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Author Topic: 74 CB550K0 idles, wont rev, coughs and sputters, little power  (Read 1372 times)

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Offline MarkP

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74 CB550K0 idles, wont rev, coughs and sputters, little power
« on: January 29, 2012, 02:11:55 PM »
Bought this bike a month ago, has 4 into 1 header and pods.  Had 38 slow and 110 main jets.  Replaced with 40 slow and 120 main jets.  Bike still acts the same.  Removed all but 1 plug (near tach cable) and they were gapped too large, regapped to recommended specs.  Plugs are black and a little wet, that was after trying to get the bike started.  All pipes seem hot.  Trying to decide if I need to go to 130 main jets or back to 100 stock.  Any other ideas before I drag this bike into the shop????

Thanks.  Mark
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Offline cmonSTART

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #1 on: January 29, 2012, 02:25:23 PM »
Have you verified the ignition system and advance are working properly?
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Offline scunny

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #2 on: January 29, 2012, 02:30:33 PM »
carbs may need a cleaning as well.
start off with the regular tune up and go from there.
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Offline TwoTired

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #3 on: January 29, 2012, 04:34:28 PM »
What settings are the air bleed screws and the slide needles?

Who did the previous carb work?

And, what else has been changed in them since it was stock?
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Offline BeSeeingYou

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #4 on: January 29, 2012, 04:36:19 PM »
Quote from: scunny on January 29, 2012, 02:30:33 PM
carbs may need a cleaning as well.
start off with the regular tune up and go from there.

I would start there too.  Sounds like it could be a restricted fuel flow.  Any inline filters in place?  Tank clean? Proper fuel level in the carbs?  Did the bike run for the PO and had it been sitting a length of time causing gas to evaporate and gum up the system?
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Offline bender01

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #5 on: January 29, 2012, 06:52:04 PM »
Is your battery good and strong?
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So, the strategy is to lie to people you are asking for help?

I think I'll be busy going for a ride.

Good luck!
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Offline Dimitri13

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #6 on: January 30, 2012, 02:10:58 PM »
I'm surprised no one has mentioned it (especially TT), but go back to stock air setup (I hope the bike came with the airbox and such), adjust everything to stock settings, and make sure it runs properly then. If any only if it does, should you consider upgrading to pod filters (which is not recommended with the stock carbs).
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Offline Bankerdanny

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #7 on: January 30, 2012, 02:57:43 PM »
When I had a similar issue with my 550 it wasn't carb related. For no apparent reason it was losing power, it would backfire and shoot flame out of one of the mufflers and the fuel mileage had dropped to like 15mpg.

It turned out when I was setting the points I had neglected to tighten the nut that connects the condenser to the 1-4 points. It vibrated loose and was causing it to randomly lose spark at two cylinders.

On the Rely Ride SeanBarney had a similar problem. Tightening the nut on the points helped at first, but eventually, once we had limped to my home we had to swap my ignition system to his bike one part at a time until it ran right. In the end it turned out to be bad condensers.

So I would recommend that you give your ignition system a thorough look see and check all the wiring connections to the points and coils.
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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 MarkP

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #8 on: February 05, 2012, 08:03:45 AM »
Currently verifying the compression and timing.  Bike did sit for a while so gas may be an issue.  Will check the condesor/points connection.  2 fuel filters, seem to flow OK.  I took the carbs apart, did not mess with the slide needles, are thos the long ones inside the carb?  Air screws turned out 1.5 turns.  Unfortunatley no stock air box so I am stuck fixing the way it is.  Thanks for the inputs, will let you know how it goes.
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Offline MarkP

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Re: 74 CB550K0 idles, wont rev, coughs and sputters, little power
« Reply #9 on: February 14, 2012, 04:45:06 PM »
Turned out that the advance was not working properly, due to missing condensers.  Ran on the dyno today, thanks for all the inputs.
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