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Author Topic: 1978 cb750k carb problems  (Read 1167 times)

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Offline Willie501KULT

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1978 cb750k carb problems
« on: August 24, 2011, 11:29:55 AM »
Hey guys,
I have a 78 cb750k with carpy 4 into 1 exhaust, pod air filters and a 120 main jet. My plan was next to move the slide needles down one notch but apparently this cant be done with my carbs. Anything else I could try? Or possibly try a different needle?

Thanks!
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KingCustomCycles.com

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Re: 1978 cb750k carb problems
« Reply #1 on: August 24, 2011, 01:08:33 PM »
Different carbs, or shim the needle with a washer. I cringe when I see a 78 post, screws on the bowls, air valves, weird isolators, accel pump, just a pain compared to the earlier carbs.
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Offline Willie501KULT

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Re: 1978 cb750k carb problems
« Reply #2 on: August 24, 2011, 01:41:34 PM »
Haha, thats what I'm starting to think too(different carbs). Although, I had heard about using washers to shim the needles and was thinking of trying that. Thanks for your help.
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Offline Willie501KULT

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Re: 1978 cb750k carb problems
« Reply #3 on: August 24, 2011, 02:42:13 PM »
Do you know if any other needles could work in the 78 carbs? Like ones from an older model cb?
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Offline Gearheadgreg

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Re: 1978 cb750k carb problems
« Reply #4 on: August 24, 2011, 03:08:45 PM »
Quote from: Willie501KULT on August 24, 2011, 11:29:55 AM
Hey guys,
I have a 78 cb750k with carpy 4 into 1 exhaust, pod air filters and a 120 main jet. My plan was next to move the slide needles down one notch but apparently this cant be done with my carbs. Anything else I could try? Or possibly try a different needle?

Thanks!
1 step larger slow jet.
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2001 Honda Supercharged Valkyrie   <iframe width="480" height="360" src="http://s1218.photobucket.com/user/meloafer/embed/slideshow/"></iframe> Just having some fun

Offline Willie501KULT

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Re: 1978 cb750k carb problems
« Reply #5 on: August 24, 2011, 04:04:14 PM »
sorry, which jet is that?
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Offline cookindaddy

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Re: 1978 cb750k carb problems
« Reply #6 on: August 24, 2011, 05:31:20 PM »
Hey King, love your posts but couldn't help thinking - could it be what we are used to?

I have a 78 CB750 K8. I learned about the carbs, took mine apart, bought a spare, took it apart, rebuilt carefully, setup carefully, kept my bike totally stock the way honda designed it and it works great, I am happy and I think I know how it works. But I couldn't help with one of the earlier ones at all.

I don't think Willie said why he wants to move the needles down one notch...

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George with a black 78 CB750K (in Lion's Head, Ontario, Canada)

Offline Gearheadgreg

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Re: 1978 cb750k carb problems
« Reply #7 on: August 24, 2011, 05:44:03 PM »
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2001 Honda Supercharged Valkyrie   <iframe width="480" height="360" src="http://s1218.photobucket.com/user/meloafer/embed/slideshow/"></iframe> Just having some fun

bollingball

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Re: 1978 cb750k carb problems
« Reply #8 on: August 24, 2011, 07:20:03 PM »
+1 cook real easy carbs to work on
Hard to help someone when they don't tell you what is wrong or why they are doing what they are doing.
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Offline Blitzburgh207

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Re: 1978 cb750k carb problems
« Reply #9 on: August 24, 2011, 08:21:24 PM »
k7 needles are adjustable if you can find them. The only place ive seen that carries them is western hills honda but theyre like $20 apiece... Otherwise you can shim them using m2.5 washers or I found some nylon "shims" factory from arctic cat that fit perfectly. 1 should be plenty. I drilled my slow jets per the i
walkthrough on hondachopper.com and have had good results. Running 130 mains right now but its a tad rich so id try 125s and go from there. Good luck! p.s. I have cycle x 4-2-1 and pods so very similar. These carbs are real picky but youll love the throttle response once you get it right!
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1978 CB750 K8

Offline MilehighCB

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Re: 1978 cb750k carb problems
« Reply #10 on: August 25, 2011, 02:21:47 AM »
As stated, the K7 have the ability to change the clips. 

I have a similar set up, Carpy exhaust, pods and also a PowerArc ignition.  I have tried several main jets and I think 135 jets will be my next attempt.  I had 140's in and then went to 130's.  Not quite the top end pull with the 130's as with the 140's, so maybe my sweet spot will be 135's.  I also drilled out the idle jets according to HC. with good results.  You can find those tiny drill bits at HobbytownUSA (behind the counter).

People bag on these carbs, but all and all they are good performers, sure they are different from the eariler carbs, but IMHO they work just fine.

Hope it helps....
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KingCustomCycles.com

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Re: 1978 cb750k carb problems
« Reply #11 on: August 25, 2011, 04:06:28 AM »
I cringe, but press on, as they do perform just fine when setup properly.  The late model F's are some of my favorite SOHC's.
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