too much fuel would cause a rich mixture fbj as you said about lowering the float hight but ! a weak spark can cause it to coke up too so pionts coils and plugs need cheaking mate also leads how olds the bike have you got the correct grade of plug etc   if it's fuel then worn jets or neddle valve could make it rich or even a blocked air bypass ( dirty carbs ) causing it to run as if on choke !                                                                                                                                                                             

Hi John, Electrics def ok, did the 500 mile round trip to barmouth and never drains battery, just usually have it set so i need to hold a whisker of throttle to keep it ticking over, better than it racing it's head off and no engine braking! Was hoping to have another look at it this weekend including checking plugs as well as carb diaprams. Might do whitby on it yet.                                                                                                                                                                             

hi again , the vacuum pistons have slight wear marks on them can that cause it to run rich............. cleaned,checked carbs ,jets are ok checked and cleaned the electrics,  ie  , starter motor , coil . very good spark. only soots on slow running jets though.

fbj if its sooting on slow running jets then i would have thought air adjusting sreew need turn out a wee bit ?                                                                                                                                                                              

unfortanitly there is only a fuel mixture screw on the bike , no air screw . the bike is a 1989 honda cb 450 ..........................                                                                                                                                                                              

Turn it in then 

As for Ks problem you must be getting air in somehow then or else your "full electronic early 1990's japanese best" cdi unit is knackered, god forbid 
Hope you get to the bottom of it and it isn't expensive.                                                                                                                                                                             

taking the bike out for a spin today ..................saturday . il write a performance report when i get back later                                                                                                                                                                              

bike run great did 50 miles , checked the plugs,  slight sooting on them tick over a bit out ......................thanks......... major improvment                                                                                                                                                                              

glad yours is getting there. Not touched mine yet, been a busy boy this weekend!                                                                                                                                                                             

got plugs out, all check out ok, other than no 4 was the tightest plug i've ever removed, thought it was gonna break off. Strangely, gap on that one was about 0.15mm bigger than the other 3. Gapped them all, still runs the same other than now it seems to be pinking at up to about 1500 revs on cyl 4....
Still suspect air leaks but not had time to test fully.                                                                                                                                                                             

it dosnt need decoking  does it kwak                                                                                                                                                                              

Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal ...nes occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (also discussed in this article).                                                                                                                                                                             

Certainly looking that way john, it has got 48k on the clock lol! Might just wind that plug out again and open the gap up again to see it it goes away, it only started doing it when i put it back in the other day after setting gap correctly from being too big. The plug was really, really tight all the way out, mght not have even been seated fully. Just another problem lol!! WN - know what pinking is caused by lol, just brought it up as it never did it before removing and gapping plugs, strange                                                                                                                                                                              

the cb runs great its just a light sooting of the plugs and the tick over                                                                                                                                                                               

Well i sorted the zephyr Stuck it on ebay as spares or repair, with all it's faults listed as known to me, and it went for £400, so not too dischuffed, as was only expecting £250. Been bought by a breaker from middlesex who's collecting it on monday. Now i just want to buy an 05 Z1000 that's in london!!                                                                                                                                                                             

hi again.............. cb playing up again weak irratic spark on both new plugs .done 700 miles on  it, ran great .             does any1 know if a faulty regulater   can cause weak spark ......cheers

Shame about the zephyr. Was almost certainly a cracked carb to engine rubber, or one of the balance point covers.                                                                                                                                                                             

well Z thou should be a blast mate enjoy and lets see if we sort the hadling probs out next  ( according to Geoff )