CB350 Rough Running Mystery, HELP!

[cjdisaffected]

Hey guys, so here's the deal.

I have a '73 CB350 with a little over 6000 miles on it, which I have owned for a couple months now.

It was running ok when I got it, but never great. So, I have undertaken most of the normal tune up items: New gel battery, new petcock (had a leak), new fuel lines w/inline filters, tore down the carbs and replaced all the seals n rings (cleaned everything), new plugs, new points, new condenser, new intake boots and gaskets (fixed a racing idle issue), new throttle cable. I sorted the timing and carb sync, but it's still not running great.

My idle is pretty erratic (and stalls often), and I am not getting the power output that I should. Additionally, the left cylinder (which was always a bit more finicky than the right) runs colder, the left exhaust is wet at the tip of the muffler (oil I think), and it shoots bluish-white smoke when I get on it.

Suspecting the worst, I put a compression tester on it, and I hit 170psi left and right (pretty rad), but I did notice the left plug is oil-fouled. So what now?

(Attached are pics of the compression test, right plug, left plug, and left exhaust.)

 

[xb33bsa]

try swapping coils and see if the problem switches to the other side
switch the blue and yellow wires and cross over the plug leads hopefully they reach
use new plugs as well good luck

 

[HerrDeacon]

It could be electrical related. How's the battery? These Honda twins need a good battery to run right. If that's ok it could be a bad coil or plug lead, have you checked for a good spark on both sides? Try swapping the coils around to see if the problem follows.

 

[cjdisaffected]

Thanks for the suggestions guys. I will def try swapping the coils tonight. Battery is brand new and holding a charge beautifully.

I agree that there might be an electrical component to the inconsistent idle/cold cylinder, but that would not explain the oil-fouled plug, oil at exhaust tip or the blue smoke would it?

How does oil end up in a cylinder that has not had it's rings/compression compromised?

 

[TheCoffeeGuy]

Check the timing chain adjuster too. as well try it with the air filters off. or did you replace them?

 

[xb33bsa]

Thanks for the suggestions guys. I will def try swapping the coils tonight. Battery is brand new and holding a charge beautifully.

I agree that there might be an electrical component to the inconsistent idle/cold cylinder, but that would not explain the oil-fouled plug, oil at exhaust tip or the blue smoke would it?

How does oil end up in a cylinder that has not had it's rings/compression compromised?

a broken or stuck oil ring does not mean the compression rings can't do their job and in fact the extra oil will help sealing
you could also have a badly worn valve guide,but i think it is more likely an oil ring
i had this same issue on my 350 when i bought it.it ran fine but 1 pipe smoked bad
i tore it down to find fresh new pistons with a broken oil ring
try to get the thing running good and see if the smoking continues if so a teardown is in order
on the 350 you can even see inside the plug hole to look at the cylinder wall

 

[cjdisaffected]

Hey Guys, so it's been a really long time but I finally got a chance to mess around with the bike again, and post up. Last night we did some multi-meter tests on both of my coils, and both are within tolerances. Next, we swapped the coils and ran the bike for a bit, but the left cylinder was still the "cold" one.

Additionally, we did some side by side visual comparison of the spark on both plugs. I understand that this is a wildly unscientific method, but whatever, I got equal and reasonably sized blue spark from both plugs, so I am not thinking that the electrical system is at fault here.

Then, took some time to inspect the piston tops and (what we could see of) the valves through the spark plug holes. As expected, the right piston was dry and perfect grey with some very minimal carbon deposits on it. The left was also as expected, a thing layer of wet-ish black deposits. The interesting bit here was the valves. On BOTH sides, the exhaust valves were dry and clean grey, while the intake valves were a bit blacker (layer similar to the top of the left piston but much less of it.) I had expected to see perfectly clean valves on the right side and one obviously oily valve on the left, owing to a worn valve guide which was causing my oil problem. So it looks like @xb33bsa might be on the right track with the cracked oil ring.

Finally we did a cold compression test (just for fun), 180psi.

So, seeing as a teardown to replace a broken oil ring is not in my immediate future, we are going to have to accept a little extra smoke from the left pipe and focus on the running issues.

I have a rough running bike, that doesn't like idling and, now I have a new symptom, the right cylinder is bogging/stalling when I throttle from idle. I am thinking about pulling the stock airboxes tonight to see what (if any) effect it has. Where do we go from here?

 

[TheCoffeeGuy]

do you have original coil and high tension wires leading to the spark plugs? Have you had these off? these wires are very old style, they have a tendency to break within the sheath. Gently start at one end and move to the other gently trying the test the flexibility of the wire. If there is a soft spot on your weak firing side, that could be your problem.

Just another thing to check, but this does sound more like electrical than fuel or mechanical.

 

[cjdisaffected]

Believe me, I wish it was the coils or the leads (yes they are both original.) I ran all the tests and everything is cool. Swapped em, and both cylinders behaved in the same way (left was colder and right bogs on throttle.) I richened the mixture on the right about a half turn and it seems marginally happier and the battery is on the tender tonight to see of that helps some (it was pretty toasted after 2 weeks on the sidelines and last night's testing.)