Picked up a 1973 CB350

LuckyB

New Member
Hey guys!
I guess this would be my introductory post. I have been researching and lurking the last few weeks.

I have a bobber and a chopper that are FI'd that I put together over the years. I do have novice-intermediate mechanical knowledge. I've rebuilt carbs on lots of bikes, I have picked up a few bikes in boxes and put them together. Engines were always working. Just needed to be put together.
So I picked up a rebel for my wife about 2 months ago. She doesn't like the feel of it and had been asking for a Cafe, so I traded the rebel for a stock 73 CB350 not running and cash. The guy swore it ran when parked (which they all do). Motor turns freely, battery was toast, wouldn't start with fluid. I opened the points cover and saw that it had a gap so figured that is what it was. Mind you I knew ( and still dont know) much of anything about points. I just know they are supposed to open and shut while turning. So I decided I would take the chance and take on the project. At the very least I would learn about older bikes and pick up some more mechanical knowledge. It also gives me a reason to be out in my favorite place, the garage.
So get it home and swap out the battery. Pulled the plugs. Looks like the guy put brand new plugs in. Right side is dark left side looked like it was new. Started reading about gapping points and setting the points. I believe I have the concept down. Looks simple enough. So hooked the light up, started with LF and started to notice something really funky. I couldn't get it timed properly. It seemed like when I set gap for LF, it would stay open for a full revolution. I checked and double checked to make sure I was on the right stroke. Same thing! Mind you im not turning with starter but by wrench. Not sure if that detail matters. Spent a few hours wondering what it could be played with adjusting the plate etc.. I figured maybe the points were worn, so I bought some from DCC and got them last night. Excited to start again I installed them. SAME THING! I compared my new points to old and they look like they are relatively new.
Not sure of the proper lingo I did a bunch of googling last night and this morning. I found that someone said it could be the advancer plate. So started looking at that. The numbers are on top and the notch on the cam is pointing straight down. On the advancer plate last night I noticed someone had used a sharpie to mark a spot at about 3 oclock. So to kind of give you an idea, the 286 is at about 11ish oclock, the mark on the cam is at 6, then there is a sharpie mark at about 3. I really dont know if any of these details are pertinent, but figured I would try.
I'm sure this has to be addressed somewhere as to what my problem could be. I just don't know the way to word it, the name of the parts etc. If I knew, I would be doing, not typing lol.
Anyway I was wondering if you guys could give me some suggestions and trouble shooting. Also Clymer manual is on the way in the mail.
Thank you to anyone that helps.
 
One other detail. Some of the stuff looks like it could be relatively new. Thinking maybe when someone was putting the new stuff on they put something on improper. I watched a video on youtube where the guy was 180 out of time because the notch on the cam was facing the 286. Well anyway thought I would mention. Thanks.
 
If the points aren't closing (on either side) then they probably haven't been gapped correctly.

Starting with the left side, the process is to turn the motor over using a wrench until the side that you're gapping is at its widest opening. Then you stick the feeler gauge into the points gap and loosen all the hardware. Tighten everything back up and now the gap is set. Next step is turn the motor over until the timing marks line up with the LF mark on the rotor. Hold the motor in place and don't let it move. Now loosen the points plate and rotate it so that a timing light just comes on. This should coincide with the points on the left side opening.

For timing on the right side, you have to set the gap in order to get the timing light to trigger at the correct time. I can't remember the exact specs, but the gap is meant to fall within a minimum and maximum value and if it does not, then it's time for new points.

Hope that made sense...
 
Ok. So the videos I watched didn't show that. They went straight for LF index mark and that is what I was doing.
So to clarify before even worrying about LF, turn motor with wrench and look for point where it opens widest?
Do I set that .015" ? Or is it just when on LF ?
 
Sonreir said:
If the points aren't closing (on either side) then they probably haven't been gapped correctly.

Starting with the left side, the process is to turn the motor over using a wrench until the side that you're gapping is at its widest opening. Then you stick the feeler gauge into the points gap and loosen all the hardware. Tighten everything back up and now the gap is set. Next step is turn the motor over until the timing marks line up with the LF mark on the rotor. Hold the motor in place and don't let it move. Now loosen the points plate and rotate it so that a timing light just comes on. This should coincide with the points on the left side opening.

For timing on the right side, you have to set the gap in order to get the timing light to trigger at the correct time. I can't remember the exact specs, but the gap is meant to fall within a minimum and maximum value and if it does not, then it's time for new points.

Hope that made sense...


Thank you for such a fast response BTW>
 
You set gap at the widest point of opening. If you set gap at the LF mark, the points will never close.
 
So I did that. Once set and passing the lf mark the light kicks on, how far into a revolution should it remain on for?

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LuckyB said:
So I did that. Once set and passing the lf mark the light kicks on, how far into a revolution should it remain on for?

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Not too long, but that's mostly irrelevant. As long as the gap is set correctly and the points open at the correct time, you don't have control over the other things (such as how long they remain open or closed).
 
So if it stays on for half a revolution or more it doesn't matter? It's been driving me crazy thinking I'm shining something wrong.

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Aside from the specifics as to how to time your specific engine, it may be helpful to understand what it is you are trying to do. Your spark plug fires when the points open, not when they close. Your ignition coil gets energized when the points close and complete the circuit, at which time a magnetic field is created in the coil. Within the same magnetic field, another coil is wound which is connected to your plug. When the points open, the magnetic field suddenly collapses, and it is this rapid change in magnetic flux that creates electrical flow in the windings attached to the plug. There are a lot of windings in this side of the coil, and there is a corresponding amount of energy, and if all is well it will be enough to create a spark at the plug. So you need to cause the points to open at just the right time. Just the right time will be before the piston actually gets to the top of its stroke because, in a gasoline engine, the fuel does not explode, it burns, and when it gets lit by the spark, it burns fairly slowly, enough so that you have to light the fire early, so when it reaches its peak, the piston will be just passing top center where the expanding chemical reaction can have the most effect. The coil only needs an incredibly short amount of time for the magnetic field to reach full strength, so the points only need to be closed for a very short time. Any longer is a waste, and the coil will simply get hotter than it needs to without any increase in performance (a big reduction in performance if it gets too hot!). Once the cam comes around and kicks open the points, energy stops going to the coil, the magnetic field collapses, and the plug fires. As long as the cam is holding the points open, nothing is happening and the coil gets to cool off until the points close again. The distance the cam rotates (in degrees) is called the dwell angle, and is simply the number of degrees that the coil is in the "off" mode. This is determined by the cam profile, which is of course fixed, but you can adjust the dwell by adjusting how far the points open when the cam is at its highest point. So a large point gap will result in a longer "dwell" , or cool down time, and a consequently shorter "charge up" time for the coil. And conversely, a small gap will do just the opposite. The manufacturer has determined the best balance. While the ratio of "on" and "off" for the coil is fixed, the actual time is not because the engine operates at variable speed. At low rpm, you would like a lot of dwell to keep the coil from getting too hot, but that same long dwell and short saturation time at high rpm may result in insufficient time for the coil to become fully saturated between firings. So set the point gap first, do it carefully and then leave it alone. Adjusting the timing afterward does not change the setting, so once done, it's done until point contact faces erode from the constant arcing, and the rubbing block that rides on the cam gets filed down. That's why points ignitions need a "tune up" after the miles add up. Be mindful that the opposite is not true. If you adjust the point gap after you set the timing, the timing will be off. This is because you set the point gap where the cam has the points open at max. It is hard to see, but the rubbing block does not ride against the cam all the way around. It is actually not touching the cam when the points are closed. As the cam comes around, at some point it comes into contact with the rubbing block and the points open. If the gap is set big, this will happen later in rotational degrees, and if set smaller, it will happen earlier, consequently changing when the plug fires. Changing the timing does not change the point gap, so you have to set the gap first, and set the timing second.

When you go to set the timing, it can be useful to get your bearings first. You know you need the plug to fire just before the piston comes to the top of the bore on the compression stroke. So you need to know which way the engine spins when it is running, and where the piston is. If you are not sure which way the engine turns, simply kick it over or hit the starter. You can get a pretty good idea of where the piston is (and which piston goes to which set of points!) by simply taking out a spark plug and putting your finger over the hole. Turn the engine over until you feel the pressure pushing your finger off the hole, and then go past and feel it suck your finger down. Go back and forth and estimate the middle where the piston is at top center. Turn it backward a few degrees, and you should see that one set of points will be very near to just opening up. This isn't very useful for tuning your engine, but it will let you know if you are in the right neighborhood in understanding all the parts. You should also see timing marks on the alternator (or where ever they are on your specific engine) in the neighborhood of lining up. This is mostly useful in verifying that you are working on the right cylinder, with the right set of points and the right set of timing marks. And this also shows the great strength of this simple ignition system. If you have to take it apart on the side of the road, you can absolutely have your bike running reasonably well (enough to get home) by approximating the point gap, and then estimating the timing this way.
 
Have you considered installing an electronic ignition on it? The Pamco unit comes with a digital advancer as well.
 
I am. Lol
Since this is something I'm going to be keeping and not flipping, I'm just going to bite the bullet. Going to do the same thing with carbs.

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