After I've 'unstuck' my thottle valves and setting the correct float height (thanks again for the tips), I put my needle in the middle position and did some plug chops.
At idle the mixture seems somewhat rich. At WOT things seemed to be looking ok (see pictures).
Then i took it for a spin, gradually opening the throttle to find my top speed. Near WOT and still accelerating at about 110km/u (70mph), the engine seized... and then unseized and i was still on my bike. I closed the choke halfway and stayed below half throttle.
So my bike seems lean at WOT. I'm currently running #42 slow jets, #135 main jets, the needle at the middle clip and D8HA plugs. I'm living in the Netherlands so that's at sea-level (some parts below).
Any suggestions how to handle this?
CB77 tuningCB77 tuning
Plug reading is really only any good at WOT under load.
Plug temperatures vary wildly and they only self clean when they are hot, so at part throttle plugs are cooler and look as if they are rich. At WOT the plug tip on a clean new plug should be almost white and you read the mixture down inside the plug where the insulator meets the steel shell. It's hard to see much in that top picture, but I don't see signs of overheating on the plug. If anything, the earth strap looks as if it isn't getting hot enough which raises a few questions. A couple of things to check: Are the exhausts and air filters stock? Is the ignition timing exactly correct? What heat range are the plugs? What fuel was it running? Are the carbs really clean including those small filters on the fuel inlet? Is the breather hole in the filler cap really open or could it be causing partial flow restriction at speed? Is the fuel tap completely clean including the screen in the bowl? If the motor did overheat Thanks for your reaction. I didn't know you had to read the plug down inside. I'll make sure to look there more carefully in the future.
I did my plug reading at WOT. I first warmed up the engine, then found myself a quiet road, accelerated to fifth gear, WOT and then killed the engine (bit of a fiddle without killswitch) and squeezed the clutch. Maybe i should keep it a bit longer at WOT. To further answer your questions: - stock (replica?) airfilters - replica exhaust yet without dampers - didn't check ignition timing, yet it runs very nicely and balanced at idle (btw i can only do static checking of the timing) - NGK D8HA plugs, 8 on the scale of 2-12 from hot to cold - fuel used is unleaded euro 95 - carbs completely cleaned - tank and fuel tap also cleaned and air hole in fuel cap is also working ok And it seems your post ended in the middle of a sentence? Here is a link to NGK. Lots of info in a couple pages of spark plug info. They explaine things a bit. But they didn't seem to be talking much about tuning either. They do say that 'at temp' cleans the plug at high temps/rpm and your plug does look cleaned!
http://www.ngksparkplugs.com/tech_suppo ... p?mode=nml Innovative Motorsports are all about tuning. Got some resonable prices gadgets as well. http://www.innovatemotorsports.com/reso ... entral.php 2000 ZX12-R Kawsaki/1966 Dream 305 CA77/78
So far so good. Good info. I'd get that bike fitted with baffles first and then try it on a dyno with gas analysis and check the full throttle mixture to be sure.
After a couple of roll on runs, it should be clear whether or not there's a fuel issue. It may have been the lack of baffles that leaned it out a little too far. D8 should be OK. I usually use a D10 on the first hard run, just to be a little safe and then switch to hotter plugs when I know I didn't do anything stupid. Yes, I did.... What I was saying that got lost was that if it did actually overheat, the cause may have been timing or partial fuel blockage or lack of baffles etc and we need to determine which. Your answer removed a lot of items from the list.
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