Cb550 Carb help

T

TowelThief

New Member
I have a 1978 CB 550 that I bought in 2010. I've never had the time to fully commit to the build until now but the building is already done. It's been at 3 shops in 6 years getting everything worked on. Engine was basically rebuilt, honed/bored, new gaskets in Oct 2012 it set until 2014 with no oil in it. In Nov 2014 due to my job I was away from home so I gave the bike to a guy to finish electrical and carb work. He did. It runs. I picked it up March 2016.

The tank is off a 75 or 76. Has the 20mm bung. The carbs are also off a 76' (087A keihin). I have tapered velocity stacks on it as well

It idles at 3k rpm. When I mess with the idle screw I can get it down to 1k but it sounds horrible like shits knocking around in the engine and it will die if I don't give it throttle. Could this be a synch issue?

It pops when idling and recently I have seen carb 1 pop out of the stack.

When I ride it and go through the gears it kind of bogs down on initial shift when letting out the clutch the eventually comes up in RPM and rides and sounds really well. There's just no power on the shift with about a 1/4 turn on throttle. And it's really annoying when I'm down shifting for a stop and the rpm shoots right back up really fast like there's no engine braking.

My air/fuel screws are about 2 turns out on each.

Just need some guidance here. I know carbs are finiky on these bikes and I really want her to run well. I'm going on a trip in 2 weeks to Tenneessee. Oil is leaking from the pan I think it's a gasket issue but it's not a major leak, probably from sitting all that time.
 
Main Jet is a 115
Idle Jet 38
Jet Needle 4th clip

(i didnt rebuild these carbs but guessing those jets are a weird combination if stock is a 100 and 38)

I put the air/fuel screws at about a 3/4 turn out and it helped....no more popping unless I full throttle and let off in higher gear sometimes.

Decent Idle at 1400rpm but when i give it a blip it will hang around 2.5-2 before coming down. It also hangs around 2.5-2k when I am in gear and stopped at say a stop sign.

The bogging when changing gears at low speed is better also.
 
Hi mate ive got similar set up got velocity stacks but a four into four slight baffled exhausts went with 120 main 42 idle 1 &1/4 turn out seems ok what exhaust are you running ?
 
yorkie350 said:
Hi mate ive got similar set up got velocity stacks but a four into four slight baffled exhausts went with 120 main 42 idle 1 &1/4 turn out seems ok what exhaust are you running ?
Click to expand...
Its the stock 4 to 1 with a custom sleeve.
 
got it to idle at 1300-1400 rpm and not hang when i blip the throttle but after a while it still wants to die......the screws are seated.

Does this mean increase slow jet size?
 
you could try going up to next size on slow jet,/ how are your plugs lookin check to see if there sooting up or wet (too rich) or light brown / white (too lean ) sounds like your getting enough fuel so shouldn't be a starving problem are you running points or electric ignition
 
you can get them from jetsRus there based in the states sound like it could be running a bit lean if you scroll thru the engine section on the forum page you can find more info on carbs n jets etc, lot more info than I got mate sometimes getting carbs n bike running perfect when you got stacks or cone filters is like being in the magic circle haha but it can be done keep posting ya progress mate sure we can cure it ;)
 
I found higher needle position worked better, 2 or 3 from top
120+ mains are great for open exhuast when racing but bike runs rich at cruising speeds 'in the real world'
Check 'O' rings in manifold to head are good plus the carb rubber to manifold.
Adding some support to rear of carbs also helps as they will sag which increases fuel level and makes bike run rich. Set float level to max or even +1mm
 
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