Handlebars

The stock handlebars on the CB350 are pretty comfortable, but they put your hands pretty high up so you look like you’re riding one of those gangsta bicycles from the 1950s.  The ergonomics of the stock bars are pretty good, though.

The mirrors are also mounted way high up, making the bike look like a goofy long-eared rabbit and screwing up the lines on what is otherwise a compact, pretty machine.  That aside, it seems like it’s working out pretty well for the guy in the CB350 ad from 1971.

CB350_1971bilahiam

I was looking for a set of handlebars that would drop the control position down a couple of inches, but nothing crazy.  I also wanted to find a way to install bar-end mirrors, and the stock bars had metal plugs welded in the ends to prevent that.  I didn’t want to change the way that the handlebars felt, but I did want a little more forward lean.  Clubmans or clip-ons would just be a little ridiculous (and soooooo 2014) on this little bike.

After some research, I decided on a set of reproduction handlebars made by Emgo for the CB400F. They’re “euro” style with a low rise and slightly less pull-back than the stock CB350 bars.  Once they arrived, I made some measurements and found that the pre-drilled holes were in the right spots for wiring and the mounting pins of the switch housings.  I was ready to install. 51WXCZH3oWL._SL1200_

It was one of the scarier operations that I’ve performed on this bike.  Because the switch wiring goes through the handlebars, it is necessary to disconnect all of these wires so that you can remove them from the old handlebars and install the switches on the new handlebars.  No less than 12 wires in the front harness must be disconnected.  For most of these terminal connections, it’s the first time they’ve seen the light of day in 40 years.  I pity the fool that doesn’t document their wiring before disconnecting it all.  I said a prayer and got started.

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Here’s everything disconnected inside the headlight bucket.

Next I disassembled the switch housings by removing the screws that help them together.  I disconnected the throttle cable from the throttle sleeve and removed the left grip.  I left the brake and clutch cables connected even though the service manual recommended removing them.  Honda can’t tell me what to do!

I taped up the disconnected end of each bundle of switch wiring in order to avoid putting stress on the terminals while pulling them through the bars.  I loosened the bar clamps to point the center hole upwards and began to slowly thread the wiring out of the old handlebars.  After about 20 minutes of gently pushing one end and pulling the other, I got the bundles out.  The handlebar was naked!  I removed it.  2015-08-23 11.14.53

I installed the new handlebars and reversed the process, slowly threading the wiring from the switch holes to the center hole.  I had some trouble getting the right switch housing mounted.  I also found that the throttle sleeve was rubbing against the inside of the housing, so I thought the sleeve was the problem.  I tried grinding down the outer edge of the sleeve, but this did not really help.  After about half an hour of cursing and moving the housing around without success, I figured out what was going on.   I had left too much wire on the outside of the handlebar inside the housing, and the bulk of the wiring was preventing the housing from closing on the bar cleanly. I pulled some of it through, and everything worked properly.

I hooked all the wiring back up and turned the key to see if there were any obvious electrical issues.  The starter begin turning over ON ITS OWN as soon as I turned the key, so I immediately turned the key back to the off position.  I almost had a freak-out, because there is nothing worse than an electrical issue.  I settled down and traced the starter switch wire.  I disconnected it and turned the key.  No starter turning.  Okay.

I opened the right switch housing back up and found that all of my fiddling earlier had worn the insulation off of the starter switch wire and it was grounding out against the handlebars.  I added some electrical tape and reassembled it.  I turned the key.  No starter turning!  I pressed the starter switch and the starter kicked right up.

The horn also seemed at first not to work, but then I discovered that I had just left its wire disconnected in the front harness by accident.

I installed the grips and discovered that the left grip actually was not long enough to cover the space between the left end and the housing.  After talking to the owner of my local motorcycle shop and comparing to some old stock he had in the back room, I believe that this is because the CB400F (which these bars were made for) has a larger left switch housing than the CB350 twin.  I’m planning to fill the gap with a bar clamp and to mount a mirror on that.  For now I’m just dealing with it and using a bar-end mirror.

Let’s do a side-by-side comparison.

Old handlebars.  Orange rabbit face.
Old handlebars. Orange rabbit face.
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New handlebars. Eh? EH?

 

I liked how the bike felt before, but I really like the way the bike feels now.  In the new riding position, I feel that I’m closer to the machine.  The position is still upright but definitely more aggressive.  If you’re thinking about doing this modification, I would recommend that you go for it.  Drop me a line if you have questions about this.

Spark timing

I had originally thought that if my motorcycle was running on both cylinders, then I shouldn’t need to manipulate the ignition timing.  If both cylinders were firing, what could possibly need to change?

IMG_20150612_111634
The points and advancer adjustments are under the chrome cover pictured here.

I could not have been more wrong.  After bringing my ignition timing and points clearance into spec, the CB350 runs much much better.  It purrs through first and second smoothly instead of rattling anemically.

Here’s what I’ve learned:  A motorcycle engine works by tightly controlling a combustion process.  The precise timing of delivery of fuel, air, and spark determines how the engine will run.  The electricity for the spark is provided via two electrically-conductive strips of metal that control the opening and closing of the ignition circuit.  These strips are placed within a few hundredths of a millimeter of a slightly-oblong metal ring that sits on the end of the camshaft.  This ring is called the points cam.  The strips are called the points.  As the engine turns, a chain on the crankshaft attaches to the camshaft, turning it and the points cam on the end of it.

As the oblong end of the points cam spins, it will briefly brush into each of the points.  This (or more specifically, the moment when it STOPS touching each of the points) causes a spark to jump across the gap at the other end of the circuit connected to that point.  You guessed it, that’s the spark plug.

There’s also a mechanical device called the spark advancer that works only at higher engine speeds, causing the spark arc to take place a little earlier in each rotation of the engine.  The spark advancer spins with camshaft, and has weights attached to it that move outward in proportion to centrifugal force and are returned to their original position by springs when engine speed falls .  The weights put pressure on the points and cause timing to be altered.  This component is necessary because there is only a limited amount of time to deliver and mix air and fuel in the cylinder before the exhaust stroke begins, and higher engine speeds necessarily shorten that period of time so the spark must be delivered earlier to provide better combustion, or in other words, the spark timing must be advanced.

Adjusting ignition timing should really be done at the same time that you adjust valve clearance.  Both adjustments require you to drain the oil from the crankcase, remove the stator cover, and manually turn the crankshaft with a wrench.  Both adjustments involve changes to components underneath the points cover.  Also, you should really do valve and spark adjustments before messing with the carburetion and exhaust of the engine,because if the engine doesn’t breathe and spark properly, then no amount of other tuning will make it run properly.

ANYWAY.  the actual operation took about two hours total.  Measurement of the points clearance was simple.  The factory service manual says to measure at the point where the gap is greatest, but it doesn’t say at what point on the crank that should be.  I just left my 0.30mm feeler gauge at the gap and turned the crank until it went in, and then kept re-inserting it while turning the crank to determine when the gap interval was over.  Looks like the greatest gap is about 90 degrees after firing.  Both sides were within 0.3-0.4mm.

I then figured out how to connect my timing light to the points, and used it to determine that each  spark plug has a complete circuit until about 60 degrees in advance of the “F” mark on its cylinder, and then the circuit is broken.  The light comes back on (spark!) around the F mark.

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Sorry for picture quality, sun was going down as I was finishing up.

I found that my left cylinder was about advanced by about the same amount of crank distance as between spark fire and top-dead-center.  This is probably about 15 degrees.  The right cylinder was retarded by the same amount, which makes sense.  I adjusted the breaker plate using a screwdriver while holding the crank at F, and then checked again at LF.  All in line.

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I put the stator cover back on, filled the case with oil, and took the bike around the block.  Man, what a difference.  So smooth, so much more power.

I realize that I forgot to re-check my points clearance again after adjusting the spark timing.  Because I put some Marvel Mystery Oil in this fill-up to see if it helps with the oil burning issue on the left cylinder, I’ll be changing the oil again soon anyway, and I’ll just re-check them again at that time.