Topic: Potential 1970 CB750 K0/K1 Hybrid

[Mikey G.]

Wow!  Just goes to show you how often I've checked this thread, no?  Anyway, no, I've still got the bike.  She's happily tucked away in the garage, fuel drained and waiting for spring.



Living in Michigan, we're at that weird part of the year where you'll have two or three 70 degree days in a row, then you'll be back to below freezing for a week.  Still, spring is getting really close, and I'm eager to get some miles in.

[Mikey G.]

Bit of a fun little update.  I had myself some extra cash, so I decided to treat myself.  My eternal quest to add more K0 and less K1 to this bike took another step forward.





So the initial plan was to get a Vietnam re-pop, but I managed to find a genuine article for just about the same amount.  Support brackets are a bit bent (I can re-use my current ones), and one bolt hole is cut out on the bottom (it'll be impossible to see when mounted), but overall it's in quite good shape.  It should fit my late-1970 frame nicely.

Speaking of, I've been looking into sandblasters for my frame.  I'll probably re-paint it myself, and I'd really like to get everything swapped to the correct year frame this summer, so I need to get that moving.  Also, don't mind my CA77 wheels.

[Mikey G.]

More proof of progress.  A bit ago I noticed that Yamiya was bringing back the red seat foam after being out of stock for a while, and my Vietnam seat was, frankly, pretty garbage.  Way too hard, shape wasn't great, etc.  So, I decided to do it right, and got me a proper set of foam and a cover.







I reused the seat pan I had, which led to some interesting fit issues.  It fit the foam "close enough", but it was definitely a struggle.  I'm still waiting on brackets (I decided to upgrade those as well) , and I may need to enlarge the holes to slide the seat back far enough to get it to line up correctly, but to say this is an improvement is a massive understatement. 

(I also found out why the Vietnam repro seats are so hard- the foam padding is literally blocks of styrofoam, cut to shape.  I was shocked when I saw it, but I suppose you get what you pay for.)

[BenelliSEI]

Nice job……. If you did that on your own I am impressed. It took two of us longer than I care to admit when I rebuilt the S/C seat with Yamiya red foam and cover! It was worth the struggle, their stuff looks great!

[Don R]

 Here's my Sandcast seat with the new red foam under the old seat cover. I have a new Vietnam seat that can use a little upgrade too, I have a good cover and an old red foam for parts. I thought I might get a replacement white K1 foam and add the ducktail from the old K0 seat.

[grcamna2]

Here's my Sandcast seat with the new red foam under the old seat cover. I have a new Vietnam seat that can use a little upgrade too, I have a good cover and an old red foam for parts. I thought I might get a replacement white K1 foam and add the ducktail from the old K0 seat.

Nice OEM seat cover Don 

[Mikey G.]

Thanks.  I've recovered the seats on pretty much every bike I own, minus my Valkyrie, so I've gotten pretty good at it.  That said, I still jabbed my hand pretty good on the seat spikes a couple times.  It's like wrestling with a fitted sheet, but it has teeth.   

I was a little concerned with how the front came together- it's a weird shape that seems like it's wrong, but looking at other K0s it seems like no, it supposed to be like that.  And while I'm usually a fan of flat seats in general, the little ducktail really grew on me, and I'm happy to finally have one.

[newday777]

It turn out good.
Is the seat pan original or the one from the Viet seat?

[BenelliSEI]

The front of mine has that weird “lip” too. They all do……

[Mikey G.]

It turn out good.
Is the seat pan original or the one from the Viet seat?

Seat pan is from Vietnam.  It's going to cause me some issues once I get my brackets on, because the bracket holes aren't in the most accurate places, and it pushes the whole seat about a half in farther forward than it should be.  The original foam pressed up against the (Yamiya) gas tank quite hard, shoving the tank forward until the petcock lever BARELY cleared the valve cover, but at least it had a chunk of foam to keep the tank away from the pan itself.

That bit of security is gone with the new seat foam, so I'm going to have to adjust holes to get the seat to sit properly.  Either widening the holes in all the brackets, or putting new blind threaded inserts into the seat pan.  Either way, a bridge to burn when I get there.

[Remcod]

Please measure and share, because im gonna face the same issue with my vietnam seat.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[grcamna2]

It turn out good.
Is the seat pan original or the one from the Viet seat?

Seat pan is from Vietnam.  It's going to cause me some issues once I get my brackets on, because the bracket holes aren't in the most accurate places, and it pushes the whole seat about a half in farther forward than it should be.  The original foam pressed up against the (Yamiya) gas tank quite hard, shoving the tank forward until the petcock lever BARELY cleared the valve cover, but at least it had a chunk of foam to keep the tank away from the pan itself.

That bit of security is gone with the new seat foam, so I'm going to have to adjust holes to get the seat to sit properly.  Either widening the holes in all the brackets, or putting new blind threaded inserts into the seat pan.  Either way, a bridge to burn when I get there.

I brought my seat pan to a welder(not a repro)and they did good repair;the fellow used a Mig with low heat and did good. I think it's possible to re-position those holes and get inserts lightly welded in.

[Mikey G.]

I finally got around to measuring where I put my seat brackets, and turns out a half inch wasn't far off.  And TBH, I didn't run all four in one go- I lined up one, used the actual bracket to figure out where the second hole went, then put the seat on the bike to figure out the position of the next bracket, etc. 

I also ended up using rivet nuts for all the new attachment points.  I know the biggest risk is the rivet spinning, but I didn't have a problem (and if I do, it won't be too hard to tack-weld them in place).  Still, it's nice to have a seat that's not smashed against the gas tank all the time.

[BenelliSEI]

Nice job….. I usually put a drop of red Loctite the shank before installing a rivnut. Seems to hold them forever.

[Mikey G.]

That's a good idea, actually.  Realistically these aren't coming off anytime soon (if I have to take the seat off I'll just pull the pin out) so hopefully it's never an issue.  But I'll keep the loctite in mind!

[Mikey G.]

Took the bike out for a quick trip today- absolute dumpster fire.  Plug 2 fouled right away, and nearly burnt my hand off replacing it.  Got it to run on 4, but despite this idle was high, and I still got the occasional off-idle problems on certain intersections.

Despite brand new lubed cables AND gauges that worked before I pulled them off to put new faces on, the needles wobble like crazy and the tach refuses to go over 5k.

Fiddling with carb screws and idle speed dials only made things worse, so I threw up my hands, may have intentionally messed a bunch of settings up because I was mad, and parked it.

Looks like we're starting from scratch.  What's another month of tuning, eh?

[BenelliSEI]

I feel your pain. The early 4 cable throttle set up on the early carbs can make you crazy! That “high idle” suggests some base issue set ups?

Since you plan on starting over, try checking out my lengthy project file “Early Sandcast Found….. “. Starting around #1278 I wrote quite a few posts showing how I initially set mine up on the bench and then do final tuning on the bike. Might help? Good luck.

P.S. do you have the correct gaskets under the four carb tops?

[PeWe]

Is rhe fuel OK?
Try another brand.

I have fiddled with carbs for a longer time. I finally found that the main problem was the fuel forcing me to adjust too rich for the pilot circuit to make engine to run evenly.

When I changed gas station to one that served good fuel, engine ran much  better when pilot circuit was correctly adjusted. Not too rich.

I also verified everything else when the bad fuel could have done more issues.
Removed all jets (not needles), carb cleaner sprayed inside and a final blow with compressed air. Also made sure that pilot jets and main jets were clean.

[Mikey G.]

Thanks for the heads up.  I'll give it a look once I get the rack pulled again.  I've got to pull the carbs on my '76 Goldwing first to fix an idle issue on that bike, then it's back to the 750.

It's very frustrating when you've got a backlog of stuff you need to accomplish but can't because you have to keep coming back to the same bike.   

[BenelliSEI]

Thanks for the heads up.  I'll give it a look once I get the rack pulled again.  I've got to pull the carbs on my '76 Goldwing first to fix an idle issue on that bike, then it's back to the 750.

It's very frustrating when you've got a backlog of stuff you need to accomplish but can't because you have to keep coming back to the same bike.   

Man…You have some punishing work lined up! I’ve worked on my buddies ‘75 GL1000 carbs and I think I’d start with the K0 first!

[MauiK3]

K1 carbs on a K0, not surprised there may be issues.
Best of luck and patience!!

[Mikey G.]

Man…You have some punishing work lined up! I’ve worked on my buddies ‘75 GL1000 carbs and I think I’d start with the K0 first!

You're not wrong, although it really becomes a question of "pick your difficulty.  GL carbs are way more complicated internally, a symptom of being essentially automotive carburators, with little to (in the case of the '75s) no changes.  Look up the Honda N600 car- same carburetor.  BUT, if you get them back together properly, final tuning isn't too horrible.

750 carbs, on the flip side, are some of the simplest carbs internally I've ever seen.  I can disassemble one of those puppies in five minutes.  But apparently getting them to work together after the fact is a nightmare.

I'll look into the carb top gaskets.  My set didn't come with any, but it can't hurt. 

And to get another baseline because this is a frankenbike, here's my current setup:

Carbs, airbox and exhaust: K0.
Bottom end: K1
Top end and intake runners: K2.

[BenelliSEI]

I only found K0 top gaskets at Yamiya, but often use the later style and just punch a 1/2” hole on centre with a hole punch.

[Mikey G.]

Could you elaborate what kind of hole you mean?  I found a set of gaskets that seem to work without modification, but I'm curious if I'm missing something important.

[BenelliSEI]

Could you elaborate what kind of hole you mean?  I found a set of gaskets that seem to work without modification, but I'm curious if I'm missing something important.

The early carbs with the single 1-4 pullthrottle cables have unique top gaskets. The later style are the same size but the centre punch outs are different. I use a gasket hole punch to make a round hole in the middle (where the cable and cable adjuster come through) and they work fine. I’ll see if I can find some for a photo.