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Author Topic: cb550F 1977 rev problem  (Read 1074 times)

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Offline emilios

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cb550F 1977 rev problem
« on: May 16, 2009, 11:45:03 AM »
Hi guys
Im trying to solve a problem on this cb550F 1977(friends bike)..
Engine start easy and revs ok at 1000 rpm but when i open throttle up to 4000 or 5000 rpm and leave it back it stays at 3000 rpm...it doesnt fell back to 1000rpm unless i unscrew the trhottle bolt(the one on carbs stay that drops or lift rpms)...
I know that first thought is sticking cables but i try with out cables connected and i had the same result...
Any thougths?
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Offline 05c50

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Re: cb550F 1977 rev problem
« Reply #1 on: May 16, 2009, 12:57:50 PM »
Vacuum leak at the carb boots, carbs way out of sync,throttle valve sticking?

...........Paul
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Wear a helmet,the life you save may be your own.Ask me how I know.               CB650C,CB550F,GL1000,CB750A

Offline cb750fbomb

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Re: cb550F 1977 rev problem
« Reply #2 on: May 16, 2009, 01:05:02 PM »
The throttle sleeves could have crap between them and the carb body. I had that problem and the action of the throttle snapping back was for sh!t. I pulled the sleeves, cleaned the outsides of them and cleaned the area they slide in. Pull the cables and lube them up good too.
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Offline emilios

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Re: cb550F 1977 rev problem
« Reply #3 on: May 16, 2009, 01:09:20 PM »
The first thing i did was to synch carbs...but i still have the problem...
If were air leaks from boots i think i would have the problem every time i open throttle but i dont...
So throttle valve is the problem? how i can solve that?
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Offline Noco

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Re: cb550F 1977 rev problem
« Reply #4 on: May 17, 2009, 06:24:13 AM »
i had the same problem, but it cleared up when i added more free play to the throttle cable.

could the return spring be gummed up, or jamming against the small set-screw (that adjusts full-stop position) on the back of the carbs?
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Offline Brian G

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Re: cb550F 1977 rev problem
« Reply #5 on: May 17, 2009, 07:48:39 AM »
Coming at the problem from a different angle.....

At the fast idle speed and the brake on, try putting it in gear then slowly let out the clutch until the engine speed drops. If, when you pull in the clutch again, the speed stays at the proper idle speed, it may be the ignition advance unit is sticking in the full advanced position. If it speeds up again then it's probably the carbs.

Hth,
Brian
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Offline cb750fbomb

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Re: cb550F 1977 rev problem
« Reply #6 on: May 17, 2009, 10:52:28 AM »
Quote from: Brian G on May 17, 2009, 07:48:39 AM
Coming at the problem from a different angle.....

At the fast idle speed and the brake on, try putting it in gear then slowly let out the clutch until the engine speed drops. If, when you pull in the clutch again, the speed stays at the proper idle speed, it may be the ignition advance unit is sticking in the full advanced position. If it speeds up again then it's probably the carbs.

Hth,
Brian
That's a good one. I need to remember that. I just pulled and lubed my advance mechanism in the appropriate places.
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'77 CB750F2
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Offline emilios

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Re: cb550F 1977 rev problem
« Reply #7 on: May 18, 2009, 06:31:21 AM »
Quote from: Brian G on May 17, 2009, 07:48:39 AM
Coming at the problem from a different angle.....

At the fast idle speed and the brake on, try putting it in gear then slowly let out the clutch until the engine speed drops. If, when you pull in the clutch again, the speed stays at the proper idle speed, it may be the ignition advance unit is sticking in the full advanced position. If it speeds up again then it's probably the carbs.

Hth,
Brian
Thanks for the advice..i will check that tomorrow...
just a question...ignition advance unit is that thing with 2 springs behind points plate?also if thats the problem i have to change it or can i fix it?
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Offline emilios

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Re: cb550F 1977 rev problem
« Reply #8 on: May 19, 2009, 10:21:49 AM »
Today i start bike and open throttle..after i leave it back and rpm stay at 3000 i put gear and leave clutch slowly....revs fell...i pull clutch again...revs stay slow at 1000rpm....So i lube advance mechanism but it didnt do anything....
I start engine again and leave revs at 3000rpm and check carbs...when i push down this big nuts with springs inside,where shaft arms hold carbs,revs fell only at carb number 2..i mean when i push down number 2 carb nut...
So i have to open carbs?
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Offline Noco

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Re: cb550F 1977 rev problem
« Reply #9 on: May 19, 2009, 10:46:11 AM »
i would make sure that something wasn't sticking (throttle pipe gummed up on bars, cables dry or binding, or missadjusted). before opening the carbs, but maybe cb750fbomb is right about the slides being gummed up
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