Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 116378 times)

Terry in Australia · « **Reply #575 on:** May 02, 2016, 12:59:37 PM »

So if you don't have the SMSU thingy your starter motor won't engage? Well there you go, I've cured cancer, there's nothing hanging off the red plug on my bike, I haven't bypassed anything, but lo and behold, I press the button, and it fires right up. I am a freaking genius!

Timbo, Cliff, if you're using the older style switchblocks like I am, without the additional wiring for the SMSU, you don't need to do anything, it'll work fine. Cheers, Terry.

maduncle · « **Reply #576 on:** May 03, 2016, 03:07:12 AM »

Quote from: Terry in Australia on May 02, 2016, 12:59:37 PM

So if you don't have the SMSU thingy your starter motor won't engage? Well there you go, I've cured cancer, there's nothing hanging off the red plug on my bike, I haven't bypassed anything, but lo and behold, I press the button, and it fires right up. I am a freaking genius!

Timbo, Cliff, if you're using the older style switchblocks like I am, without the additional wiring for the SMSU, you don't need to do anything, it'll work fine. Cheers, Terry.

Excellent ...

timbo750 · « **Reply #577 on:** August 28, 2016, 12:31:55 AM »

Well its been far too long. But it's been a cold and wet winter in Melbourne, work and the kids sport have also been taking up too much time.

I had to actually take a few steps back with the wiring. I was worried that I was attaching the main loom in the wrong spot on the frame so I pulled it out so I could get the carbies and throttle cables in, which I managed to do today.

One of the hardest parts of all to find was the little split pins on the choke linkages, no where local had anything small enough. Got some mail order from Brisbane , after paying for postage it cost me about 30 bucks for the little suckers but I now have a few spares.

I am now hoping I can keep things moving along so I can be riding before too long. No timeline though, that always backfires.

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maduncle · « **Reply #578 on:** August 28, 2016, 03:04:12 AM »

Quote from: timbo750 on August 28, 2016, 12:31:55 AM

Well its been far too long. But it's been a cold and wet winter in Melbourne, work and the kids sport have also been taking up too much time.

I had to actually take a few steps back with the wiring. I was worried that I was attaching the main loom in the wrong spot on the frame so I pulled it out so I could get the carbies and throttle cables in, which I managed to do today.

One of the hardest parts of all to find was the little split pins on the choke linkages, no where local had anything small enough. Got some mail order from Brisbane , after paying for postage it cost me about 30 bucks for the little suckers but I now have a few spares.

I am now hoping I can keep things moving along so I can be riding before too long. No timeline though, that always backfires.

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Hey Tim - glad you are back into it.

You can use race wire and race wire twist pliers instead of those little split pins on the carries - works a treat.

Let me know if you want to see how that wiring harness fits to a complete bike - mine is in and all tucked out of the way.

timbo750 · « **Reply #579 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 #580 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 #581 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 #582 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 #583 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 #584 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 #585 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 #586 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 #587 on:** September 03, 2016, 05:49:51 PM »

Its the internal springs that are missing

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knottedknickers · « **Reply #588 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 #589 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 #590 on:** September 03, 2016, 06:37:14 PM »

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

timbo750 · « **Reply #591 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 #592 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 #593 on:** September 03, 2016, 08:11:20 PM »

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

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timbo750 · « **Reply #594 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 #595 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 #596 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 #597 on:** September 04, 2016, 01:44:52 PM »

Timbo...how about some pics

timbo750 · « **Reply #598 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 #599 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.

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Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 116378 times)