Honda CL450 fouled plugs

I'm having a difficult time getting a friends Honda Cl450 to quit
fouling plugs. I'm familiar with vintage HDs and Brit bikes but this
old Honda is making me tear my hair out. I've cleaned the carbs
thoroughly and rebuilt them with new jets, readjusted the valves,
checked the points, compression (140 psi) but the bike fouls the plugs
(black soot) within 10 minutes of start up. Other than replacing the
carbs completely, i'm out of ideas. Anyone out there familiar with
these old Hondas? Help is greatly appreciated. -Billy

 

Thanks a lot for your response.
It is a 1971 CL 450 Scrambler.
I have checked the vacuum slide. it moves freely. replaced the jet
needle and needle jet. replaced the float needle and seat. also set
the float height at 20mm. replaced the main jet and pilot jet. soaked
the carb bodies in chem dip for a day, blown out all the passages.

Somehow the engine is getting too much fuel. I can turn the mixture
screw in all the way and it doesn't affect the idle. On other
carburetors i've worked on this tells me i am getting too much fuel
through the pilot jet, but i can't seem to find any smaller jets for
this cv carb. the bike runs good until the plugs foul and then it'll
pop and sputter. its got to be a simple problem. i've worked on
motorcycles professionally for 16 years but this has me stumped. is
there a problem with these carbs where the cv slide fails to raise and
lower properly? i know the later kehin cv carbs have a rubber diapragm
to aid the vacuum slide.

 

The carbs are shot. See my response to someone asking about a CB500T
(same engine and carbs, really).

Bloody awful carbs on those lumps....

 

I read your response. i agree.i think somehow the carbs are worn to
the point of the slides not opening quick enough to let enough air
through. the problem is if i buy another set off e-bay from some m/c
junkyard, chances are i'll have the same problem.

 

You're probably right.

 

Probably an idle though after all this:
"Are you sure you've got the proper heat range on those plugs?"

 

To answer everyones questions: i failed to mention that i replaced the
mixture screws. that didn't help. i also inspected where they seated
and the was no noticable damage.
i've also been through about 6 sets of NGK B8ES plugs, that are
constantly being cleaned in the bead blaster and returned back to the
rotation. I've also tried hotter B7ES plugs, no difference.

 

that is something i have not tried. to answer the question, it runs
fine before the plugs foul. no black smoke or anything. once its hot
it smokes a little but not enough to pull the top end. i will try that
tomorrow and let you know.
i tried that technique on a harley i had 16 years ago, it had a
sticking valve. it worked great!

 

i set the float levels when i rebuilt the carbs, holding it horizontal
until the needles just closed with no gasket at 20 mm. maybe i'll try
setting it lower.
i haven't tried holding the spark plug off of the head, just laying it
on the head i get a nice blue spark. i have a brand new battery and
i'm using the electric start.
i haven't disassembled the advance but it seems to be advancing ok.
i've had it up to 40 and there haven't been any flat spots.

 

How far out do you have the mixture screws? 1 1/2 turns should be a
good starting point...

Fwed

 

i had it about 1 1/2 turns out but have had it turned 3/4 to all the
way in and theres not much of a difference. the plugs just take
another minute or two to foul. the carbs have to be completely worn
out but i want to eliminate any possibilities that i've overlooked
something simple before i make this girl spend $200 and up on a set of
decent carbs.

 

So you're saying that adjusting the mixture screw pretty much makes no
difference at all?

 

Does it start right up? If not, you may have an ignition timing
problem....Still not sure what size you are using, but maybe try using
smaller jets. Also, this may be a dumb question, but have you check the air
passages or changed the air filter? You may not be getting enough air. I
am gonna assume the bike is all timed properly too.
I had a similar problem on another bike I have.....I ended up using a
smaller jet, dialed in a different ignition timing, used a hotter plug, and
also readjusted the air/fuel mixture screw. This took me a while to figure
out the proper way..... my main issue was it was hard starting, but it also
fouled plugs.

good luck...

Fwed

 

The mixture screw makes little difference. the engine fails to stumble
when i turn it in or out.

The bike doesn't have a starting problem. It starts right up, no
problem.

Right now the air cleaners are off, still fouls plugs. I even pulled
the mufflers, the plugs should've lightened up, they stayed black.

I bought a K & L carb kit and rebuilt the carbs . It came with
everything but the needle jet so I had to buy another kit that came
with needle jets.

I'd like to experiment with smaller jets but on e-bay they cost $20
each ($80) I already have $90 in carb kits invested in these
carburetors. I'm thinking about soldering up the jets and redrilling
them to a smaller size.

 

I just realized after my post that it could be getting oil from worn valve
guides too, in which case the "fix" won't do anything and you're back at
square 1.

 

I decided to take a break from the Honda today and finish up my 73
Norton fastback and 72 roadster. At least when Amal carburetors are
junk, its easy to tell.