Topic: trying to get a 77 cb550 running

[osnomad]

Hi all. I recently picked up a77 cb550 that had been sitting for quite a while. The gas in 2 of the bowls had gelled, the other 2 were empty. I've spent quite a bit of time cleaning the carbs and i'm pretty confident that all the gunk and varnish is gone. I have new fuel in a clean tank.

My problem is that I can't seem to get it running consistently. To get it started, I have to shoot some starter fluid in the carbs or it just won't start. Usually i open the throttle, spray some starter fluid, close the throttle and the choke then fire it up. It cranks a few times then starts and shoots right up to about 3k rpm. if i keep it choked it will run like that for a while. i can then slowly open the choke till it's about 1/2 way open but no more than that or it will just die. I also cannot rev the engine at all without stalling it out., even with the choke all the way on. This behaviour makes me think it's running lean but i pulled the plugs and they are sooty (new plugs) indicating a rich condition.

If anyone has any ideas as to what i could try I would be most appreciative.

TIA
-john

[TwoTired]

Have you adjusted the main idle knob?
Have you adjusted the fast idle cam coupled to the choke?
Are you absolutely, positively sure that all the tiny passageways are clear in the carbs?
How did you verify that the idle jets were flowing freely?
Are all the head pipes getting hot/same temp?
What are your pilot screw settings?
Have you done a carb sync yet?
Did you replace the o-rings in the carbs?
Are the slide cutaways facing the air filter?

Starter fluid?  Gee, I haven't used that since 1964 on a cold Illinios morning...

[osnomad]

i've adjusted the main idle screw a million different ways now.

The fast idle cam on the choke does work.

i can't honestly say that i am absolutely sure that all the passageways are clear in all the carbs but i am pretty sure they are. I have blown carb cleaner and air thru every oriface i found inside and out.

all the headpipes are indeed the same temp

the pilot screws are now at 3 turns out. (pilot screws are on the motor side of the carbs)

i haven't done a carb sync because nowhere have i found instructions on how to sync these particular carbs.

i did not replace any o-rings in the carbs. i did replace the 2 float needles that were in the gelled bowls but those are the only parts i replaced.

could you enlighten me as to the cutaways on the slides?

this is the first time i have worked on bike carbs at all. before this it's been cars only for me.

i think this can of starter fluid i have is FROM 1964

[TwoTired]

Okay, assuming you have 77 model carbs...

The book says that the pilot screws should be around 1 1/2 turns out from seated.  These meter fuel not air.  Turn in- lean, turn out- rich.  You need a right angle screwdriver to adjust these properly on the bike.  I made one for myself.   But, elsewhere on this site is a discussion of where they can be purchased.  Be careful not to ruin the needle or seat by tightening it up too much.  1 1/2 turns is starting point appropriate for a bike with stock exhaust and induction components.

The float height for these carbs is 14.5 mm.  If you set them to 22mm like what the clymer manual says... well, that's wrong.

I'm not sure about the 77 carbs but the older model slides have a keyway.  If you swapped the slides 3 and 4 into 1 and 2 carb bodies they would be backwards and won't close or work properly.  The bottoms of the slides are angled, and the side that faces the air filter should open first.

Carb synch is described in the Honda CB550 Shop manual.  Chapter 19 covers your carbs.  Do you have 4 manometers?  Or, are you planning to just mechanical sync them?
BTW, your carbs must be synced to number two as that one does not have a slide position adjustment.

Hard to say for sure with the current problem description.  But, your carbs have four fuel metering devices,  Main jet for WOT, slide tapered needles and jet for mid range throttle, idle or slow jets for low throttle position, and then the fine tune idle mixture screws and seats.  Your current problem description does fit the slow jets or circuits being clogged.  They are only .38mm (about .016 inch) in diameter, are pressed in, and they and pathways behind them are difficult to flush clear.  If they are blocked, then the engine would only run when the carbs are operating on slide needles.  And, without the addition of idle circuit flow, choke would be required for mixture offset.

But, I'm just guessing...

[bryanj]

If its been stood awile i will just about guarantee that the pressed in pilot jets are blocked, you can remove them with care by gripping with vice grips but not too hard and pulling/twisting at the same time. BE CAREFULL as new ones dont exist

[osnomad]

So here's where I stand now...

I took the carbs apart for the 20th time and re-cleaned all the orifaces i could find. readjusted the pilot screws to 1.5 turns and made sure the floats were at 14mm. I checked the sync with the 1/8 drill bit method just to get it close. The sync was very very close and the floats were also very close to spec. I put the carbs back on and tried again and lo and behold I was able to get it started without the starter fluid! So my guess is that there must have still been some crud in the carbs that i missed the other 19 times I had them apart. i couldn't get the pilot jets out of their seat and i was afraid to damage them so I just shot carb cleaner thru them in both directions. They were definitely already clear so I don't know if that made the difference. So I am definitely on my way now. Thanks for all your suggestions. I was reluctant to take the carbs apart again having done it so many times but your responses made me think otherwise.

thanks again!!!

[Magmotor]

Okay, assuming you have 77 model carbs...
Is a '74 that much different than a '77???The book says that the pilot screws should be around 1 1/2 turns out from seated.  These meter fuel not air.  If we're talking about the same valve, see pic, it adjusts air, not fuel. Page 109, original service manual and no right hand screw driver is needed. All are accessible.   You need a right angle screwdriver to adjust these properly on the bike.

The float height for these carbs is 14.5 mm.  If you set them to 22mm like what the clymer manual says... well, that's wrong.   If I adjusted my float to that height it would be permanently closed. Where did you get that information?
I'm not sure about the 77 carbs but the older model slides  What slides are you referring to? I don't have a clue as to what this is.  
BTW, your carbs must be synced to number two as that one does not have a slide position adjustment

  Your current problem description does fit the slow jets or circuits being clogged.  They are only .38mm (about .016 inch) in diameter, are pressed in,  The slow jets are a screw in type. Page 113 #11 and are easily removed for cleaning.

This information your giving is so much different than mine I had to ask.....[/size]

[MetalHead550]

Yes the 74/75 carbs are different than the 77/78 carbs. Dont know about 76 models.  The mixture screws on your carbs are on the air filter side(as in your pic) so it meters air while the mixture screw on the the 77 carbs is on the intake manifold side so it meters fuel.  So screwing in the mixture screws on youre carbs makes them rich cuz it closes off air while screwing in the mixture screw on the 77s make for a leaner mixture since it closes off fuel.  So theyre bass ackwards.  This goes for float hight and needle jets too...different carbs.  The slides are the cylinders with the long needle on the bottom that goes into the main jet.  They are what move up and down within the carb body according to throttle position.

[Magmotor]

OK thanks...!!! for the years to be so close I didn't realize there was such a diff in carbs....good information to know....

[TwoTired]

Magmotor,
My info is from the Honda Shop manual CB500-550 chapter 19 supplement to the K3 '77. 
AFAIK only the 77 and 78 CB550K models used this carb type.  All the F model CB550s and all CB500-CB550 K models prior, used the carb body style as in your picture.  However, the setups (jets, needles, etc.) were different inside to match displacement and exhaust type.

I took my spare77/78 carb bank apart.  The slides don't have any keyway for this model.  They can be installed backwards in any carb with the cutaway on the wrong side.  I'll let someone else determine what the behavioral symptoms are when this configuration is installed on the bike.  Can't be good, though. 

Cheers,

[Magmotor]

 ???Iam still confused about these slides your talking about...does my 550 have em? If so, they past me right on by.... Got a pic or a drawing of em? Thanks..

[TwoTired]

The Honda Shop manual calls them throttle valves.  These are the things that go up and down in the carbs when you operate the throttle grip.

[Magmotor]

gottcha....thanks...

[SteveD CB500F]

The K3 did have totally different carbs to the F1/F2 models.  See pic of my K3 carbs and compare to the earlier pic. The quickest way to tell them apart is to check the carb-top screws.  Early carbs had the two side-by-side (like the 500) and the later carbs have them on the front and rear ends.

The most obvious difference riding is that the K3 takes longer to warm up and runs lean. It also does 60 to the (UK) gallon - my 500 manages about 50 (on a good day)

[Magmotor]

That sounds nice but would you translate that for us non-international memebers....lol.....I just checked mine today and am getting 35.25 mpg....not bad but....could be better...(was 26 mpg last week) .i've got some samll backfire when I let off the throttle...valve's I would imagen....i'm constanly adjusting those damn things...probably bad cam, worn rockers etc: ......i'll keep messen with it cause it's too much fun not too...!!! 

[Dennis]

Magmotor,
UK gallon is 20% larger than US gallon.
UK gallon = 5 US quarts = 4 UK quarts  (UK quart is 40 ounces)

I hope that answers your question