Honda cb350 - Pictures, tips and links

Bought my Honda cb350 in April of 2009 from EPE Motorcycles as my first japanese bike. After finding a matching gas tank and side panels off of an online auction and getting them installed I have been in love with my Honda cb350 ever since.

End of 2009 Update

I've been having to replace the left spark plug about once every 2 weeks as it is oil fouled. This does not bode well. Ace Motorcycle and Scooter has it for the winter and took a look at it. It needs new pistons, rings, seals and cylinder; ouch. Found a guy with pistons and cylinder off a K4 model with 8,000 miles on it and registering 115psi cold. The Clymer manual says 120psi is good cold compression and the asking price is great. He also has NOS rings still in the original box with part numbers. If these parts check out this would save me some decent cash. Keeping my fingers crossed.

Here is the upside of the top end repair: I think this bike performs pretty damn well for a now 37 year old bike. If it had bad seals and poor compression in this state I'll have a bike with an adolescent heart come spring. This both excites me and worries me that I may not want to ever let this CB go.

My guess is that a transmission job will be in the future as well. Second gear has slipped into neutral a couple of times this year and there are a couple phantom neutral gears between 2nd and 3rd / 3rd and 4th. With a supposed 300,000 bikes sold from 1969 to 1973 I feel my odds are good. With other bike purchases in my head this may be my first and last bike as other bikes come and go.

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?

10W40 - says it right on the stock dip stick.

What spark plug should I use?

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

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 6 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.

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

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 the screw will add more air or lean the mixture, turning it in makes the mix more rich (adding more fuel). Again, checking for air leaks is key if normal settings don't work. You can use the spray carb cleaner trick I mentioned in the other email 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.

Update: The heavens opened up and a great light shineth down in the form of 100s of ebay searches. I kid, like I've sort of been saying I'm new to this, but figuring this new game out has been half the fun. 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 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.

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

Checking the Timing

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

Oil Change

It's a pain in the butt but clean the teeth of the oil centrifuge for every oil change. There is no oil filter on the Honda cb350 and so that's where the junk ends up. Little bits of metal cling to the teeth of the centrifuge and cleaning it only adds life to your cb350.

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.

Resources for your Honda cb350:

• 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)
• 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.

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.