Topic: Cb550 hesitates at 1/4 throttle when warm

[gregripko]

Noticed after riding a while that the bike accelerates amazing when cold... But when it warms up I lose power in the 1/4 throttle... Like a hesitating blubber sound... That's only cured by 1/2+ throttle...

#100 mains
#38 slows
4th position clip
Stock airbox with oiled uni filter
Mac 4 into 1
1976 Kcb550

(Jets and carbs clean)

[flybox1]

mixture just needs to be dialed in....what do your plugs tell you?

[iron_worker]

Engines that are cold require an over-rich mixture to run properly. Thus, running problems that get worse as the engine warms up leads me to believe it's over-rich. It has the right amount of fuel for cold running but since a warm engine allows fuel to vaporize better it actually requires less fuel.

Let me guess ... doesn't require much choke or any to start when cold?

IW

[gregripko]

It requires choke to start.... I am 1.0 turns out though so maybe a half turn out will cure it

[gregripko]

Turned .5 out and noticed the rpm increases if I have 3/4 choke on within a few minutes.... Are the air screws that sensitive? Or does the bike richen up that much when it heats up? It's just runs really rough.... Hope this isn't related to my pamco

[BuffaloBill]

My 77 550F, stock jetting, airbox, exhaust, new paper element, ran poorly when opening the throttle a small amount when at a 50mph (about) cruise.  After a bunch of experimenting, I found much better performance by dropping the needles one position from stock.  Not sure if my condition was exactly like yours though.

[dave500]

the thing with an oiled filter is they aint stable as far as restriction goes,the oil will slowly drain down and change the air flow somewhat,,this isnt important on say a dirt bike where we would be always cleaning and re oiling them often daily,,they work well and trap every speck of dirt when used like this,,the paper type are more stable as far as this variable is concerned,,the difference between a filter oiled a month ago and just this day might be more or less with too many variables on these carbs,they are finicky with that sort of thing,if you bought your bike with the 4-1 exhaust the needle clip might have been lowered(to raise the needle for enrichenment)as a matter of course,,this is wrong,any carb alterations should be done once the engine has been test ridden,and with the ignition set to exacting specs,i think your slightly rich in the idle off idle.

[gregripko]

When I got this bike in November it had uni pods #100 mains, #40 slows, and clip in the 4th slot from the top... Ran pretty good but I wanted to throw the airbox on it as I heard it would give me better performance... With the pamco I have the advance timing set to the right notch of the advance notches:
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TF 1.4

[dave500]

that  timing is correct if it was running at some rpm and a strobe was used?set at the point when it stops advancing?the pamco is a highly reguarded unit!your bike may have had jetting changes done"as a matter of course"with the non stock filter it had,now its back to stock you may find its slightly richer than it should be,not a big deal under an engine always under full load acelleration or power needs,,but once in cruise/traffic mode it might be over rich and cause that blubber,if the needle clip has been lowered(making it richer)before you got the bike id put it back to the middle slot where the stock setting should be,you have to disrupt the sync though in doing this and itll need to be vacuum synced again,,just for the record any good bench sync is only done to get the engine running,,then it gets properly vacuum synced once it running,,any bench sync is only a stop gap temp set up!!!