Hiya,
Hope someone can help, have my suspicions but would like other opinions.
Basically, if i set the carb tickover screw so that it ticks over without having to hold throttle, as soon as throttle is blipped revs will not drop below about 4k, hangs there for ages, eventually settling back down after around 20 to 30 secs. If i lower it so that the tickover drops back to normal, it will then settle down to being stupidly lumpy and cutting out unless throttle it held ever so slightly.
Cable is free, throttle linkage on carb is free, carbs have been cleaned out twice very carefully.
Any ideas or suggestions before i start paying someone to look at it?
Thanks                                                                                                                                                                             

sticking sliders inside carbs  / fuel levels to high  float bowl may need adjusting /or maybe a splitting intake manifold ??   i would have thought one of those three maybe look for cracks around the rubber intakes first as its the easyest to spot other wise its carbs out  good luck let us know how you get on                                                                                                                                                                              

hiya kwak ..... without actually hearing the bike running sounds like air is getting in somewhere it shouldnt .... an easy test is a 50/50 solution water and washing up liquid and a 1/2 inch paintbrush or something similar .... run the bike up to temperature and get it to where its ticking over fast and dab around the intake rubbers and piping with the solution and see if the engine speed drops if it does theres your air leak .... or i`m not sure what carbs are on it ... if they are the diaphram type carefully check the rubbers against a strong light to make sure there are no pin holes in the rubber diaphrams ...... if so it will have the opposite effect and will be burning excess fuel a bit like running with the choke part way on ...... hope these easy tests helps ........ nellie.......                                                                                                                                                                             

Carbs have been stripped & cleaned !    This makes me suspicoius of incorrect float height, incorrect pilot screw settings & carbs not being correctly balanced after overhall ........ solution = check all settings again, bench set carbs, refit them then set correctly using vacum gauges                                                                                                                                                                                 

Hi all, Cheers for your input. Other thing i've just remembered is that one of the air filter to carb rubbers doesn't fit right, which must make a difference as that carb will be breathing easier? Right, carbs have been disassembled, but only as far as float chambers off, and cleaned out with carb cleaner and compressed air, not removed pilot screws, but no idea if they were set correctly anyway as bike new to me last year and problem apparant since then. As far as diaphrams concerned, if i blow compressed air through the carb venturis, the slides rise, and fall when it is removed. Presume that if they behave this way they should be ok? My suspicions are badly balanced, but also air leak somewhere, as i believe it's a common symptom of the revs no settling? My initial thoughts were maybe pilot jets blocked on one or two cylinders, causing the need to wind the tickover screw in, but this making it run on the main jet and never settling back down, however now fairly confident that the jets are clear. When in normal running, bike performs well, does about 50mpg, doesn't leak fuel, and quite some float height is correct. Definately needs balancing, have some old gauges, but until i get it ticking over right is it pointless trying, or just as Nellie says, set tickover high and balance it from there. Will try leak tests etc too. Thank very much guys, determined to sort this                                                                                                                                                                              

hiya kwak .... before you put the carbs back on did you check that the butterflies were opening at the same time and height  .... easiest way to do this is with a drill shank about 1/8 inch or 3.5mm and use it like a feeler guage just wind open the tickover screw and slide  the drill shank in on the carb thats directly altered by the tickover screw and alter the screw till its a snug fit and not tight between the butterfly valve and the bottom of the intake .... then work your way outwards altering the butterflies with the valve adjustment screw (not the tickover) till all the valves have the same gap .... wind the tickover down a couple of turns and twist the throttle gently a couple of times to make sure they are lifting and returning all even then refit the carbs back on the rubbers...... start the engine then tweak the tickover screw again to how you want it ........ doing this can take a lot of pain out of balancing with the guages ..... you probably know how to do this but any one reading this who dont could save them a few quid.... hope this helps ..... nellie                                                                                                                                                                             

Before you do final carb balance with gauges check valve clearances are ok, this will give smoother readings.                                                                                                                                                                              

Well, i did sorta eyeball 'em, but not used any measuring device, as just thought that balancing would take care of it, but it's all good advice and taken note of. Wanted to have a go at it tonight, but no garage and rained all night since i finished work.
Single cable throttle setup (well pull/pull), onto linkage, tickover screw directly adjusts same point that throttle cable pulls.
Haynes suggest balancing 1+2, 3+4, then balancing the 2 balanced pairs to finalise.
Stupid question, but any recommended rpm to have engine running at while balancing?
Cheers guys.                                                                                                                                                                             

we used to balence them at 1500 rpm then slowly rais to 4000 and drop agian but you can do it by eye with the butter fly's as some one said earlyer   i dont think blowing air in the ventrury proves diaphrams ok as you got the cabs off why not take them out and look for pin holes ? if left they will lean out the mixture in one pot i have a gpz split its no. 3 piston that way so worth the extra work if you got em off allready !                                                                                                                                                                             

Well, they're not off at the mo as not stripped it again since the barmouth trip. And they're a complete bitch to get out, really tight as airbox hardly moves back. But will have a go soon, just probably have to wait until after cornwall trip as if i end up with an unuseable bike i'll be knackered lol!

I've got a set of 4-pot Morgan carb tune vacuum gauges you can borrow if you think they'll benefit somehow.

Drop me a PM if you'd like to borrow them.                                                                                                                                                                             

That's a very kind offer Mr P, thank you. Will see how I get on once i start a-messin, and let you know                                                                                                                                                                              

Another thing that can cause that is a slightly bent needle. Can be enough to stick the slides too.                                                                                                                                                                             

yeah, checked that sorta thing, but the slides are as free as a bird.                                                                                                                                                                             

Does it happen all the time with the engine hot or cold?                                                                                                                                                                             

Yeah, makes no difference, if it'll tickover without conking, the rev's will hang up.                                                                                                                                                                             

Another thought. Does it have points? or at least a mechanical advance and retard? Had a problem once where the weights were sticking which made the timing go strange and that had a similar effect.                                                                                                                                                                              

Definitely not, full electronic early 1990's japanese best!
God, don't even wanna think how mucg worse it could be if i had all that to contend with too!                                                                                                                                                                             

hi everyone , got the same problem with the cb 450, revs dropping , carbs running rich , sooting the spark plugs up . can the spark plugs soot up if there is to much air intake or would it run lean,also if a engine needs decoking would it cause the above problems.......................had to lower the float heights so i could use the bike............cheers for any advice.

hi kwakarider, does the spark plugs soot up , does it drain the battery. .,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,for the above message ive backed the pilot screw off a bit aswell .