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Author Topic: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them  (Read 3816 times)

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Offline Jerry Rxman Griffin aka MuthaF'er

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77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« on: June 25, 2018, 11:27:24 AM »
I'm playing with my Webers and they are #$%* to get into the rubber manifolds. The OD on the Webers spigot is 39mm while the ID on the rubbers I have are 37.5mm. I'm thinking mine may be 69 - 76 K/F intakes?

Does anyone have the ID measurements of the 69-76 intake rubbers carb side and/or the measurement of the 77/78 CB750K intake rubber? The 77/78 750K PD carbs have larger OD measurement from my understanding.

AND what about a source for the 77/78? Quality of that source's product?
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline TwoTired

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #1 on: June 25, 2018, 11:55:10 AM »
I don't know if this helps,  But, I have experienced the swelling of the carb couplers using wintergreen oil and a solvent.

If you just dipped one end, it would take an hour or two, maybe a bit longer to get the inner dimension you want.

Good luck!
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Offline kmb69

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #2 on: June 25, 2018, 12:35:41 PM »
The 77-78 manifolds are just under 39mm ID.
JTMarks77 has a genuine Honda set on eBay for $150.
Cruzinimage has a repro set for $50.
The repros are usually somewhat softer that the Honda parts from my experience.
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Offline MRieck

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #3 on: June 25, 2018, 12:38:15 PM »
 I have the reproduction 77/78K insulators from Vintage CB on my bike for the 34 RS's. The quality seems good but you have to spend a bit of time aligning them. They make mounting the RS's much easier.
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Offline 754

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #4 on: June 25, 2018, 01:33:13 PM »
Don't the 77/78 rubbers screw on .?
 I made a suggestion on the other thread, preformed angled silicone hose. 
 Will warn you, tricky to cut
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #5 on: June 25, 2018, 02:15:07 PM »
Thanks guys. Cruzin $50, Vintage $100, and RP (really proud) Marks $150. No more restorations so I'll save at least $50. If this dinosaur cool Weber doesn't pan out I'll be doing the RS34 thing so either way it'll be easier. JT wants to get into my Cruzan rum money! Maybe Cruzin Cruzan?!

#$%* Frank, if they DID screw on it'd still be easier than what we went through. I'd call them "slip on" but that makes it sound easy. I could always roto rooter them with my Dremel.
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Offline 754

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #6 on: June 25, 2018, 02:35:01 PM »
I suspect the spacing is different between 77 and 78 carbs, and that the RC is closer together.
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Offline kmb69

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #7 on: June 25, 2018, 03:09:13 PM »
Quote from: 754 on June 25, 2018, 02:35:01 PM
I suspect the spacing is different between 77 and 78 carbs, and that the RC is closer together.

Pretty sure the carb spacing is the same on all SOHC 750 versions.
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Offline seanbarney41

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #8 on: June 25, 2018, 05:50:00 PM »
the 77/78 boots are wayyyy shorter than 71-76.  They look totally different.  No idea whether that means they won't work with the RC manifold or not. 

Hardened up old boots are easy to hog out with a flap wheel on a die grinder.
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Offline BPellerine

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #9 on: June 25, 2018, 05:52:24 PM »
had an rc on my bike before,it fits,rubbers are diff on the 77/78 though.I used the older style to mount it,dont know why it fit,only had it on for a test of the carbs,memory not so good but I remember having to use 2 pairs of the same rubbers,to make it fit.bill
« Last Edit: June 25, 2018, 05:57:31 PM by BPellerine »
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Offline MoMo

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #10 on: June 25, 2018, 06:08:07 PM »
I may have a set of Cruzin Image for a cb900 I could send you if the sizes are right. Post  measurements you need and I'll check against what I have.  Freebie of course if it'll work...Larry
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #11 on: June 25, 2018, 06:45:00 PM »
Lot of good info here guys!

Shorter would be better IF THEY STILL FIT the RC spacing-wise. I know the 77/78 F look different and the picture I saw on Vintage CB750 of "their" K's looked different too if that picture was correct. Spacing should be the same though?!

Larry, the carb spigot size is 39mm. The head spigot size is ~ 34mm inside the ridge. I just don't have any extra room length wise. Less than an inch leftover with earlier K's boots at the rear of the Webers vs the frame tubes.

I'm hoping I don't have to use all the same part number Bill. I ordered a CruzinImage set. $62 so I won't lose a lot if so.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline scottly

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #12 on: June 25, 2018, 07:54:31 PM »
Jerry, the OD of the K7 carb is 39.6-39.8mm. The ID of the boot is about 37mm, due to the raised ring that fits into the groove in the carb. If you hadn't been in such a dang hurry, I could have saved you 60 bucks. ;)
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #13 on: June 25, 2018, 08:40:46 PM »
Thanks Scott. I'm looking for that extra 1mm of the K7/8 boot. Plus if it's a little shorter too then it's even better. Experimentation. Not in so much of a hurry that I haven't had the time to dig into it since Sept  :D I will be running out of time again when Bonneville rolls around. July and August are my only bike wrenching months. I have to get the head back on, the Webers or the Mikuni RS34's dialed in then tear into the 900. Sometimes the biggest limiting factor is parts acquisition and shipping. If I can skip that hurry up and wait thing I'm good  ;D

Is that boot a K7/8? If so what is the ID without the ring included?
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Offline scottly

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #14 on: June 25, 2018, 08:49:51 PM »
It's an original K7, slightly hard ::). The ID without the ring is about 39mm.
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Offline MoMo

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #15 on: June 26, 2018, 11:20:47 AM »
IMG_9857 by Lawrence Moulder, on Flickr


Brand new Cruzin Image boots that are a tad over 39 one end and 43 other, overall length roughly 1 1/2".  Yours if you can use them, or if you can't and anyone else can let me know....Larry
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Offline scottly

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #16 on: June 26, 2018, 05:41:10 PM »
The ID without the ring is closer to 38.5mm. The boots in the pic are carb side down..
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Offline madmtnmotors

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #17 on: June 27, 2018, 09:22:33 AM »
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Offline MoMo

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Re: 77/78 CB750K Intake boots/manifolds/carb holders whatever you want to call them
« Reply #18 on: June 27, 2018, 09:55:01 AM »
Quote from: madmtnmotors on June 27, 2018, 09:22:33 AM
C.I. carb boots have gotten some poor reviews:

http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841






Ones I have did not fit the 900 very well plus the finishing was so poor(rubber flaps that needed to be cut) I decided to order OEM Honda...Larry
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