HONDA SERVICE BULLETINS:
At the moment I don't have my hands on the actual service bulletins, just this list of what they are. Note: "The Wrench" was a news
bulletin published by Honda.
||CB650 Valve Cover Installation
||CB650 Head Torquing
||CB650 Faulty Exhaust Valve Guides
||CB650 Cam Chain Installation
Some people have complained about a general lack of power, usually problems revving past 5500 rpm or so under load. I limited
the options down to fuel delivery, air delivery, and timing. To make a long story short, it was air delivery - even with a new filter.
The inlet cover that holds the filter in place was restricting the airflow! I discarded the cover and used washers to hold the filter
in place. See picture below. Another idea mentioned to me was the gas cap vent becomming plugged, preventing adaquate fuel flow to the
carbs at the higher rpm. Hopefully one of these ideas will work for you.
These bikes all seem to have problems with charging at some point, so don't worry.
Actually, go ahead and worry, just don't be suprised.
The most common problems:
- Bad rotors, windings short out. Heat breaks down the rotors insulator material.
- Regulator/Rectifier can go bad, usually caused by a bad rotor!
- Bad wiring between stator assembly and the regulator/rectifier.
- Brushes inside stator cover can wear out. (I'd say the least likely of them all)
You will need a strap wrench to hold the rotor in place while removing it's center bolt. To actually remove the rotor, you will
need a flywheel puller. Some people have said that you can use the rear axle shaft (18mm?) from the bike to thread into the rotor
and do the same job. This is up for grabs, because the first time I tryed it I ruined the axle. (Fortunatly it was lent to me by the
salvage/parts shop I bought the rotor from). The next time I did it, I used my own axle, but instead of tightening it all the way I
threaded it in, and took a hammer to the backside of the bolt flange. This worked like a slide hammer or dent puller does, and it was
incredibly easy. See picture below.
Poor charging was the first problem I encountered with the bike. If you're having you're own problems, just take a deep breath, because
with any luck it's not nearly as bad as what I had to go through.....
- Previous owner said the rotor was replaced. (Might have been, or not. I don't know)
- Led me to assume the rotor was good. (Mistake)
- Stator tested out good, so I replaced Regulator/Rectifier, used from a junkyard
- Didn't work, took R/R back to junkyard and exchanged it for a different one.
- Still didn't work, so threw in the towel and took it to a shop.
- Shop said it was the R/R(!?), replaced it, and it worked for a month(!? - No idea why)
- Took it to shop #2, diagnosed problem as faulty rotor.
- Went to different store and ordered a remanufactured rotor.
- Worked, but in the end cost me at least three times as much as it should have.
I'd strongly advise following the Motorcycle Charging Systems Fault Finding Chart before replacing anything at all - the problem is that one thing can lead to another and you'll be chasing issues and spending big $$$. For example, your regulator/rectifier may be bad, however, the reason it may have gone bad is because of a faulty rotor, which I would say is the more common issue on the 650. The rotor windings short out (sometimes intermittently at higher rpms) and it draws more amps than the regulator can handle. So if you start guessing, you'll end up replacing the regulator/rectifier over and over until your pocket book can't handle it, then you'll try replacing the rotor, but when you do that chances are your regulator/rectifier is already bad from before, then your replace the stator, wiring harness, etc...DON'T FALL INTO THIS TRAP!!! Follow the fault finding chart, and if you're unsure or uncomfortable with this type of diagnosis work, just take it in to a professional. It will be less expensive in the end!
What further complicated this situation was a messed up wiring problem. The original owner ripped off the headlight bucket and signals
to install a fairing. The owner I bought it from had attempted to remove the fairing and "reconstruct" the wiring. It was a hack job
beyond belief. Wires hanging everywhere (including grounds). Bought a original used harness and installed that.
-CARB VENT HOSES:
The vent tubes on the carburators rot and fall off. They are more or less impossible to replace without seperating the carbs. Having these tubes fall off is not the end of the world,
you can either try to hang them in place or take them off. Some people have said that fuel poured out of the holes, this is an indication
of a more serious problem as it is a vapor vent (probably bad floats). You can usually find a similar rubber "T" at a hardware store, or purchase the originals
from Honda (for $33 each) if you really want to. The biggest problem with not having these tubes in place is that it introduces the possibility of road dirt and grime getting into your carb bowls.
1981-82 CV STYLE (VB44A,B,C)
1979-80 MECHANICAL STYLE (PD51A/B)
- NAPCO: H-0177
- KEYSTER: KH-1078N
- K & L: 18-2572
- CYCLEWAREABLES: CW18-2572KL
-PRESSED IN SLOW-JET REMOVAL (1980-81 VB44 CV Carburators):
Just rebuild the carbs already...and be thorough, or you'll become and expert at pull them off really
SLOW JETS - These generally suck on the VB series carbs, although the VB44C set from the 1982 models do in fact
have threaded slow jets. The other's aren't so lucky - they're pressed in, and according to Honda cannot be removed.
Of course, everything can be removed, the hard part is putting it back together (functionally, anyways).
If you've invested in a rebuild kit and your carbs are a 1980 or 1981 CV model, you've probably received a set of threaded slow
jets, and have no idea what to do with them.
If you want to convert a pressed in slow jet model VB44 to a threaded VB44C type, you're a brave soul. Here's what you do:
- Remove Old Slow Jets
Now I've heard people talking about pulling them out with pliers or vice grips - those people are talking about
the 1979-1980 PD50A / PD50B carbs - NOT the CV (Constant Velocity) style. The slow jet / emulsion tube is pressed
deep into the carburator body, next to the main jet. To get it out, use a screw extractor or similar method.
Again, keep in mind this is not necessary to get your carbs in working order with the stock press fit jets!
- Drill/Tap Out Emulsion Tube Holder (Aluminum Casting)
The replacement (and check for yourself here) is generally a 5mm emulsion tube/jet which tapers to a 6mm thread. The
pitch of the thread on my replacements was M6x0.75 - try finding that tap at a hardware store. It's a Japanese thread
standard (JIS-B-0252). A lot of early Hondas had JIS threads, before the inclusion of ISO standards. Actually, just
trying to find any metric taps can be a challange at times. But be smart and use a thread pitch gauge to make sure you
have it right, and then check Ebay or search online for the tap. You can really screw things up in a hurry, and be
left with a set of useless carbs. If you're not comfortable, then stay far, far away. If you're ready to roll, then
drill out the carb body with a 5.2mm drill bit (or 13/64ths if you live in America, being careful by measuring to avoid
going to deep of course, and continue by tapping M6x0.75 right hand threads. I had to grind down the neck and tip of my
tap in order to allow it to tap deep enough without bottoming out on the point.
- Make Sure You Have The Right Replacement Slow Jets!
After I drilled out and tapped my slow jet emulsion tube, I threaded in the "replacement" slow jets I received in the
aftermarket rebuild kit. It worked for crap...the bike was running crazy rich, and I couldn't tune it down. Then I
compared the original, pressed in slow jets to the replacements. The air holes in the replacement were much, much smaller
on the aftermarket slow jet! I ordered a set of four stock Honda slow jets (for the 1982 VB44C carbs), screwed them in, and
voilą - the mixture was great, and then perfect when I tuned the pilot screws and sync'd everything up.
This project is a serious undertaking. Anytime you take a drill to your carbs, you're asking for trouble. If you have
questions on this procedure, shoot me a message.
-OTHER CARB "ISSUES":
Boy, with all the comments and questions flooding my inbox, I must have heard it all. A couple of things...
- Know your limitations - Only do what's absolutely necessary!
Don't do foolish things like split the carb rack unless you have some experience. 99.9% of the time
this is totally unnecessary to get your bike back in running condition. I'll outline the procedure for
cleaning the VB series carbs later on, but as a rule of thumb you need to take off the bowls, slide covers,
needle jets, jets holders, jets, floats, float valves, idle/pilot screw (keep track of that washer and o-ring!),
etc. Then you spray with carb cleaner, and then you blast with compressed air. And then you repeat. If you
don't have compressed air, get some. Also, don't dip the carb rack! There are all kinds of o-rings in the fuel
delivery pipes and a number of other plastic/rubber components that will take damage unless removed first.
- If it ran good before, don't fiddle around!
Don't mess with pilot screw settings unless you're replacing them, or you know how to tune carbs. It's nothing
personal, but more people mess around with the pilot screws and sync screws when it's really not necessary.
Learn how carbs work first before attempting to troubleshoot problems. You can't troubleshoot problems
for a mechanism you don't understand!
- Troubleshooting Carbs Isn't Difficult!
And I'm sure I'll get complaints on this one, but it's true:
-Is gas getting to the carbs? Crack open each drain screw on the bowls and see if gas drips out. Simple.
Very common, on Honda's single cam bikes in general. Usually oil will weep out the sides where the oil galleys are. SEE PIC BELOW. Also,
don't "mirror polish" your gasket surface here or anywhere else on the motor. If you look closely, you will be able to see the machining
marks on all the gasket flanges from original production.
-CAM CHAIN NOISE:
Another very common problem. Chains stretch, and the tensioner can wear out too, allowing the chain to fly all over the place. Sound has
been mistaken for bottom end noise, make sure you periodically adjust the tension before making any assumptions. I really wouldn't worry
about this thing breaking - and you'll never get rid of the noise completely. I replaced my chain and tensioner with OEM Honda parts, and
it sounds exactly the same. Bottom line, they're noisy but they'll keep working forever.