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Author Topic: 1978 cb750 shut of on me?!?  (Read 659 times)

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Offline Seans405

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1978 cb750 shut of on me?!?
« on: October 05, 2023, 06:05:16 PM »
Hey guys. Long time lurker, first time poster. Had an odd issue today. I have a 1978 cb750, SOHC, going down the highway I had some room, so I decided to give it the beans. In 5th, about 7k rpm’s and climbing, throttle started to cut out. I’d crack the throttle and it sounded like it wanted to pep back up but didn’t (bike did not die at this point) I looked down. Saw regular oil pressure. Got over to the emergency lane, and when I came to a stop, she died. Looked at the gas and saw i wasn’t low. Shrugged my shoulder and it started right up with no hesitation, hopped back on the road and rode home with no problems. I currently have Murray’s 4 to 2 carbs. Any ideas or advice is welcome
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Offline HondaMan

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Re: 1978 cb750 shut of on me?!?
« Reply #1 on: October 05, 2023, 06:43:36 PM »
How are your fuel lines routed? Picture?
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Offline seanbarney41

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Re: 1978 cb750 shut of on me?!?
« Reply #2 on: October 05, 2023, 07:22:55 PM »
7k in 5th?  That should be around 80-90 mph.  How much faster did you think it was gonna go with a carb set up that is a huge downgrade from stock even if it is tuned correctly?   

But yeah, sounds like a fuel flow problem.
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Offline grcamna2

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Re: 1978 cb750 shut of on me?!?
« Reply #3 on: October 05, 2023, 08:34:56 PM »
You might also check your ignition switch,if you hadn't looked at it yet.
They do loosen up a bit over time where the plug connects.
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Offline newday777

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Re: 1978 cb750 shut of on me?!?
« Reply #4 on: October 05, 2023, 08:35:25 PM »
Welcome aboard the forum Seans405

What is  I looked down 'Saw regular oil pressure.' ?
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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 Stev-o

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Re: 1978 cb750 shut of on me?!?
« Reply #5 on: October 06, 2023, 06:49:15 AM »
Quote from: newday777 on October 05, 2023, 08:35:25 PM
What is  I looked down 'Saw regular oil pressure.' ?

Assume he has a gauge mounted on the case.

Fuel issue, do you has inline filters?  Clogged tank cap vent??
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Offline Kaze

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Re: 1978 cb750 shut of on me?!?
« Reply #6 on: October 06, 2023, 07:19:24 PM »
Have you been riding this bike regularly for some time and this is a new development? Or was it sitting a long time and you've just come back to it?
Have you been working on it lately, or made any changes that might have lead to this issue?
Have you put any additives in the fuel recently?
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Offline Seans405

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Re: 1978 cb750 shut of on me?!?
« Reply #7 on: November 13, 2023, 07:00:31 PM »
Hello all, just wanted to give a little update. Thank you all so much for welcoming me and giving me advice. Turns out that the vent hole for the tank was blocked off and causing the bike to starve!
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Offline Stev-o

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Re: 1978 cb750 shut of on me?!?
« Reply #8 on: November 14, 2023, 07:00:39 AM »
Quote from: Seans405 on November 13, 2023, 07:00:31 PM
Turns out that the vent hole for the tank was blocked off and causing the bike to starve!

That was my guess, glad you got it sorted
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline newday777

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Re: 1978 cb750 shut of on me?!?
« Reply #9 on: November 14, 2023, 07:14:59 AM »
Quote from: Seans405 on November 13, 2023, 07:00:31 PM
Hello all, just wanted to give a little update. Thank you all so much for welcoming me and giving me advice. Turns out that the vent hole for the tank was blocked off and causing the bike to starve!
As a FYI hit the notify button at the bottom to get notice of replies.
Also,  be sure to answer questions given to you.
Thanks for the update and positive conclusion
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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
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