Topic: Getting my K0 back on the road

[WideAWAKE]

Figured I’d start a thread to document my process and keep myself accountable to finishing.

I’m sure I’ll have a ton of questions as to the smaller details of this bike as I’m not super versed in these 750s.

I’ve already been given a ton of help on another thread trying to sort out what I actually got.

Frame, engine and pipes are K0 - body work and carbs not so much.

My goal is to get it as close to original as possible (within reason). I’m more looking to make a solid clean driver out of it that I am not scared to drive or get dirty and loose it’s value. Some of the restorations I see on these old bikes look better than anything that would have ever rolled off the showroom floor and I won’t be going there haha.

 I had a difficult trying to find a body kit as Yamiya is sold out with no foreseeable restock BUT I found that CMS stocks the Yamiya kits and sells the pieces individually which was actually cheaper than buying from Yamiya.

I bought everything but an air box. I currently have a 3 bolt air box and didn’t want to have to buy an air box and hardware to make the Yamiya one work so I will be painting the one I have.

My bike is a very late K0 so I’m not sure at which point they started transitioning to the push pull carb but they are on my bike and I’ll be keeping em. My front fender is also a double rolled which could also be a transition piece. It’s in great shape but I may be replacing it with a single cut.

I will be pulling it down to the frame for a repaint.

As for the motor - I did get it to fire up before I started to break down the bike and it sounded pretty heathy. - I will clean, paint, retorque the head, cam chain, timing and valve clearance - ride it and see if it needs a rebuild. If it does, I’ll pull it and rebuild.

It may be a little bit of a slow build as of lately I’ve been working on a few different bikes but they are pretty much almost done so hopefully that give me more time on this.

So far I’ve rebuilt the handlebar controls, pulled the carbs and I’m almost through with them, just need some fuel line to get em all back together. 

I have a lambretta motor on my bench at the moment and it’s clogging up my shed. It’ll be back together and out by the end of the week and I’ll start tearing the rest of the 750 down to the frame for paint.

[seanbarney41]

I think your plan is a good one.  These bikes are satisfying to ride!

[HondaMan]

Lots of non-K0 parts on that one!
But, that doesn't change things much. They all will work together and make a reliable ride.

[WideAWAKE]

Thank Sean - can’t wait to get it done.

HondaMan - you are certainly correct. I’ve come to understand very well (atleast with my other 70s Japanese bikes) that the last month of two or a production year with changes  seems to be a transition period - this bike being just that. So while the numbers are K0 it  just squeezed by.

Fenders look original and k1 (based on the bolt holes in the rear)

I know the last two owners of the bike who have had possession of it since the 80s. Two owners back got it without a tank and side panels. He had a 73 tank and figured he’d make it look like a 73 so he swapped the ears and headlight bucket out (I have the originals which were candy gold, now with a rattle can black paint job over them - ughh haha).

Two owners back also painted the air box black and the last owner stripped it back to bare plastic as he was going to try and bring it back to original but had too many projects going on - called me and we’ll now it’s mine haha (too cheap not to take it). I feel the air box is another transition piece. As I opened it up early on and could still see a little smidge of gold paint.

Exhaust is hm300.

[Stev-o]

Looks like a great project, subscribed.

With these old bikes, they is no tellin' what has been changed out and why?

[HondaMan]

Those carbs are certainly not K0: they look like mid-year 1975, the 086a variety from the 750F0/1 bikes. If that is so, they probably have the #2713101 Or similar) needles in the slides, which can make the engines with K0 cams feel 'flat' between 2000-3500 RPM or so. The later cams opened at 0 degrees BTC intake, so they are set leaner. You can try lifting the needles to the bottom notch to work around that, and make the mainjets #110 with the air screws about 3/4-7/8 turn out (instead of 1 turn) to blend in the earlier-opening cam's performance. Alternately, you could install the standard #27201 needles (if you can find them!), avaoid the rebuild kits' brass parts today. They are ALL incorrect, and run very, very lean, making the engine feel very weak.

[WideAWAKE]

Honda man - you are correct on all accounts there and I really appreciate that info! I’ve tried to do all the reading and research I can but it’s a lot to learn.  - I’ll get some genuine main jets on order. 

I’ve had a couple dozen xs650s and RDs and a couple smaller CBs (still got my 160)- very familiar with the garbage brass. I got rebuild kits for these pretty much just for the float bowl gasket haha.

Knowing the carbs are that late I continue my plans of using them but be on the lookout for an earlier set.

[WideAWAKE]

Looks like a great project, subscribed.

With these old bikes, they is no tellin' what has been changed out and why?

It seems it’s just better to accept what we got and move forward than wonder why it is the way it is. It’ll hurt your brain trying to figure out why the POs did what they did haha.

[WideAWAKE]

Those carbs are certainly not K0: they look like mid-year 1975, the 086a variety from the 750F0/1 bikes. If that is so, they probably have the #2713101 Or similar) needles in the slides, which can make the engines with K0 cams feel 'flat' between 2000-3500 RPM or so. The later cams opened at 0 degrees BTC intake, so they are set leaner. You can try lifting the needles to the bottom notch to work around that, and make the mainjets #110 with the air screws about 3/4-7/8 turn out (instead of 1 turn) to blend in the earlier-opening cam's performance. Alternately, you could install the standard #27201 needles (if you can find them!), avaoid the rebuild kits' brass parts today. They are ALL incorrect, and run very, very lean, making the engine feel very weak.

@HondaMan
It’s slow goin over here but I did pull my needles and they are indeed #27201 needles. Currently sitting on the second slot from the bottom. I’ve also sourced some genuine Keihin 110 jets.

Would you suggest dropping the needle one more slot or letting it ride as is??

[WideAWAKE]

Also made a little headway on the tank

[MrGardman]

Wow, the tank looks super.

[PeWe]

Needle OK for better flowing 4-4 as K0 had. HM300.

Later K2 and up had needles in the middle due to the more restrictive HM341 4-4. Smaller main jets too.

[WideAWAKE]

MrGradman - thanks! It’s definitely slow goin.

PeWe - I appreciate that info. I’ll let em ride as is.

[WideAWAKE]

So I picked up an earlier set of carb bodies and internals - a bit crusty but I’m sure they’ll clean up after a hot bubble bath and some soda blasting.

I got a few questions as to the nuances of these carbs from year to year.

I currently have some later (75ish) carbs and from what I understand the carbs were all pretty much the same internals, so I should be good to swap my internals to the older bodies??

Also, on the push pull mechanism, I’m wondering what the physical differences are. At first glance the differences seem cosmetic, as in the finish of the pulleys look cad plated on my current set and the older ones look like raw aluminum??

Can anyone help me sort out what a proper set of 70 (k1) carbs and pulleys should look like compared to my current set up.

Any and all help is greatly appreciated. (I’ve hunted for photos and comparing what I got but still not quite sure).

[seanbarney41]

K0 carbs should not have the same rack, any pulleys, or any push/pull mechanism...pull cable splits into 4 separate cables that just go into the tops of the carbs, with return spring underneath the screw on top, just like a dirt bike x4

[MauiK3]

Nice project!
Funny how candy blue green looks very blue on these devices we use.
When you soda blast what soda medium do you use?

[WideAWAKE]

K0 carbs should not have the same rack, any pulleys, or any push/pull mechanism...pull cable splits into 4 separate cables that just go into the tops of the carbs, with return spring underneath the screw on top, just like a dirt bike x4

Yes, that I know.

My bike is very late and has quite a few “k1” parts on it. A transition bike so to speak.

I’m not looking to drop 1000 bucks on k0 carbs so K1 carbs will do.

That is why I asked what the difference was from later carbs and K1 carbs. Not K0.

[WideAWAKE]

Nice project!
Funny how candy blue green looks very blue on these devices we use.
When you soda blast what soda medium do you use?

I’ve used the heavy grit from HF. It’s easy to get and works quite well for the stuff I use it for. It’s not gonna blast paint, but cleaning carbs and hubs it works quite well.

[WideAWAKE]

With the info from Magpie’s thread I made some screens for my side covers.

Get the tabs a little warm and they fold right over. I did notice that if I didn’t fold em all down the corners had a little movement  I figured it’s my luck, they may have a little rattle at a specific RPM and I’d spend 6 months trying to track down a strange noise I couldn’t quite put my finger on once I’m up and running, only to find out it was my screen. Truth is, 4 folds is probably just fine though.

[MauiK3]

That looks great!

[WideAWAKE]

Thanks for the encouragement Maui!

Soo I’m starting to get my handlebars back together and I got a question about the master cylinder.

Although I think it’s an original Honda bit from the time, I’m not sure it’s from this bike. It looks correct but all the ones I’ve seen are anodized black like the switches and well… as you can see, mine is silver.

I have a very similar (original) master cylinder on my cb500T although the top cap is not dished like the one on this 750. And sorry but this is the only pic I could find that showed the aster on the 500

Can anyone shed some light on the situation? What should a correct one be? Is mine correct??

[Don R]

 If you pull back the rubber boot its usually black underneath. The sun fades them badly. The concave top is early and if there's no fill level line inside, it's real early.

[HondaMan]

Those carbs are certainly not K0: they look like mid-year 1975, the 086a variety from the 750F0/1 bikes. If that is so, they probably have the #2713101 Or similar) needles in the slides, which can make the engines with K0 cams feel 'flat' between 2000-3500 RPM or so. The later cams opened at 0 degrees BTC intake, so they are set leaner. You can try lifting the needles to the bottom notch to work around that, and make the mainjets #110 with the air screws about 3/4-7/8 turn out (instead of 1 turn) to blend in the earlier-opening cam's performance. Alternately, you could install the standard #27201 needles (if you can find them!), avaoid the rebuild kits' brass parts today. They are ALL incorrect, and run very, very lean, making the engine feel very weak.

@HondaMan
It’s slow goin over here but I did pull my needles and they are indeed #27201 needles. Currently sitting on the second slot from the bottom. I’ve also sourced some genuine Keihin 110 jets.

Would you suggest dropping the needle one more slot or letting it ride as is??

With #110 mainjets, use the middle notch in the 27201 needles. That's the K1 combination. When Honda went then to the HM341 pipes (more restrictive above 5000 RPM) the neeldes had to be raised a notch to #4 slot because of the slowed airflow thru the engine. When using the free-er flowing HM300 pipes, lowering the needle a notch keeps the mix more linear around the middle RPMs.

[WideAWAKE]

If you pull back the rubber boot its usually black underneath. The sun fades them badly. The concave top is early and if there's no fill level line inside, it's real early.

I pulled it apart earlier today to get the guts out to rebuild.

It’s black on the inside of the handlebar clamp and under the boot.

Looks like it was anodized black. Seems it hasn’t fared as well as my switches which still look quite well.  I’ll have to get it back to black.

There is what I believe to be a fill level line (a groove around the inside about a half inch down from the top of the cap). I’ll snap a pic tomorrow.

[WideAWAKE]

Those carbs are certainly not K0: they look like mid-year 1975, the 086a variety from the 750F0/1 bikes. If that is so, they probably have the #2713101 Or similar) needles in the slides, which can make the engines with K0 cams feel 'flat' between 2000-3500 RPM or so. The later cams opened at 0 degrees BTC intake, so they are set leaner. You can try lifting the needles to the bottom notch to work around that, and make the mainjets #110 with the air screws about 3/4-7/8 turn out (instead of 1 turn) to blend in the earlier-opening cam's performance. Alternately, you could install the standard #27201 needles (if you can find them!), avaoid the rebuild kits' brass parts today. They are ALL incorrect, and run very, very lean, making the engine feel very weak.

@HondaMan
It’s slow goin over here but I did pull my needles and they are indeed #27201 needles. Currently sitting on the second slot from the bottom. I’ve also sourced some genuine Keihin 110 jets.

Would you suggest dropping the needle one more slot or letting it ride as is??

With #110 mainjets, use the middle notch in the 27201 needles. That's the K1 combination. When Honda went then to the HM341 pipes (more restrictive above 5000 RPM) the neeldes had to be raised a notch to #4 slot because of the slowed airflow thru the engine. When using the free-er flowing HM300 pipes, lowering the needle a notch keeps the mix more linear around the middle RPMs.

That you very much for the reply.  Very much appreciate the help.

I’ll stick to the 110 and the middle notch.