Mikuni BS32 rebuild with a few questions please

wrote:

Adjusted floats now they are 4mm below edge... new air filter, b8es spark plugs, valves were adjusted, carbs cleaned, jet needle clip is in the middle position. pilot mixture screw is 2 turns out. carbs are bs32

now the problem is spark plugs are lean to my knowledge. Cold start is difficult, because it runs on middle 2 cylinders, but it gets better if i put my hand over airbox intake (lean again?)

in need of a third opinion here.

Those plugs look fine.  Try 3 turns open on the pilot screws.  Regarding the poor cold starting, did you make sure the choke tube is open?  Did you make sure the choke passage in the float bowls are clear?  

I agree the plugs look ok. Maybe a touch leaner on the right hand plug. You want the bottom ring of the plug (last thread) to be dark and consistent color 360 degs. That is your lean rich indicator. The left plug looks good. The right has inconsistent color and a tab lighter. That indicates slightly lean. The other thing I see on the plug is the earth strap is a consistent color from tip to weld. That’s typical for a heat range to hot. Get the tune correct then start watching the color on the earth strap. You want it to be a lighter color changing to darker color just as the strap starts to make the bend. After your tune is good and you continue to see the earth strap as is ( constant color) then consider going to B9eS plugs. 

Cool, now I at least know not to panic too much about the plugs. I read somewhere about an article that kz650 runs very lean and that the model i have has poor midrange performance.
I am trying to tune them "perfect" with colortune and carb sync. Today i was on and off the bike at least 6 times, plugs out and reading them. As Mikaw suggested I will consider buying B9ES plugs. I dont even know how much mileage the current ones have. Too bad I did not score any decent info for my model (F3) with BS32 carbs. Found out on another thread that floats are supposed to be 18.6mm, and i set them to 19mm. Maybe that 0.4mm too much to get 4mm fuel level when it should be 3mm.
i opened up the pilot screws as Nessism suggested. One more cold start for testing tomorrow. If I have the same symptoms I should definitely clean the carbs again and check choke operation.

tnx guys

NGK ‘s are getting hard to find, and there are fakes out there. Nippon Denso are great plugs also B8eS = W24ES-U…. B9eS = W27ES-U. I’d tune with what you have now. The slightly lean condition might be hiding the heat range. Did you set fuel level using the clear tube wet method?

Spark plugs are not a problem where i come from. Denso are great alternative.
Yes, i set fuel level off bike, clear tube, leveled out. I did not get any decent info, and 4mm is probably too low, when it should be that 1mm higher.
Will definitely tune with what i have now and ride it for a couple miles, so i have some sort of a baseline.
I closed the airbox a little (for testing purposes), low end got better but around 70mph and 5000rpm in 5th gear it showed same symptoms as red lining it, stuttering.... upon that i confirmed i was running rich.
fine tune is needed, thats all...
carbs came in a box... bike as non runner.

hi guys, the pilot jet plugs are missing in my mikuni carbs, how would they act without those plugs? actually, i've threaded the holes and installed m6 stainless steel plugs on fuel resistant gasket maker, see the piccie

another question, any info on rejetting both KZ750 keihin carbs and GPZ750 mikuni carbs for pod filters and straight thru zorst (i have both of them, tho d'rather use keihins and keep mikunis for my gpz engine)

 

wrote:

hi guys, the pilot jet plugs are missing in my mikuni carbs, how would they act without those plugs? actually, i've threaded the holes and installed m6 stainless steel plugs on fuel resistant gasket maker, see the piccie

 

To my knowledge, it would probably be a little rich, since they share the inlet from main jet. Or the main would be rich, because now both jets have unrestricted flow. I do have those plugs installed, so i cant give you any better answer right now.

I cant help you with rejetting, but i come from another gpz 900 forum where everybody just stays AWAY from pod filters. Too much hassle and too little income...

Maybe I missed this somewhere on the thread, but what about the large aluminum plug? What does it do, and does it just press in? I have one missing (see carb on far left) and I think the ones that do have the plug had an oring on top to mate flush with the bowl gasket, as they're recessed slightly into the carb body. Can someone set me straight? '82 KZ0650 CSR, Mikuni BS32, coded 1479. Thanks!

The aluminum plug is required.  When Mikuni is manufacturing the carbs, machining the carb bodies, that passage allows them to drill some of the passages in the carb body.  After the drilling, they press fit a plug into the carb body to plug the hole. 

The plugs over the pilot jet are needed also.  There is a small O-ring on the plug to seal the passage.  On these carbs, the pilot jet pulls fuel from the main jet passage, via a diagonally drilled passage in the carb body.

BTW, I have carb O-ring kits for those carbs.  And I may have a spare aluminum plug also.  

That is a great explanation...thanks! I'd love to get one of the o'ring kits and a plug if you have one. Looks like I may be to contact you at the link in your signature? Thanks again.

mjudge wrote:

That is a great explanation...thanks! I'd love to get one of the o'ring kits and a plug if you have one. Looks like I may be to contact you at the link in your signature? Thanks again.

email me at nessism AT sbcglobal DOT net to discuss.

O-rings shipping today, Mike.

Thanks

Ed