Topic: '82 cb650sc cafe project

[kerryb]

Well, this is an '82 so when I held pd42's up to the engine they obviously don't fit.  To make it work I would need to build a mounting plate...is this re-racking the carbs?  Not sure if I'm up to the task and since the existing cv carbs work fine, the motivation to try is not there yet.  Achieving the precision needed to make the chokes work smooth is not something I have the tooling for.  But we can always pipedream right?

[SOHC4 Cafe Racer Fan]

Well, this is an '82 so when I held pd42's up to the engine they obviously don't fit.  To make it work I would need to build a mounting plate...is this re-racking the carbs?  Not sure if I'm up to the task and since the existing cv carbs work fine, the motivation to try is not there yet.  Achieving the precision needed to make the chokes work smooth is not something I have the tooling for.  But we can always pipedream right?

Re-racking the carbs is re-mounting the individual carburetors so that they are aligned with the head intake ports. 

As a practical matter, the the easiest way to allow your bike to used the CB750 carburetors is to swap out your head for a 1979 or 1980 unit.  In my opinion, the juice is not worth the squeeze.  You are not running an overbore kit and cam, so the carburetors will not have an enormous effect.  And right now, your CV carburetors sound like they are working fine. 

[Godffery]

 So here is a weird story...
A friend stopped by my shop one day, looking for a set of Carbs for a CB650 he was working on. It seems that the PO had totally destroyed the original set, but he brought them with for a size & spacing comparison. I knew that I did not have a set from a 650 but told him he was welcome to rummage threw what I had, well he finds a set that had the proper dimensions but oddly enough, they were from a Kawasaki ZR550 (Zephyr).  Well Damned if they didn't work like they were made for the CB650, he literally just bolted them on, fired it up and set the idle...?!   
 But... Here's the thing; I can't remember if his was the early model 650 or the later?   

[seanbarney41]

That would be pretty epic trip to discover you can just slap on some mikuni vm24s from a kz650...

[SOHC4 Cafe Racer Fan]

I do recall someone making a mention of some model Kawasaki that has better CV carburetors that work with the later head (81-82).  I don't have any more than that though.

[kerryb]

Finally made some progress on frame modifications.  Found a race car shop to bend some tubing, (second attempt) and after much guesswork and fitting, I have a beginning for the new tail section.  Rear wheell is currently blocked up at full shock compression to maintain clearance between the hoop and the tire.
On another note, Pd 42 carbs fit nicely in the stock boots...so a re-rack of the carb bank is looming on the horizon.  it could be quite the adventure.

[kerryb]

A little more progress...currently perfecting my technique of bending a slug around a corner.  Seeking advice about slugs, plates, and gussets for joining tubes that don't meet square.

[kerryb]

Thanks calj, I seriously considered the 1/2 lap method, but the time needed to sneek up on those angles and lengths convinced me otherwise.  I wanted to eliminate the down slope completely but the existing tubing was getting too narrow to take any more off, so here's my solution...a solid slug turned to fit.  Then slit and bent to the right angle for the new tube.  The slug is in for these pics, would you approve?

[Godffery]

 Well kerryb, I would say you came up with a pretty clever solution there!

[kerryb]

Thanks...what's a tubing sander?  I could always use a new tool!  Does it do more damage than good, like a belt sander, or clean up previous work like a random orbit sander?!?

 Thanks Godffrey, I do what I know the best I can and make stuff up when presented with new problems.

[kerryb]

[quote author=calj737

That’s an example of a tubing sander. The belt allows you to wrap around the tubing to sand/grind/polish the circumference without grinding flat spots in a round tube. Very useful tool.
[/quote]

Now that's a nice machine!  I should have one of those in my arsenal.

[kerryb]

+1 on the Metabo, that's what my grinder is, and it was money well spent!

[Ramrod_Racing]

So here is a weird story...
A friend stopped by my shop one day, looking for a set of Carbs for a CB650 he was working on. It seems that the PO had totally destroyed the original set, but he brought them with for a size & spacing comparison. I knew that I did not have a set from a 650 but told him he was welcome to rummage threw what I had, well he finds a set that had the proper dimensions but oddly enough, they were from a Kawasaki ZR550 (Zephyr).  Well Damned if they didn't work like they were made for the CB650, he literally just bolted them on, fired it up and set the idle...?!   
 But... Here's the thing; I can't remember if his was the early model 650 or the later?   

I do recall someone making a mention of some model Kawasaki that has better CV carburetors that work with the later head (81-82).  I don't have any more than that though.

I just picked up a set of ZX600C (1st gen Ninja carbs) for my '82. I believe they are common to the mid-80's GPZ550's as well. Anyhow, I was planning on needing to do some fiddling to make them fit, but I'll be dammed if the spacing and engine side O.D. are exactly the same. O.D. on the intake side is slightly smaller, so you'd need to form a solution there.

[kerryb]

Thanks ramrod, that's nice to know what will fit, it completes the story.  I'm leaning toward a set of pd42b's because I have them on the shelf, they fit the intakes, and it will puzzle those in the know.  Making a new rack,  throttle shaft and choke shaft will be a goodle challenge for my meager fab skills.  Is there any good reason against using aluminum for the throttle  and choke actuator shafts?  It sure would be easier to work with, and has enough strength to do the job. As for the airbox, there are so many good ideas out there to simulate the conditions of a stock setup that it will be fun to get creative while trying to make it look good and tuck it up under the seat.

[kerryb]

Making some progress, but now I have a style/engineering question.  In these photos the tubing is tacked together, but not finish welded.  I'll disassemble everything for that so I can position the frame on the table.  Before that happens I want to finalize the shock mounts which is where I'm questioning my judgement.  (remember...I tend to overthink!)  The shock is positioned to get the desired position of the rear hoop with the stock shock length.  After cutting out a gusset (there will be four, two pairs) the gusset looks too big.  The circles represent "speed" holes and the thickness is about .107".  So,...do they look too massive? Should I trim them back, a little, a lot, or none at all?

Positive and/or negative opinions welcome.

[Godffery]

 I to, would trim some fat a bit on those gussets. 

[kerryb]

Better?"

.075" mild steel, still two pieces separated about 1/2" to provide leverage to hold the shock mount post.

[Godffery]

Yes I would say better.
The angle of the shocks may be a bit too far forward though.  To check for proper top post location, use a ruler or string from the forward swingarm pivot point, back to the lower shock mount on the swingarm, then (keeping the forward end on the pivot point) rotate the other point up to the frame and see where it lands.

[kerryb]

Yes I would say better.
The angle of the shocks may be a bit too far forward though.  To check for proper top post location, use a ruler or string from the forward swingarm pivot point, back to the lower shock mount on the swingarm, then (keeping the forward end on the pivot point) rotate the other point up to the frame and see where it lands.

I agree, the shocks "appear" to be leaning too far forward.  I've been stuggling with this design issue from the beginning.  If I get longer shocks, that allows the tops to reach the new top tube (the hoop) and still hold the frame up where it needs to be.  My other option is to move the lower mount further forward.  But that will bring with it a change in geometry that will affect spring rates, and I only want buy 1 new set of shocks!
So... help me pick the right set of new shocks, l'll measure the length, and depend on the collective expertise of the forum to select a good spring/damping rate in a reasonably priced/performance shock.  Keep in mind, i've never ridden a modern sport bike or a new shock (except on my harley) so I have no credentials for selecting a shock!  Where do we start?  Rider weight, swingarm length, angle of the shock off vertical, or some mystical mix of all of these.  What is the specs of the stock shocks? Is that knowlege even helpful?  I figure the budget is as large as the profits from selling off the tank, seat, sidecovers, and other bits that will never go back on this bike.

When I get out to the shop later, I'll do the string arc method to test your theory.   

[Godffery]

After finding your top mount location, position the swingarm so that the front sprocket shaft, Swingarm pivot pin & axle are all in alignment. Then measure the distance from the newly established top shock location, to the lower shock mount on the swingarm. (I'm guessing it will be in the ballpark of about 13 or 14"?) That will determine your ideal shock length.

[kerryb]

so many factors, and no engineer in sight...oh well, here goes.  So I lined up the driveline parts(sprocket, swingarm pivot, and axle) set the back wheel on the lift, relaxed the straps on the fork so it could rebound, and put the new shock mount/gusset where I wanted to see it, and measured the desired shock length.  Near as I can tell, the shock length should be 14.125" to 14.25".  I'd rather have the shocks too long than too short, so I found 14.5 inch shocks for a low price on DCC website.  These are rated for 365 lbs per shock.  Do I now put the engine back in so I can weigh the back end of the bike to add the rider weight to it?  Note: I still have the triple trees dropped down the fork tubes 1 1/2", so maybe a 14.5" shock is actually the right length.  Probably need to put some 14.5" struts on it and measure to seat height to make sure we can still reach the ground.  (I'm only 5'8" and shrinking!)

[kerryb]

I knew somebody was going to tell me that!  Okay, okay...I'll contact Nils and do the right thing, but only because you said it's the right thing to do.  If it weren't for the wisdom and generousity of this forum, I wouldn't be this far along in my training and successes. 

[Godffery]

There are so many Crap shocks on the market today, it caused a fails gauge of what to expect for the average shock.  So as a reference, Just about any Good set of shocks will start around $400+. If you find something (No name or off brand) that "looks" good, for less then that, chances are they are crap. =/

[kerryb]

I got a nice reply from Nils offering a cbx shock at 14.3".  Two versions, adjustable rebound or not.  Then I noticed they are eye to eye, not eye to clevis which my frame is set up for.  Now what...am I missing something obvious, or did I not supply the right info?  The cbx weighs more than the 650, do I need to consider spring rate in this choice?

[Godffery]

   Stock CBX has the clevis.

 https://partstream.arinet.com/Image?arik=Vkgcs9tma3XMhDIifYPQ&arib=HOM&arim=oQP8CsBN5kh1yW4tp4C9BQ2&aria=Za0_M9PGk7WRoCUgOvFMRA2&ariz=3&ariv=https%3A%2F%2Fwww.midwestactioncycle.com%2FOEMpartfinder.htm

https://www.midwestactioncycle.com/OEMpartfinder.htm#/Honda_Powersports/CBXA_(80)_SUPER_SPORT%2c_JPN%2c_VIN%23_SC03-2000021/REAR_SHOCK_ABSORBER_80/CBX-80-JPN-A/2Y144220AF1442202501A