Issues adjusting A/F mix on CB550F — I've hit a wall dialing these in

[jamesfacts]

I've been struggling with dead spots in the throttle on my '76 CB550F, and I believe the issue lies in the A/F adjustment of the pilot jet. I have the adjust dialed in kinda close, but I can't seem to get it just right, and I hope someone will have a tip to help get me over the finish line.

Symptoms:
-Reluctant to start when cold, needs throttle opened to around 4k
-Good performance under wide open throttle, hesitation / bogging at 10-30% throttle. Particularly an issue in trying to maintain highway speeds
-High idle. It seems happiest idling ~1800, but it won't idle at all under 1500 rpm or so.

Setup:
-Stock 069a carbs, stock 4-1 exhaust, fresh Uni pod filters. Running stock 38 pilot jets (look perfectly clean to me, pulled them all out to inspect) and 110 main jet, which seems to be the consensus with pods at sea level.

I've fiddled quite a bit with the A/F screws, and they're definitely in a place where the bike runs worse when they're adjusted in either direction. Somewhat at a loss on how to adjust from here. I was thinking maybe I should get an IR thermometer and measure how hot each cylinder gets? Dial the A/F screws from there?

Or is this the symptom of something else? Float height incorrect, maybe?

 

[carnivorous chicken]

Have you checked your timing, synced your carbs, and adjusted your valves?

 

[jamesfacts]

Have you checked your timing, synced your carbs, and adjusted your valves?

Timing is good, carbs are vacuum synced close but not perfect. Carbs 2, 3, and 4 are nearly equal, carb 1 bounces around more than the other three and is difficult to get precisely where the other three are.

I have not checked valves, but I can't see how this is anything but a fuel issue. Runs very good at 30% throttle and higher, which is what leads me to suspect the pilot circuit.

 

[cxman]

i run 40 slows in mine with 105 mains 2nd notch 1.5 turns

 

[hillsy]

I have not checked valves, but I can't see how this is anything but a fuel issue. Runs very good at 30% throttle and higher, which is what leads me to suspect the pilot circuit.

It probably is carb related however tight valves will make your bike idle like crap - and this can affect the lower end running. You should always ensure your valve clearances are correct before you move to the carbs when you are trying to resolve running issues.

 

[crazypj]

I set the float height 1mm higher than stock and also dropped the needle one clip.
'traditionally' you would raise needle but I found it made bike run rich not much off idle

 

[jamesfacts]

i run 40 slows in mine with 105 mains 2nd notch 1.5 turns

Good info, thanks for posting!

It probably is carb related however tight valves will make your bike idle like crap - and this can affect the lower end running. You should always ensure your valve clearances are correct before you move to the carbs when you are trying to resolve running issues.

Yea, that's a probably a worthwhile avenue of investigation.

I set the float height 1mm higher than stock and also dropped the needle one clip.
'traditionally' you would raise needle but I found it made bike run rich not much off idle

Hmmm... I didn't think needle position would have much influence on low-end throttle. I can give it a shot.

 

[hillsy]

All the fuel circuits "overlap" into each other so adjusting the needle will affect idle to some extent.

 

[Jayowen]

when you cleaned carbs did you get the emulsion tubes out and clean them? when i did my 550 carbs i got everything spotless except i forgot the tubes. took them out and they were all clogged up. cleaned them and now it runs well

 

[jamesfacts]

All the fuel circuits "overlap" into each other so adjusting the needle will affect idle to some extent.

That's good to know, I can totally go back and mess around with them.

when you cleaned carbs did you get the emulsion tubes out and clean them? when i did my 550 carbs i got everything spotless except i forgot the tubes. took them out and they were all clogged up. cleaned them and now it runs well

Yep, I replaced the emulsion tubes, but there wasn't any sign of trouble with the ones I took out. ¯\_(ツ)_/¯

 

[crazypj]

re-setting float height has a larger effect and worked for me.
Bike went from a 25mpg - 110mph to a 42mpg-130 bike with same riding style (I did do a 591cc conversion at the same time though )

 

[jamesfacts]

re-setting float height has a larger effect and worked for me.
Bike went from a 25mpg - 110mph to a 42mpg-130 bike with same riding style (I did do a 591cc conversion at the same time though )

I'm getting pretty shitty mileage, too, around 25-28mpg. So, float stock height is 22m, to move the float higher I want to set it at 20-21mm?

PS—Did you once mention you had more than 100k on your CB550?

 

[crazypj]

set to 23mm,
21 is lower and give a higher fuel level causing rich running (and even worse gas mileage)
I messed with mine every coule of months for about 2 yrs before I got it right
Yes, I have over 106,000 on it. pretty damn tired so I 'retired' it until I can get around to a rebuild
For a long time I used the picture I took of it rolling up to 100,000 as an avatar.
It would barely do 100mph at the time, 70,000+ miles at ridiculous speeds and rpm took it's toll
I know I did more than 5,000 miles with broken speedo cable and then a broken speedo drive
plus the usual week or two waiting for new cable when it broke so I'm estimating at least 106,000, it could be higher
Broke at least 5 speedo cables over several years.
Fitting the dual disc must have done something to them as they usually last at least 50,000+ on most bikes

On the original print you can just make out the mileage
I took pic with Cosina CSR 35mm film camera hanging around my neck 8)

 

[brightrider]

i run 40 slows in mine with 105 mains 2nd notch 1.5 turns

I run exactly the same with no issues. It took me a lot of fiddling to land at this setup using trial and error...but that's where I ended up. On another 550 build I did later, I mirrored these settings from the start and that bike has run perfectly from Day 1. IMHO, rejetting is necessary when using pods on the 550. I also find that it is crucial to be certain that carbs are sync'd.

 

[cxman]

I run exactly the same with no issues. It took me a lot of fiddling to land at this setup using trial and error...but that's where I ended up. On another 550 build I did later, I mirrored these settings from the start and that bike has run perfectly from Day 1. IMHO, rejetting is necessary when using pods on the 550. I also find that it is crucial to be certain that carbs are sync'd.

its the best setup i have used on stock carbs with pods

but run a coil relay and make sure your timing and valves are correct