Topic: Adapt front end to CB 750

[aminemed]

I do not plan to ride it daily. It will be a bike that I will take on week end and I'd like to spend the rest of the week admiring how good looking it is:) I'm okay to spend a bit to pursue my goal and achieve what I would like in terms of weight saving and handling improvement. Spending 1 to to 2k seems to be a decent budget for me for now on this bike

[przjohn]

I am a fan of the OEM look for a restoration. Problem is, that can be one of the most expensive options. Exhaust alone can almost bankrupt a project. There are some great custom bikes done by members on this forum that look like a blast to ride and I bet turn a lot of heads. These bikes are done very well by folks who know the ropes. Reality though is that there are a ton of hacks out there who think that the best tool in their shop is a Sawzall. These projects usually start out with the best of intentions but for what ever reason, be it limited skills or resources, they end up as hacked up pieces of garbage always needing "Just a Carb Cleaning" on Craigs List asking for stupid coin.

A couple of grand goes quick when working on vintage bikes but you can spend it as smart money. The fork spring and emulator mods with decent shocks just mentioned are a couple of those mods, money well spent if you are looking for a good rider. If you want less weight up front skip the beers and burgers on Friday Night. Not exactly the option I could ever take, but it is an option.  That bike has some nice potential, best of luck to you and be sure to post some pics of your progress.

[camelman]

If you're looking to make your bike lighter, then the easiest way to do that is to improve your suspension. It won't physically made your bike lighter, but it will feel much lighter and be much more flickable. The stock suspension often uses too soft of fork springs, which makes a bike feel sluggish and heavy when trying to transition into or out of a turn. Stiffening up the fork springs (calculate what spring rate you need using the tools suspension providers have on their websites) will make an unbelievable difference if the bike is softly sprung to start with. The same goes for the rear, although rear shock spring rates aren't usually too stiff on these CBs from my experience. Better rear shocks will make a big difference though.

Regarding types of springs, I prefer single-rate over progressive. I find progressive springs to be mushy and vague in handling as compared to single rate springs. Race Tech makes some good options, and they have damper improvements that can significantly improve the control of your suspension over bumps.

One final note is that rebuilding a wheel can pay dividends on ride control and comfort. The stock wheels aren't as round now as they once were, and you'll feel that as vibration and vagueness in handling.

Camelman

[aminemed]

I guess that the emulators from race tech  you are talking about are only working with single rate spring, I am right ? what rear shocks do you recommend ?

let me add something as well, I'm quite focused on weight loss not to be able to ride the bike faster, that's not my goal at all, it is more to be able to handle it better. Right now, doing several feet with the bike while pushing it with my hands, when it is next to my door for example (engine off) is a real nightmare. I remember that once I was completely exhausted after having pushed the bike on 30 feet to move it around the house (on a plane surface thanks god!)...that's where my weight obsession is coming from

[Rookster]

Maybe the brakes are dragging or the wheel bearings are shot.  A CB750 should roll around quite easily.  It is heavy compared to vintage British bikes but nothing compared to a full dress Harley. 

What you are asking for doesn't compute with what you have.  The CB750 was a UJM (universal Japanese motorcycle) not a race bike.  It was built to have good power, brakes, and reliability.  That's why so many of them got Vetter windjammers and tall sissybars.  They can be made much sportier but that takes commitment to performance not looks and more than $2k.  Today's brat bike is nothing more than a newer version of the chopper.  It is not some homage to the performance bikes of the 70s. What you want to build is a customised vintage motorcycle.  Don't expect it to be better than the stock version of that bike and you won't be disappointed. 

Scott

[camelman]

Correct on single rate springs only for emulators. Progressive springs and emulators don't play well. If you're concerned about where you're spending money, then just try new springs first. They'll make an amazing difference, but will need appropriate damping characteristics to give you the best performance.

I'm with Scott on the difficulty of moving the bike. It shouldn't be hard to move it around on a flat surface. I'd look at that front brake soon since it can cause the front wheel to slide when accelerating if it is dragging hard (it's happened to me before).

[scottly]

I know a thing or two about weight reduction.
For the front wheel, I used thin one-piece rotors from a Yamaha; these are about 2 pounds lighter each than a stock 750 rotor. Phenolic caliper pistons will save another 1/2 pound or so. Ditch the stock speedo drive, and replace it with an aluminum spacer, as well as the steel spacer on the other side. A spoke wheel with a steel rim is 1 pound lighter than a Morris mag, so an aluminum rim should be lighter yet, but I don't know how much.
Regarding the motor, the only simple bolt-on weight saver I know of is the alternator rotor; the early models had a flange on the rotor that weighed 1.234 pounds more than the later rotors. You did remove the starter clutch mounted on the back side of the rotor, as well as the drive gears, correct?
Switching from the stock 4 into 4 pipes to a 4-1 will save 20 pounds or more, depending on which systems. If your stock pipes are in good condition, with no damage or rust, they can bring a good price from those interested in restorations.

[Don R]

 You'll get a few offers to trade out those heavy old 4-4 mufflers for a sweet light weight header.  I'll go first L0L.

[aminemed]

i am going to change the steering head bearings and wheel bearings then. Do you know where to get the Timken ?? otherwise, i would go with the all balls.

And for the rotors, how can i swap a yamaha rotor to cb 750 ? is it an easy conversion ?

[scottly]

*Warning* After clicking on one of the OP's pictures, my protection software blocked a "severe" attack...