Carb return spring on '77 CB550F

[alexdecker]

Hey all

I got a throttle that is not returning fully. I inspected cables, throttle pipe etc. all with no problems. When I disconnect the cables from the carb, the carb still doesn't return fully to the idle screw stop. This makes me think that the return spring is the problem. If I open the throttle fully, it will snap fully back. But if I only open it 1/3, it will not snap all the way back.

My question is: Is there anything else that could cause this? Is there some screw I can have tightened too much in the carb rebuild, that will hinder the spring in doing its work? Could something else bind, or maybe a third thing? Most people on the forums says that its very unlikely that the spring is faulty. Although it does seem like that would be the exact problem in this case, I just wanna make sure there is nothing else Im missing, before I go looking for a replacement.

- Alex

[Bryanj]

More likely the shaft is tight in the bushings

[Robert W]

Did you re-synchronize the carbs with the idle adjustment screw turned in a lot? This will affect the carbs returning to the stop screw when the spring return doesn't have enough snap to go into the over ride.

[alexdecker]

More likely the shaft is tight in the bushings

Can you put a few more words on it? Was looking at the parts lists on CMS, but not completely sure what parts you are talking about.

[alexdecker]

Did you re-synchronize the carbs with the idle adjustment screw turned in a lot? This will affect the carbs returning to the stop screw when the spring return doesn't have enough snap to go into the over ride.

I didn't, and it sits in a really nice spot. Wish it was that simple though - would make for less of a headache

[Oddjob]

The return spring on those carbs is very strong, too strong, some would say. Remove the spring and move the butterfly by hand, if smooth it’s the spring if not then it’s something like a bent needle for instance

[Johnwebley]

Does it have a "closer " cable?

And will that fully close the carbs

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[McCabe-Thiele (Ted)]

If you press down on one of the 4 brass caps in the linkage does that shut the throttle?

Might be worth checking each in turn ?

[Bryanj]

The shaft i mean is the one that runs accross the mounting bracket and is not available seperate nor the bushes in the bracket that the shaft turns in.

If somebody in the past has tried to remove the shaft without drilling out the locking pins it damages the bushes

[alexdecker]

Thanks for all the replies guys!

 The carbs does have a "push" cable, and when I reverse throttle, the carb closes all the way. Also when I push the brass caps, the carb closes all the way. Also, I hope its not the shaft and bushings. This is a fairly new problem, and last season, the carbs closed fine (after I restored them), but this season all of a sudden they are hanging a bit.

I will test the spring as Oddjob is suggesting and go from there. Update will follow.

[neat street]

Also check if the carbs are `gummed up` this can also stop them from returning fully?

[McCabe-Thiele (Ted)]

Thanks for all the replies guys!

Also when I push the brass caps, the carb closes all the way.  This is a fairly new problem, and last season, the carbs closed fine (after I restored them), but this season all of a sudden they are hanging a bit.

If pushing on the brass caps closed the Carbs that might indicate an issue with the bench sync assuming all bits under the cap (springs & plungers) are fitted correctly .

Not that it's a problem, do the threads above the lock nuts look reasonably even?

As you may know there is a pretty detailed  thread on hanging throttle issues.

[alexdecker]

Hey Ted!

Did a search but can't find that thread! Is it on here or somewhere else?

- Alex

[McCabe-Thiele (Ted)]

One thread in Anoraks Corner started by K2-K6 on first page, zCarbs an on depth discussion,
another under tricks and tips started by Bryan, basic bench sync carbd

[alexdecker]

The return spring on those carbs is very strong, too strong, some would say. Remove the spring and move the butterfly by hand, if smooth it’s the spring if not then it’s something like a bent needle for instance

How smooth is it supposed to be? With the spring off, I can move it up and down manually, and it doesn't seem like it is hitting any resistance, but it's not like it's feather lite either. Just with a normal amount of resistance I guess.

With the spring on, I can still move it just with my fingers, which makes me think that I might actually have a weak spring?

- Alex