off not an easy task and probably contributes to the rubbers getting damaged.
I will keep reading your post with interest. As im sure will others.