[Cam’run_1776]

Hello, all:
I am a Maryland resident currently working on building a cafe racer out of a 1982 CB750K and 1981 CB750C. This is my first build and I'm a new rider, so although I generally work through the process on my own, I'm hoping to use this site to avoid stylistic or mechanical oversights on account of inexperience. I bought the 1981 CB750C first, then bought the 1982 CB750K after realizing it was an easier starting point (confirming what I read on this site).

 

[BigAl8295]

Welcome.

What is the mechanical status of the two bikes?

As a new rider what are you hoping to achieve with this build?

 

[TrialsRider]

stylistic oversight number one: you bought the custom classic version and not the sports model to build on, the wheel sizes are all wrong, frame and suspension components are all marginal and the bikes weigh a ton.
... the last parts are more mechanical, although my eye goes straight to things like alloy rim upgrades and the such so in a way mechanicals can really bolster the stylistics, but that's just me.

 

[Cam’run_1776]

Welcome.

What is the mechanical status of the two bikes?

As a new rider what are you hoping to achieve with this build?

The 1981 ran fine, but had 43k miles on the odometer (speedometer was not working so I don't know the actual mileage) and looks like it was laid down (apparently damages are limited to scratches on the right side and none to frame). The 1982 runs great to my ear, but my buddy (I'm unsure of his credibility/knowledge) said he could hear a knock when idling. Also, there was some white smoke from one exhaust pipe, but this got better the more it was run. FYI, this is the status after cleaning the carburetor and airbox/filter. When I bought it, it was not running and had not run in many years.

 

[woodsman]

Doesn't look like you allowed for rear wheel travel.

 

[dirkchecken]

ive always loved the styling of the k models, like the sport f the best. i would put a little effort in getting the k model riding and looking good. i know my answer doesnt help in your quest for a “cafe racer” . the c model is a awfull starting point . your using the k front attached to the c frame and rear? i would use the k frame, plus you have wire wheels. the k might look ok with rearsets, different bars, 4-1, plus other performance upgrades, good luck and carry on

 

[Cam’run_1776]

stylistic oversight number one: you bought the custom classic version and not the sports model to build on, the wheel sizes are all wrong, frame and suspension components are all marginal and the bikes weigh a ton.
... the last parts are more mechanical, although my eye goes straight to things like alloy rim upgrades and the such so in a way mechanicals can really bolster the stylistics, but that's just me.

I agree that the Custom version is not ideal, so most of what I'm using is from the CB750K. I'm not installing the wheels/tires until the end to avoid damage during the build. I have the Custom's 19" comstar for the front and 18" comstar for the back, as well as new 400-19 and 450-18 Firestone Deluxe Champion tires.

 

[Cam’run_1776]

ive always loved the styling of the k models, like the sport f the best. i would put a little effort in getting the k model riding and looking good. i know my answer doesnt help in your quest for a “cafe racer” . the c model is a awfull starting point . your using the k front attached to the c frame and rear? i would use the k frame, plus you have wire wheels. the k might look ok with rearsets, different bars, 4-1, plus other performance upgrades, good luck and carry on

Ultimately, the only parts from the C model that I plan on using is the frame, and that could change if I find that it differs from the K, but I don't want to cut up both if I don't have to. Based on research and direct comparison (I have them both in front of me), the frames are exactly the same shape and only differ in the location of a few attachment points (like fuel tank, side panels, etc.), but I'll switch if I find out I'm wrong.
I like the wire wheels but the rear is 17" and I already bought the 18" rear comstar and tire, so I'm going to see how that comstar setup turns out first. Rearsets are on my list and I already have different bars and a 4-1 exhaust, but if you have any other performance upgrades in mind, I would appreciate your input.

 

[dirkchecken]

[QUOTE="Cam’run_1776, post: 650801, but if you have any other performance upgrades in mind, I would appreciate your input.
[/QUOTE]
might get some performace with some am26 or conti classic attacks, dont know how much performance your going to get with the firestones........... need a little help here gang.

 

[Cam’run_1776]

Doesn't look like you allowed for rear wheel travel.

I am going to replace the CB750C shocks with the longer K model ones, but that could still be a problem because I'm also installing the battery under the cowl and larger diameter wheels. If you know what travel I should account for, please let me know.

 

[TrialsRider]

... 400-19 and 450-18 Firestone Deluxe Champion tires.

naturally
and no front fender

 

[TrialsRider]

I am going to replace the CB750C shocks with the longer K model ones, but that could still be a problem because I'm also installing the battery under the cowl and larger diameter wheels. If you know what travel I should account for, please let me know.

What kind of battery?

 

[woodsman]

I am going to replace the CB750C shocks with the longer K model ones, but that could still be a problem because I'm also installing the battery under the cowl and larger diameter wheels. If you know what travel I should account for, please let me know.

This is not a roadworthy, let alone performance, motorcycle. Parked is it's highest and best use.

This is an '80's Honda performance bike.

You don't need bigger or longer you need proper.

 

[Cam’run_1776]

naturally
and no front fender

Neither bike came with one but I’ll get to that at some point.

 

[Cam’run_1776]

What kind of battery?

Scorpion YT14B-4. Specs are 12V, 12Ah, 220CCA sealed AGM.

 

[TrialsRider]

It's not the battery specs you need to worry about, it's always a matter of: is the charging system compatible with the change in battery technology. Your bikes have dirty old charging systems that were adequate for an ancient technology lead acid battery, which is very forgiving of over-voltage.

LED lights?

 

[Cam’run_1776]

This is not a roadworthy, let alone performance, motorcycle. Parked is it's highest and best use.
View attachment 105357

This is an '80's Honda performance bike.
View attachment 105358
You don't need bigger or longer you need proper.

I can’t see the rear suspension on Spencer’s ride, so are you talking about tires now? If so, I’ve read that low profile tires are best for cornering on tracks, whereas bigger ones perform and ride better on regular roads.

 

[Cam’run_1776]

It's not the battery specs you need to worry about, it's always a matter of: is the charging system compatible with the change in battery technology. Your bikes have dirty old charging systems that were adequate for an ancient technology lead acid battery, which is very forgiving of over-voltage.

LED lights?

Yes, LED lights. I thought AGM batteries worked with the stock charging system because they are still lead acid. If not, do you have suggestions on how to update the charging system? Just an aftermarket rectifier, or is it more involved?

 

[woodsman]

I don't know what you have been reading but if a bike to ride is your goal then you are headed the wrong direction.
The frame mod doesn't allow for wheel travel and the correction for that is not longer shocks. In Ontario, where I am, the tires you bought aren't road legal. Look at the shape, does it look like it is made for cornering? You swapped out substantially lighter wheels, with a much greater selection of tires, for just about the heaviest thing Honda built. Putting the battery higher doesn't lower the c of g. Removing the air box from the bike brings in a host of new issues. Worry about a new pipe when you start scrubbing those.

 

[Cam’run_1776]

I don't know what you have been reading but if a bike to ride is your goal then you are headed the wrong direction.
The frame mod doesn't allow for wheel travel and the correction for that is not longer shocks. In Ontario, where I am, the tires you bought aren't road legal. Look at the shape, does it look like it is made for cornering? You swapped out substantially lighter wheels, with a much greater selection of tires, for just about the heaviest thing Honda built. Putting the battery higher doesn't lower the c of g. Removing the air box from the bike brings in a host of new issues. Worry about a new pipe when you start scrubbing those.

Unfortunately that all makes sense, so I need to think about how I want to deal it all. FYI, I removed the airbox temporarily and plan on putting it back. The 750C had a mouse nest and the 750K had a dead snake.