Topic: Cb550 carb question

[P.abrera]

Goin over my carbs for my 76 cb550. Is there supposed to be a hose linking 1/2 and 3/4? Whats the purpose of these outlets?

[DaveBarbier]

Yes, a black rubber hose connecting the two pairs. That's an air vent so all the bowls can be at atmospheric pressure while the bike is sucking up fuel. They could be open like that and function the same but highly likely that little critters and debris can make it's way in. I bet you could get the hoses on without breaking the rack apart.

There should also be a nipple (to where those little hoses vent to) with a hose attached that gets routed behind the carbs and ultimately between the engine and swingarm down by the center stand.


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1978 Honda CB550K

[P.abrera]

Thanks dave.

Darn, was hoping the lack of the connecting hose might be a major contributor to my rough running. Guess theres no easy fix for getting the tuning right on these


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[DaveBarbier]

Can you describe the rough running? Is your bike stock or do you have intake/exhaust mods? If that's the case what size jets do you have?


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1978 Honda CB550K

[P.abrera]

Im in the process of carb tuning. Will clear tube to double check float levels and even flow before pulling the carbs to re-confirm jet #'s. Its on 2nd notch from top of the needles and and about 2 1/2 turns on the mix screws. Digging up my notes and pics to reconfirm but if memory serves theyre 38/100. 

Running the cruzinimage 3mm overbore with a baffled 12" shorty. It starts ok, with choke but is slow to react to revs and likes the choke and feathered throttle to maintain idle. Seems very lean. Cylinder 1 has gone cold since my last test run around the block. Theres good spark coming off the coils/wire to # 1 and I've tried swapping plugs to no avail, so it must be some kind of fuel delivery issue. Hoping for some time this week to tinker. Confident a vacuum synch will help a lot.


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[P.abrera]

Solid advice advice, as always, Cal im running the airbox but the filter is open to the elements...btw, what do those nipples look like? 

...oh boy, i get the feeling im not gona get the kinda answers im looking for with that question


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[streak09]

I'm going to take the high road and post a picture of the nipples you are looking for... well at least I think these are the ones you are looking for, this wouldn't be my first choice site for the other type  .

[P.abrera]

I'm going to take the high road and post a picture of the nipples you are looking for... well at least I think these are the ones you are looking for, this wouldn't be my first choice site for the other type  .

Nice nipples you have there
So theres just a tube between 1/2 and 3/4? And a nipple at either end 2 and 3?


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[mrfish2]

So theres just a tube between 1/2 and 3/4? And a nipple at either end 2 and 3?

Yep, that's basically all there is to it. The nipples circled in the photo should have tubes running from them to just under the airbox.

[P.abrera]

Where are you guys sourcing jet kits for the 550 carbs? Im assuming i need to try bigger mains with the big bore kit and all? It likes the choke to maintain idle too., bigger slows?


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[DaveBarbier]

PD46c slow jets aren't available from Keihin. You'll have to go aftermarket.


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1978 Honda CB550K

[P.abrera]

Where are you guys sourcing jet kits for the 550 carbs? Im assuming i need to try bigger mains with the big bore kit and all? It likes the choke to maintain idle too., bigger slows?


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Slow jets effect idle, not mains. Jetsrus or Sirius are 2 recommended vendors for Keihin brass.

You shouldn't be struggling for idle too badly, especially with the stock airbox. I'd make sure your fuel level is dead on (measure your float, then confirm with clear tube method), maybe adjust the mixture screw or needle clip position.

After the bike is warmed up, and you're running it, how does it behave? There's lots of variables for getting the state of tune right that have nothing to do with jets. Just saying-

Will pull the carbs next weekend and re-measure float settings (22mm) and clear tube to reconfirm 3-4 mm below bowl seam. Need to get a hold of a vacuum synch rig.


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[P.abrera]

YOU need to make one. Search "DIY manometer". Dang, you scrap together enough pieces and parts, and with talent and ingenuity you build a really great bike. Then you want to buy a vacuum gauge? You're kidding me, right!

Haha i actually have access to one at a buddies shop across town, just need to get around to getting out there. But a DIY does sound like fun. will report my findings.


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[P.abrera]

Cleared a fuel delivery problem in #1 and went over my float settings again (22mm) and bench synched with a 3 mm drill bit. Clear tube check shows im off though. #1 at 8mm below bowl lip. # 2 at 7mm. #3 at 7 mm, and #4 at 5 mm. And now ive got a leak at the fuel-T o-rings into 1 &2 from pulling them apart and cleaning . Back to the drawing board...


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[Deltarider]

 

And now ive got a leak at the fuel-T o-rings into 1 &2 from pulling them apart and cleaning .

That's why I always advice not to separate them. Cleaning? Please have a look at your carbs after a few rides. They'll be as dirty as before. For maintenance separating is not needed. There is not a manual that recommends it. On the contrary. It's overkill and you only make things difficult.

[P.abrera]

Agree. I avoided it first time i "cleaned" but fuel stopped flowing into #1 after initial startup/test run and separating the rack became necessary to replace the cruddy/brittle fuel lines.


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[P.abrera]

4 mm below bowl top. Thats more like it. New o-rings on the fuel-T solved the fuel leak and hopefully the new fuel lines lines stay gunk free for a while. Moving on to the pesky cam chain tensioner screw now...


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