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Author Topic: 1977 CB750 Choke Won't Close  (Read 852 times)

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Offline Runningdog

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1977 CB750 Choke Won't Close
« on: January 17, 2022, 10:09:15 AM »
I have cleaned and reassembled the carbs on my 1977 CB750K.  Assembly of all parts appears correct, as most parts only go in one way.  However, when the choke control is pulled up (by hand or by cable), the butterflies do not close.

If I operate the #3 and #4 butterflies by hand, all four close, but if I operate the #1 and #2 butterflies, only those two close.

Hopefully, the photos show the linkage assembly well enough.

I miss Frank.

« Last Edit: January 17, 2022, 10:28:54 AM by Runningdog »
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Offline madmtnmotors

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Re: 1977 CB750 Choke Won't Close
« Reply #1 on: January 17, 2022, 11:00:04 AM »
The 77/78 PD carbs use choke linkage that is not "direct drive" but use coiled spring connections. If there is any misalignment of the choke plates that cause any kind of drag the spring(s) will not close the choke plates. Move the plates manually while looking/feeling for any kind of drag/resistance. On some PD carb rebuilds I have had to loosen one or more choke plates and retighten in order to eliminate interference due to a slight misalignment. It doesn't take much...
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TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Runningdog

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Re: 1977 CB750 Choke Won't Close
« Reply #2 on: January 17, 2022, 11:33:59 AM »
Thanks MMM....I thought that's kinda what it looked like was supposed to happen, I'll get a man on that.

Modified this message minutes later, a bit of loosening and retightening a couple of butterfly screws solved the problem.....easy...thanks.
« Last Edit: January 17, 2022, 11:41:45 AM by Runningdog »
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Offline madmtnmotors

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Re: 1977 CB750 Choke Won't Close
« Reply #3 on: January 18, 2022, 04:46:38 AM »
Cool, glad you were able to get it sorted. I've gotten pretty good at carbs but I still don't like working on them!
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TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline BeaverBike

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Re: 1977 CB750 Choke Won't Close
« Reply #4 on: October 12, 2022, 10:36:26 AM »
Hey guys,

I am glad I found this post.  I'm having a very similar, if not the exact same, issue.  #3 and #4 choke plates don't fully open.  Feels like this is due to spring tension.  When simulating engaging the choke cable, #3 and #4 fully close, but not #1 and #2. 





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1977 CB750

Offline BeaverBike

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Re: 1977 CB750 Choke Won't Close
« Reply #5 on: October 12, 2022, 10:40:00 AM »
Photos are worth a thousand words, right?
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1977 CB750

Offline denward17

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Re: 1977 CB750 Choke Won't Close
« Reply #6 on: October 12, 2022, 12:17:15 PM »
Quote from: BeaverBike on October 12, 2022, 10:40:00 AM
Photos are worth a thousand words, right?

Linkage on 2-3 is not connected correctly to 1-2....Tab on 2-3 is bent up and over tab for 1-2...

See this thread....

http://forums.sohc4.net/index.php/topic,100352.75.html
post #80
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Offline BeaverBike

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Re: 1977 CB750 Choke Won't Close
« Reply #7 on: October 12, 2022, 12:33:39 PM »
@denward

Good eye!  I completely missed that.  Man... I wonder how that tab got bent.  Thank you, sir!
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1977 CB750
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