CB 750 Custom

I have a 1981 CB750 Custom and the charging system I know is going bad
could it also cause a high rpm miss?
I've checked the plugs and they are in excellent shape I'm leaning
toward the carbs need work,I'm interested in what others may
think......

 

Quite possibly, yes.

Sort the charging system first. One way to check is to lob a brand new
fully charged battery in. It should run fine at high rpm for a while,
until it starts to discharge. If it misfires straightaway with a brand
new battery, then the problem lies elsewhere.

It's unlikely to be the carbs unless the bike has been laid up for
some time and the fuel has evaporated in the carbs themselves. My next
port of call would be the plug caps, and then, yes, the carbs.

 

I went ahead and purchased a new rotor, reg-rec,brushes and stator do
you know how hard it will be to get the rotor off i did purchase the
special tool to remove....

 

If you bought the right tool (and well done for doing so), then it's
easy. Just block the back wheel (stick it in gear and shove a broom
handle through the spokes to stop the wheel turning), and wind in the
extractor.

So often, people buy those three-legged pullers instead and rip the
rotor apart.

That said, I think you've gone too far: I mean, I seriously doubt the
reg/rec, rotor, stator *and* brushes are all fucked, but hell, if it
doesn't work when you've replaced that lot....

 

I know the reg-rec is shoot as well as the rotor so i figured while
I've got it apart I'd replace the stator and brushes
I also bought a nice little voltmeter gauge to let me know it the
charging system is not charging while riding....
Thanks for the help...

 

I was told by a long-time specialist on the 70's and 80's big Hondas
that it was quite common to see rotors and stators damaged from a simple
tip-over while parked because the aluminum housings that keep them
aligned are easily distorted. Sure enough, when I replaced friend's
rotor, you could see the scuff marks on the bad rotor. Luckily, he had
a parts bike with an intact right cover.

I think it was on the cb1100f.net forum where I saw the advice that the
rear axle from the cb750 makes a workable rotor puller. In my case
friend had a parts bike, so I used that one's axle with a pretty weak
electric torque wrench, locked the rear wheel as best I could and in two
or three blips of the wrench, off it came. Undoubtedly the special
puller is preferable to avoid turning the engine backwards but
apparently many have used the axle trick without harm. Of course, my
friend didn't want to spend money on special tools! If I were doing it
again and had no parts axle, I'd simply buy a similar bolt in as high a
tensile grade as I could and round the tip with a grinder to simulate
the axle. I'd always be on a budget with such a bike, nobody would let
me learn on their show bike!


The expert (Mike Nixon at themotorcycleproject.com , nice guy) gave me
quite a few pointers, one of them was to measure the charging current by
substituting the multi-meter leads for the main fuse contacts and
putting the meter on the main fuse contacts (ie. remove the fuse). Even
low-cost meters these days can measure up to 10 ampere dc current for a
short time. He advised that 5-7 amps was good. It seems this is a
more thorough charging test than voltage across the battery. If you
could borrow clamp meter from somebody, that would make it even easier.

 

paul c wrote:
....

Oh, another on-a-budget trick Mike has at his website is how to make a
high-current meter out of #8 wire and a couple of clamps for less than 5
bucks. Seems 6 5/8ths or so inches of this wire has exactly .001 ohms
resistance so you just put your meter on dc milli-volts and pretend they
are amps! Not needed in this case, but useful for deciding that your
starter is bad before you pull it out.

 

Interesting. I hadn't heard that.

This is true of many bikes.