Topic: just need some direction

[1hotz]

I have a 1976 cb550k. I received this bike from a friend, and it had a few things done to it when i received it. after fixing a few problems, I have a new one. This CB has aftermarket exhaust (side kickouts, open pipes), and pod filters (stock airbox was missing when I got it). I know that this leans the bike out, pretty hardcore, but I don't think that is my only issue. It idles fine at every choke position, but when I start to kick the throttle is when the problems arise. At full choke I can pull the throttle all the way open, but it only rev's to about 8000 rpm. At slightly less than full choke I can pull the throttle all the way, and it rev's all the way up. Anything less than that on the choke, it will barely rev at all (4000 rpm max) then it kinda sputters out. When under load with the choke full on I can rev to about 4000 rpm, with hardly any power. If i turn the choke a little off it has loads of power from 2000 to 4000, but then it sputters out again. anything more off on the choke it will not accelerate at all. I went through the FAQ and read the lean, and rich conditions, and I have some symptoms of both. I am confused, so any help would be greatly appreciated.

Thanks in advance
Dan.

[eldar]

More than likely you are not rich in any area but it is hard to say. Do you know if the jets are stock?
Might want to pull those an check and while at it, give the carbs a cleaning if you have not done so. Without knowing the history since you got the bike, I would suggest a full tune up.

[TwoTired]

The mechanical slide carbs on this bike are sensitive to Air filter and exhaust restriction changes.  Exhaust backpressure has a richening effect at idle speeds as does air filter restriction.  The air filter restriction lowers the baro pressure in the carb throat commensurate with the flow restriction.  The more effective the filter, usually the more restriction you have.  It is similar to the choking effect.  What the restriction does is suck harder on the fuel metering device.  Without it, the mixtures are lean.

The choke severely restricts how much air the engine can gulp.  Try running around the block with you hand covering your mouth and one nostril.  It is ridiculous to expect the engine to rev with any power while the choke is on.

You have three fuel metering devices on each carburetor, The slow jet and it's fine tune Idle air bleed screw, Throttle valves on the slides, and the main jet.  If you are going to try and retune your carbs without the use of a dynomometer, you'd better learn to read what your combustion temps are (mixture inferred) by reading your spark plugs.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

You can search this site for "plug chops" for more info.

It is absolutely pointless to fine tune carb jetting without having ALL the tune up items addressed and spot on adjusted.  This includes:
Tappets adjusted
Cam chain tension adjusted,
Compression test,
Spark plugs clean as new with correct gap and heat range.  I prefer NGK D7EA for year round use.  If running long and hard in high temps go with D8EA.
Ignition timing and points gap correctly adjusted and mechanical advance verified functional.
Carburetors vacuum synchronized.
Idle air bleed screws set equally across the bank.
Air filter clean as new and correctly oiled, if appropriate.

Only now are you ready to check mixtures.  Since you have made modifications from stock, you can expect to make changes to:
The slow jet and it's fine tune Idle air bleed screw, Throttle valves on the slides, and the main jet on each carburetor.

But, you can start with the stock setting and changes as required.  (assuming the carb internals are clean and flowing and all internal orings are in good sealing condition.)

Without knowing how your replacement equipment equipment behaves compared to the stock components, I can only make an educated guess that you will have to use a larger main, Raise the slide needles, and use a larger slow jet (if you can't improve idle throttle response by turning your Idle air bleed screws IN.

Best of luck!