CB72 - It lives!

Moved under its own power for the first time in at least 25 years:

http://www.flickr.com/photos/39665805@N05/4426557037/in/set-7215762250168
7588/

Right hand pot doesn't like running under 1500 rpm which makes starting
from cold a fine art. I've got a new pilot jet which I hope will fix
that.

A few other bolts to tighten and split pins to fix and it can be given a
test ride.

Amazingly the 30 year old rectifier works, I was anticipating grief with
the charging.

 

Beautiful, really nice job. I have enjoyed seeing this project unfold
through your posts over the years.

Is that the word HAGON I can can see on the shocks?

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Mike Buckley

Bloody well batted. That looks like a nice job.

 

Yup, original shocks are unobtainable and the ones on the bike were
shot.

 

Lord yes it does. I haven't ridden one of those since 1979

<hurries off to clone number plate>

 

Beautiful job, young Pigwanker. Just beautiful.

 

Wow.

I am in awe of your spotlessness............

 

<Drool>

Boxerboy

 

That looks rather nice, congrats to a job well done.

 

Thus spake Mike Buckley () unto the assembled multitudes:

<takes hat off>

Absolutely bloody gorgeous.

 

bloody hell, you've dnoe a nice job on that. Looks better than new!

 

Wish it ran like it. Hopefully new genuine pilot jet arrives tomorrow.

 

Bad form etc. The pilot jet fixed the idle problem but can anybody
explain when ignition advance should kick in? The CB has a spring
mechanism on the cam shaft which advances the ignition, on mine it
appears to be advancing as soon as you open the throttle, I thought
advance happened higher up the rev range?

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Mike Buckley

This is the bit where I say:

"**** originality, Boyer Bransden are your friends".

Seriously, springs? **** that. Put them away in a box, so you can pass
them on if you sell it.

 

What are you using to test it, this does not sound right.
You need a proper strobe timing light, there will be timing marks ISTR
under a cover on the LHS but ICBW.
Do you have a Haynes or similar BOL ?.

 

Yours is doing what it's supposed to do. It's springs: the moment the AA
plate starts twirling, centrifugal force is going to start stretcvhing
them.

It's a very crude system. But it works.

 

I have a proper strobe light (tenner from Amazon), and it shows my
static timing was pretty much spot on, but the slightest rev increase
and it advances quite a lot. Weak advance springs seem to be a bit of a
problem on these. They can be replaced, possibly without removing the
camshaft, but even so the engine has to be dropped in the frame.

Electronic ignition is available (for about $300!!) but it still relies
on the mechanical advance on the camshaft, so in this case I might get
some benefits but not really the one I'm most after. They also recommend
going to Dyna coils at the same time, so even more expense.


I'll see how it goes on the road before deciding what to do.

 

If it's the same as on my old CB250-K4 then the spring has weakened and
the cam is going to full adjust too early. There were a pair of springs
on my one.

 

Drop the engine just to reach the timing adjust springs? Yeuk. On the K4
they were under a nice shiny cover held by two 8mm bolts.

 

It should be on the static marks at tickover and then advance progressively,
reaching the full advance marks at typically around 2800 rpm [1].

If is advances too early it will lack torque at low rpm for pulling away.

[1] 2800 is from memory, RTFM if you have one, someone will doubtless
tell me that I have it rong <B-).