1975 Honda CB750 - Leaking carb...

Greetings... I've been trying to sort this one out for a while...
thank you in advance for any advice.

First I had a very steady gas leak from the carburator to the point
where the engine would flood.
I adjusted throttle and float heights and now the bike stays running,
but carb no 2 still leaks - sometimes just a drip, other times a
drip-flow. What puzzles me is that (1) the fuel jets don;t seem
clogged, and (2) the leaking doesn't begin until the engines been
running for a while.
Would you recommend adjusting the float hieght on no.2 in order to
"fix" the problem?
If not, where else should I look? (I've never had to take the carbs
apart so if that's required, please know I'm a complete novice - but
trying hard to learn... I love this bike, even though it's causing
headaches).
Also, I'm upgrading the capacitator from the original to modern. I've
purchased the parts and want to take it to a machanic for installation.
what is a fair price for this service?
thank you.

 

The float valve may have some debris or gum and varnish keeping it from
closing fully.

Check the level, but look at the float valve seat with a magnifying
glass. The tiniest bit of varnish can block the valve from seating.

Replacing the capacitors on the points should take no more than 1/2 an
hour, if the mechanic stops for a cup of coffee. Maybe $25 for the
labor?

 

First of all, check your points - if they are pitted (ie:
capacitor/condensor is
failing, which is the usual reason they are replaced) then replace the
points
too. Second, don't just change parts to get "modern" ones without any real
reason for it. The points capacitor(s)
are always changed when the points are changed (unless the guy doing the
work is a real cheapskate) and what you got in there is extremely unlikely
to
be 31 years old, and original. A new capacitor isn't going to help the
borderline spark on these bikes get any better unless the original part is
failing and the spark you have now is total garbage. If you really want to
improve your spark with modern components, put in an electronic ignition,
new wires, etc.

Ted

 

Thanks for the advice on changing the points. you're right, but I'm
actually upgrading the capacitator because the battery isn;t
sufficiently charging while I operate the bike. I tested the current
and was hardly getting 12 volts when I'd rev the engine.

 

Then you should figure out what is wrong with the charging system and
fix that.

The capacitor just reduces ignition point arcing. If you have 12 volts
to the coils that will give you a reasonably strong spark of around
9000 to 12000 volts.

 

voltage measurements at the battery terminals don't tell you
much about whether the bike is charging the battery properly or
not.

The first question you need to ask is, is the battery taking a charge
at all?

If you go out and start the bike, ride it for a couple hours, then
shut it off for a couple hours, then start it again from the battery, then
the battery is taking a charge.

The next question to ask is, is the battery holding charge?

If you go out and do all this and it works, but then you leave it
set overnight with a battery cable disconnected, and in the morning
you reconnect the cable and the battery won't start the bike,
then the battery isn't holding a charge.

If the battery is taking but not holding a charge, then it's bad and
needs replacement.

If the battery is not taking a charge then you need to put a current
ammeter in series with a battery lead. If the bike starts, then
supplies any amount of charging current to the battery, then the
bike charging circuit is probably OK. In that case you need to
take the battery out, charge it with a battery charger, then put it back
in, if it will not start the bike, the battery is bad.

If you can charge a battery with a charger, and it sits for a week and
still starts the bike, however once the bike is running over time the
battery gets discharged, only then should you start questioning the
bike's charging circuit.

A bad battery can make the bike charging circuit look like it's
not working.

A bike's electrical system isn't designed to recharge a good battery
that has been drained down to zero.

If the charging system in your bike is working properly it will
supply anywhere from 1.4 to 4.2 amps to a good fresh battery
that has been drawn down after starting the bike. When a good
fresh battery is _fully_charged_ in your bike it will not draw more
than about 20-30 milliamps of charge current.

Ted