Honda cb350 - Pictures, tips and links

My Honda cb350 twin

Keeping your Honda cb350 running:

Shop Manual:

This one is a no brainer. I found this cb350 twin shop manual some time ago. Enjoy the freebie.
Note: This shop manual is from 1974 and covers more than just the cb350 line, but also the cl350, sl350, cb250 and cl250 models.

What oil should I use?

First of all do not use motor oil designed for cars. The cb350 twin, as well as most japanese motorcycles, has a "wet clutch" which means the same oil flowing through the engine gets into the clutch plates as well. Modern car oil has additives (some call them friction modifiers) that can make your clutch slip over time and wear out faster. So if the oil says it's ok for wet clutch motocycles engines, you are good to go.

I use 10W40 in the spring and fall and 20W50 in the hot months.

What spark plug should I use?

NGK B8ES / ND: W24ES plugs seem to be the concensus in shop manuals, online and by mechanics.

Cam Chain Tensioner Adjustment

It turns out that both the Clymer and Hanyes manuals are dead wrong about the cam chain tension adjustment proceedure, that it to say that one crucial step is very very wrong. Only the Honda shop manual has it right. I figured this out after a recent adjustment to the tensioner that resulted in louder than normal cam chain noise. I then compared the 3 manuals to see what in the world I had done wrong. Getting down to business: make the tensioner adjustment 90° A.T.D.C (after top dead center) not *at* top dead center. In other words while rotating the stator counterclowise and watching the left valves, you hit top dead center (T.D.C.) and then keep going aproximately 90 degrees. This make all kinds of sense, right? Right! You know how you have to hold the stator in place with a wrench when at T.D.C. for other adjusments? It's a bear, right? Well, you are keeping the cam chain taut while at this position. The cam chain needs to be relaxed so that the tensioner can pop into place when you loosen the adjustment screw. After you pass T.D.C. you feel the slack in the whole stator to cam chain to rocker arm system. Your valves are still just about closed *and* the cam chain is not taut allowing the cam chain tensioner to do its thing when the adjustment screw is loosened.

Everyone with a Cylmer or Hanyes manual open it up to the cam chain tensioner adjustment section and add the words "90 degrees after" right before it states T.D.C on the page.

Identify Your cb350 (VIN/Tank Color)

You can't always go by the year on the title. It was a common practice to title a Honda as the year it was sold rather than the release year. Even if you have the original title it could be titled as a later year than it is. Use the following chart to correctly identify your cb350 twin.

Step by step carburetor rebuild:

There is this excellent post on a Honda CB350 twin CV carburetor rebuild. For a first time carb rebuild on set of CV carbs Darth's post was extremely helpful. Nice step by step instructions and large pics to guide you through.

Carb rebuild parts:

I've had my carburetors off at least a dozen of so times after having stalling problems and have learned a little. First off most gaskets that come in carb rebuild kits do not fit the float bowl properly even the authentic Honda parts. I've tried a handful of carburetor kits and the float bowl rubber gaskets are always too big. The last time I had to cut it and shorten the length or I bleed gas all over the place.

Update: Finally found the float bowl gaskets to buy. They look more like the outline of home plate. Round carb gaskets have never worked for me. These float bowl gaskets have worked the best so far. I picked them up from Sirius Consolidated Inc and dealing with them has been awesome. The part number as of Jan 2010 is SCI2634. Sure it is two more gaskets than I need, but they are also less than $20. These gaskets also fit.

One down side to CV carbs is there is no vacuum port to use a carb sync tool, but they do make up for it in smaller differences by there very design. As long as all your jets/passage ways are clear, your needles/floats look good and are adjusted at the same height there are really only two things you can adjust once you get everything back together: Mixture screw & Idle stop (there is a third, but I'll get to that).

Stock carburetor, jetting and air mixture screw chart by engine number

Carb Specifications |CB/CL350 |CB/CL350|CB/CL350|
                    | Engine# | Engine#| Engine#|
                    | 1000001 |1045165 | 1065279|        |        |        |
                    | 1045164 |1065278 | & Later| SL350  |CB/CJ360| CL360  |
===========================================================================|
Setting Mark        |  350A   |  3-C   |   3-D  |   A    | 745B   | 747B   | 
--------------------|------------------------------------------------------|
Venturi Bore        |  28 mm  | 28 mm  | 28 mm  | 24 mm  | 28 mm  | 28 mm  | 
--------------------|------------------------------------------------------|
Main Jet  Pri.      |  #60    |  #70   | #70    |  #120  |  #68   |  #68   |
--------------------|------------------------------------------------------|
Main Jet Sec.       |  #115   |  #110  | #105   |  ---   |  #68   |  #68   |
--------------------|------------------------------------------------------|
Air Jet Pri.        |  #50    |  #150  | #150   |  #150  |  #150  |  #150  |
--------------------|------------------------------------------------------|
Air Jet Sec.        |  #50    |  #50   | #50    |  ---   |  #50   |  #50   |
--------------------|------------------------------------------------------|
Pilot Air Jet       |  #90    |  #90   | #90    |  ---   |  #85   |  #85   |
--------------------|------------------------------------------------------|
Needle Jet          |  ---    |  ---   |   ---  |2.515mm |  ---   |  ---   |
--------------------|------------------------------------------------------|
Slide Cutaway       |  ---    |  ---   |  ---   |  2.5   |  ---   |  ---   |
--------------------|------------------------------------------------------|
Pilot Jet           |  #38    |  #35   |  #35   |  #40   |  #35   |  #35   |
--------------------|------------------------------------------------------|
Pilot Screw Turns   | 3/4±1/8 | 1±1/8  |  1±1/8 | 1±1/8  | 1±1/8  | 1±1/8  |
--------------------|------------------------------------------------------|
Float Level (mm/in) | 19/0.75 | 21/.83 |26/1.05|26/1.05**|18.5/.73|18.5/.73|
============================================================================
                    |** SL350 K1-K2 -- 25/0.98

Another break down:

Carb model 350A
engine serial # 1000001- 1045164
Float level 19mm
Standard main jet #60 primary #115 secondary
Standard slow jet #38
Idle mixture screw initial setting 3/4 turns from closed
Idle speed 1200rpm.

Carb model 3B & 3C
engine serial # 1045165- 1065278
Float level 21mm
Standard main jet #70 primary #110 secondary
Standard slow jet #35
Idle mixture screw initial setting 1 turn from closed
Idle speed 1200rpm

Carb model 3D, 722A, 726A, 728A
engine serial # 1065279 and subsequent
Float level 26mm
Standard main jet #68 primary (722A,726A) #70 primary (3D,728A)
Scondary #70 (3D,728A), #105 (3D, 722A, 726A)
Standard slow jet #35
Idle mixture screw initial setting:
3/4 turn from closed (3D)
1 1/8 turns from closed (722A, 726A, 728A)
Idle speed 1200rpm.

The standard mixture screw setting is 1&1/4 - 1&1/2 turns out (see above). You turn the mixture screw all the way in and then back it out the above turns. If there are no other major issues with air leaks and the rest of the top end, those screw adjustments should be the same on both sides. Before my cb350 was repaired this winter I had to adjust mine slightly different on the two sides. Turning out this screw will add more gas to both the idle and off-idle throttle position and is also known as making the mixture more rich. Turning in the mixture screw makes the mix more lean (reducing the amount of gas to idle/off-idle). Checking for air leaks is key if normal settings don't work. You can use a spray carb cleaner trick I'll mentioned at the end of this section for this.

The idle stop screw sets the position that the butterfly valves rest at. The throttle cable pulls on both sides and opens those valves letting more air in and the carburetor responds by drawing more gas to match. It's strange, but the needle lifts on its own due to pressure changes. You can see about where mine are set at, but bottom line once the engine is warm you should be idling between 12k & 18k RPMs when the throttle is fully released.

The third factor is how throttle cable is adjusted as it is attached to the those butterfly valves. This is a real bitch to get at as the adjustment screws are in between the carburetors, but make sure that when turn the throttle both valves get pulled at the same time.

If you are still having problems, check for other sources of air leaks. One helpful trick is to spray carb cleaner around the carbs especially near the intake manifold while the bike is running. If the RPMs climb while spraying then you have an air leak. Using the finer nozzel can help you pin point where the airleak might be.

Honda's XL250 1972 - 1976, CL350, SL350, CB500 K Four 1971 - 1973, CB550 K 1974 - 1976, CB500 F Supersport 1975 -1977, and Kawasaki's KZ250 1981 - 1983 EX305 1983 KZ305 1981 - 1988 KZ400 1977 - 1979 KZ440 1980 - 1983 ZN700 1984 - 1985 KZ750 LTD 1980 - 1983 KZ750 Spectre 1982 - 1983 KLT200 1982 - 1983 KLT250 1982 - 1985 float bowl gasket needs.

Sweet.

Additional specs

NGK: B8ES / ND: W24ES Gap .028-.032in
Ign point gap .012-.016in
Ign Advance "F" 10° BTDC
Max advance 37°- 43° BTDC
Advance starts @ 1300rpm
Max advance 3900rpm
Dwell angle 105° (on 2 cylinder scale)
Condenser capacity 0.22 - 0.26 MFD

Sirius also has plenty of other "consumable" OEM new parts, like jets, needles, points, etc.

Before checking the Timing

Make sure your battery is fully charged if you are going to check it by hand turning the stator (static timing check). The induction timing light gun will not up trigger properly if the battery is not fully charged.

Oil Change

There is no replacable paper oil filter or similar oil filter we think of on today's engines on the Honda cb350 twin. There is, however, an oil filter centrifuge that simply traps the little bits of metal within the body of the centrifuge. On my cb350 these little bits of metal cling to the teeth inside the centrifuge, but I've seen other 350 twins that the centrifuge is perfectly smooth on the inside. It's a pain, but cleaning this out only adds life to your engine.
Here's a quick run down of an oil change on a cb350 twin and most older japanese twins:

1. Warm up the motorcycle by running it for 5 minutes.
2. Loosen the oil drain bolt located underneath the engine at one of the lowest points to the ground.
3. Once the drain bolt is out let the oil drain out for a minute or two.
   • Obviously you want to catch the oil in a basin and recycle the used oil.
   • I will rock the bike from side to side a bit to get more oil out.
   • You may also want to slowly crank the kick-starter as this pushes oil that is in the oil pump and other places out so that oil can drain.
4. Replace the drain plug making sure that any seals or o-rings are in decent shape and that the oil drain plug is tight.
   • For 350 twins only: clean out the oil centrifuge which is accessible on the right side of the bike (close to the exhaust header) by removing the 3 bolts, removing the cover and then removing the "circlip" to release the oil filter cap.
   • I've seen these centrifuges look completely smooth on the inside to having about 12 teeth.
   • These "teeth" make cleaning the inside more difficult, but it means less bits of metal floating around your engine.
5. Using a funnel with the dipstick removed, fill the engine with "wet-clutch" safe motor oil. My cb350 dipstick says 2 quarts, but I usually add a little less than that.
   • Wet-clutch describes a type of engine where the clutch plates are sitting in the same oil that runs through the engine. Modern motor oils have friction modifiers that have a negative impact on the clutch plates and over time reduces the life of your clutch.

1973 K5 model

I ended up with a rare model and a one off in the Honda cb350 line. It's a 1973 super sport (cb350G) and the only Honda cb350 of that era to have a front disk brake. All other front brakes in the line are drum style.

Is my cb350 a cb350g K5 model?

There are a couple of things you can check to tell it you have a cb350g K5 model. The most sure fire way to know is by the VIN number. Keep in mind that the engine might have been swapped at some point in the bikes life. Check both the frame VIN number and the engine VIN number. Maybe you have a frankenstein bike.

Here is who you can check to see if you have a cb350g K5 model:

• The frame VIN number from a cb350g will start with CB350-50XX..
• The engine VIN number from a cb350g will start with CB350E-50XX..
• The front disc brake is a good sign you have a K5 model
• As far as I know only the cb350g models have a shifter pedal that doesn't have a connecting linkage

Hidden steering lock

I was about to buy a steering lock for my Honda cb350 when Chad of Ace Motorcycle and Scooter pointed out a built in steering lock located between the front forks just above the front wheel. It's a tiny barrel with the key hole pointing towards the ground at the same angle as the forks and pushes a bolt out that locks the front steering. Sweet! Chad at Ace just saved me a bunch of money with his honesty and I highly recommend them if you ride in Chicago.

Conclusion:

Honda cb350s are amazing machines, powerful, nimble and timeless.

Over all my Honda cb350 is an absolute joy to ride with plenty of power and maneuverability. This bike is great for the city and decent for a quick jump on the expressway. This cb350 was my first bike and it is like a first love in a way.

Disclaimer

I am by no means an expert, just sharing what I've learned and found along the way. Local groups and help forums are how I learned and making mistakes along the way as well. For local groups I strongly recommend vinmoto.org. Hopefully there is one near you, but if not then start one. Believe me, there *are* other people like you interested in old motorcycles in your area. All the Vin Moto (vintage motorcyclists) groups are non-clubs. That is to say that there are no dues, no attitudes and no elected positions. I've hung out with both the ChiVinMoto (Chicago Vin Moto) and MilVinMoto (Milwaukee) and everybody has been very helpful and willing to freely share what they know. They are all good people. 'Nuff said.

Resources for your Honda cb350:

• VinMoto (Vintage Motorcyclists)
• ChiVinMoto (Chicago Vin Moto) - Chicago, second to none and the local vinmoto group is no different.
• Ace Motorcycle and Scooter
Hands down the best repair shop in Chicago, IL for your vintage bike is Ace. Everyone that works there are truly wonderful people. I trust them implicitly, but don't take my word for it, read their Yelp reviews. They just completed a top end rebuild job on the cb350 and worked with me to find the best and least expensive parts. They even went above and beyond to inquire through local online vintage motorcycle groups to find parts for me. Here is another big plus in my book; they don't charge you extra if you bring in your own parts unlike many other places I've gone to.
Ace is the...! (copyright pending)
• Soup or Wesman's cb350 house of knowledge My good friend and garage-mate shares what he has learned along the way.
• An amazing story of rumor turned into true story and the largest unclaimed motorcycle graveyard east of the mississippi - Dynamite Dave's journey is epic and worth reading.
• Identify your Honda cb350 year and model here.
• A great site for parts MotorCycle Solutions LLC
• Another great site for Honda cb350 parts and other classic 70s Honda bikes North City Vintage Honda
• The Honda Cb350 Wiki Pedia site. Short and to the point.

Comments:

That twitter thing

Believe it or not, there are a decent number of vintage japanese riders and wrenchers on twitter.com. You can follow me at http://twitter.com/cb350 about my cb350 adventures.