Author Topic: 75 cb750k carb options?  (Read 1138 times)

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Offline Mantree

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75 cb750k carb options?
« on: February 20, 2022, 04:25:10 PM »
I cant keep my factory carbs on good running order anymore since they are so warn, they won't stop leaking and any time they sit for over a week they get fouled up and need cleaned again. So dose anybody have a suggestion on a less temperamental set of carbs since this is about to be used as my primary mode of transport.
« Last Edit: February 20, 2022, 04:28:16 PM by Mantree »

Offline blackbike

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Re: 75 cb750k carb options?
« Reply #1 on: February 20, 2022, 09:51:43 PM »
I cant keep my factory carbs on good running order anymore since they are so warn, they won't stop leaking and any time they sit for over a week they get fouled up and need cleaned again. So dose anybody have a suggestion on a less temperamental set of carbs since this is about to be used as my primary mode of transport.
Get them ultrasonic cleaned, get a rebuildkit and rebuild them. Should as new again...

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Offline Gurp

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Re: 75 cb750k carb options?
« Reply #2 on: February 20, 2022, 10:15:15 PM »
IDK if hestill does it but Harrisluv used to do a amzing job getting peopels carbs done right.
But really it depends what you want to spend. CRs or the cycle X 4 into 2 setup seemed popular
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Offline Don R

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Re: 75 cb750k carb options?
« Reply #3 on: February 20, 2022, 10:37:47 PM »
 I've never owned the 4x2 carb set but have seen several sets for sale used and wondered why. May or may not be the cyclex ones.
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Offline pjlogue

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Re: 75 cb750k carb options?
« Reply #4 on: February 21, 2022, 02:14:06 AM »
Carbs should not foul up that quickly unless you have really bad gas or your fuel tank is in bad shape and rust silt is getting into the carbs.  I would suggest you do the following:

Clean out your fuel tank.  De rust it if needed and make sure that the inside is very clean.

Be sure your fuel tubing is routed properly.  Many times the fuel tubing can cause fuel starvation issues.  The tubing should be kept as short as possible and there should be no "n" bends in the line.  One "u" bend is OK.  The idea is to have no places where air can get trapped in the  line.

Complete rebuild of carbs.  All brass should be removed and carefully cleaned.  Do not us "new" aftermarket brass.  Keep the stock Kleihn brass and clean it carefully.  Do not try to remove the brass metering jets the brass needles drop into.  These stick up into the throat of the carb and you will more than likely ruin them by trying to remove them.

Carb bodies should be ultrasonically cleaned and soft wire worked into the internal passages.  Pay particular attention to the air passage from the air filter side of the carb to the idle air needle and from the air idle needle to the slow jet.  This passage can become clogged up with deposits and it will really effect carb function.  After you have run a soft wire into these passages use a can of carb cleaner and flush the passages out and then use compresses air to clean and dry them.

About the only 2 things I can think of that would require getting new carbs is physical damage to the carb bodies from dropping them or being heavy handed or the carbs have been so neglected that acid has formed over a long time in the float bowl and eaten away the metal the main jet screws into and/or the fuel float pivot stanchions where the pivot pins can no longer function.

A further note.  The fuel floats and their respective fuel float pins and seats should never be swapped/mixed.  Keep each carbs parts together and separate from another carbs parts.  If you mix them up you will probably have endless problems with fuel leaks.  If you have already mixed them up take the plunge and buy new valves and seats. 

-P. 

Offline Mantree

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Re: 75 cb750k carb options?
« Reply #5 on: February 21, 2022, 06:12:23 AM »
The issue is that when I got the bike it had been sitting in my uncles garage and 2 of the bodys are corroded to the point that the float valve won't seal. I have actually been struggling with these carbs since I inhareted the bike and found that if I wasn't going to ride for a week or more I needed to close the petcock drain the bowls and and give the bike several kicks to cleen out the carbs so they wouldn't gum up the idle jets.

Offline newday777

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Re: 75 cb750k carb options?
« Reply #6 on: February 21, 2022, 06:24:04 AM »
Carbs should not foul up that quickly unless you have really bad gas or your fuel tank is in bad shape and rust silt is getting into the carbs.  I would suggest you do the following:

Clean out your fuel tank.  De rust it if needed and make sure that the inside is very clean.

Be sure your fuel tubing is routed properly.  Many times the fuel tubing can cause fuel starvation issues.  The tubing should be kept as short as possible and there should be no "n" bends in the line.  One "u" bend is OK.  The idea is to have no places where air can get trapped in the  line.

Complete rebuild of carbs.  All brass should be removed and carefully cleaned.  Do not us "new" aftermarket brass.  Keep the stock Kleihn brass and clean it carefully.  Do not try to remove the brass metering jets the brass needles drop into.  These stick up into the throat of the carb and you will more than likely ruin them by trying to remove them.

Carb bodies should be ultrasonically cleaned and soft wire worked into the internal passages.  Pay particular attention to the air passage from the air filter side of the carb to the idle air needle and from the air idle needle to the slow jet.  This passage can become clogged up with deposits and it will really effect carb function.  After you have run a soft wire into these passages use a can of carb cleaner and flush the passages out and then use compresses air to clean and dry them.

About the only 2 things I can think of that would require getting new carbs is physical damage to the carb bodies from dropping them or being heavy handed or the carbs have been so neglected that acid has formed over a long time in the float bowl and eaten away the metal the main jet screws into and/or the fuel float pivot stanchions where the pivot pins can no longer function.

A further note.  The fuel floats and their respective fuel float pins and seats should never be swapped/mixed.  Keep each carbs parts together and separate from another carbs parts.  If you mix them up you will probably have endless problems with fuel leaks.  If you have already mixed them up take the plunge and buy new valves and seats. 

-P.
Well said P.

The one thing I've found is the float valves should be replaced in addition to the cleaning of the carbs and derusting the tank(or maybe someone sealed the tank pooly and the sealer is failing, abive all, cleaning first!!!)

16011-329-004 is the float valves. You need 4 of these.....
#2 is the fiche number
https://www.hondaparts-direct.com/oempartfinder#/Honda_Powersports/CB550KA_(76)_550_FOUR%2c_JPN%2c_VIN%23_CB550K-1230001/CARBURETOR/f77665b3-598c-4e35-ad4b-7a873770e3e5/906a1415-2e5e-430c-9f5f-f7a37528e39f/y
« Last Edit: February 21, 2022, 06:25:58 AM by newday777 »
Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline Mantree

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Re: 75 cb750k carb options?
« Reply #7 on: February 21, 2022, 06:30:20 AM »
Carbs should not foul up that quickly unless you have really bad gas or your fuel tank is in bad shape and rust silt is getting into the carbs.  I would suggest you do the following:

Clean out your fuel tank.  De rust it if needed and make sure that the inside is very clean.

Be sure your fuel tubing is routed properly.  Many times the fuel tubing can cause fuel starvation issues.  The tubing should be kept as short as possible and there should be no "n" bends in the line.  One "u" bend is OK.  The idea is to have no places where air can get trapped in the  line.

Complete rebuild of carbs.  All brass should be removed and carefully cleaned.  Do not us "new" aftermarket brass.  Keep the stock Kleihn brass and clean it carefully.  Do not try to remove the brass metering jets the brass needles drop into.  These stick up into the throat of the carb and you will more than likely ruin them by trying to remove them.

Carb bodies should be ultrasonically cleaned and soft wire worked into the internal passages.  Pay particular attention to the air passage from the air filter side of the carb to the idle air needle and from the air idle needle to the slow jet.  This passage can become clogged up with deposits and it will really effect carb function.  After you have run a soft wire into these passages use a can of carb cleaner and flush the passages out and then use compresses air to clean and dry them.

About the only 2 things I can think of that would require getting new carbs is physical damage to the carb bodies from dropping them or being heavy handed or the carbs have been so neglected that acid has formed over a long time in the float bowl and eaten away the metal the main jet screws into and/or the fuel float pivot stanchions where the pivot pins can no longer function.

A further note.  The fuel floats and their respective fuel float pins and seats should never be swapped/mixed.  Keep each carbs parts together and separate from another carbs parts.  If you mix them up you will probably have endless problems with fuel leaks.  If you have already mixed them up take the plunge and buy new valves and seats. 

-P.
Well said P.

The one thing I've found is the float valves should be replaced in addition to the cleaning of the carbs and derusting the tank(or maybe someone sealed the tank pooly and the sealer is failing, abive all, cleaning first!!!)

16011-329-004 is the float valves. You need 4 of these.....
#2 is the fiche number
https://www.hondaparts-direct.com/oempartfinder#/Honda_Powersports/CB550KA_(76)_550_FOUR%2c_JPN%2c_VIN%23_CB550K-1230001/CARBURETOR/f77665b3-598c-4e35-ad4b-7a873770e3e5/906a1415-2e5e-430c-9f5f-f7a37528e39f/y
I cleaned and sealed the tank a few years back and always run a filter inline ever since I had a bike that had so much rust I had to go through the carbs after a week of riding.

Offline ekpent

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Re: 75 cb750k carb options?
« Reply #8 on: February 21, 2022, 06:33:13 AM »
I've let my 750's sit all winter and start them up in the spring without the idle jets getting clogged. Never had a problem in just a week. A leaky petcock when turned off will cause them to leak out the overflow or into the airbox. Maybe really look the float needle over well and make sure the spring tip that touches the float tang still work. These carbs are very simple with few moving parts and easy to tear down and service.

Offline Mantree

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Re: 75 cb750k carb options?
« Reply #9 on: February 21, 2022, 07:38:38 AM »
I don't have photos since the bike is down a hour south but understand me when I say the castings in the bowl looks like Swiss cheese the way its pitted and corroded. I would love to buy a better set of factory carbs but they aren't cheep to replace.

Offline Stev-o

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Re: 75 cb750k carb options?
« Reply #10 on: February 21, 2022, 08:05:06 AM »
... the castings in the bowl looks like Swiss cheese the way its pitted and corroded.

If that is the case, I would get another set of carbs.  Forum member Scott recommends this guy for carb rebuilding [if you dont fell comfortable doing it] Or, if you are in CO, Hondaman maybe could help.

http://www.oldschoolcarbs.com/the-carburetors/

Depending on the model, I may have a spare rack for sale [would need rebuilding]
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline ekpent

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Re: 75 cb750k carb options?
« Reply #11 on: February 21, 2022, 08:16:16 AM »
My friend and I always called those "cocaine" carbs when you crack them open for the first time and they are full of white corrosion powder, maybe from water or condensation. Not good when the jet towers are eaten up etc.. I use them for parts if they are too far gone.

Offline Mantree

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Re: 75 cb750k carb options?
« Reply #12 on: February 21, 2022, 08:25:09 AM »
... the castings in the bowl looks like Swiss cheese the way its pitted and corroded.

If that is the case, I would get another set of carbs.  Forum member Scott recommends this guy for carb rebuilding [if you dont fell comfortable doing it] Or, if you are in CO, Hondaman maybe could help.

http://www.oldschoolcarbs.com/the-carburetors/

Depending on the model, I may have a spare rack for sale [would need rebuilding]
My bike is a 74. I tried getting someone in northern CO to rebuild them but they quoted me 400 a carb so 1600 for the rack of 4. Where in CO is hondaman? I go down to Denver every few weeks but I live in fort collins up north, my wife goes to the winter park area 2 times a month over ski season. If you are willing to part with a set in rebuildable condition I can pull my jets and find a gasket kit.

Offline Don R

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Re: 75 cb750k carb options?
« Reply #13 on: February 21, 2022, 08:32:18 AM »
 I think the white corrosion is often from a fuel additive they used for a while. If the carbs were parked with that in them, the white corrosion starts.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline Stev-o

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Re: 75 cb750k carb options?
« Reply #14 on: February 21, 2022, 08:40:08 AM »
... the castings in the bowl looks like Swiss cheese the way its pitted and corroded.

If that is the case, I would get another set of carbs.  Forum member Scott recommends this guy for carb rebuilding [if you dont fell comfortable doing it] Or, if you are in CO, Hondaman maybe could help.

http://www.oldschoolcarbs.com/the-carburetors/

Depending on the model, I may have a spare rack for sale [would need rebuilding]
My bike is a 74. I tried getting someone in northern CO to rebuild them but they quoted me 400 a carb so 1600 for the rack of 4. Where in CO is hondaman? I go down to Denver every few weeks but I live in fort collins up north, my wife goes to the winter park area 2 times a month over ski season. If you are willing to part with a set in rebuildable condition I can pull my jets and find a gasket kit.

Hondaman charges $200 for a rebuild, believe he is in the Denver area.  [$1600 is crazy!]

http://sohc4shop.com/catalog/product_info.php?products_id=47

What model carbs do you need?  I can look later to see what I have.
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........


Offline Mantree

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Re: 75 cb750k carb options?
« Reply #16 on: February 21, 2022, 05:36:31 PM »
I'm looking around for a set on ebay but cash is a bit tight right now. Why do you suggest geting rid of the filter? I'm running honda fuel line and a high flow petcock and the clear filter never has more than 1/3 air.
If the bodies are that bad you can always get a set off e-bay.

https://www.ebay.com/itm/224813745050?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=224813745050&targetid=4581183927179148&device=c&mktype=&googleloc=&poi=&campaignid=418233787&mkgroupid=1241348861725295&rlsatarget=pla-4581183927179148&abcId=9300542&merchantid=51291&msclkid=489565a59f1a1debce3407b1826d64b9

I would also get rid of the in line fuel filter.

-P.




Offline pjlogue

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Re: 75 cb750k carb options?
« Reply #17 on: February 22, 2022, 02:55:16 AM »
I'm looking around for a set on ebay but cash is a bit tight right now. Why do you suggest geting rid of the filter? I'm running honda fuel line and a high flow petcock and the clear filter never has more than 1/3 air.
If the bodies are that bad you can always get a set off e-bay.

https://www.ebay.com/itm/224813745050?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=224813745050&targetid=4581183927179148&device=c&mktype=&googleloc=&poi=&campaignid=418233787&mkgroupid=1241348861725295&rlsatarget=pla-4581183927179148&abcId=9300542&merchantid=51291&msclkid=489565a59f1a1debce3407b1826d64b9

I would also get rid of the in line fuel filter.

-P.




I have always had trouble using in line fuel filters because they would always cause a vapor lock.  Others on here have had no problems but I suspect the  majority have had problems.  Because these bikes use gravity feed and it is relatively low hydrostatic pressure, the fuel line routing and anything that can trap a bubble of air becomes a problem.  Also, the heat from the cylinders can cause the fuel in the lines/filter to vaporize if they are run down behind the cylinders.  This is what I experienced when using a filter.  There was no room up behind the cam cover so I ran the lines down behind the cylinders.  Warm/hot days I would get vapor in the filter and fuel starvation.

-P.

Offline Stev-o

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Re: 75 cb750k carb options?
« Reply #18 on: February 22, 2022, 07:07:16 AM »
Dont pay $200 for a set of carbs on ebay!  I have a rack for $75...
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline ekpent

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Re: 75 cb750k carb options?
« Reply #19 on: February 22, 2022, 11:27:07 AM »
Dont pay $200 for a set of carbs on ebay!  I have a rack for $75...
Sweetheart deal !!

Offline Mantree

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Re: 75 cb750k carb options?
« Reply #20 on: February 23, 2022, 08:47:48 AM »
I'm looking around for a set on ebay but cash is a bit tight right now. Why do you suggest geting rid of the filter? I'm running honda fuel line and a high flow petcock and the clear filter never has more than 1/3 air.
If the bodies are that bad you can always get a set off e-bay.

https://www.ebay.com/itm/224813745050?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=224813745050&targetid=4581183927179148&device=c&mktype=&googleloc=&poi=&campaignid=418233787&mkgroupid=1241348861725295&rlsatarget=pla-4581183927179148&abcId=9300542&merchantid=51291&msclkid=489565a59f1a1debce3407b1826d64b9

I would also get rid of the in line fuel filter.

-P.




I have always had trouble using in line fuel filters because they would always cause a vapor lock.  Others on here have had no problems but I suspect the  majority have had problems.  Because these bikes use gravity feed and it is relatively low hydrostatic pressure, the fuel line routing and anything that can trap a bubble of air becomes a problem.  Also, the heat from the cylinders can cause the fuel in the lines/filter to vaporize if they are run down behind the cylinders.  This is what I experienced when using a filter.  There was no room up behind the cam cover so I ran the lines down behind the cylinders.  Warm/hot days I would get vapor in the filter and fuel starvation.

-P.

My bike has a bit of clearance there since it has a sportster tank on it so the fuel line runs up and over the throttle linkage and down behind the carbs it's 1/4 li e from the pet to the filter and honda 5.5 line from the filter to the carbs with a brass t fitting between the 2 pair of carbs

Offline Stev-o

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Re: 75 cb750k carb options?
« Reply #21 on: February 23, 2022, 09:31:34 AM »
Dont pay $200 for a set of carbs on ebay!  I have a rack for $75...
Sweetheart deal !!

They appear clean but will need a rebuild...


'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........