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Author Topic: 78 750f Keihins carbs on a k4?? doable?  (Read 2552 times)

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Offline ianfotheringham

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78 750f Keihins carbs on a k4?? doable?
« on: February 11, 2012, 02:29:28 PM »
pickup up a barn find the other day with a Keihins carb bank seemingly off a 78 cb750f....wondering if there will be any issues mounting them to the 74 cb750k4 engine on the bike?

i know the choke will be different than stock - but i have the cable and will be able to mount it somewhere else...any other compatibility issues anyone knows of?

should be a bit better than stock if they work tho right? more flow and whatnot....

help before i blow cash rebuilding them!


thanks!
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Offline 754

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #1 on: February 11, 2012, 02:32:35 PM »
 they work..
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Offline SOHC Digger

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #2 on: February 11, 2012, 02:35:32 PM »
The main benefit over the K4 stock carbs is the accelerator pump.  In reality, many people with the later PD style (which is what the 78F had) convert back to the round top (stock for the K4).

If you decide to use the PDs on your 74, you will need to use the later style intake boots.
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Offline ianfotheringham

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #3 on: February 11, 2012, 02:38:07 PM »
good thing the bank came with them on...what about any increase in power due to the larger inner diameter?

thanks guys
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Offline Terry in Australia

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #4 on: February 11, 2012, 02:46:30 PM »
Yeah mate, they work very well on early K series bikes, I saw 125 MPH on an otherwise stock K2 after installing them, and only removed them because I hotted up another engine and installed CR's, which were an absolute PITA. You'll need to use K7/8 intake rubbers to make 'em fit your head, F2/3 rubbers are too big for your early K series inlet spigots.

The PD carbs work best with the stock airbox, but be careful when you re-install the OEM sidecovers, the F airbox is a little bit wider than the K airbox (which you can't use on the F carbs) and I cracked my left sidecover putting it back on. If you're using Joe's new repro sidecovers it won't be a problem, they're a lot more flexible than the brittle 40 year old originals. Cheers, Terry. ;D
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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline ianfotheringham

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #5 on: February 11, 2012, 02:49:14 PM »
was planning on going with pods anyway...despite the flack traditionalists may give for the move...will be re-routing all the electrics and oil reservoir up under a custom cafe seat to keep it clean....
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Offline Terry in Australia

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #6 on: February 11, 2012, 02:52:33 PM »
No worries mate, I've re-installed K&N pods on my K1 and they work fine, you'll need to rejet your carbs to around 125-130 to make them work though, or else it'll run like shiite. Cheers, Terry. ;D
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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline SOHC Digger

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #7 on: February 11, 2012, 02:57:30 PM »
Quote from: ianfotheringham on February 11, 2012, 02:49:14 PM
was planning on going with pods anyway...despite the flack traditionalists may give for the move...

It's not the traditionalists who give flack about pods.  It's those who see pods as under-performing.  Yes, they look like a performance item, but in reality, they fall short of your expectations.  If you haven't bought the pods yet, you may want to look at other alternatives, such as Tintop's anti-pod setup.  Terry, you have run the anti-pod.  What are your thoughts?
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Offline Terry in Australia

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #8 on: February 11, 2012, 03:17:34 PM »
G'Day Digger, The anti-pod works very well and I'd recommend it to anyone. The only problem I have with mine, which was the prototype, is that the rubber is so soft I found it impossible to refit the horns back on to the carbs, so after stuffing around for an hour (4 times my usual attention span) I installed the old circular K&N's that I've had in a box for many years.

The "Pods are bad" theory is over blown, in my opinion, I've had them on bikes for years with no major issues, my only recommendation would be to buy quality pods, i.e., K&N's, there are a lot of cheapies out there, but they're rubbish. Cheers, Terry. ;D

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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline ianfotheringham

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #9 on: February 12, 2012, 06:19:00 AM »
alright team, what about the right hand control?

the bike (i'm not sure i am allowed to call it that in its current state) came without the right hand control (killswitch/starter/throttle) which will of course need to be replaced....i know the part numbers for the k4 and the F throttle cables are different, as are the controls, but will either work? they both have push and pull cables....and the lengths would have to be about the same...just wondering if i need to be picky here or should i just get the first, cheapest one that comes up?

for example - current ebay auction #: 250991600897
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Offline Terry in Australia

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #10 on: February 12, 2012, 11:20:14 PM »
I used my K1-K6 throttle assembly with F2 throttle cables and choke cable/lever assembly. Cheers, Terry. ;D
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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline Xnavylfr

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Re: 78 750f Keihins carbs on a k4?? doable?
« Reply #11 on: February 13, 2012, 04:06:59 PM »
You can use any CB right hand control, except for the KO model( 4 SEPERATE CABLES at the carbs). The wire colors are the same  and will be a plug and  GO.


Xnavylfr(CHUCK)
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