New GPz 750 owner - popping and not much power

Hi folks,

I've posted a couple of times on this board before, but now I'm an official KZ rider. Just took delivery on a 1983 GPz 750. (My "other" bike is an '82 Yamaha SECA 750 converted to fuel injection).



Anyway, this GPz is not fuel injected, so I have to deal with the carbs a bit. The bike starts OK and runs OK, but my SECA pulls quite a bit better, and the GPz is popping all the time once warm - at idle and under load.

I checked the plugs and all but one look great. #2 looks a bit lean - not bleached white or anything, but less tan than the other three and a bit of white showing through. I would guess that's part of my problem, but the other thing I'm wondering about is whether the jetting is right. The bike has a nice, brand unknown, 4-1 header on it. I'm planning on pulling and cleaning the carbs regardless, but I'd like to check, and maybe change, jets while I'm in there. Does anyone have any recommendations as to best jetting for this bike, stock airbox, with this 4-1 header, and running at 6000+ ft elevation?

Thanks in advance for your help.

Cheers,
Paul

To further narrow things down, I ran the bike for a few minutes and used an IR thermometer to measure temperatures of the exhaust headers. 1 and 4 were about the same (515 degrees or so), 2 was relatively hot (about 650), and 4 was relatively cool (but still 300 degrees).

So, although the plugs look OKish, I'm guessing rich on 3 and lean on 2.

Any thoughts?

Thanks,
Paul