Desperate need of some kz650 experts here...

hi all,
looking to pick some peoples brains...
my friend brought a 1979 kz650B
the previous owner fitted it with individual K&N Pod filters & a 4-1 Harris Exhaust

i wont tell the full story but basically the engine is all good and everything is either in spec or been replaced...

so the problem is it was extremely difficult to start then run very bad and wont accelerate.
fitted
new inlet rubber and the rubber caps
new plugs
carb refurb kit
set the floats 'wet'

i balanced the carbs now there was no air leaks and set the pilots.
it was running good and he took it out for the weekend and was apparently a lot better (too him)
when i tried it, it was awful... popping, misses, no acceleration
he has a jet kit from sigma in america

so right now the bike starts fine and idles perfect...
but any load like trying to pull away and ride it still pops back through the filters, then when at about half throttle it wont accelerate and pops more!
if you pin it at full throttle eventually it runs past and starts to pick up but still not right...

the jet specs are...
stock pilots screws
size 20 slow jets
size 122.5 mains
stock needles on one slot up from the bottom

this got it running its best

i spoke to my trusted jet suppliers and they're sending me a air correction kit to put in the holes where the air filters fit.
and one size down from stock slow jets..?
they also recommend i drop the mains down to 107

so wondered what you guys think? im sure you know these bikes better then me and someone here must have some ideas whats wrong?
thanks
J

First at all
Your main problem is not only the carb adjustment
It could be the valve adjustment and/or ignition timing.
Fuel flow from the fuel tank, clocked petcock and fuel filter, carb internal fuel and air ports clogged , air leaking intake boots., wrong setting of the float bowl high, and so on.
A little bit out of spec form the fuel inlet (tank cap vent clogged) to the end of the exhaust pipe, everything is possible and can disturb a good running engine like your K&N pots.
Many engine components can be weak or out of spec.
I would say take a service manual for your bike an do a basic maintenance.

www.manualedereparatie.info/manuale/Kawa...dereparatie.info.zip

Something i will not understand:

K&N filter = more air flow
air correction kit = reducing air flow
drop the mains down to 107 = less fuel = lean air/fuel mix, sorry to say, what is the logic of this set up

Once you've tuned it up try this jetting. Main jets 112.5, pilot jets 17.5 and the needle clip in thd middle slot

I would agree that the suggested jetting baldy110 indicated is a great starting point.

hi , thanks for the reply
so the float bowls have been set 2-4 mm below the bowl surface.
the cam chain tensioner was completely knackered so hat was changed and the cam timing was checked.
all valve clearances were checked and within spec.
compression test showed all cylinders where good.
the point and condensers have been replaced and set correctly.
it has new inlet rubbers.
its got a new fuel tap

we had the bike running and sprayed brake cleaner all round the carbs and inlets to check for leaks and nothing... bike just sat perfect at idle so i would say there's no funny air leaks.

the bit about droping to lower slow jets then stock... i dont understand either and i said that to him on the phone ... but its getting to the point ill try whatever.
this is not my first bike doing this kind of thing and its never straight forward but this one just doesn't seem to get better either way.

i will try your suggested jetting later today, thanks

Baldy's jetting has made mine run near perfect but I have the needle clip in the 5th slot......... Baldy uses a washer under his needle too so this moves it close to the 4th slot which is stock....... Like others say check the basic stuff too. Run smooth bores now (little more power and running exc mid and top and good but not perfect at idle) and don't have anything but good things to say about the perf of the old stock 24s with pods and a header.

So
Fitted the air correction kit
One slot up from the bottom on the needles
17.5 slow jets
115 mains

Perfect!

Starts, idles, pull away, revs right up through the gears

Thanks for the advice!

Now only issues is the rear brake....
Someone changed to a new swing arm and rear disk brake.

They fitted a master cylinder off of something else, and used the stock brake pedal..

The problem is there is so much travel on the pedal to move enough fluid to get a brake...
Can anyone recommend a master cylinder that works with the stock pedal?

I know this is the wrong section but rather then opening another post... or should I do that

Have you bled it? Otherwise its just a basic hydraulic system. If there is too much travel needed from the pedal then you need a bigger bore master cylinder. I would find what bike it came from and pull up a rebuild kit for it to find the bore size. Then look at rebuild kits for other models looking for a bigger one.
I'm sure there are other solutions for it though and someone else will chime in.

Good luck, Matt

Hi Jackson I am having similar carb problems and have found that these Mikunis can really get to bouncing around with pods if you don't rig up something to replace the support that the airbox provided. In my case, this is causing air leaks. The kz650's carb boots can be problematic, so even if they are sealing now, it probably won't be long before they start to leak if the rear of the carbs is unsupported.
I would love to see what others have done for this situation.

I've been running pods for 30 years without supporting the carbs have yet to have an issue with that. I guess if the intake boots sre marginal then that might cause issues but wont be a problem with good ones.

That surprises me, good to know though, Baldy. What I ended up discovering is that the boots had been replaced by the previous owner, and they are excellent quality, and in pristine condition. He also replaced the mounting screws with stainless. Ordinarily, I would be like hell yeah, but I could not get these tight enough to seal with any screwdriver or JIS driver that I owned. I replaced them with allen socket heads. That did the trick and just to make sure I supported the carbs with some stainless lock wire. Now the carbs feel as solidly mounted as a bike using the stock airbox, and the bike runs consistently. Blurry cell phone pics, but I think you can see what I did...

KIMG0055 by Sean Barney , on Flickr

KIMG0056 by Sean Barney , on Flickr

I never supported mine either and mine mainly finally went to hell because of age I think more than anything...... but after just putting on new ones I plan on wiring them up when I winterize....... sound like a easy and good thing to do....... and I second the allens...... much tighter and easy to remove.