Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 114944 times)

timbo750 · « **Reply #600 on:** August 28, 2016, 09:55:02 PM »

Cliff, thanks for the offer. I am going to get the throttle cable in place and working first, whilst I am on the subject, I am concerned that something is not right with my carbie assembly as there is a lot of resistance in trying to move the assembly by hand. Is that normal?

Terry in Australia · « **Reply #601 on:** August 29, 2016, 03:03:12 AM »

G'day Timbo, welcome back! Well I hope you're using two cables on those carbs, you can get away with just the "pull" cable, but if you lose the spring, you need your "push" cable to close the slides. They are a bit stiff to rotate the slide puller linkage and most CB750's have a heavy throttle pull with the stock spring. Not much getting around it, with only one spring to close 4 slides. Cheers, Terry.

maduncle · « **Reply #602 on:** August 29, 2016, 04:55:28 AM »

Quote from: Terry in Australia on August 29, 2016, 03:03:12 AM

G'day Timbo, welcome back! Well I hope you're using two cables on those carbs, you can get away with just the "pull" cable, but if you lose the spring, you need your "push" cable to close the slides. They are a bit stiff to rotate the slide puller linkage and most CB750's have a heavy throttle pull with the stock spring. Not much getting around it, with only one spring to close 4 slides. Cheers, Terry.

What Terry said.

Plus - trying to move the assembly "by hand" I am guessing means pushing on the point where the cables attach to see how well it moves? Yes it is hard, but it is easier with throttle cables on a throttle. And if you find it stiff on the throttle - check your cable routing.

timbo750 · « **Reply #603 on:** August 29, 2016, 01:34:29 PM »

Yeah, I was trying to move it by hand but I was expecting more return from the spring. I am hoping to get the throttle all hooked up the weekend so will see how it is then.

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timbo750 · « **Reply #604 on:** September 03, 2016, 01:00:58 AM »

Just found out the reason for the lack of return in throttle, no springs inside the carbies. I rebuilt these a long time ago so I can't remember all the detail of what I did then.

But in looking around the shed I managed to find only one. I also pulled apart a couple of other carbies I had and they didn't have any either. Are they actually required? I would assume so as all the diagrams I can find show them in there. Now I just need to find 3 more.

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seanbarney41 · « **Reply #605 on:** September 03, 2016, 06:28:18 AM »

You have k0 carbs?...or no, and you are getting confused by a diagram for k0 carbs?

timbo750 · « **Reply #606 on:** September 03, 2016, 04:15:29 PM »

I will be honest I don't know what carbs I have, the bike had been molested so much before me I now don't assume anything.

Sean, are you saying that only K0 carbs have the return spring? Or only K0 don't have them?

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Retro Rocket · « **Reply #607 on:** September 03, 2016, 04:26:07 PM »

Yes, KO carbs have individual throttle cables to each carb, which meet up to the throttle cable to the bars, here's a pic of KO carbs...

http://i.ebayimg.com/images/g/2~IAAOSw7ThUnEzQ/s-l400.jpg

timbo750 · « **Reply #608 on:** September 03, 2016, 05:49:51 PM »

Its the internal springs that are missing

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knottedknickers · « **Reply #609 on:** September 03, 2016, 05:59:57 PM »

Like #7 in this diagram (fr. p. 77 of the 1969-78 CB750 Shop Manual)?

timbo750 · « **Reply #610 on:** September 03, 2016, 06:33:34 PM »

Number 7 is it, I think its number 6 on the diagram for the later carbs. I can't work out why they are not there but I now need to find some.

seanbarney41 · « **Reply #611 on:** September 03, 2016, 06:37:14 PM »

Later than k0 only have one throttle return spring for the whole rack

timbo750 · « **Reply #612 on:** September 03, 2016, 07:04:20 PM »

Thanks Sean. That means nothing is missing, but it still doesn't explain the tight throttle. It will not return on its own to idle.

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seanbarney41 · « **Reply #613 on:** September 03, 2016, 07:27:50 PM »

Cables installed and adjusted correctly? You gotta have some slack in the adjustment or the pull and the push will fight each other. Also check cable routing for binding. The honda manual is your friend here.

timbo750 · « **Reply #614 on:** September 03, 2016, 08:11:20 PM »

They won't return before the cable are even connected.

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timbo750 · « **Reply #615 on:** September 03, 2016, 10:43:23 PM »

Ok, so it seems I went looking for something that doesn't exist. The throttle mechanism was hard to move once it was all assembled and wouldn't return on its own.

So I started looking for answers. When apart the carbies and linkages moved moved freely but the sum of all parts was the issue. What also didn't help is the stupid clymer manual shows the K0 diagram for the K1-K6 carbs and I started to look for the internal springs, I found a spring that should of been the right size and it fitted and so the confusion gathered momentum.

I have now reassembled and used some silicone spray in a few spots and also got some extra tension on the return spring and things are starting to work as they should, although I still feel the throttle is still tight without the cables connected.

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knottedknickers · « **Reply #616 on:** September 04, 2016, 08:22:48 AM »

Just to clarify: the diagram I attached is from the Honda factory manual ((c) 1977; downloaded from this site), not the Clymer manual. So whether it's K0 or K0-6, I don't know. Having said that, the partzilla diagram for '76 doesn't show the spring... (http://www.partzilla.com/parts/search/Honda/Motorcycle/1976/CB750K+A/CARBURETOR/parts.html) I honestly can't remember whether mine had springs in there or not!

01Thomas · « **Reply #617 on:** September 04, 2016, 12:20:03 PM »

The carb in the above diagram is clearly a K0 carb, which has a 4-into-1 cable arrangement. These four carbs each have their own cable tensioning set-up (items 1, 2, 3) on the carb top whereas the K1 carb and later have a crossbar-linkage system.

seanbarney41 · « **Reply #618 on:** September 04, 2016, 01:44:52 PM »

Timbo...how about some pics

timbo750 · « **Reply #619 on:** September 04, 2016, 02:41:59 PM »

Ok. Will try to get photos tonight when I get home from work.

I also have to ask about 2 little tubes coming of the carbs, I think they are air vent tubes maybe but what I need to know is where they go to so I can get some hose long enough.

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seanbarney41 · « **Reply #620 on:** September 04, 2016, 05:11:23 PM »

Yes, vents for the float bowls. You just need about 12 inches for each. They just drape over the airbox. Leave them open.

timbo750 · « **Reply #621 on:** September 04, 2016, 05:28:11 PM »

Thanks Sean

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maduncle · « **Reply #622 on:** September 05, 2016, 03:54:44 AM »

Quote from: timbo750 on September 04, 2016, 05:28:11 PM

Thanks Sean

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Clarke Rubber sell good rubber vacuum tube that fits onto the float overflow tubes real nice. I got it all for my Cb750 from my local store.

Terry in Australia · « **Reply #623 on:** September 05, 2016, 04:01:09 AM »

Ha ha, it's easy to get confused when you're not playing with these things regularly Tim, but as has been said above, only the K0's had individual expanding coil springs inside each slide, the K1- onwards had a single linkage that opened and closed all the slides at once, with one single external retracting coil spring.

Once you've hooked up the cables with a smidgeon of slack for both, you should be able to turn the throttle, let go of it, and have the spring pressure snap it closed. If it doesn't, well, it's back to the drawing board mate.........

timbo750 · « **Reply #624 on:** September 05, 2016, 03:55:03 PM »

Didn't get to the shed last night for some fresh happy snaps but here are a few from last week. I have now got the throttle doing what it should, it returns on its own and not too hard turn to turn where it matters. also got the grips on and the clutch handle finally on, which is my next challenge. I used an aftermarket Nissin brake master from DCC and at the moment the only clutch handle with the same shape and profile is all shiny and the brake is matt black.

As you will see from the photos I put franks frame kit a little too far back but all still works.

Also, anyone got photos of where the overflow tubes should sit at the back of the engine and also where the fuel lines run through it all?

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Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 114944 times)