Topic: Potential 1970 CB750 K0/K1 Hybrid

[Lucien Harpress]

I don't remember, but probably.  I may just nab a fresh set to be sure.

[BenelliSEI]

Did you install new plugs? Any chance they are fake NGKs?

[Lucien Harpress]

No, plugs are new.  They're the same as in my GL1000 and I had spares.

[BenelliSEI]

No, plugs are new.  They're the same as in my GL1000 and I had spares.

Try swapping than around and see if the “no spark” moves with them or stays with the cylinder. Have you shortened and reconnected plug wires to the caps?

[Lucien Harpress]

It definitely stays with the cylinder- I tested the plug on the lead for 1 and she fired just fine.  Cylinder 2 worked on and off, but I eventually lost spark on that one as well.

Your mention of points got me thinking, so I decided to take a chance and picked up a Tytronic ignition.  I have electronic ignition on my GL1000 and love it.  I'd kept the points on my 750 so far because they've worked.  If I'm having to question that now, might as well upgrade.  That said, I'll hold on to the points plate, just in case.

[Lucien Harpress]

It what I will call a learning experience, my electronic ignition arrived in the mail today.  Figuring it wouldn't be a huge job to swap it over, I pulled the points off, and commenced to the install.  Everything went decently well, until I got to adding the magnetic pickup on to the advance mechanism.  While it took me a second to realize, there's a little locator pin to help you reference the points lobe.  Problem is, the Tytronic ignition doesn't account for this pin.  I tried to remove it, and it wasn't budging. 

Now, I'm REALLY not a fan of doing something that I can't UNdo later, and to get this ignition to fit I would've had to grind off this pin.  And that wasn't something I was comfortable doing.

Long story short, the electronic ignition is back in the box, and a points plate with genuine Tec points and condensers is in the mail.

(It's a bit of a weird setup.  I replaced both points with afermarket at the same time, and while 2/3 conked out, 1/4 has been humming just fine.  That said, WAY back I was getting some bad arcing from 2/3, so I replaced the condenser, and JUST that condenser.  That was probably aftermarket too, and while it's not that old, I'm curious if that's accounting for the dodgier-that-usual spark.  Ah well.  The whole mess is getting replaced once the points arrive, so I'll find out one way or the other.)

[grcamna2]

It what I will call a learning experience, my electronic ignition arrived in the mail today.  Figuring it wouldn't be a huge job to swap it over, I pulled the points off, and commenced to the install.  Everything went decently well, until I got to adding the magnetic pickup on to the advance mechanism.  While it took me a second to realize, there's a little locator pin to help you reference the points lobe.  Problem is, the Tytronic ignition doesn't account for this pin.  I tried to remove it, and it wasn't budging. 

Now, I'm REALLY not a fan of doing something that I can't UNdo later, and to get this ignition to fit I would've had to grind off this pin.  And that wasn't something I was comfortable doing.

Long story short, the electronic ignition is back in the box, and a points plate with genuine Tec points and condensers is in the mail.

(It's a bit of a weird setup.  I replaced both points with afermarket at the same time, and while 2/3 conked out, 1/4 has been humming just fine.  That said, WAY back I was getting some bad arcing from 2/3, so I replaced the condenser, and JUST that condenser.  That was probably aftermarket too, and while it's not that old, I'm curious if that's accounting for the dodgier-that-usual spark.  Ah well.  The whole mess is getting replaced once the points arrive, so I'll find out one way or the other.)

Terry from Australia has installed a few of those Tytronic ignitions;send him a PM and ask how he installs with that pin.

[HondaMan]

It what I will call a learning experience, my electronic ignition arrived in the mail today.  Figuring it wouldn't be a huge job to swap it over, I pulled the points off, and commenced to the install.  Everything went decently well, until I got to adding the magnetic pickup on to the advance mechanism.  While it took me a second to realize, there's a little locator pin to help you reference the points lobe.  Problem is, the Tytronic ignition doesn't account for this pin.  I tried to remove it, and it wasn't budging. 

Now, I'm REALLY not a fan of doing something that I can't UNdo later, and to get this ignition to fit I would've had to grind off this pin.  And that wasn't something I was comfortable doing.

Long story short, the electronic ignition is back in the box, and a points plate with genuine Tec points and condensers is in the mail.

(It's a bit of a weird setup.  I replaced both points with afermarket at the same time, and while 2/3 conked out, 1/4 has been humming just fine.  That said, WAY back I was getting some bad arcing from 2/3, so I replaced the condenser, and JUST that condenser.  That was probably aftermarket too, and while it's not that old, I'm curious if that's accounting for the dodgier-that-usual spark.  Ah well.  The whole mess is getting replaced once the points arrive, so I'll find out one way or the other.)

This is/was an issue with the Dyna units, too. The pin doesn't come out of the advancer very well: it galls the hole and prevents ever going "back" to holding the pin again. That's why so many have gone to 4into1.com and bought their cheesy advancer, then removed its cam and installed the Dyna or Tytronics cam on it instead of their OEM version.

[Lucien Harpress]

Interesting.  Well, for now the plan is to see if I can get a set of genuine points and condensers to work.  If not, and I decided to give the electronic ignition another go, I'll probably look into sourcing a spare advance mechanism and grinding that pin off.

[Lucien Harpress]

Alrighty, so couple of updates:

- Genuine points arrived in the mail.  I still need to set the gap and timing, but at least it's installed.  I wanted to finish up swapping my bars and controls, first.

- Speaking of...





So while it's too early to speak on the turning, there is a LOT I like about these early carbs so far.  Mostly due to access issues.  The later round-top carbs probably function better, but you could tell the top linkage was definitely a design compromise.  Fuel line routing seems easier on these, access to sync port and mixture screws is easier, and overall they just seem cleaner.  I may change my tune when it comes to setting them up, but so far I'm liking them.

I'm still waiting on a couple clips and hoses before I can start this puppy up for the first time, but I'm getting excited.

(Speaking of, the four vent hoses that lie over top of the airbox- how far do those go down?  Do they just sit on top, or are they long enough to drape down the backside of the box?  A minor silly question, probably, but I figure now is the time to get the correct answer.)

[grcamna2]

Where did you purchase your points?  pics ?

[BenelliSEI]

Original vent pipes went up and over, about 1/2 way down the back on my K0.

[Lucien Harpress]

Where did you purchase your points?  pics ?

Points were a used set from eBay.  Not new, sadly, but Tec everything (points, plate, condenser).  Plan is to dress the points and see if they still work, fingers crossed.

Benelli- Thanks.  I think I ordered 10ft of hose, so that should be more than enough.

[Lucien Harpress]

Points are in and ignition is timed.  I'm not 100% happy- 2/3 is right on, but 1/4 is ever so slightly late, even though I've got the points plate cranked all the way counterclockwise.  Still, I got spark on all 4 (even IF it seems a bit weak to my eye), so I'm going to run with it for now.  Plus this seems to be a not-unheard of occurrence, so I don't feel too bad.

UPDATE:  Call this one my bad.  I hooked up the gas IV to see if I could get some signs of life, and instead I got all manner of odd pops and farts, nothing that sounded normal.  On a whim I swapped the coil leads and managed to get it to run, very poorly.  If I had to guess?  Probably managed to get the cam lobe installed backwards.  Oops.

That said, I found a decent ignition advance for a good price, so that's in the mail, in case I give up on the points and swap the electronic in instead.   

[Lucien Harpress]

Got my first taste of tuning K0 carbs and it was... interesting.  The hardest part was getting things to a close enough baseline so I could even think about fine-tuning it. 

(Well, right behind that time it ran for a bit, it died, I couldn't figure out why, and it took me 20 minutes to realize it was because I forgot to turn the gas back on.)

Either way, before I ran out of gas for real (out of my IV tank) I managed to get the carbs pulling equal vacuum at idle.  I would kind of go all over the place when I revved and wouldn't like to get back without a bit of persuasion, but following the gauges I got them close.  Cables are next, and those seem to be oddly inconsistent.  At least for a baseline, how much free play should be on the cable housings between the tops of the carbs and the splitter?  My manual says about 1mm, but should the free play on that section be pretty tight (with all your slack on the adjust near the handlebars)?

In any case, it was a fun first go-around.  I've got spark on all 4, so electronic ignition stays in the box for another day.  And setting timing is  LOT easier when you've got the cam facing the right way.     I'll pick at it some more this week.

[jakec]

I would say play value on the cables should just be more than zero, and after that as long as they're all the same, then it's fine. Tuning my carbs was a hassle like I mentioned before. But once I got it, they've been good. At first you think the individual idle adjustment is a pain but then you realize it's actually nice having a thumb screw for bench sync.. as long as you don't bump it once it's set.. lol. I ended up needing a new cable, and it didn't come with rubber boots (motion pro, it was $30 instead of $100+). In the end this actually made adjustment easier even though it's not totally correct. Yes someone pointed it out at a meet. Haha. If you're having trouble syncing always make sure the cable hasn't fallen out of the 4into1 housing before changing your adjustment.

[Lucien Harpress]

I got a bit sidetracked by re-arranging my garage space.  On the downside, I had to take quite a bit of time away from the 750, but on the upside my shop space is MUCH more usable.

That said, after a bit of fiddling with carb settings, I ended up pulling the rack again.  I was getting fuel overflow from carb 3 way too often, and even while running the bike was far from consistent.  I decided to swap the brass floats for the plastic ones used in post-K1 bikes, and I ended up swapping over the float valves as well.  The floats themselves have an additional sleeve soldered into the pivot point, so they rock side to side a bit less, and I've had more success with plastic floats over the brass ones anyway.  The newer float valve springs seem to be a bit "snappier" than the ones that came in my K0 carbs, and they always worked fine when my bike was a K2.



It was a bit cold to do real tuning today, but I'm hoping to hit it hard this weekend.  Maybe get it good enough for another road test.

[Lucien Harpress]

This bike puzzles me.  Carbs went back on, I decided to pour some fuel into them just just to see what would happen, and despite different floats AND float valve, carb 3 still overflows. 

I did a bit of testing (namely removing the bowl and physically closing the float valve with the floats, using my fingers) and still got a decently large dribble of fuel when I turned on the gas.  So, back out the rack came, and is currently sitting on my bench until I get the gumption to rig up some bench tests.

Obvious culprit is a bad float valve, but getting two bad ones in a row, isolated to the same carb body is a bit of a coincidence too far.  Hopefully digging into things a bit more might shed some light.

[newday777]

Aftermarket float valves or from a Honda with parts number label?

[newday777]

David Silver Spares and CMS have original Honda float valves as well as they appear available from Honda

https://www.davidsilverspares.com/parts/by-part-number/part_16125235004/

https://www.southsoundhonda.com/--xpartsstream#/s/HOM//16011-375-004//1/y

Aftermarket float valves have been known for not operating correctly and give problems setting.

[Lucien Harpress]

I just confirmed that the float valve in question IS a genuine Honda part, and the valve itself isn't the problem- for whatever reason, I'm getting leakage from between the valve body and carb body itself.  So, either the gasket is shot, or I've got to clean up the sealing surface on the carb body.  I probably should've checked this before reinstalling the carbs, but this is the first time I've had this particular issue surface.

UPDATE: I'm an idiot.  The valve wasn't screwed down all the way. 

[newday777]

Thanks for the update

[BenelliSEI]

Welcome to the Idiot Club. Last time I had a similar issue I’d put a float in upside down!

[Lucien Harpress]

I'm still picking at carburetors.  I don't know why, but these carbs are being SHOCKINGLY annoying when it comes to float valves.  Everything is genuine Honda, but I'm still getting all kinds of weird fuel levels, gas out the overflow tubes- heck, once I somehow managed to get fuel dumping on to my engine and airbox, but the overflow hoses were bone-dry!  Still, my last bench test confirmed everything was finally sealing up, and checking with a clear tube reveals consistent fuel height, so I'm making progress at least.

Idle is locked down and good.  I'm getting a real bad stumble off- idle, but I haven't locked down the sync on the cables yet, so I won't start diagnosing that problem until I do.

[newday777]

I'm still picking at carburetors.  I don't know why, but these carbs are being SHOCKINGLY annoying when it comes to float valves.  Everything is genuine Honda, but I'm still getting all kinds of weird fuel levels, gas out the overflow tubes- heck, once I somehow managed to get fuel dumping on to my engine and airbox, but the overflow hoses were bone-dry!  Still, my last bench test confirmed everything was finally sealing up, and checking with a clear tube reveals consistent fuel height, so I'm making progress at least.

Idle is locked down and good.  I'm getting a real bad stumble off- idle, but I haven't locked down the sync on the cables yet, so I won't start diagnosing that problem until I do.

Hondaman posted about new float valves are different height than the original. Even from Honda.