Topic: Need some carb help -- WITH VIDEO

[mrfish2]

Okay so lets get some basics out of the way:

1976 CB550K
087A carbs
MotoGP Werks exhaust
single K&N filter in place of stock airbox
115 mains
needle clip in 4th position from the top (stock setting)
#38 pilots (from JetsRUs, so good quality)
Air screws 1.5 turns out
Floats are brand new OEM Honda, all set to roughly 22 mm, +- .5 mm
Float seats/needles are Keyster brand, also brand new

I'm having a terrible time trying to get my bike dialed in. After a friend helped vacuum sync the carbs it'll idle fairly well, but after revving it up it takes FOREVER to come back down to idle. It also blows black smoke out on the initial rev up, leading me to believe that the needle clip is a little rich. I can't for the life of me figure out why the revs would hang up so much. Yes, i've checked for vacuum leaks around the carb boots, there are none. The throttle cables are not binding up, after letting go of the throttle everything snaps back as it should and the slides are not sticking either from what I can tell.

And here's the video of my predicament, this was after warming the bike up to operating temp

[goldarrow]

No airbox?

Try 105 mains for exhaust changes, 40 slow jets for no airbox. 

[harisuluv]

Hanging RPMS are a very common issue.  There are multiple causes.  One cause is a lean condition.  You said you have black (rich) smoke at low RPM, so you would think this would conflict with being lean.  However, remember that you can be lean AND rich at the same time, at different ranges.

Plugs will tell you the story.  However, I am willing to bet that being at stock needle clip is not going to do it with that setup.  You have the stock airbox on but if I remember it's not going to function anything like the stock airbox anymore with the single big K&N filter mod.  Probably more like pods.

If you're rich at the low range, you might want to adjust your mixture screws out 1/8-1/4 turn at a time and see if that improves at the low end. 

[mrfish2]

For visual reference here is the air intake setup I have

Try 105 mains for exhaust changes, 40 slow jets for no airbox. 

This was a WOT plug chop with 105 mains


And another WOT chop with 110s


Thus why I settled with the 115s.

I figured I might have to adjust the needle clip to the middle position, I'll try and find the time to do that tomorrow (between mowing 2 yards).

[harisuluv]

Stock is 4th from the top, so moving it to the 3rd (middle) would actually lowering the needle making it even leaner.  You want to lower the clip hence raising the needle (5th position).

[mrfish2]

Ohhhh, okay I understand now. All this adjusting over the past few days has gotten me so backwards haha

[mrfish2]

Changed the needle clip to the 5th position and it was literally the same, nothing changed at all. I probably need to vacuum sync them again since taking the slides out.

[flybox1]

then you are still lean at WOT
order 120's, leave the needle clip where it is.

[mrfish2]

I figured that might be the next thing to do, thanks Fly. I'll get those ordered and changed out and report back.

[mrfish2]

Put the 120s in, no change still. And it still stumbles pretty bad coming off the line. And it's blowing even more smoke out when I rev it up. I'm getting extremely frustrated by this thing.

[goldarrow]

And it still stumbles pretty bad coming off the line. And it's blowing even more smoke out when I rev it up.

Sounds super rich

[mrfish2]

I'm considering going back to the stock airbox with a Uni foam filter and starting over, at least it'll be easier to tune.

Edit: definitely super rich now, rode around town never getting above 5k and it fouled 2 plugs

[chewbacca5000]

Most of the time when this happens to me it is my throttle cables are worn out, need adjusting, lube, or replacement.  Try rolling the throttle forward to get it to "calm down" and report back.

[mrfish2]

Well Chewy, i would definitely try that given old cables, but both of my cables are brand new, less than 40 miles on the pull cable, and they are definitely properly adjusted. Rolling back on them doesn't affect it at all.

[goldarrow]

I would start at 38 and 105

[chewbacca5000]

Unless you know someone who has had success with a single large pod I would go back to the stock setup for carb setting and air box.

Air leaks can be hard to find.  Could be an exhaust leak as well. 

[mrfish2]

Through all the searching I've done on this forum and others I haven't been able to find anybody running the same setup as me, that's kinda why I wanted to work it out so I could say I had something unique.

Yeah, tomorrow I'm just gonna put the stock airbox back on, go back to the 4th needle clip, and try the 105 mains. That configuration seems to work best from what others have reported.

[flybox1]

Understand that the 120s are only for 2/3-WOT positions.
They will have zero effect on idle, or off the line performance
You need pilot jet and mixture screw adjustments for that...but befpre you can make those changes, you have to get jetting for WOT and 2/3 throttle(main jet and needle clip) done first.
Leave the 120's in.

[flybox1]

Your whole setup is lean.
120main
40pilot
Needle in the 4th from the top.

[harisuluv]

That K&N basically just takes up the same amount of space as the stock setup.  Is unable to even be seen, and a doesn't even get maxed airflow tucked in there, basically surrounded.  I guess it's unique but only you would know about it.

[goldarrow]

Understand that the 120s are only for 2/3-WOT positions.
They will have zero effect on idle, or off the line performance
You need pilot jet and mixture screw adjustments for that...but befpre you can make those changes, you have to get jetting for WOT and 2/3 throttle(main jet and needle clip) done first.
Leave the 120's in.

The pipes he has does not call for 120 main. 

[mrfish2]

The pipes he has does not call for 120 main.

True, but the pipes combined with this air filter have proven otherwise. It flows a lot more air at WOT, you can see above where I did WOT plug chops with 105 and 110 main jets and it was way too lean. 

[mrfish2]

Your whole setup is lean.
120main
40pilot
Needle in the 4th from the top.

I'll give that a whirl

[flybox1]

With new or clean plugs in, let it idle under a fan first, and then check the color.
You will have to adjust your mixture screw to get a light tan color indicating a close to correct mixture.

[mrfish2]

With new or clean plugs in, let it idle under a fan first, and then check the color.
You will have to adjust your mixture screw to get a light tan color indicating a close to correct mixture.

That's another issue. Since adjusting the needle clips last time it doens't want to idle anymore, just sputter and die. I figure this is because I haven't been able to vacuum sync them yet. Still waiting on my Morgan Carbtune to come in the mail.

[flybox1]

cart before the horse, man.
how will you use a vacuum sync if you cant get your bike to idle? 
even with a bad bench sync, your bike will idle.   
a vacuum sync device will not help your bike to idle well if your air fuel mixture is not close to being correct.
if you bike wont idle right now, your air fuel mixture is still off.  (pilot jets and mixture screws)

needle clip position can change and your bike will still idle. 

maybe this visual will help wrap your brain around it.

[mrfish2]

It's high time I updated this thread. So it turns out that my issues with tuning the bike ended up being bugerred emulsion tubes (I'll get some pics up of them later). Along the way somewhere someone had hammered the tubes out and destroyed the inside.diameter, thus allowing different amounts of air/fuel to flow between the carbs.

Well after sourcing a used set of emulsion tubes from a guy on ebay me and a mechanic friend were able to get the bike dialed in pretty close. I ended up putting the stock air box back on to eliminate the K&N filter as a tuning variable and the way the bike is running right now I doubt I ever put the K&N filter back on.

The setting we ended up settling with are:
38 pilot jets
115 main (will do a plug chop later to confirm it's not too rich, but for now runs great)
Needle clips in 3rd position
Screws at 1.5 turns out

The bike takes off from idle without any hesitation now, and runs strong and smooth all the way to redline in all gears. The revs don't hang up anymore either. Needless to say I'm extremely please that for the first time since owning this bike I can finally rack up some worry-free miles.

[harisuluv]

That's good, there are a lot of people trying to bypass the emulsion tube issue and instead try and correct the main jet and slow jet to significantly outside of spec.  It is a band aid that helps but not a real fix like you are experiencing.

This is also why I have turned away some jobs that are disassembled already, it's not a plus, it's a negative, if done incorrectly, the emulsion tubes (which are in fact a jet!) are easily mushroomed and damaged.  A set that has never been into before is always better/preferred than rebuilding an already "rebuilt" set.