Topic: Look, squirrel! Or, how bike projects shift quickly; new CB750 K6 project for me

[grcamna2]

Your bottom photo with the white paper gauge resting on the gasket surface is correct.

[gearsoup]

Your bottom photo with the white paper gauge resting on the gasket surface is correct.

So it's 26mm from that surface?
I've found a couple YT vids that state differently, so I'm not sure which way to go 

And here's one that uses the other surface:

I'm not arguing one way or another, I just want to make sure that how I do it is accurate

Image taken from the FSM:

[grcamna2]

HondaMan Mark just wrote a reply to this issue not long ago.

[gearsoup]

HondaMan Mark just wrote a reply to this issue not long ago.

Oh, cool, I'll see if I can find it, would you happen to know the thread by chance? I read the carb section in his book, but he didn't make mention of it there..

[grcamna2]

HondaMan Mark just wrote a reply to this issue not long ago.

Oh, cool, I'll see if I can find it, would you happen to know the thread by chance? I read the carb section in his book, but he didn't make mention of it there..

    I can't recall right now,sorry.
He was speaking about where to check the float height and he mentioned there are a notch/'s on certain early carb. bodies(K0/K1)and you can use those;which I think is a notch which allows direct access to the flat gasket surface,imo.
Send him a PM and ask him to add to this thread.

[gearsoup]

I can't recall right now,sorry.

Good idea, I did just that. While we're waiting, I did find this one comment by him here, post #17:
http://forums.sohc4.net/index.php/topic,194513.msg2276780.html#msg2276780
In it, he does state "from the gasket surface". No biggie, carbs are still on the bench. A half hour of printing and I'll have the proper gage ready to go. (yeah yeah, 5 minutes with tin snips in sheet metal)

(it is a whole 2.4mm difference between the two surfaces, certainly want it done proper)

Before and after pics below 

[HondaMan]

I was told by the PO that "oh, I had a guy rebuild the carbs completely". Seeing that it runs and starts rather poorly, I'm a tad bit skeptical of the work that was done....

Yeah, that's the statement that brings these carbs to my bench, trying to make them work again...
Replace the brass, park the bike unless you've got LOTS of time and more brass parts to try to get it close to running right again. While it is possible with K&L brass to get the post-1975 versions running usefully, I've not seen that with the Keyster brass, yet. The Keyster brass is death for the pre-1976 versions of the roundtop carbs, in my experience: I've seen some run with modified jetting (like #140 mainjets) and emulsifier tube holes (like 0.045" holes in the large ones, 0.032" holes in the smaller ones) and #42.5 or #45 pilot jets, and deeper float bowls, but they don't have the top end speeds of yore. During the 55 MPH speed limit that wasn't a serious problem: today in the American West that would get you run over from behind by a semi. Interstate speeds out here run to 90 MPH in real traffic: I returned from Squaw Pass last Fall and had to best that to pass a semi full of gravel on its way down the interstate: when I looked down at the speedo after the windy, rocky (literally) passing maneuver, we were coming back from 108+. The Keyster stuff wouldn't do that here.

[grcamna2]

I can't recall right now,sorry.

Good idea, I did just that. While we're waiting, I did find this one comment by him here, post #17:
http://forums.sohc4.net/index.php/topic,194513.msg2276780.html#msg2276780
In it, he does state "from the gasket surface". No biggie, carbs are still on the bench. A half hour of printing and I'll have the proper gage ready to go. (yeah yeah, 5 minutes with tin snips in sheet metal)

(it is a whole 2.4mm difference between the two surfaces, certainly want it done proper)

Before and after pics below 

Mark,what about his question on exactly where to measure the float height from ?

[gearsoup]

Replace the brass, park the bike unless you've got LOTS of time and more brass parts to try to get it close to running right again.

So, emulsifier tubes, slow jet, main jet to be replaced with OEM. What about the needle seat (not sure of the proper name of the receptacle that receives the float needle), is Keyster okay, or should that also be replaced by OEM?  For the parts I just listed, is https://www.jetsrus.com/index.html good to go, assuming I go with Keihin badged items?

As stated in one of my responses, I DO have another set of carbs (same year) with OEM brass. The only issue is; 2 are definitely good (varnished, but good), 1 is so-so, and the 4th is.... 

[gearsoup]

Mark,what about his question on exactly where to measure the float height from ?

Mark was kind enough to answer the question in my carb-specific thread: http://forums.sohc4.net/index.php/topic,194651.msg2278808.html#msg2278808

(On the 76, it's to the lip/ridge, not the gasket surface).

Looks like I've got a task of replacing as much brass as I can. Emulsifier tubes, slow and main jet should be doable, not sure if the float needle seat is needed, or is aftermarket acceptable for those. At least I am starting off with OEM needles up top, so it's just bottom end stuff. Fun times.....

[gearsoup]

I'm embarrassed to admit how long it took me to get that darn airbox back on. I should have sprung for new boots on that side of things, but I thought they were pliable enough....
In actuality, I had the insulator boots clocked too high and the carbs were pointed well up towards the rider. Looking at photos, they should only be slightly elevated at the rear. Adjusted them all down a touch and the box slid on with just a bit of persuasion. No cussin, kids were about

[PeWe]

We are many that have had that problem.
There are threads about it with photos of how carbs need to sit. (Carb boots orientation)
+ the orientation of the rubber stacks.
The wider part up close to the clamp on carb.
My box did not sit high enough for the M6 bolts to match frame and box bracket

I had totally forgotten it. Last time before my K2 build early 2019 was  my K6 1982.  It got pods 1983-84.

[BenelliSEI]

I'm embarrassed to admit how long it took me to get that darn airbox back on. I should have sprung for new boots on that side of things, but I thought they were pliable enough....
In actuality, I had the insulator boots clocked too high and the carbs were pointed well up towards the rider. Looking at photos, they should only be slightly elevated at the rear. Adjusted them all down a touch and the box slid on with just a bit of persuasion. No cussin, kids were about

I just had the same fiddle on the K6. New boots on the air box made it much easier.

[grcamna2]

We are many that have had that problem.
There are threads about it with photos of how carbs need to sit. (Carb boots orientation)
+ the orientation of the rubber stacks.
The wider part up close to the clamp on carb.
My box did not sit high enough for the M6 bolts to match frame and box bracket

I had totally forgotten it. Last time before my K2 build early 2019 was  my K6 1982.  It got pods 1983-84.

I hope to someday locate a small custom(quality)maker of rubber carb/airbox boots who makes great rubber products for many Japanese bikes that last as long as the originals sometime soon;not holding my breath,but actively searching. 

[BenelliSEI]

FYI….. The manifold rubbers I bought from vintagecb750.com did not fit correctly. I haven’t figured out if I ordered the wrong ones or they are junk. But, the airbox boots/velocity stacks are soft, fit perfectly and are inexpensive. They worked well.

[gearsoup]

Yep, I had heard some less than stellar reports of aftermarket carb boots, so I bit the bullet and went with OEM units. Upon inspection, the ones that were already on the bike ARE OEM and were still in decent condition. I'll hang onto them as I'm relatively certain that this isn't going to be my last CB750 to land in my garage.....

[HondaMan]

As stated in one of my responses, I DO have another set of carbs (same year) with OEM brass. The only issue is; 2 are definitely good (varnished, but good), 1 is so-so, and the 4th is.... 

Is that a mouse in there? 

I just installed a set of aftermarket intake hoses last week for a test-run of a 750 engine I just finished. Talk about a guessing game: they have no marking whatsoever(!), and I bought them some 3 years ago, never looked at them before last week. It took about an hour of twisting and playing with them to figure out which ones went where to make the flat 'face' to stick the carbs into. I only bought them for these startup run-tests. I notched them on their 'top' carb ends to remind me when I next use them: fortunately I didn't have to install the airbox behind the carbs for this test, as I became less sure that one would fit if the engine was in a frame.

I suspect these are the same ones you got, BenelliSEI? They feel soft as silicone might. They are pretty, but not nearly as strong as the OEM versions.

[BenelliSEI]

“ I suspect these are the same ones you got, BenelliSEI? They feel soft as silicone might. They are pretty, but not nearly as strong as the OEM versions“

Sounds like it. The ones I received had a sticky label on the bags, but no actual markings. You have more patience than me! I never got the. Even close to lining up. Maybe I’ll try again on the S/C that’s still in my engine stand……

[HondaMan]

“ I suspect these are the same ones you got, BenelliSEI? They feel soft as silicone might. They are pretty, but not nearly as strong as the OEM versions“

Sounds like it. The ones I received had a sticky label on the bags, but no actual markings. You have more patience than me! I never got the. Even close to lining up. Maybe I’ll try again on the S/C that’s still in my engine stand……

I wasn't convinced that the 'angle of the dangle' was right for the carbs after I got them to mount up, they looked kind of "high" above the transmission. It was on a test stand, so I didn't have a frame around it to try for an airbox fit-up. The engine only had to run to about 5k RPM after 7-8 minutes of warmup running (1 pint of gas), so the carbs didn't even have to be 'close' to the right angle(s) for it to run this simple test - it's mostly for oil leak searches after the build. So, I really don't know if they would work on an actual bike?

[gearsoup]

Update:
Keihin brass came in, got the carbs buttoned up. Installed the battery and Delkevic 4-1 exhaust. Being the impatient sort (I really should let the gasket sealant sit for 24 hours) I decided (probably a bad idea that I'll regret) to fire it up and just see if it runs.

Well, my handlebar start switch isn't doing anything. I recall it being finicky when I bought the bike, so it's likely corrosion or a loose wire somewhere. So, that left trying the kick start...
3 kicks in and she was running! I was pleased, but then looked down and saw some gas puddling up on the floor. It appears that carbs 1 and 2 are either not set right on the float, or the needle isn't seating properly.  (this is with the bike on the centerstand, fwiw)

In addition, I'm only running on cylinders 1 and 4. So, have to trace down the right side coil wires and make sure nothing is broken/disconnected.

Would anyone be able to point me towards a "how to diagnose coils and/or ignition switches"? (I haven't read that chapter yet in Mark's book)

[newday777]

The other possibility is a bad condenser on 2/3. Had that last summer on a friend's K4.

[BenelliSEI]

Check power to the coil that runs 2-3. Black with white stripe. Did you clean and gap, both sets  of points?

[gearsoup]

Check power to the coil that runs 2-3. Black with white stripe. Did you clean and gap, both sets  of points?

No, I was too curious if my carb rebuild actually worked and how the exhaust was going to sound 

I'll dig into it this morning when I get back from church, seems rather straightforward.

[PeWe]

If engine has points, a short caused by condenser wire connector where it connects by a small screw with nut will disable  that point. Fiber washer must  sit correct too.
Very easy to happen.

[gearsoup]

Update:
After snowblowing the drive enought to get out, church and breakfast, I've had time to fiddle with things.
1-4 gap was tight at .01" and had some corrosion/arc buildup. Quick work with a fine needle file and it was cleaned up. Adjusted the gap to .014" (using the tools at my disposal, I opted to use a .0001" test indicator to measure deflection when using the shims; overkill?)
2-3...well, that had almost zero gap. What the heck is up with that?! Again, cleaned it up and adjusted it.

Now, on to timing (using a test light):
1-4 was to the right of the "F". (forgive my noob ignorance here, does that make it advanced?) I adjusted the main plate to get it to light up right on the nose of the "F hash mark.
2-3 was the reverse, almost 3/16" beyond the "F". (again, noob here; is that retarded timing?) (that's not politically correct anymore, what word is proper?) 
I adjusted the 2-3 plate itself.

I'll get back out in the shop later this afternoon to double check my point gaps are proper after all this fiddling.

I must say, on a personal note; I find it almost cathartic to work on this bike. Just focused on the task at hand, learning as I go, it's peaceful (although I wasn't feeling that when I was putting on the airbox last week!)