Topic: Keihin 069A throttle slide and choke tuning (CB550F)

[lymbic]

Bike has been running very rich since I got it. I am running as close to stock as possible - 38 pilot and 98 main, stock airbox, 4-1 exhaust, but I am
currently missing the muffler. To cover all of the basics, I have replaced the old air filter and foam in the case with new ones as close to original as possible, new exhaust gaskets, cleaned all jets (had to replace two out of four pilots), cleansed float needle to get good spring back, set float height to 22mm, replaced spark plug caps with NGK 5 kOhm, new spark plugs gapped to .026”, intake valves to .002”, exhaust valves to .003”, points timed with test light, replaced petcock with repro that has 1 outlet instead of two, routed fuel line as down hill as possible with 1/4” brass tee near center of 2-3 carbs, fixed intake leaks where boots meet airbox on 1 and 4, fixed exhaust leaks on 2 and 4 after replacing gaskets by torquing nuts evenly, I’m sure I had other intake leaks at breather tubes considering I just realized they both were rotted out pretty badly.

Compression is low for now since the bike sat since 81, but I’m trying to get it running decent to break it back in and hopefully loosen any buildup on the piston rings.

I need to replace o rings while I have the carbs out of the bike again, and I’m pretty sure I had a blockage in the vacuum passageway for 1-2 carbs, but Im looking to bench tune the throttle slide heights and choke settings for now. #1 carb throttle slide height is visibly lower than 2, 3, 4. And #4 choke setting is higher than the rest. Any tips on setting these close to stock on the bench before putting them on the bike and dialing with the motion pro?




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[Clinto]

From looking at the pictures, they look pretty close to me. You adjust slide height for individual carbs by the adjuster screws on the top of the carb rack. From the carb faq:

"When I rebuild a set of carbs, I always bench sync them before I re-intall them. Basically, I use a 1/8" drill bit as a gage. Here's how you do it: Adjust the idle screw (the main one) until the 1 carb outside of it is open enough to just let the 1/8" drill bit through. Then adjust the sync screws on the other 3 carbs until the drill bit just fits them as well. You'll probably want to close the idle screw before you bolt them back on the bike, 1/8" openeing is pretty big. This isn't a perfect sync, as there are other things that will affect the airflow to a given cylinder, but it will get you pretty close."

[lymbic]

From looking at the pictures, they look pretty close to me. You adjust slide height for individual carbs by the adjuster screws on the top of the carb rack. From the carb faq:

"When I rebuild a set of carbs, I always bench sync them before I re-intall them. Basically, I use a 1/8" drill bit as a gage. Here's how you do it: Adjust the idle screw (the main one) until the 1 carb outside of it is open enough to just let the 1/8" drill bit through. Then adjust the sync screws on the other 3 carbs until the drill bit just fits them as well. You'll probably want to close the idle screw before you bolt them back on the bike, 1/8" openeing is pretty big. This isn't a perfect sync, as there are other things that will affect the airflow to a given cylinder, but it will get you pretty close."

Making it simple, thank you. As far as the choke, I assume this is much less important and I can just eyeball

[TwoTired]

Clinto's reported procedure will not always work well, as it does not allow for proper slide travel.  An eighth inch drill bit won't ensure that the slide can travel to the bore floor.  This allows all the slides to be adjusted and skewed so that the big idle knob can't properly position for idle speed.

Pick a carb to be master, back out the idle knob and ensure that the master's slide can reach all the way to the bore floor.  Adjust, if necessary.  Lock that adjustment down and never touch that adjustment again.  Now you can use the idle knob to lift the master's slide for your drill bit fit.  And without moving the idle knob, adjust the non master carbs to the same setting as the master.  This will allow you to set idle speed as desired later on with the idle knob.

Just remember never to mess with the "master carb" adjustments again, especially when doing the vacuum sync. Adjust the other carbs to the vacuum level of the master.

Cheers,

[Bankerdanny]

Use the drill bit method to get your baseline, but unless you plan to run without a muffler all the time then fine tuning it without one is not particularly helpful. Also make sure your air filter setup is the one you plan to use. The settings that are best with open header and no filter aren't the ones that will be best with both in place.

For the choke butterfly just make sure they are all closed when the choke arm is raised. You have to adjust them in order from left (#1) to right (#4)

[lymbic]

Clinto's reported procedure will not always work well, as it does not allow for proper slide travel.  An eighth inch drill bit won't ensure that the slide can travel to the bore floor.  This allows all the slides to be adjusted and skewed so that the big idle knob can't properly position for idle speed.

Pick a carb to be master, back out the idle knob and ensure that the master's slide can reach all the way to the bore floor.  Adjust, if necessary.  Lock that adjustment down and never touch that adjustment again.  Now you can use the idle knob to lift the master's slide for your drill bit fit.  And without moving the idle knob, adjust the non master carbs to the same setting as the master.  This will allow you to set idle speed as desired later on with the idle knob.

Just remember never to mess with the "master carb" adjustments again, especially when doing the vacuum sync. Adjust the other carbs to the vacuum level of the master.

Cheers,

TwoTired, will the needle be visible at all when the slide is at the bottom of the bore floor? Right now if I back the idle screw all the way out, all of the slides are only slightly lower than originally pictured when looking down the intake side. No gap left in the exhaust side

[TwoTired]

The slide bottom has a "cutaway" where one side is cut at an angle.  This cutaway is in the inlet side or filter side.  It will not ever reach the bore floor.  The engine side of the carb slide will reach the bore floor.

I don't bother with drill bits.  I use a light bulb or small flashlight at the far end.  When the light shuts off during master adjust, the slide is at bottom of travel.  Doesn't matter which end of the carb bore you look at.   I also adjust the others in the same way during a bench sync.  However, during a vacuum sync, never adjust a "master" carb's slide travel and you won't get issues with the idle knob not allowing a low enough idle speed.

Cheers,