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Only Running On One Cylinder

damonbauer

New Member
Joined
Sep 30, 2022
Total Posts
7
Total likes
0
Location
Nashville, Tennessee, USA
I’m having a heck of a time getting my ‘72 CB350 running properly. As of now, it only runs on the LEFT cylinder. Here’s what I’ve done/tried/troubleshot:

- Rebuilt carbs. Set floats with carb in the vertical position, with the float tang just barely resting on the float needle); they are at 25.6 - 26.4 mm
- Checked compression at each cylinder by shoving a paper towel in each, starting and watching the paper towel shoot out (yes, poor man’s test but it’s all I got)
- Check (two different sets) spark plugs have spark by grounding the wire & plug, then starting
- Battery is at 13.11v
- Getting power all the way to the points
- Adjusted the cam chain tensioner
- Gas in the tank, petcock allowing gas to flow to carbs. Bowls are filling.

Now… for where I think the problem is:
- Installed new ignition points
- The points plate was slightly bent, so I pounded it on an anvil as flat as I could
- Points cam advancer seems to operate smoothly
- Timed properly, at least how I understand it. Gapped left point to spec, then rotated plate in order to get test light to fire at LF. Then adjusted right point to get test light to fire at F, 180 degrees after LF.

Finally, I know the right cylinder isn’t firing properly because:
- The left exhaust header is SCREAMING hot, but the right is barely warm (I can keep my hand wrapped around it while the bike is idling)
- While idling, I can independently pull the left throttle cable at the carb only, and the bike revs. When I pull the right throttle cable at the right carb, the bike dies.
- While idling, when I pull the left spark plug wire from the spark plug, the bike dies. When I pull the right spark plug wire from the spark plug, the bike continues idling.
- While idling, I have to keep the throttle slightly open, or the bike dies.

OK… that about covers it.

I’m about 75% confident that I’m setting the timing properly (can I get confirmation here?):
I think I’m on the compression stroke by holding my finger over the spark plug hole, rotating the engine and feeling a bit of air as well as hearing a “pssssst” sound. Once the rotor passes TDC, the rotor jumps and advances really quickly. So I stop at the LF mark and set the point. Then, I rotate 180 degrees to the F mark and set the point.

Could the fact that I had to pound the points plate flat be causing the points to misfire? Am I missing something obvious? Any help appreciated, I’m getting pretty discouraged :/ I’m happy to take pictures or videos if that would help! Thanks!
 
Pictures always help. You've used the basic method of setting the timing and if done as you describe, should work at least well enough to get it to run on both. After setting the right points to get the timing at the F mark, did you then check the resulting points gap? Both sets of points should fall in the .012" to .016" range. Next step would be to verify that the right plug is actually sparking, you can even take a spare plug and connect the right plug cap to it, lay it on the head fins and run the engine on the left cylinder to see if the right side sparks. Beyond that, you can swap the points wires at the coils so the right coil works from the left points and vice-versa. If the problem switches to the other side then you either have a bad coil or a bad plug cap or plug. Also, since you used a test light, the bulb actually came on when you set the right points to open at F? If the points were changed and the fiber insulator washers weren't assembled in the proper order on the points wiring connection at the points itself, it can be grounding out on the frame of the points to the plate.
 
What does your right side (non-firing) plug look like?
What's the condition of the condenser and coils? Are your points contacts clean and the wiring connections clean? You might be getting a spark visually but might be wimpy and not great to run on.
Any chance your choke flap is down and not connected to the left carb, or you forgot to install the little black plug over the primary main jet in the carb. Are you sure the idle passage is good? Have you tried starter fluid in the non firing side?
 
The carbs can be switched from left to right and right to left. Prop the chokes open, no need to hook up the throttle cables, work the throttle on the right side with your fingers. Attempt to start the engine. If the right cylinder runs then the problem is with the right carburator which is now on the left cylinder and not functioning. Or, as stated above, spray some starting fluid in the right carburator throat whilst it's still on the right hand side and the engine is running on the left cylinder, if the right cylinder fires briefly then it's most likely a carburator problem although sometimes cylinders with low compression or weak spark will function somewhat with starting fluid but not with gasoline.
 
Switch plug wires and see if the problem follows.

Bill H

Ah, thanks all for the rapid responses!

I didn’t even think to swap plug wires…

I just tried that, and the problem follows - the bike won’t start at all. A couple things I noticed:

- When I swapped the left plug wire to the right, a VERY loud “snap” could be heard at the right carb. I only tried starting a couple of times for fear of harming the right carb…
- Right spark plug was wet with gas
- Right spark plug wire end was broken in half, wrapped with electrical tape. There looks to be some corrosion on there…

I’m not sure what/how to test on these wires/coils since they’re a sealed unit. BUT it seems fair to assume the right wire (and therefore the coil) is bad? If so, is replacing both the right thing to do?

Video of spark plugs & carb noise: https://imgur.com/a/WaKZtIL

e087698f11b06cc6765e52a3d1b6aa5f.jpg

8ea9912b1e8af9937c52dae68cf2ffda.jpg

5654837a06ae888ebaa86dd2e4494eee.jpg

dce694c3d3aa19e5bf93332a80abcd82.jpg
 
Coils. $52 each + $8 for boots. $112 total.
Screen Shot 2022-10-18 at 9.27.45 AM.png
The issue might be resolved using these parts. An auto parts store should have similar units.
Screen Shot 2022-10-18 at 9.27.26 AM.pngScreen Shot 2022-10-18 at 9.28.26 AM.png
My bike had a replacement boot, seems to work fine.
IMG_1286.jpg
 
[emoji106] I bought 2 new coils just to be safe. 4into1 was charging be $17 shipping [emoji15]… so I went to eBay and found the same coils, sold by 4into1, with free 4 day shipping!

Do I need the spark plug wire splicer?
 
The first pic shows incorrect spark plugs. R for resistance and the standard boots already have the resistance.

Also pounding the plate was certainly less than ideal.


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Whoever suggested swapping plug wires ...
Well that ONLY works if you swap the Wires at the Points TOO and then re-adjust the gap and timing and ,... well you get the idea.
It's not a simple just move them over process.

Also another thing that will KILL Spark is a Bad Condenser.
There are (2) Twinned together mounted above the coils.

If one has failed it won't suppress the arcing and the spark will be crap.
You CAN However swap the Condenser Wires between Coils to test that.
 
I think he meant to switch the yellow wire with the blue wire which power the coils, then swap the plug wires. Black ground wires stay where they are. Could be a bad condenser.
:)
 
Bill (old timer) was thinking in terms of the 400 series which has a 360° crankshaft, both plugs fire at the same time with a wasted spark.

Black ground wires stay where they are.

Except that on these vintage Hondas, black is not ground - it's switched 12v power.
 
Alright, I got a new set of coils and wires installed. Strong spark on both sides now. Both sides burning fuel, as the right exhaust header is now hot just like the left.

I took the bike out for a quick ride… and it just doesn’t have any “get up”. It seemed like no matter what gear I tried (specifically 2nd & 3rd), the bike will not go past 5k RPM. It kind of bogs down and hangs out there. Am I wrong to expect it to wring out, especially at a lower gear like 2nd?

My hunch is that this is a carb or an ignition timing issue…

I have:
- stock carbs (Keihin 722a) with 70 / 105 (main) & 35 (slow) jets
- stock air filters (certainly need replaced, they might be original)
- some ridiculous mufflers that PO welded to stock headers; the welds are atrocious and have lots of holes & leaks


Sent from my iPad using Tapatalk
 
Hmm, more puzzled this afternoon.

I’m back to no spark on the right side. Tried different plugs, even the left plug that’s working… no spark whatsoever.

- I swapped the condenser wires at the blue wire coming from the ignition coil. Still no spark on the right. Does this indicate a bad condenser?

FWIW, I did recheck static timing, and it’s spot on.
- Verified points gap on left
- Set left and right with timing light
- Confirmed right gap is correct
- I have to get my hands on a timing light in order to do dynamic test


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Can you generate a spark MANUALLY?
By that I mean putting piece of paper in the Points on the side that has Spark to insulate that one from overcharging and burning out the coil.
Then allow the side with NO Spark to Charge and Open the Points.
That Coil "SHOULD" Discharge and provide Spark when the points OPEN.

Also Un-Screw the Plug Cap from the Plug Wire and look down inside for evidence of arcing.
You can CUT back the wire by 1/4-1/2" and get a fresh end to screw into the Plug Cap.

Let us know how this works out.
 
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