'72 Honda CB 450 Starting Problem

I have a '72 Honda CB 450 that is having starting issues. It has sat in
the garage for a couple of months, so I just went on and put a new
battery in it. The plugs were replaced about six months ago. I got it
to start and run for a brief moment several times....it would rev up
then plunge and die. Now, it turns over but will not start. In the past
this bike has ran really well, and was rode on a regular basis. IT
would fire right up with the electric start, and would idle like a
purring kitten. Any ideas? Thanks....

-Matt

 

try starting. when it doesen't start, pull plug. Do you see or smell gas?
If so, try starting with plug out. Do you see spark?

Ted

 

Enough fuel in tank, gas turned on, need to switch to reserve tank, choke
cable still connected at carbs?

 

Will try this in the morning when I work on it again. Will put in new
plugs just in case...then go from there. Will let you know what I
see.....

 

-Matt

Full tank of fuel....tried gas in both on and reserve position....choke
connected and working fine....usually use it a little to get her
started anyway....

 

Clean and re-gap the ignition points.

Put 3 or 4 ounces of Berryman's B-12 Chemtool Choke and Carburetor
Cleaner in a full tank of gas and go for a slow ride. As the idle RPM
increases turn it down. Increase in idle RPM means the B-12 is cleaning
the gum and varnish out of the idle jets and the idle mixture passages.

The idle mixture screw on that model isn't really a mixture screw. It's
an idle air bypass screw, so turning it clockwise reduces air flow and
makes the idle mixture downstream of the screw richer.

 

Ok, I think all the fuel related items are fine. Just checked all
lines, filter, tank, carbs are getting gas. Tried cranking with each
plug out and no spark. I should be seeing them fire while they are out,
right? I think maybe they are not firing at all....

-Matt

 

My first bike was a Honda CB450. - Memories....
Yes. You should see a spark, (cranking with the plugs in contact with
the engine.)
If not:
First check for voltage at the points.
Check points, (for gap & operation) & condenser next, then coils.
Best of luck,
MadDog
R75/5 Forever!

 

Remove the points cover. Check for DC voltage at the wire on the points
when each set of points is open. If you have voltage there, you have
power all the way from the battery, through the fuze, ignition switch,
kill switch, and through to coils to the points.

If you con't have DC voltage (12 volts if the battery is a 12 volt
battery) then start tracing connections back to the battery.

 

Hey Matt,

Unless the point contact surfaces are in perfect condition I'd just
replace the points and condensor then try it. If the point contact
surfaces are perfect, try replacing the condensor. It is so cheap
that it's not worth trying to test the condensor. A bike that has been
sitting a
long time isn't going to have gone out of tune, since the rubbing block
hasn't been turning, the points aren't going to go out of adjustment.
But, condensors can go bad by just sitting - they can dry out internally
over time. To really test a points condensor properly you need an
oscilloscope to look at the waveform.

This has 2 coils, right? If nothing is sparking I would think it would be
unusual to have 2 coils both go bad at the same time.

Make sure to check the point gap with a feeler guage first, before
replacing anything. Points that are grossly out of adjustment will
not cause a spark.

Ted

 

Ok, so now I know I don't know what the hell I am doing. I was able to
verify (finally) that I AM getting spark at both plugs. So I am back to
square one. This might give folks an better idea of what happened the
last time she ran....she started to rev up then quickly died when I
tried to give to some gas to idle it down....then in BACKFIRED. That
was the last I saw of her....does that give folks an idea of maybe what
went wrong or what might be off? Thanks for all your help and patience
by the way.... - Matt

 

OK, if you have spark on both cylinders and you have gasoline TO the
carburetors, that doesn't mean the engine is getting enough gasoline
FROM the carburetors.

The old gas probably evaporated in your float bowls and the resulting
gum and varnish
has caused the float valves to stick shut and the idle jets and idle
passages to get plugged up with goop from the evaporated gas.

Go to any decent auto parts store or Wal*Mart and buy a 15-ounce can of
Berryman's B-12 Chemtool Choke and Carburetor Cleaner. You can get it
in liquid form and aerosol form. I buy both.

Squirt the aerosol B-12 down the fuel hose to the carbs, or make a
mixture of 50/50 B-12 and gasoline and squirt that down the fuel hose
to fill up the float bowls. Leave that stuff in the carbs for half an
hour and reconnect the fuel hose and start the engine.It will run on
B-12 and the exhaust will stink and burn your eyes from the alchohol
fumes.

Then, if the engine will idle and respond to the throttle a little bit,
put 4 ounces of the liquid B-12 into a full tank of gas and go for a
slow ride. As the idle RPM
increases turn it down. Increase in idle RPM means the B-12 is cleaning

the gum and varnish out of the idle jets and the idle mixture passages.


The idle mixture screw on your carbs isn't really a mixture screw. It's

an idle air bypass screw, so turning it clockwise reduces air flow and
makes the idle mixture downstream of the screw richer.

You can clean out part of the idle mixture circuits without taking the
carbs off the engine if you remove the idle mixture screw. Tturn the
idle mixture screw clockwise until it stops turning, counting the
number of full turns in, and write that down.

Then you can squirt aerosol B-12 through the hole that the screw came
out of. When you go to reinstall the idle mixture screw, turn it all
the way closed, then unscrews it the same number of turns out from
completely closed that you wrote down.

It will probably be about 1.25 turns.

 

Matt,
Just an idle thought: Have you checked the throttle cable for
operation?
MadDog

 

Ok, you guys have saved the day. I did the whole float cleaning
process, and you were right...the floats were gummed up and sticking. I
cleaned everything up with the Chemtool, put it all back together, and
it started right up!!!!! You guys kick major ass.

BUT - of course one thing leads to another. In the process of doing all
this, the right side float bowl is cracked...the corner litterally just
cracked off. So, now I have to replace that piece. Any ideas on where I
might be able to find this part?

Thanks a million for all your patience and help...

Best,

Matt

 

Thanks FB....this really helped a lot!!!! The bike runs now, I just
have to replace the right side float bowl that cracked in the process.

Best,
Matt

 

If the cracked off piece is on the bowl part instead of the sealing
lip/flange of the bowl, you can repair the float bowl with a bit of
QuickSteel. I used this on my wife's Wolverine carburetor float bowl,
after "someone" punched a hole in the bowl with a screwdriver, tapping
on the side of the bowl. That was 5 years ago. It's a semi-permanent
repair.

Jim

 

JB Weld will work for stuff like this too, it is probably the same stuff.
Just make sure to clean the area well, and take the bowl off and
prop it up before gluing.

Ted