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Author Topic: CB550F stumble  (Read 574 times)

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Offline Tempast

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CB550F stumble
« on: July 16, 2014, 09:17:16 PM »
Hey guys so my '77 550F is a bit of a weird bike, when I brought it out this summer to ride it for the first time I knew there were going to be some issues.

First electrical, fuel pissing, float heights and general maintenance.

So when I roll from a light, letting off the clutch and giving it throttle it starts to gain speed (like 10 km/h) then the RPM drops for a second and I give it more throttle.
It's a really weird bog and has surprisingly always happened (with my plugged up Sankei 2005 replica stock muffler, with the muffler from a 3 cyl diesel light tower, don't ask, and now with my 12" shorty) 

It also stumbles at speed at certain throttle positions. From 1/4 to 1/3 it's fine, give it close to half and it stumbles, then 3/4 it gains RPM then goes like a bat out of hell.

I'd love to know what my RPM is doing but my tach doesn't read right. I've tried 3 different tachs and they all read the same. Got a new cable coming in soon and hopefully that fixes it. I've pulled the bottom part out of the valve cover and had a look, all the teeth look pretty good, but there is a small tight spot when spinning it. Hopefully that's not my issue.
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Offline Bankerdanny

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Re: CB550F stumble
« Reply #1 on: July 17, 2014, 09:33:59 AM »
I wonder if your clutch is not adjusted correctly or the cable is sticky. It slips a bit initially, then grabs, causing the bog in rev's.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Duanob

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Re: CB550F stumble
« Reply #2 on: July 17, 2014, 01:50:19 PM »
550 carbs man! Clean, clean and then clean them again.
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1976 CB550F2 Barn Find
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Offline Tempast

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Re: CB550F stumble
« Reply #3 on: July 17, 2014, 05:40:39 PM »
I'm thinking I need to mess with the jets (i have a unifilter and no backpressure muffler)
ill see if I can mess with the clutch. I adjusted it initially when I insured the bike this year


also the inside of these carbs should be very clean. I had them out multiple times when adjusting float height but I need to remove them again because it tends to piss fuel from the number 3 carb when I've pulled the throttle all the way.
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Offline Dr. Noisewater

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Re: CB550F stumble
« Reply #4 on: July 17, 2014, 10:42:21 PM »
Could be your condensers going out. I battled a weird stumble for awhile until one of my condensers totally failed. Very cheap fix.
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