Topic: Potential 1970 CB750 K0/K1 Hybrid

[BenelliSEI]

Sounds good, enjoy!

[Lucien Harpress]

Minor update to my previously mentioned carb sync adapters:  DO NOT BUY THESE.  I repeat, DO NOT BUY THESE.

I had assumed the tube was solid all the way through, threaded at the end, with a collar slipped on to hold the o-ring.  As it turns out, the threaded portion at the end is a separate piece, brazed (?) on the rest of the assembly.  The actual joint line is TINY- width of a human hair?  I just snapped BOTH of them, only with the pressure of putting the vacuum gauge hoses on them. 

So now I get to go back to plan A (shorter adapters and be REALLY careful not to cross-thread the inner ports) after I figure out how to back out a threaded stub from carb 3.   

[Lucien Harpress]

Proof of goodies!










The battery box is rustier that I expected, but most of the worst of it is hidden under the rubber bumpers or battery.  It's solid enough to use.  The slider tubes on the forks are shot, but I can re-use the ones I have.  And the frame will need some work (cleanup, one small hole patched, paint), but in ways is more solid than my current frame is.

I'm still waffling on getting correct K0 carbs.  I can't afford a set right now, but I've also got quite a few things I don't need that I can sell.  I've got two frames (plus a third once I get the '70 cleaned up), plus some KZ1300 and Valkyrie parts I won't need that might get me close.  Or I may use the cash for my other projects.  It's tough to say.

On the plus side, I got my CB750 together and as tuned as I can sitting in a garage.  Idle mix might be a hair rich, and I don't think the sync is 100% locked down, but I won't know more until I get some real rides in.  And the snow has to go away for THAT to happen.

[BenelliSEI]

Looks like mine before I got started! Mine was a May/70 too. Good luck on your new project!

[Lucien Harpress]

More presents came in the mail today!




While these weren't exactly "cheap", I have seen them worse.  They'll need a full go-though, but apart from at least one crusty looking float and a 110 main jet that doesn't match the 120 in the other three, these look easily rebuild-able.   Bowls will need polished, and I'll probably need to zinc plate most of the choke linkage, but apart from that (and oddly enough) I finally have back the style of carbs the bike originally came with.

[grcamna2]

Looks good !

[Lucien Harpress]

Started the teardown and cleanup today.  Apart from some niggles, there's a lot of good here.



There's a bit of pitting on carb 1, but nothing more than cosmetic.  I'll need at least one 120 jet, because for some reason a PO switched one (and just one) jet to a 110.  While the floats on that same carb don't have any holes in them (that I can tell), they ARE dented, and I'm wondering if that was enough to make the guy think he needed a smaller jet.  Either way, I'm replacing the jets and floats both.

I pulled all the choke linkage as well, as that will all need to be cleaned of rust and re-plated.  I'm going to need one of the rubber cones that fit on the choke shaft as well- I got all of them off without breaking them EXCEPT for the last one.  I'll pop a thread in the Wanted section here in a second.

[Lucien Harpress]

Chipping away at my K0 carbs.  Got one (mostly) done, only three more to go.





Thinks went pretty smoothly, for the most part.  All the individual choke linkages were cleaned and re-plated, jets cleaned out, and floats tested.  I wanted to get this one 100%, but the idle adjust knob was worse than I remembered, so all 4 of those are taking a quick dip in Evapo-rust and will be plated as well.

Not too much weirdness so far- the needle clip was in the 4th position rather than the 3rd, so I swapped that back for now.  This particular float valve looks a bit sketchy- the body is rough, but the actual sealing surface may be okay.  Somebody at some point had vapor-blasted the tops and bowls, and while they look nice, I personally didn't like how they looked like they'd been spray-painted silver.  So those got a quick polish and look much much better.

[BenelliSEI]

Those look like the ones I did. Nice work. I think I’m going to take mine apart and have the bodies vapour blasted. The covers I had done ended up with a lovely, super clean finish, that looked very original.

[Lucien Harpress]

I thought about a vapor-blast, but decided to pass for now.  The bodies are actually pretty nice, and the carbs I've seen that have had it done almost look spray-painted silver.  Not a complaint necessarily, but it doesn't fit my preference right now.

Carbs are nearly done.  I'm waiting on a small piece or two (decided to shoot my last pilot jet somewhere into the abyss of my barn when I was hitting it with compressed air and didn't hold on tight enough), and the adjustable choke linkages will need cleaned and plated as well.  In the meantime, I got some more goodies in the mail.



The throttle cable necessitated a switch back to stock bars.  Not the worst thing, as the lower bars I put on years ago are a bit TOO low, truth be told.  New right switch cluster as well, and a replacement throttle tube because it was cheap.

I also lucked into a cheap K0 master cylinder as well.  I really only bought it for the lid, but once it arrived I realized it's not in that bad of shape.  The anodized finish is lighter than stock, but they all are at this point, and it's much better than most I've seen.  I'll have to rebuild it, plus grab the parts for the K0-only lever adjustment, but I've dealt with worse.

[newday777]

1 40 low speed jet

[newday777]

You should have it Tuesday

[Lucien Harpress]

Awesome.  Thank you sir!

[MauiK3]

Great project, looking good.

[Lucien Harpress]

Final pilot jet came in, so I did some final assembly and am happy enough to call these carbs done!









I did a wet fuel test to confirm the float valves and carb bowl gaskets worked, and saw no leaks.  I may do a clear-tube test to see if the actual fuel levels are identical, but everything I'm seeing is promising.  I need a set of the rubber dust caps before I commit to putting all the necessary stuff on, but this is one major hurdle down.

[newday777]

Very cool 😎
What are the carb body numbers on them?

[BenelliSEI]

Don’t the rubber caps come with a new 1-4 throttle cable set?

[Lucien Harpress]

newday: The carbs are stamped with B750A.  I was curious and tried to find out what the difference between these and 7A carbs, but I couldn't find a good answer.

Benelli: They didn't come on the set I bought.  I poked around at a couple options, but I need to get paid first.

[BenelliSEI]

newday: The carbs are stamped with B750A.  I was curious and tried to find out what the difference between these and 7A carbs, but I couldn't find a good answer.

Benelli: They didn't come on the set I bought.  I poked around at a couple options, but I need to get paid first.

I have a few sets of toasted, original cables. If they have any caps, I will let you know.

[newday777]

newday: The carbs are stamped with B750A.  I was curious and tried to find out what the difference between these and 7A carbs, but I couldn't find a good answer.

Benelli: They didn't come on the set I bought.  I poked around at a couple options, but I need to get paid first.

B750A are 4into1 cable (I just needed confirmation of that)
7A are the beginning of the 2 cable roundtops. Started on the K1. I have a set of 7A. And others sets of 657B, 086A.

[newday777]

My carb sheet by model and carb numbers confirmed by original bikes I have and have worked on.

[Lucien Harpress]

Thanks for the info.  For comparison, I think I'm currently running either 657Bs or 086As (although I haven't gotten them to play nice with the K0 Airbox yet, if I do at all).

Benelli- If you've got a set of caps, I definitely won't say no.  Let me know what you got!  Just to confirm, it's the ones that fit over and cover the brass adjusters on top of each carb.

[BenelliSEI]

Thanks for the info.  For comparison, I think I'm currently running either 657Bs or 086As (although I haven't gotten them to play nice with the K0 Airbox yet, if I do at all).

Benelli- If you've got a set of caps, I definitely won't say no.  Let me know what you got!  Just to confirm, it's the ones that fit over and cover the brass adjusters on top of each carb.

Understood. Will dig around later in the week and see what I can find.

[Lucien Harpress]

Thanks.  I appreciate it.

Did a bit of puttering around in the garage, and had some good, and some bad.  On the one hand, I managed to get the lid off my (fairly decent looking) K0 master cylinder, and the inside looks surprisingly clean.  I still need to pull the plunger, and it's fairly frozen in place, but I got the clip out and have it soaking right now.

On the other hand, I tried to fire up the bike as it stands, and somehow managed to lose some cylinders.  I managed to get it running on three, but then it dropped down to two.  I pulled the plug, and I'm getting intermittent-to-no spark on either plug 2 OR 3.  This is the second time I've lost spark since replacing both the wiring harness AND coil, (plus the points and condenser, if I remember correctly) and I think last time it was the same 2/3 coil.  Not a fan of chasing sparks on a brand-new electrical system, but here we go.

[newday777]

Aftermarket points and condensers?