Hi everyone,
Despite a lot of research on this forum and others, I have a problem with my 1983 KZ440/400 that I can't solve. It must be simple but, being quite new to mechanic, I can't find the solution. Let me try and give you the most info I can.
Here is the deal. Last year, I bought a KZ440 LTD for a few hundred euros (I am French). It wasn't running when I bought it and after a few weeks of discovery/cleaning (carburetors mainly and electronics)I got it started. After a few more weeks, I realised that the engine was that of a Kz400 B2, with a kick (so I have no idea what's the real mileage on this bike). The meter says 9 000-ish... Another important info, it was missing the airbox cap, the part with the filter in it. A friend with a 3D printer managed to create one for me based on the dimensions of the original one (found on various forums) and I have now something that is the closest to stock airbox. I did valve clearance, checked the compression (150-ish psi on both cylinders), synced the carbs and adjusted the fuel levels with clear-tube methods. I set the pilot screw to 2 3/4 out as stated in the FSM. It was running well but maybe too rich (it lacked power and, despite reaching 100km/h, as soon as I went WOT in 5th gear, the engine would start losing power and I would have to release a bit of throttle to have it run smooth again). To adress that, a mechanic suggested that I give it a bit more air. I modified the openings on the air cap, making them wider, and it gained a bit of power but still this high-end problem at full throttle.
Recently, I realised that I wasn't running stock spark plugs. The PO had B9ES and when I had replaced those, I bought the same. Thinking that this might be the key to my high-end problem (remember I am new to mechanics), I bought the stock ones (B7ES NGK) and tried starting the bike. No luck. Worse, it now shows signs of running lean with a hanging idle and backfire on my left cylinder when I give a bit of throttle at idle. When starting it cold, it needs 30 seconds of choke to warm up and idles fine after that but as soon as I open my throttle, it stays in high rpms and takes some time to go back to normal idle.
I checked for leaks on the boots (there were none but I still replaced them with new ones) and on the vacuum lines, no success. Today, I tried replacing the spark plugs, putting back the old B9ES ones, but the problem is still the same. So, while this annoying situation started when changing spark plugs (this is litteraly the only thing I changed before the whole idling situation went crap), it doesn't seem to be related. Which means I am completely lost. One more precision, it has electronic ignition and not mechanical points and the timing advancer is well lubricated so I don't think that the problem comes from there (I checked the ohm resistance on ignition coils and the pick-up coil and it looks good). Also after testing the compression again today with the engine well warmed up, I noticed that my left muffler was less hot that the right one. And, last thing, I have a small oil leak on the top of the engine, where the tachometer is connected to the engine.
Does anyone has a clue as to what might be happening here ? That would really help me. I attach a picture of my two carbs with new boots and ignition.
Thank you for your time.