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Author Topic: 750K4 - Removing carbs for the first time. Any words of advice for a novice?  (Read 227 times)

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Offline djwillard18

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A significant gas leak appeared the last time I attempted to ride to work. After a little poking around I believe the leak is at the T-inlet on the left pair. After doing some forum-research, I think it is probably the O-rings on both sides of this piece.


I've never removed the rack of carbs before and want to reduce my odds of messing anything up.


(1)  How should I approach this?
(2)  Tips/tricks and things I should never do.
(3)  Other than replacing these O-rings, what should I think about doing while they're off?


Thanks in advance for your time and sharing your knowledge!

'74 CB750K4 (current)

'81 650 Maxim
'80 XS11

Offline MauiK3

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Remove the tank and air box
Drain the bowls
Try to mark the rotation of the “insulators”, the rubber connectors between the carbs and head.
Note the routing of all the lines, photos help. Note how the fuel lines go from the peacock to each pair of carbs, don’t ask why I say this.
If your band clamps are in bad shape plan on replacing them, this goes for the insulators too, if they are stiff it will be hard to get them to seal and drive you nuts.
If the fuel lines are stiff  ( 5.5mm, Black Honda is the best) and old, plan on getting new ones.
Disconnect the cables. Note routing.
Rock the carbs off the rubber insulators
After you have them on the bench, it’s all you.
Might be a good time to look inside each carb.
If you have an ultrasonic cleaner and some 50-50 simple green and water a good cleaning will be great.
I’m sure I missed some things here.
1973 CB 750 K3
2009 Ruckus!

Offline djwillard18

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Thank you, MauiK3.  Just need to make some time and space to work on this. Have to order some supplies, too.

Sent from my SM-G930V using Tapatalk

'74 CB750K4 (current)

'81 650 Maxim
'80 XS11

Offline ekpent

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 Have a heat gun handy and warm up the rubber manifolds until the are hot and supple and soft as a babies behind  ;) A little grease or such and heat will help on the install also. Looks for some 8mm x 2mm rings for the fuel tees.You need 8 pcs to do both. New fuel line is a good idea while they are off also. Do not fiddle with the synch adjuster nuts when breaking down the rack,no need to. Its all a pretty easy project.
 +1 on replacing those clamps if they have stretched a little and the old rubber has shrunk.
« Last Edit: October 09, 2018, 05:16:38 am by ekpent »

Offline flybox1

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Just a general cleaning and spray/through of all jets and passages.
The best thing for your carbs is the OEM Keihin brass parts (if you are retaining stock configuration).  Jets, needles, and emulsion tubes.
No need to throw them out if they are dirty or slightly scuffed from your bikes PO....they're still good.
Check that they are clean and clear thru, and put them back in.
The stuff they sell in cheap kits just isnt as good as it needs to be...
'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 Johnie

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You said you are a novice...those sync adjusters ekpent is talking about are the nuts that are over the arm on top of each carb. If you turn those you have to sync the carbs all over again. Once you take the philips screws out from the back of the rack the carb arms will slide right off. Good luck and hit us up with more questions...it's really quite simple and you will find that out after your first time. Make sure you change those o-rings in both fuel T's. I get mine from NAPA part number 727-2605.
« Last Edit: October 09, 2018, 05:57:13 am by Johnie »
1969 CB750K0 - Candy Blue Green
1970 CB750K0 - Candy Ruby Red
1970 CB750K1 - Candy Gold
1973 CB750K3 - Candy Bacchus Olive
1974 CB750K4 - Flake Sunrise Orange
2000 1500 SE Wing
1971 CB750K1 (next project)
1969 CB750K0 (The Patina Bike - Blue / Green)

Oshkosh, WI  USA

Offline djwillard18

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Thanks, Johnie, flybox1 and ekpent.


Yes, I am a novice, so all tips are appreciated!  The NAPA part number is a great help.


Probably tackle the tear-down Sunday after I get a heat gun.
'74 CB750K4 (current)

'81 650 Maxim
'80 XS11

Offline Progas

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Replace the intake manifolds while you have the carbs off, you'll be way ahead of the game.

Offline evanphi

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Yeah if those rubbers are stiff buy new ones. Go with original Honda (still available!) The aftermarket ones fall apart quickly.
--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline djwillard18

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Do you think this deal is too good to be true?  Four Genuine Honda manifolds (insulators), with 8 clamps for $65.


https://www.ebay.com/itm/Genuine-Honda-CB750-Intake-Insulators-Carb-Holder-w-Clamps-K-71-76-F-75-76/192606997978?hash=item2cd8458dda:g:WAgAAOSw44BYE7Yz:rk:12:pf:0



'74 CB750K4 (current)

'81 650 Maxim
'80 XS11

Offline Johnie

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Heat gun = a hair dryer.
1969 CB750K0 - Candy Blue Green
1970 CB750K0 - Candy Ruby Red
1970 CB750K1 - Candy Gold
1973 CB750K3 - Candy Bacchus Olive
1974 CB750K4 - Flake Sunrise Orange
2000 1500 SE Wing
1971 CB750K1 (next project)
1969 CB750K0 (The Patina Bike - Blue / Green)

Oshkosh, WI  USA

Offline madmtnmotors

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Do you think this deal is too good to be true?  Four Genuine Honda manifolds (insulators), with 8 clamps for $65.


https://www.ebay.com/itm/Genuine-Honda-CB750-Intake-Insulators-Carb-Holder-w-Clamps-K-71-76-F-75-76/192606997978?hash=item2cd8458dda:g:WAgAAOSw44BYE7Yz:rk:12:pf:0

For the price I would probably try them. I would plan to inspect them at least once a year for signs of distress (i.e. cracking). I may order a set just to have them on hand. Cheap OEM style clamps will set you back close to $20 for eight, so you get the boots for about $50.

If you look at the seller profile it is the ebay outlet for CB750Supply.com. They get $75 for the boot/clamp combo on their website:
https://www.cb750supply.com/products/6/fuel-system/54/carb-holders
« Last Edit: October 09, 2018, 08:12:26 am by madmtnmotors »
TAMTF...


Wilbur



My most recent project "Evolution": http://forums.sohc4.net/index.php?topic=100352.0
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
                                           http://oldmanhonda.com/MC/wiring750K1.html
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
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
Sent from my Tandy TRS-80!

Offline ekpent

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 I've done many ,many cb750's and have never replaced a single rubber manifold ever. Your call but there have been complaints with some of the aftermarket ones. Heat makes the old ones workable but I always ditch the old clamps into a keeper box and upgrade with better.

Offline PeWe

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PITA to mount the carbs on the carb boots without warming them first, even when they are new. I use a heat gun, not for hair since it will burn :) Keep distance and move constantly. Same gun used for bearing assembly and fork seals removal/assembly.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline djwillard18

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Do you think this deal is too good to be true?  Four Genuine Honda manifolds (insulators), with 8 clamps for $65.

https://www.ebay.com/itm/Genuine-Honda-CB750-Intake-Insulators-Carb-Holder-w-Clamps-K-71-76-F-75-76/192606997978?hash=item2cd8458dda:g:WAgAAOSw44BYE7Yz:rk:12:pf:0

For the price I would probably try them. I would plan to inspect them at least once a year for signs of distress (i.e. cracking). I may order a set just to have them on hand. Cheap OEM style clamps will set you back close to $20 for eight, so you get the boots for about $50.

If you look at the seller profile it is the ebay outlet for CB750Supply.com. They get $75 for the boot/clamp combo on their website:
https://www.cb750supply.com/products/6/fuel-system/54/carb-holders

Thanks for your advice.
'74 CB750K4 (current)

'81 650 Maxim
'80 XS11

Offline flybox1

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PITA to mount the carbs on the carb boots without warming them first, even when they are new.
Sure!
But, if you cant sneak off with your significant-others hairdryer, a little gen-purpose grease on the insides of the boots goes a long way...
'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 madmtnmotors

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Do you think this deal is too good to be true?  Four Genuine Honda manifolds (insulators), with 8 clamps for $65.

https://www.ebay.com/itm/Genuine-Honda-CB750-Intake-Insulators-Carb-Holder-w-Clamps-K-71-76-F-75-76/192606997978?hash=item2cd8458dda:g:WAgAAOSw44BYE7Yz:rk:12:pf:0


Be sure to keep the original boots if you try the aftermarket ones. If the aftermarket ones fail miserably you can always reuse the original ones, even if you have to warm them up as suggested to make them a little more pliable.  8)
For the price I would probably try them. I would plan to inspect them at least once a year for signs of distress (i.e. cracking). I may order a set just to have them on hand. Cheap OEM style clamps will set you back close to $20 for eight, so you get the boots for about $50.

If you look at the seller profile it is the ebay outlet for CB750Supply.com. They get $75 for the boot/clamp combo on their website:
https://www.cb750supply.com/products/6/fuel-system/54/carb-holders

Thanks for your advice.
TAMTF...


Wilbur



My most recent project "Evolution": http://forums.sohc4.net/index.php?topic=100352.0
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
                                           http://oldmanhonda.com/MC/wiring750K1.html
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
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
Sent from my Tandy TRS-80!

 

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