Author Topic: Anyone successfully put 750K carbs on a 750A? Anything compatible?  (Read 6806 times)

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Offline Ved

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Anyone successfully put 750K carbs on a 750A? Anything compatible?
« on: September 13, 2010, 12:08:42 pm »
I know the 750A carbs are smaller than the K, but how much smaller are they, and is the diameter of of the intake manifold boots the same? What carbs will work on the 750A?

Pretty much fubarred one of the carb bowls trying to back out a stuck drain screw. It cracked, and the split in two completely. I'm thinking JB weld may be a temp fix as I can't seem to find any 750A carbs on ebay right now.

1977 CB750A
Your a good friend, but if the zombies ever chase us... I'm tripping you...

Offline jweeks

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #1 on: May 24, 2011, 07:19:23 am »
Just use the manifolds from a K model and the carbs bolt up. Yes, they work with a little tuning.

                                                      Jon Weeks

Offline rklystron

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #2 on: May 27, 2011, 07:24:08 am »
+1 to Mr Weeks. I have done it myself with great results.
1970 CB750 K0 (Bought in 73)
1972 XL250 (Bought new in 72)
1973 ST90 (Free)
1975 XL250 (Free)
1975 Rickman CR750
1982 CBX1000 Pro-link
1975 CB750 DRAG BIKE
1977 Custom Built CB750 Sturgis Bike (GL front end).
1977 CB750 F2 (Big Resto)
1977 CB750A (Auction Buy)
1978 CB750 K8 (My San Francisco ride)
1984 VFR750 (Bought New)

Offline rklystron

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #3 on: May 27, 2011, 10:36:48 pm »
As for my 1977 CB750A. When I got this bike at a local auction several years ago, it looked fine but drove like CT70. Very doggie motorcycle. So since you have access to the camshaft easy with the A frame I decided to change that with a 41a. Then looking at these 24mm A carbs I replaced theses with some 28mm 1972 K Carbs and insulators. The carb change was a simple swap with some jetting at the end. Then I replaced the ignition with a dyna 2000 with 5 ohm coils. Changed this bike from an old man's go to church bike to something that can get up and go when called to do so. Very happy with this A and the simple mods to make it perform like a real motorcycle.
1970 CB750 K0 (Bought in 73)
1972 XL250 (Bought new in 72)
1973 ST90 (Free)
1975 XL250 (Free)
1975 Rickman CR750
1982 CBX1000 Pro-link
1975 CB750 DRAG BIKE
1977 Custom Built CB750 Sturgis Bike (GL front end).
1977 CB750 F2 (Big Resto)
1977 CB750A (Auction Buy)
1978 CB750 K8 (My San Francisco ride)
1984 VFR750 (Bought New)

Offline tomsweb1

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #4 on: May 30, 2011, 04:53:02 am »
Do you remember the jetting changes you made?
Present: 1978 CB750A, 1978 CB400A, 1983 Nighthawk 550, 1984 CM250C

Past: 1977 XL100, 1982 KZ1300

Offline rklystron

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #5 on: May 30, 2011, 11:21:45 pm »
The jetting changes were pretty simple for my bike. Clip positions ended up being 2nd from top. Main jet @ 115.
1970 CB750 K0 (Bought in 73)
1972 XL250 (Bought new in 72)
1973 ST90 (Free)
1975 XL250 (Free)
1975 Rickman CR750
1982 CBX1000 Pro-link
1975 CB750 DRAG BIKE
1977 Custom Built CB750 Sturgis Bike (GL front end).
1977 CB750 F2 (Big Resto)
1977 CB750A (Auction Buy)
1978 CB750 K8 (My San Francisco ride)
1984 VFR750 (Bought New)

Offline dtmmil

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #6 on: September 16, 2011, 04:59:46 pm »
I have also heard from several on HC.com that swapping over to the roundtop style K or F carbs is a much needed swap, wakes the A bikes up. And JB weld works with gas if done right.

Offline Shea

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #7 on: September 24, 2011, 02:15:44 pm »
I have also heard from several on HC.com that swapping over to the roundtop style K or F carbs is a much needed swap, wakes the A bikes up. And JB weld works with gas if done right.

HC? wouldn't mind finding out what it takes to switch over the carbs and make my little bike get up and go

Offline raymond10078

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #8 on: September 24, 2011, 07:03:19 pm »
HC = hondachopper.com
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

fuwad84

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #9 on: January 19, 2012, 10:17:02 pm »
Hey can I get some more info about swapping out the stock carbs? What other carbs will work with very little modification on a 77 hondamatic? Are full rebuild kits easy to find for K carbs?

Offline boatsdickson

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #10 on: February 03, 2012, 02:36:04 am »
Awesome to finally see a Sam video. Truly a beautifully crafted machine.

Id like to resurrect this thread for a question or two while I do some searching on the rest of the site....

I just built a hybrid bank of carbs for my friends 76 hondamatic 750, which utilized a majority of my original 78 k set (42B I think), and also using the vacuum advance diaphragm from the Auto set of carbs. Im now wondering if I should have just put a complete set of k8s on instead of messing with blending the two sets of carbs.

1: With that being done and said, Im having trouble with the idle returning to low with a blip of the throttle and Im wondering if I shouldve just put the carbs on without the vacuum advance from the Auto.

2: Also, I used the throttle 'cam' from the Auto and I believe its a larger circumference than the K set. My description of a throttle cam is the round device that retains both throttle cable ball ends and allows the throttle cable a groove to lay in as the throttle opens and closes. It now seems that the throttles range of nothing to WOT is about 1/2 of a revolution of the hand grip. Hope this makes scence.

Im gunna do some digging on this and possibly pm a few of the original posters but maybe a few others have a quick answer to this.......thanx, Boats,
"No. We're all our own prisons, we are each all our own wardens and we do our own time. I can't judge anyone else. What other people do is not really my affair unless they approach me with it. Prison's in your mind. Can't you see I'm free"?  Testimonial of Charles Manson

Offline Secbyte@ptd.net

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #11 on: June 01, 2012, 12:15:38 pm »
Ved: I have a set of carbs from a 1976A that look in good shape that I will never use (gone fuel injected!!). You can have them for shipping cost. I am in Alberta, Canada. I'm guessing the shipping cost would be $20.00 to $30.00?

Take care; Clifford

I notice nobody seems to follow up with this.... What does he mean " I went fuel injected"?  You can get a fuel injected kit for these?

George

Offline boatsdickson

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #12 on: June 01, 2012, 02:17:05 pm »
I may be wrong but I wouldnt think he meant 'went injected' with his 76a. Hell anything is plausible with money & knowledge.

And too follow up my previous post, K carbs can be made to run well on an Auto. I recently put a rack of K8s on a 76A. I just havent set down to build a thread about it yet.
"No. We're all our own prisons, we are each all our own wardens and we do our own time. I can't judge anyone else. What other people do is not really my affair unless they approach me with it. Prison's in your mind. Can't you see I'm free"?  Testimonial of Charles Manson

Offline raymond10078

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #13 on: June 01, 2012, 04:52:41 pm »
Certainly no "kit".

Certainly was someone with the time, experience, knowledge, and money to create a system.

I have talked to one other person who did put K carbs on, reporting a decent power increase.

I have also talked to someone else that recommends the Yamaha Maxim/Seca 650 CV carbs, which except for a main jet change, are reportedly a bolt-on without any other carb changes.  That is the path I have chosen (650 Seca carbs - plus a non-auto cam) - the carbs are waiting on rebuild parts - and my time. 

I'll ride it for a while in this configuration before stepping up to a 836.  We'll see how long . . . .
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline Retro Rocket

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #14 on: June 01, 2012, 08:32:40 pm »
Ved: I have a set of carbs from a 1976A that look in good shape that I will never use (gone fuel injected!!). You can have them for shipping cost. I am in Alberta, Canada. I'm guessing the shipping cost would be $20.00 to $30.00?

Take care; Clifford

I notice nobody seems to follow up with this.... What does he mean " I went fuel injected"?  You can get a fuel injected kit for these?

George

Yes fuel injection, microsquirt controller and GSXR600 throttle bodies, actually works out pretty good for a reasonable out lay. I am going to do this on my 1000cc engine as soon as it is run in properly... There's a few guys here that have done it already....
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline dave the welder

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #15 on: June 03, 2012, 06:28:14 am »
check this out  go to  HONDACHOPPER.COM.go to community, go to the my rides gallery,scroll down to supercharged/fuelinjected 77 750a.the author s name is 23 tbucket this thing  is amazing!!!!
« Last Edit: June 03, 2012, 06:30:17 am by dave the welder »
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Offline Retro Rocket

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #16 on: June 03, 2012, 04:09:26 pm »
check this out  go to  HONDACHOPPER.COM.go to community, go to the my rides gallery,scroll down to supercharged/fuelinjected 77 750a.the author s name is 23 tbucket this thing  is amazing!!!!

Yes, he has a build thread on this forum as well.... ;)
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline raymond10078

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1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline dave the welder

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #18 on: June 04, 2012, 07:13:34 pm »
sorry if this is jacking your thread but i just put a set of round top carbs on my 77 750a. you need to use therubbers that are used with the round tops.the air filter rubbers fit from the A carbs.the biggest problem i ran into is both throttle cables will NOT work.they are way to long so you need to use the cables from the same year as the carbs.now for the good part.after installing everything(took less than an hour)it fired right up idled great even in gear.the acceleration was smoother than the stock carbs.the only problem i noticed is if you crank the throttle wide open from idle it will hesitate slightly,however i drive like an old man(because i am)and the throttle response is great   no pic necessary if you can take off the old carbs you can do this swap
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Offline raymond10078

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #19 on: June 04, 2012, 07:48:04 pm »
The other benefit for the "K" carbs, or the round-tops - the carb rubbers remain available.

Now - maybe your ready for a "K" or 75-76 "F" cam!
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline dave the welder

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #20 on: June 13, 2012, 09:16:58 pm »
just to update the air filter boots will not work.you can force them on but when you tighten the clamps they pop off.suggest using an air box from an earlier 750
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Offline Mr Freeze

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #21 on: December 06, 2012, 10:06:37 am »
So what are the years of the roundtop carbs?

Offline dave the welder

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Re: Anyone successfully put 750K carbs on a 750A? Anything compatible?
« Reply #22 on: December 06, 2012, 04:26:28 pm »
71-76 are the easist to find
don't buy it build it