CB350 Overheating?

[Caferacerdude]

Hey just having some issues with a 1973 CB350G Super Sport I bought recently.

I recently installed some new mikuni carbs onto the bike and they seem to be running well. They are running a little rich but I can deal with that for now until I solve some of the bigger issues. When I start the bike and take it for a 5 minute spin when I come back the left exhaust pipe wrap is smoking and extremely hot. Im not sure whats going on or what the issue is. Also it seems like the battery is being drained at an unusual level and is not charging correctly. I am not an electrician in any way and im not really a mechanic either so Im not sure where to proceed. any help in any way would be fantastic!

Thanks!
John

 

[sadtaco]

There are several things to check here. If you replaced the carburetors or installed new ones, they most likely have factory jets in them. If your bike has aftermarket exhaust and/or air intakes, that will not work. You will need to upgrade the jet carburetor jets; these are the needle jet, main jet, and pilot jet. If you have never rebuilt a carburetor or rejetted, its very easy, just do a search online. If your exhaust is hotter on one side than the other, then your carburetors are most likely not balanced. You can do this two ways; bench sync them, or sync them with a manometer. Motion Pro makes a good one, but they are about $100 new. Lot of people will make their own.

Balancing requires knowledge of how a carburetor works and what the components are. If you use a manometer, you do it while the bike is running. Bench synchronizing requires the carburetor assembly to be out of the bike but fully assembled. If they are not balanced, then one or more carburetors will run richer or leaner than the others. Since you have two pipes; 2 into 1 on each side it sounds like, from what you have described your carbs are likely not balanced. I can also assume this to be the case since you admitted you aren't an expert at this, and you must at a minimum at least bench sync them after installation.

Timing can also be another factor; if the timing is advanced, then the bike will run lean, and hotter. Retarded timing will richen the fuel air ratio. What makes you think it is running richer? You can tell by pulling the spark plugs out and comparing them to a "spark plug conditions" matrix online; just search those keywords. Does the bike run crappy or better when it is cold or warmed up? These are all symptoms and variables of running lean or rich.
My advice to you is to have a professional adjust the intake and ignition system. Unless you know what you are doing, chances are you wont improve it and may actually make it worse.

Lastly, the bike has a generator, not an alternator. Generators do not charge the bike at idle, they are only capable of charging at a certain RPM and above. Alternators charge no matter what when the engine is running. You can verify this by taking a multimeter and checking the battery voltage when the bike is off and fully charged. Next, put the bike in neutral, start it up and run at idle. Take the multimeter and check the battery voltage; it should be under 12v. Finally, run the bike at 3000 rpm and check the battery voltage; it should be 12 to -14v, 12 is best and means the voltage regulator is doing its job. If it is not then something is wrong with the charging system (generator or voltage rectifier/regulator).

 

[crazypj]

The charging system has been covered multiple times. It doesn't charge below 2,000 rpm so you need to be above that as much as possible.
5k and above is good.
No one makes 'pre-jetted' carbs that don't need further work, you have to swap stuff and change jets for YOUR motor.
Carburation becomes very dependant on exhaust system when stock air box is removed, the length, diameter and restrictions of pipe/silencer have a huge effect on size of main jets.
Slide cut-away may need changing.
I hope you have a lot of patience to play with this stuff

 

[mydlyfkryzis]

Lastly, the bike has a generator, not an alternator. Generators do not charge the bike at idle, they are only capable of charging at a certain RPM and above. Alternators charge no matter what when the engine is running. You can verify this by taking a multimeter and checking the battery voltage when the bike is off and fully charged. Next, put the bike in neutral, start it up and run at idle. Take the multimeter and check the battery voltage; it should be under 12v. Finally, run the bike at 3000 rpm and check the battery voltage; it should be 12 to -14v, 12 is best and means the voltage regulator is doing its job. If it is not then something is wrong with the charging system (generator or voltage rectifier/regulator).

Alternator: Makes AC Current - CB350 has alternator
Generator: Makes DC current - They also have brushes.

I think you are mixing alternator and generator with the difference between a permanent magnet alternator and an excited field alternator (or Generator). The excited field can cope with varying RPM more than a PM type.

Your comment about not charging at idle on CB350 is definitely right.

However, even an excited field alternator can is affected by RPM (But less so). The real problem is that most of 1960-70 era motorcycles did not have enbough capacity in the first place. The smaller 4 cylinder Hondas are excited field, but they had issues at idle speeds too.

If you add a 55Watt halogen bulb to these old bikes without reducing the other lighting loads, you will have charging issues, especially at idle.