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Author Topic: cb750 carb idle problems,so frustrated,, help needed  (Read 483 times)

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Offline crxnug

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cb750 carb idle problems,so frustrated,, help needed
« on: July 15, 2022, 11:06:53 PM »
Im restoring a 1975 b Cb750, When i got the bike it ran and would idle, even though it leaked  fuel from float overflow which turned out to be float valve being installed upside down by previous owner,so i rebuilt carbs, ultra sonic cleaner, check float level, new spark plugs  the problem i having is bike is hard to start and  once started wont hold a idle, does anyone know what the problem could be. im so frustrated right now ,I havent sync the carbs as without being able to idle that would  be a issue. any help on what would be the problem would be much appreciated
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Online seanbarney41

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Re: cb750 carb idle problems,so frustrated,, help needed
« Reply #1 on: July 15, 2022, 11:32:56 PM »
really not trying to be a smart ass but...have you tried turning in the idle screw?
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If it works good, it looks good...

Offline newday777

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Re: cb750 carb idle problems,so frustrated,, help needed
« Reply #2 on: July 16, 2022, 02:42:16 AM »
Quote from: crxnug on July 15, 2022, 11:06:53 PM
Im restoring a 1975 b Cb750, When i got the bike it ran and would idle, even though it leaked  fuel from float overflow which turned out to be float valve being installed upside down by previous owner,so i rebuilt carbs, ultra sonic cleaner, check float level, new spark plugs  the problem i having is bike is hard to start and  once started wont hold a idle, does anyone know what the problem could be. im so frustrated right now ,I havent sync the carbs as without being able to idle that would  be a issue. any help on what would be the problem would be much appreciated
What carb kits did you put in when you rebuilt the carbs? Did you use the kit brass parts?
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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 newday777

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Re: cb750 carb idle problems,so frustrated,, help needed
« Reply #3 on: July 16, 2022, 02:59:26 AM »
Another thought is have you checked for vacuum leaks around the intake boots with light shots of carb cleaner or unlit propane?
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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 ekpent

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Re: cb750 carb idle problems,so frustrated,, help needed
« Reply #4 on: July 16, 2022, 06:43:50 AM »
Quote from: seanbarney41 on July 15, 2022, 11:32:56 PM
really not trying to be a smart ass but...have you tried turning in the idle screw?
I'll give that a +1. Large knurled screw on top of the carb rack.
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