Author Topic: 1980 DOHC Honda cb750 Carbs  (Read 1435 times)

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Offline BenelliSEI

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1980 DOHC Honda cb750 Carbs
« on: April 23, 2019, 02:36:30 PM »
A friend of my son’s bought an unfinished cafe project bike. No history, no info. They couldn’t get it to start, so guess where it ended up? In my shop.......

Wiring is a mess and there is a ridiculously small battery under the Seat hump. I strapped on a full size battery and sorted enough wiring to get a healthy spark. Set up a temporary oil light and fired it up. Oil pressure and it idles well. Choke off and it holds idle. Any throttle application kills it instantly. Pulled the carbs off and they are pretty crappy AND the idle mixture screws were barely screwed in!

Not splitting the rack (not my bike, not that keen), but stripped and cleaned #3 and #4 first, blew them all out and I can stand the two carbs in my ultrasonic tank for a good bubble. Will finish them and then do the other two. 4 X kits ordered and a new accel. pump kit too. After that a bench sync. And then back on.........

Any special trick or issues to watch for? The floats are plastic and seem to have no height adjustment? Any clues/information appreciated!

Offline BenelliSEI

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #1 on: April 25, 2019, 06:32:59 PM »
Anyone have some useful advice? Kits arrived today......

Offline jgger

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #2 on: April 25, 2019, 09:00:24 PM »
Probably not the issue,  but.......I did a guys quad having the same issue, only one carb. His had a filthy gas tank that they cleaned out. Put fresh gas and it would idle like a clock,  turn the throttle and it would die instantly. I thought maybe a bad diaphragm in the CV carb but everything inside looked good. Finally pulled the main jet and it was corked up with the crap from the tank but it didn't show any signs of being dirty when it was in place. R and r plus a good cleaning and all was good.

No new parts needed on that one.
"The SOHC4 uses a computer located about 2-3 ft above the seat.  Those sometimes need additional programming." -stolen from  Two Tired

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Offline BenelliSEI

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #3 on: April 26, 2019, 02:37:57 AM »
Thanks! I’ll post results.

Offline MikeSimon

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #4 on: April 26, 2019, 11:14:28 AM »
A guy named Mike Nixon "wrote the book" (literally) on Honda carb service.
The CBX community swears by it.
As far as I remember, he had one out for the DOHCs also.
he has a web-site called Motorcycle Project. Google this and you may find it.
1973 CB350F -sold
1974 CB350F -218 orig miles, sold
1976 CB750K - in restoration

Other Hondas:
3 x CBX
CB1100R
GB500
Plus Kawasakis, BMws & Ducatis

Offline BenelliSEI

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #5 on: April 29, 2019, 07:04:50 AM »
Thanks Mike. Found the info. Nixon did a set of CBX carbs for me and the work was SUPERB.

Offline Magpie

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #6 on: May 14, 2019, 11:45:29 PM »
One of the carb Bibles http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf  Helped me a bunch when mine were all apart in a plastic tote when I got my 1980 cb750F. Cliff.

Offline BenelliSEI

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Re: 1980 DOHC Honda cb750 Carbs
« Reply #7 on: May 15, 2019, 07:13:16 AM »
Got it stored awa. Thanks, for the link!