Topic: Potential 1970 CB750 K0/K1 Hybrid

[Lucien Harpress]

Hopefully this pain in my backside is the last time I have to worry about it.  Engine is back in.



There's still going to need to be some frame touch-up on the paint, but better than I was expecting.  I'm waiting on a couple random pieces (rear shocks, new coil, regular chain because I'm not a fan of the clearances on my o-ring chain), but once I get those reassembly should go pretty quick.

[RAFster122s]

Congratulations on getting engine back in, it looks great!

[grcamna2]

Congratulations on getting engine back in, it looks great!

Yes it does look very nice 

[SOHC4 Cafe Racer Fan]

That's super clean!

[RAFster122s]

New bike clean, tidy, and as good or better than new…should be from all the effort, sweat and money Lucien has poured into the restoration.

[Lucien Harpress]

Doing the work as I can as parts dribble in from the mail.



I was going to replace the intake clamps, but new ones are either the wrong color, or the wrong style.  So, I took the set I had, dunked them in Evapo-Rust for a couple days, then after a quick round in my electroplating setup they came out... rather well, I think.

Oil filter went on today.  The only current bugbear is the breather line from the rear of the engine case up to the oil tank.  It's a goofy size (7mm ID, thin wall), and the initial line I ordered off Amazon didn't have a high enough heat rating.  I'd use the one that came off my bike before, but the line for the K0 is longer than later models, so it's too short.  I had to resort to grabbing one from Yamiya, but now I'm waiting on shipping. 

On a more long-term scale, next time I get paid I'm going to grab one last can of paint to hit the couple pieces I didn't last time (foot pegs, battery and tool trays) plus touch up the nicks on my frame.  But that's an update for a later day.

[BenelliSEI]

Looking really nice. Well done!

[Lucien Harpress]

After putting in an order for a new non o-ring drive chain, paint for the battery and tool boxes plus frame touch-ups, and a fresh (non-painted) spring for the side stand, I think I finally have everything I need to finish this bike up 100% at least on the way.



It'd throw on the exhaust pipes just to see how the bike runs, but I seem to remember the footpegs are an absolute pain to take on and off with the pipes in the way.  And the pegs have to come off to get painted.  Same with the sidestand.  There's a decent chance I can get the bike on the road this year- it'll be weather dependent, and probably chilly, but knowing I can cross this project off the list in 2023 would be a good feeling.

[jakec]

When I installed an x ring chain on mine with stock sprocket sizes, I had to shave down the chain guide that attaches to the inside of the sprocket cover. When the cover was on the sprocket couldn’t turn at all. I just did a little shaving and it’s fine.

[Lucien Harpress]

Brand new chain arrived in the mail.  A half hour later, and I no longer have a glorified rolling engine stand.



I actually have an o-ring chain that I ran briefly, but swapped it out for a regular one for a couple reasons, mostly personal preference.  Main thing is that I get they technically require less maintenance, but a lack of maintenance is what broke my last one.  I figure forcing myself to stay on top of it would be a good thing.

Still, now I'm just waiting on paint at this point.

[Lucien Harpress]

All my last parts for painting have been pulled, and although I don't have a picture of it, as of today have been painted.



I also did a couple frame touch-ups where getting the motor back in chipped the paint, and put an order in for some replacement springs so I can get all the footpeg hardware back to a silver like it belongs.  I see no issue with getting the exhaust back on this weekend and getting it all tuned up next week. 

[grcamna2]

All my last parts for painting have been pulled, and although I don't have a picture of it, as of today have been painted.



I also did a couple frame touch-ups where getting the motor back in chipped the paint, and put an order in for some replacement springs so I can get all the footpeg hardware back to a silver like it belongs.  I see no issue with getting the exhaust back on this weekend and getting it all tuned up next week.

The rack of 6) carbs on the bench;what do they fit ?

[Lucien Harpress]

My Kawasaki KZ1300.  They're the only twin-barrel CV carbs ever made, far as I can tell.  They're pretty straightforward design-wise, but I've been struggling with that bike for going on 10 years now.  Once my 750 is taken care of I want to knuckle down and finally get the 1300 figured out.

[newday777]

My Kawasaki KZ1300.  They're the only twin-barrel CV carbs ever made, far as I can tell.  They're pretty straightforward design-wise, but I've been struggling with that bike for going on 10 years now.  Once my 750 is taken care of I want to knuckle down and finally get the 1300 figured out.

I wondered what those fit when I saw them earlier

[Lucien Harpress]

I'm calling this one tentatively finished.  With the exhaust on she fired up pretty quickly, and today I spent about a half hour dialing the carb sync in 100%.  I forgot how much of a royal pain in the backside it was to get to the sync ports, and the rubber dust caps are quite annoying, but with any luck I won't have to touch them for a minute, so it's all good.







Other than any issues that show up on a shakedown run, I'm also reading 15.5 volts at the battery at higher RPMs, so I need to look into adjusting the regulator.  I wondered why my blinker changed speed so much while revving, and this might explain it.  Still, it hasn't blown up my battery yet, so I'm not at risk for immediate failure at least. 

(You may notice the puddle under the center stand.  THAT nearly gave me a heart attack.  After running the bike for about a half out, I shut everything down and was ready to pack up my tools when I noticed something dripping under the bike.  After doing about three laps of the bike and tearing it half apart looking for some kind of oil leak, I realized what it ACTUALLY was- condensation dripping from the exhaust pipes because it was like 40 degrees out.    )

[Lucien Harpress]

Happily, today I got the bike in good enough shape for a quick shakedown run.







I had some iffy stuff happen yesterday, so this was less a proper ride and more double checking a few problem areas.  My oil light was on the fritz (coming on when I revved it, but on when it was at idle), so thankfully that went away.  I was chasing fuel leaks at the petcock, but a couple spare clips solved that.  I also wanted to check for oil leaks, and thankfully I did NOT find anything there.

Actual performance was quite nice.  I swapped out my rock-hard Chinese replica rear shocks for a pair of still-Chinese Tec shocks, but they at least had the correct spring rating, the ride was quite pleasant.  Combine that with a crank balance, and this bike has never been smoother.  Power delivery it also smooth with no hesitation, so all good things there.

The only downside is that when the bike is hot it tends to idle down and eventually die.  A quick search points to an overly-rich idle setting, and at least one of the plugs I could get to seemed pretty black and fluffy.  This is odd, because I was able to get a rock-solid idle while I was doing my carb sync, but I guess on the road is a different animal.  Still, looks like an idle-drop is in my future.

[BenelliSEI]

Looking good!

[Lucien Harpress]

Going to have to pull the carbs again, I think.  I took it out for another ride today, and while on the throttle the bike pulls strong and feels really good, idle is a different story.  It felt weak, and wanted to die after revving before slowly coming back up.  Back in the garage I found out that cylinder 2 isn't pulling it's weight, and seems to run best with the air screw on that carb run all the way in.

Plan is to pull the rack, do another quick clean just to be safe, set the mixture screws at one turn out per the manual, and try tuning it from there.  I don't think the idle passage on that carb is plugged (because turning it out DOES change how it runs- it just runs worse), but it never hurts to be sure.

[Lucien Harpress]

I learned today that clear coat on an air-cooled engine turns yellow pretty quick when it gets hot.  Who knew?

 

I'm NOT pulling this engine again.  Right now the only really bad part is the cooling fins on the top end, and I might, MIGHT be able to mask and paint it with regular silver.  I'll have to pull the exhaust, and I'm up the creek without a paddle if the bottom end starts looking bad.  But I'm also not putting up with with a yellow engine I put this much work into. 

Ah, well,  With enough drop cloths and masking tape I can make something work.

[BenelliSEI]

What a peeve. Ride it!

[Lucien Harpress]

I'm not too overly worried about it.  My riding season is pretty well over with anyway.  I was also getting real funky stuff happening with the idle (the bike ran best with the air mix screw on 2 all the way closed, for example), so the carbs are out on my bench, tore apart for a full clean. 

Really all I'd have to do to touch up the top end is pull the exhaust, and I can do that in my sleep at this point.

[jakec]

What shocks did you get? I still have my originals and they need to be replaced. As for your carbs you might want to read my post from this spring, maybe just as a checklist, I was also having idle problems. They are all dialed in now.

[Lucien Harpress]

Here's where I got my shocks from.  Be warned, build quality still seems like typical "Chinese Reproduction"- not horrible, but you can tell they're $99 shocks.  Still, the spring rate is MILES better than the pair I pulled off, which was the rock-hard springs these usually come with.

https://www.tecbikepartsusa.com/HONDA_CB750_CB750F_SuperSport_Shocks_p/j-sh02a-h750.htm

I'll take a look at the carb checklist.  This set has always been pretty clean, but I also never had them apart, either.  I boogered up the threads on the sync port for carb 2 a while ago, so part of this teardown was to get at and re-tap correct threads back into the carb body.  The bodies still seem really nice, but the main needles for 1 and 4 are pretty black.  Thankfully they're not too complicated to deal with.  I've been inside GL1000 carbs, so 750 carbs are a cakewalk by comparison.

[BenelliSEI]

Just reading your last post reminded me of a modification I’ve often thought of making. Instead of plugging the sync ports on the carb bodies, I want to find or make a nipple that screws in the hole. Locktite it in place and plug it with a rubber cap, sort of like on a KZ1000 I restored a few years ago. So much more convenient than those screw in sticks! The KZ acually had these built into the rubber manifold.

[Lucien Harpress]

I had an XS1100 that was set up the same way- screw in nipples capped off by rubber caps.  It's not a bad setup, and if you get some of the smaller screw-in adapters it's real easy to add them.  I've heard of worries that a sufficiently powerful backfire can pop the cap off, but keep some spares with you and it's not an issue.

I solved my problem by getting some new adapters that neck down in the middle, enough to clear the choke linkage.  I haven't tried them yet, but they should work.