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Author Topic: throttle return spring is weak  (Read 1232 times)

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Offline 78whiteorbs

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throttle return spring is weak
« on: July 14, 2015, 03:24:28 PM »
Cb750k8 motor and carbs on a frankenbike.
return spring is the clock wound type and it appears to be fully wound but with the cables removed from the throttle tube The throttle returns smooth but with less tension than I have ever encountered. Nothing is binding and action is smooth and unrestricted/un obstructed but return doesn't snap back like it is suppose to At the speed that I would say seems normal.
I added an extra spring and it now works perfect. Seems I read a post about this somewhere back eons ago but can't find it  now of course.

Any thoughts ? I thought initially maybe the spring wasn't wound tight enough but less splitting the rack I couldn't see how to get another revolution out of it . Doesn't look like it would be able to either but I have been fool plenty before.
I am still running a push cable with my extra Spring.
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Offline fmctm1sw

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Re: throttle return spring is weak
« Reply #1 on: July 15, 2015, 05:37:18 PM »
I had the opposite problem with my 550.  It was really hard to turn.  I ended up extending it a bit with a hook shaped piece of scrap I had laying around.  It's still pretty hard to turn but much better. 

How long has it been like that?  Did you have the carbs apart?  Can you shorten it a bit like some of us have done with the advancer springs?  Someone correct me if I'm wrong but I think you can get that spring on and off without splitting the carb racks...
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1973 CB350G
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Offline harisuluv

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Re: throttle return spring is weak
« Reply #2 on: July 15, 2015, 06:04:58 PM »
k8 you can't, it's around the throttle rod.  k7 it is external and attaches to the backplate. 

my first thought is if the stock spring isn't enough to close them, it's binding or sticking somewhere.
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Offline 78whiteorbs

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Re: throttle return spring is weak
« Reply #3 on: July 15, 2015, 07:53:10 PM »
Quote from: harisuluv on July 15, 2015, 06:04:58 PM
k8 you can't, it's around the throttle rod.  k7 it is external and attaches to the backplate. 

my first thought is if the stock spring isn't enough to close them, it's binding or sticking somewhere.

Around the rod.
stock spring closes them fine , just doesn't snap as fast as all the other CB750s I have had. Brand new cable with the push cable off and there aren't any obstructions , I eliminated all (throttle sleeve, housing, etc. ) this is pulling the cable manually, straight out with no bends in the sheathing anywhere. Slides aren't sticking and the action is smooth as silk just weakened.

Before I pulled the engine and carbs for a frame swap IIRC correctly the action was nothing out of the ordinary.
engine ran fine and carbs just had clogged accelerator circuits .The throttle was fine. Works fine with the extra spring but I dislike the shade tree mechanics when I know it isn't necassary  with proper fixing.
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Offline flybox1

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Re: throttle return spring is weak
« Reply #4 on: July 16, 2015, 08:59:03 AM »
does the snap improve at all with no cables attached?

my PD's slides return with guillotine-like force  :o ;D
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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"Knowledge without mileage equals bullsh!t" - Henry Rollins

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Offline 78whiteorbs

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Re: throttle return spring is weak
« Reply #5 on: July 16, 2015, 09:07:30 AM »
Quote from: flybox1 on July 16, 2015, 08:59:03 AM
does the snap improve at all with no cables attached?

my PD's slides return with guillotine-like force  :o ;D


Nope, cables same thing. I didn't split the rack or anything when I cleaned em either so beats me. That's what I am looking g for is the guillotine force . It seems that they were that way before but I wasn't to picky with the fine tuning as I just wanted to hear the engine run on all fours before swapping  frames for the build. May have been this way all along and it just didn't make the radar.
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Offline flybox1

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Re: throttle return spring is weak
« Reply #6 on: July 16, 2015, 09:21:47 AM »
if you havent cleaned them really well beforehand, there may be debris slowing or preventing turning ease of the throttle bell.
get an old towel between the carbs and the engine case.  spray down the carbs bodies, throttle mech. between 2&3, and springs with carb cleaner, especially where the throttle shaft enters each carb body.  a little wd40 spritz at these spots might help decrease the resistance....
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline 78whiteorbs

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Re: throttle return spring is weak
« Reply #7 on: July 16, 2015, 09:29:10 AM »
Quote from: flybox1 on July 16, 2015, 09:21:47 AM
if you havent cleaned them really well beforehand, there may be debris slowing or preventing turning ease of the throttle bell.
get an old towel between the carbs and the engine case.  spray down the carbs bodies, throttle mech. between 2&3, and springs with carb cleaner, especially where the throttle shaft enters each carb body.  a little wd40 spritz at these spots might help decrease the resistance....

 Tried all that
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Offline flybox1

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Re: throttle return spring is weak
« Reply #8 on: July 16, 2015, 09:33:13 AM »
post up a picture of the return spring pls
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline 78whiteorbs

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Re: throttle return spring is weak
« Reply #9 on: July 18, 2015, 07:12:12 AM »
Solved! The number 1 cylinder side of the spring had moved out of where it should be by about 180 degrees. So it was indeed a weak spring from under tension. Moved it back removed my hack and all is well!
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