Help! 1984 Honda V30 Magna

I'm trying to help out a friend of mine with his 1984 V30 Magna. The
problem is that it won't idle unless the choke is on. As soon as you
give throttle it will starve and stall. This bike has not had the
preventive maintenance that is should have. I removed the carbs,
disassembled them cleaned them up, blew out all the passages etc.,
replaced the rubber mounts, (what a job, I'll never own a V4) put in
fresh gas and it still runs the same. By playing with the choke and
throttle I got it off the pilot circuit and it will rev up, so I don't
think it's bad fuel pressure. Any Ideas?
Dave

 

Ooooh, you're going to hate what I have to say, because you're probably
going to be doing that job all over again :-(

This is probably the most frequently encountered problem in the world
of CV carb-equipped motorbike riding. Your motorbike doesn't even
*have* a choke, Dave. It has a *starting enrichener* which is a tiny
carburetor built into the side of each main carb. It has its own little
throttle valve, and a jet that sucks gas right out of the float bowl.
When you move the "choke" lever to full ON, you are just opening that
little valve and bypassing air around the closed throttle buttefly...

OK, so you decide you're done with the "choke", you figure the engine
is warm enough to idle on its own, but the engine stalls. The idle
mixture you need to run the engine has to come through the plugged up
idle jets and the plugged up idle passages and it has to get past the
plugged up idle mixture screw that tweaks the fuel air mixture to make
it rich enough so the engine will run with the startening enrichener
turned off...

CV carbs don't have much vacuum downstream of the throttle butterfly,
Dave. The engine has a hard time sucking any fuel through the idle jets
and passages if they are clean and correctly adjusted, when they are
dirty, it's no joy in Magnaville...

If somebody elese has drilled out the EPA antitamper plugs and tweaked
the idle mixture screws, you might help get the engine running by
turning all the idle mixture screws out half a turn and turning the
idle speed knob down as far as you can go and have the engine still
idle...

(google for kaybearjr@aol +EPA for a description of the plug removal
procedure and fuel/air screw adjustment)...

But I think you probably didn't do a good enough job cleaning the carbs
out (google for kaybearjr@aol +idle jets to read how to clean out and
adjust those pesky idle mixture screws and jets)...

The alternative is that you have vacuum leaks around rubber hoses or
the rubber boots that hold the carbs on the cylinder heads. If the
engine runs well enough to allow you to do it, squirt water around the
boots and the hoses. If the idle speed gets higher while you're
squirting water around, it's a leak...

But, if the engine runs well enough so you can go for a ride, and the
exhaust pipe goes fartPOP! (or piffle-piffle-SPLAT!)when you roll off
the throttle, it's probably lean idle mixture because your carbs are
still plugged up...

 

krusty kritter wrote:>

Man, it is fun reading your stuff in this group.

 

My little Nissan pickup truck has a computer controlled carburetor that
has a solenoid that shuts off the gas when I'm coasting. The exhaust
goes fartPOP! and piffle-piffle-SPLAT! like some senior citizen that
just ate beans...

 

Really, though. You know your shit.

Thanks for helping me learn some stuff.

I like your style.

Props, even.

--
RCOS #7
2005 FJR1300AT [V4? - no]
1992 GL1500 (sold) [V4? - no]
1985 CB700SC [V4? - no]
1984 XL500R (sold) [V4? - no]
1979 SR500E [V4? - no]
1971 CL175 [V4? - no]
1969 Schwinn Sting-Ray (totalled) [V4? - no]

 

Hey, Mr. kritter. Your posts refer repeatedly to CV carbs. What does
'CV' stand for? "choke virtual", maybe. I guess my CJ360T doesn't have
CV carbs---the carbs seem to have real choke plates.

Still no joy with my CJ that was idle for 13 years. Spark, air, and
timing seem to be okay. About to try the Berryman's B-12 Chemtool as
you suggest. I removed and inspected and was able to blow air through
all the jets, but maybe the idle circuit passages are plugged. I hope
so---otherwise I am stumped. But I'd better not hope for that unless I
can certainly get them unplugged with the B-12 stuff ...

 

I looked at the carburetor parts fiche for your CJ-360T at
www.partsfiche.com...

It does have CV carbs. I could see the diaphragm set listed. I could
see the idle jet, the main jet, and a third jet, a #67 sized jet which
may or may not be the starter jet. I couldn't see a starter valve or a
choke plate on that drawing...

Are you sure you're not looking at the throttle butterflies? The
throttle butterflies will be on the side of the carb that attaches to
the engine, if your carbs had choke plates, they'd be closer to the air
filter box, so you would see two sets of movable round plates, one set
at each end of the carbs...

CV stands for "constant vacuum". CV carbs are also called "constant
velocity" carbs, because the venturi area is variable, according to how
high the vacuum slide rises in response to the engine's actual demand
for *air*, instead of the rider's desire for more *power* at any given
instant..

The old style slide valve carb may still be found on some dirt bikes.
Slide valve carbs pollute the air, because the rider can't judge how
far to open the throttle for rapidly increasing and decreasing RPM and
load conditions. If the rider opens the slide too far, engine vacuum at
the needle jet may be too low, and gas doesn't get sucked out of the
float bowls. OTOH, maybe the slide isn't opened far enough, there is
too much vacuum, and an unnecessary amount of fuel is drawn through the
needle jet, only to be kicked out of the exhaust pipe unburned...

The CV carb takes direct control of the fuel air mixture out of the
rider's right wrist. And that helps to keep our planet's air
invisible...

Other posters have been talking about ultrasonic cleaning of really
grungy carbs. I've never had one get that bad...
----------------------------------------------------------------------------
The first CV carbs most motorbike riders might be familiar with were
the old SU carbs found on British cars from the 1930's to the 1960's.
The SU carb had a butterfly throttle, just like a modern CV carb. When
the driver pushed the gas pedal, the throttle opened, and a vacuum
slide would be raised as air flow increased through the engine. The
vacuum slide would pull a tapered needle out of a brass tube that was
about 1/8th of an inch in diameter. That was the *only* fuel metering
circuit in the carb.

If the mechanic wanted a richer mixture, he could raise the needle a
small amount by loosening a set screw and moving the needle. If he
wanted an even richer mixture or wanted to synchronize the carbs, he
could turn a nut on the bottom of the brass tube, and lower the tube in
relation to the tapered needle. The brass tube had to slide a bit
through rubber seals, and the seals would be prone to leakage if the
owner like to fiddle with his SU carbs a lot. And the choke system was
really silly, the brass tube would be pulled down through the rubber
seal, increasing the wear on the rubber seals My Triumph TR-4's nice
hot exhaust maniforld was right under the carburetors, ready to catch
the gasoline drippings.

Later model SU carburetors eliminated the leaky rubber seals and had a
bypass air passage with a screw for idle speed, richness and
synchronization adjustment...

By the late 1960's, the old SU carbs were replaced by Bendix diaphragm
CV carbs that looked a lot like Bing "constant depression" vergasers...

Later model CV carbs from the 1970's had more fuel and air controlling
circuits than simple British Amal slide valve carbs that had only a
main jet, an idle jet, and a tapered needle (total of three
"circuits")...

Japanese Mikuni carbs added an air emulsion circuit, where air was
mixed with the gasoline before it was sucked into the venturi. This
greatly reduced the size of fuel particles and made the engine much
more responsive to carburetor throttle changes. Mikuni also added the
starting enrichener circuit that I've been describing, replacing the
old choke plate sytem. But choke plates could still be found on Keihin
carbs on Kawasakis well into the 1970's...

The superior throttle response of Mikuni carburetors encouraged many
riders to abandon their primitive 3-circuit Amal carbs and find a way
to bolt or clamp a Mikuni on in its place so they could enjoy a
motorbike that started easily and accelerated smoothly...

 

Yes, upon disassembly I found three jets that I naively thought of as
idle, main, and power.

Definitely each carb has two butterflies. The ones closer to the
airboxes are operated by a lever marked CHOKE. No butterflies are shown
in the diagram, but you can see the linkage between the chokes as item 9
(JOINT SET, CONNECTOR).

 

I take it that a CV carb is characterized by the diaphragm and the
sliding needle.

Those are parts of what I have been thinking of as the power circuit.

Where is the vacuum supposed to be constant?

 

Right under the vacuum operated slide. Instead of having a round
venturi that tapers down from a large round section to a smaller round
section and expands back to a large round section again, the throat of
the venturi is sort of d-shaped and the highest vacuum should be right
there at the needle so the vacuum can suck fuel past the needle jet/jet
needle combination orifice at part throttle, then at 3/4th to full
throttle, the nj/jn combination offers less restriction to fuel flow
than the main jet...

If your carb has a power jet, you'll usually see an external brass tube
running from the float bowl up the side of the carb to a discharge port
downstream of the throttle butterflies. It can't get enough vacuum to
overcome the weight of the fuel in the float bowls until the engine is
running at full throttle...

 

Thanks for your informative posts. I'd be obliged if you could try to
find any improvements or anything wrong in the following plan,
especially regarding damage to the rubber and plastic parts.

I would remove the carbs, remove the diaphragm/pistons and bowls, remove
all the small parts (slide valves, jets, idle-mixture valves). Then I
would warm the carb bodies, bowls, and small parts in the sun or maybe
in a toaster oven (hopefully to something like 110 F) and spray B-12
into every little hole and let it soak. I would repeat with ordinary
spray carb cleaner (methanol, toluene, methyl chloride) and maybe again
with B-12, until I could see solvent flowing out of every little hole.
Then I would reassemble and reinstall and drive with B-12 in the fuel.

One thing I'm worried about is damage by the solvents to the rubber and
plastic parts. I don't know where all of those parts are and I don't
think I can remove all of them. For instance the tip of the float
needle looks like rubber, and I believe maybe the throttle shafts have
plastic seals/bearings. I expect the diaphragms would be ruined by the
solvents, but it's easy to keep those safe off to the side.

 

If you push the float pivot pin out, you can remove the float and the
float valve, which has, as you say, a rubber tip...

There's no good reason to heat the carburetors. All that would do is
cook the gum and varnish in the carb bodies and make it even harder.
Carb cleaner has a low evaporating temperature. You're better off with
cold carburetors, as the solvent will have more time to work before it
evaporates...

If you can find a more powerful carb cleaner than B-12 and you can
squirt it through all the holes, you should be able to get almost all
the crud out...

fuel.

Just ride easy with that stuff in the gasoline, you don't wan't to wash
the oil film off the cylinder walls and run the piston rings dry. Keep
the RPM really low and try to ride the motorbike with the engine as
close to idle RPM as is safe so it will have to draw gasoline mixed
with B-12 through the idle jets...

Like I said above, you can remove the float pivot pin and pull out the
float and the rubber-tipped needle valve. You might even want to remove
the float valve seat. There may be a filter up under that seat. B-12
will make the rubber diaphragms swell up, but they will return to their
original size when they dry. I never noticed any damage to the throttle
shaft seals from spraying carb cleaner on them...

 

Except <pedant mode> plenty of old CV carbs don't have diaphragms.

 

I don't care whether it's pedantic. Let us identify the essence of CV
carbs---CVness itself---what it is to be CV---the minimal CV sine qua
non---and so on.

I seem to recall working on a couple of passenger-car carbs that each
had a "power piston" that acuated metering rods depending on air pressure.

 

I just closed the chokes all the way and opened the throttles all the
way and was able to get fire for half a second. That is the most life
the thing has shown since '92 ... probably I'd never tried that before ...

Can we say that that is consistent with plugged idle passages?

 

Yes, you got some fuel past the jet needle...

The normal way to start an older engine with a real choke was to close
the choke all the way and crank the engine until it started blubbering
like it was going to fire, then open the choke about 1/3rd and give the
engine a little throttle...

If you gave the engine too much throttle, you wouldn't have enough
vacuum downstream of the butterflies to draw fuel through the idle
mixture outlet ports...

Four stroke engines have lots of problems with low engine vacuum and
infrequent intake strokes, as I explained about 2 weeks ago to the
rider who was having problems starting his Sportster...

 

I had cleaned the carbs before in my own stupid way ... I used water and
liquid wrench and didn't use carb cleaner. I freed up the pneumatic
pistons on that first go-round, but left some water in the carbs, which
led to a float valve being stuck open. The bike had a strong gas smell
whenever the fuel valve was open.

Did the job right this time, using a can of aerosol carb cleaner to
clean the carbs inside and out. Sprayed through all the passages, but
didn't see any gunk or chunks. There was something chalky like lime on
the bowl valve needle and inside the bowls, so used Lime Away followed
by carb cleaner on the jets and needle. Made sure the bowl valve and
floats were moving properly.

It started on the second kick. I don't know that I did much good with
the carb cleaner, but at least I could use it to verify that the
passages were clear and dry. I ran out of my other carb cleaner and
used the Berryman's B-12 Chemtool from Walmart, but its aerosol
behaviour was somewhat troublesome, spraying too fast and then too slow.
Sometimes it shot the nozzle extension tube out of the nozzle onto the
work. It seemed that I had to turn the can upside down to get any
liquid to come out. Not saying that it's bad stuff, but I liked my
other carb cleaner better.

Now I seem to have a valve tappet that is too tight and making an awful
racket. I think I had the cam rotated to the wrong position when I
adjusted the tappet.

 

Alcohol added to your pump gas emulsifies water in your gas tank, and
that's a good thing to a certain extent. The water gets turned to steam
and goes out the exhaust pipe, maybe taking some carbon with it.
Alcohol also has the property of evaporating at a lower temperature and
condenses water in your fuel system under various conditions.
Eventually though, the alcohol in your old gasoline will evaporate, and
whatever water is left combines with CO2 from the atmosphere and makes
the calcium carbonate you found in your float bowls...

Hooray! Another motorbike brought back to life!

Maybe shaking the can would help? And I've run into the problem with
the nozzle extension tube, too. It's just a press fit in the spray
nozzle. Maybe the tube could be carefully superglued to the nozzle? Who
knows?

The resurrection of old crocks must continue, regardless of the hassle
and time consumed...

Valves usually make noise when they are too LOOSE and they clatter...

When they are tight, the cam lobe suffers in silence or maybe squeaks a
little if it doesn't have enough oil on it...

 

You are right. The left intake tappet was way too loose (maybe 2mm) due
to being 360 degrees out of phase when I adjusted it.

Thanks for that warning and for your remarks on the other thread.

 

You would still have to explain where the calcium came from, if the
stuff was actually lime.

I can say that the chalky stuff was removed by Lime Away. Before The
LA, the deposits on the walls of the bowls were light colored and
somewhat rough and dry and were not removed by carb cleaner. After the
LA, the remaining deposits were darker and smeary and rather easily
removed by wiping with a carb-cleaner-soaked paper towel.