I hope someone here can brag about giving us a solution!! We have a 1977 kz650b1 that my son and I have had an awesome time restoring. We picked it up last summer and spent the last year cleaning, replacing and repairing things to get it to a "daily driver" condition. It has 23000kms on it, 700 of which we put on it this season during our test and tuning sessions. The story goes that an older gentleman purchased it brand new in '77 and rode it for a few seasons, parked it and then it sat for quite a while. There was no history of it in the licensing office and there was no stolen reports linked to it. It must have been a very long time between road worthy. It has the correct original carbs with pilot screws and no air screws. We replaced the (sadly) rusted original exhaust with a Delkevic 4 into 1. The original air box with new boots to the carbs have been installed as well as a new air filter. Compression test is 140 psi across all cylinders. We have been chasing a fouling plug problem. They all get carboned up fairly evenly with 2 being the cleanest but far from good. The rundown of what we have done so far is- throughly cleaned the carbs with ultrasonic cleaner (jets and needles are all stock size) float levels are set to 4.5mm below the carb bowl joint (in an effort to lean it out) and checked with the clear tube method on the bike, the pilot screws are set to 1-1/4 turns out, if we set them below 1 turn out we get the deceleration exhaust popping. It did give a slight sense of highest idle when adjusting them. The intake boots are in great condition no cracks and are quite pliable. We checked and adjusted the valve clearances, all are set to .15mm clearance. The ignition coils, wires(emgo) and non resistor NGK plug caps have all been replaced and the spark looks good, we installed the WG relay mod as we were losing about 1.2 volts to the coils through the cleaned but original wiring and replaced the spark plugs (numerous times now-NGK br8es, br6es, br8eix and br7es) The gas tank is clean (we put an inline filter in as a precaution), with the original petcock which works but will let a very small slow drip through when set to off, found during a bench test of the petcock. The battery is new and settled at 12.8 volts and the charging system is functioning as intended. We replaced the points and condensers, the points were set to .35mm and static set up to the F mark and was double checked with a strobe. The ignition advance starts at 1500rpm and is all in around 3200rpm. The rich problem happens around the transition between idle and 1700 rpm. If you hold the throttle to maintain 15-1700rpm for a few seconds then raise the rpms it belches black soot and stumbles a bit then accelerates normally. We've had the carbs out numerous times to check double and triple check every setting and passage. The pilot air jets and passages have been cleaned almost every time since that is what the problem seems to be. But the overall operation is pretty good and it cold starts easily with choke and not easily without the choke. It runs through the grars and accelerates well. When it's ridden for a few hours it runs progressively worse until it starts to foul out the spark plugs. Some thoughts- We've been running 91 in it as it has no ethanol in it locally, maybe we should try some ethanolated 89?The installed pilot jets are 15 with the 50 additional jet below it, is it even an option to get a smaller pilot jet even though it seems wrong to do?We replaced the coils and caps since there is no local availability of b7es or b8es spark plugs, I trust this is the correct way to solve the double resistance issue?We've replaced most of the items listed even though they didn't really test out as "failed or bad" but as attempt to solve the fouling. The inital operation was fair and things have become progressively better with each component we replaced, except it continues to foul the plugs.I hope someone here has (unfortunately) been through this and is willing to help out with some ideas. We will forever be in your debt!
Thanks for any help!!