Topic: Erratic / Jittering timing

[kurtkarram]

73 cb500, finally got a timing light and noticed my 2-3 timing was erratic. 1-4 is consistent and perfectly aligned with the F mark. For 2-3, it moves around. One "position" occurs more frequently which is lined up with the F mark. The erratic changes show as being retarded every time, lining up more or less with the T mark. This causes the idle to walk up and down. However, Revving the engine past full advance, the jitteriness looks to go away. Not sure if it's because its just it's firing so fast that the jitteriness just doesn't show up. It seems to run very well after 3000rpm, but has a bit of a vibration in the handlebars after 5k and doesn't really go away up to the redline. I'm also thinking this is the reason for popping on no throttle deacceleration. It's soft and sounds like popcorn, but pops more frequently at higher rpms. My thought is that the late firing isn't burning all the fuel, which gets sent into the exhaust and pops there.

Anyway, any ideas on the cause? I don't think is would be a bent advancer shaft, as 1-4 is perfect. Condenser issues? Coil issues?

[TwoTired]

Mark your throttle to note where your problems occur.  Allow the engine to operate under the conditions you object to for a few seconds.  Then simultaneously hit kill switch, pull in the clutch, and chop throttle.  Take out the spark plugs and examine the spark plug deposits.  Describe what you see or post pictures for us to see.

Are springs on your spark advancer loose?

What brand points and condenser are you using?

Cheers,

[kurtkarram]

Attached are the plugs. Left to right is cylinder 1 to 4.

Springs were shortened by 1 loop previously. Advancer comes into play at correct rpm and is between the two dashes.

Points and condensers are stock. I cleaned up the points with sandpaper, but there is still a very small white patch on the 2-3 point. Wondering if I need to clean that up better...

[TwoTired]

The grit in sandpaper is sacrificial, meaning it leaves some grit behind in the surface of the subject.  Common sandpaper is usually made with a grit that is an insulator.  This is why you only file point contacts, as you don't lose contact area with that method, and leave behind spires of material that hinder full contact of the points.  Sanding points only shortens their life.

"Stock" points can be made with different brands.  And the Diachi brand is known to cause problems in both the point set and the condensers.  If I recall correctly, Denso, and NDK are good reliable quality brands, but may be hard to find.

Is the point cam shaft bent or have side play?  Was it was used to rotate the crankshaft?

Cheers,

[seanbarney41]

The inductive pick up clamp on your timing light can cause faulty readings.  Try flippiong the clamp the other way way over when it gives you problems.  Also may try powering the timing light with a spare 12 volt battery that is NOT connected to the bike.

[kurtkarram]

The grit in sandpaper is sacrificial, meaning it leaves some grit behind in the surface of the subject.  Common sandpaper is usually made with a grit that is an insulator.  This is why you only file point contacts, as you don't lose contact area with that method, and leave behind spires of material that hinder full contact of the points.  Sanding points only shortens their life

interesting, common-motor collective sands, which is why I followed. I actually went and sanded the 2-3 point before I saw your post.. more on that.

"Stock" points can be made with different brands.  And the Diachi brand is known to cause problems in both the point set and the condensers.  If I recall correctly, Denso, and NDK are good reliable quality brands, but may be hard to find.

From the logos I see, the points look to be Diachi while the condensers are Denso I believe.

Is the point cam shaft bent or have side play?  Was it was used to rotate the crankshaft?

Doesn't look like it. I took the point plate off and cranked the motor. Focusing on the inner bolt hole, I saw no movement indicating a bent shaft. However, for some season my battery just doesn't crank the motor very fast. Even if it's fully charged. Might not have been spinning fast enough to catch a bend. Here is a video of it: https://youtube.com/shorts/f4KbtJaQvCQ?feature=share

Anyway, after sanding down the 2-3 points (before I knew It was bad to sand points) the erratic timing seems to have dissapeared. I also took videos of these in action, but are a little harder to see though the camera due to the recording frame rate.
1-4 video:

2-3 video:

In these videos the timing is now not erratic. (I adjusted the plates so the timing for 1-4 and 2-3 were exact after the video). However you can still hear the walking idle. Much more noticable on a cold start where it idles at a lower RPM.

[kurtkarram]

Not sure if fixing the timing issue really helped anything, so while it was idling scratching my head I said why not test for air leaks 1 more time. Even though I've checked before, I found an air leak in the #1 manifold gasket. The o-ring that goes between the engine and the metal manifold tube. Seems there might be a *slight* air leak from #2, but nothing noticeable on 3 and 4. Video here: https://youtube.com/shorts/sb5BTG7_PtE?feature=share

Time to order some new O-rings. Best place to get them? Are they just a standard size o-ring? I only see them online from common-motor but I'd like to get them at a hardware store because i'm inpatient.

[newday777]

I don't know the size but found the part number and Amazon prime can get them to you in 2 days

Honda 91302-001-020 O-Ring (30.8MM) https://www.amazon.com/dp/B00AAH75RE/ref=cm_sw_r_apan_i_PSK5R1W8CVPP9WHKZ8NH

[HondaMan]

The O-rings in the manifold castings are the same as the ones in the valve caps, so you already have a set!

[kurtkarram]

Went to harbor freight today and got the metric Oring kit. Unbolted the manifolds and slid back the carbs, took out the crusty old orings and put in the new ones.
After installing, it started and idles noticeably better. Much more consistent. After letting it warm up, I synced the carbs again. Checked the plugs and they look like the brown they should be. However there are still some issues:
Still pops on deacceleration. Only when the throttle is completely closed and RPMs are above 3k. Very quiet popping. I feel like this might be dirty pilot circuits. Not sure what else.
Big issue:
After riding 3-4 miles, the bike would not get down from 4k rpm. Had to shut the engine off and coast down to my driveway because it wouldn't engine break, just pull.
I'm thinking air leak, because starting and pulling choke brought the idle down. It happened again later today on another ride, however just restarting it fixed the issue.

[HondaMan]

Went to harbor freight today and got the metric Oring kit. Unbolted the manifolds and slid back the carbs, took out the crusty old orings and put in the new ones.
After installing, it started and idles noticeably better. Much more consistent. After letting it warm up, I synced the carbs again. Checked the plugs and they look like the brown they should be. However there are still some issues:
Still pops on deacceleration. Only when the throttle is completely closed and RPMs are above 3k. Very quiet popping. I feel like this might be dirty pilot circuits. Not sure what else.
Big issue:
After riding 3-4 miles, the bike would not get down from 4k rpm. Had to shut the engine off and coast down to my driveway because it wouldn't engine break, just pull.
I'm thinking air leak, because starting and pulling choke brought the idle down. It happened again later today on another ride, however just restarting it fixed the issue.

This sounds like one carb in the set has a plugged pilot jet. This causes the need to raise the idle with the idle setscrew, and then when the engine is warmed up and can idle a little better with 3 cylinders, it idles high. I've seen this many times.

After the jets are all clean (and check the little emulsifier holes on the pilot jets, too), do a vacuum balance (if you have gauges) and the popping will likely quit. It is coming from the cylinder that is too lean at that RPM range, as the fuel will not fire when too lean, and will tend to get really rich and wet from unfired fuel before it finally does: that's when it pops.

[kurtkarram]

Started disassembling the bike to take the carbs off and I noticed probably the biggest reason why it idled high. The return throttle cable nut loosened, and the cable slipped out of it's path. Snapping the throttle felt like it was fully closed, but it was being held open by the cable mess.

I already had it setup to take the carbs off so I did and checked the pilot jets. Looking through into the sky into the main holes I noticed 2 of the jets weren't completely clear. I cleaned these well until they all had clear open holes.

Seemed to idle smoother, but it still walks a bit and pops on deacceleration. I have a 4 carb vacuum gauge sync kit but I find it difficult to use. Each line has a restrictor valve to make the needles jump less, but I'm never sure how tight to go. As I tighten it, the needle's "vibration range" gets smaller, but the "read value" will change. So at one setting with all the needles at a medium bounce they could be "synced", but if I tighten them to a light bounce, all the values change.

[seanbarney41]

Hook all the gauges to the same vacuum source, adjust the needles so that they don't bounce and all read the same vacuum, then hook em up to all the cylinders and your ready to go

[Deltarider]

Hook all the gauges to the same vacuum source, adjust the needles so that they don't bounce and all read the same vacuum, then hook em up to all the cylinders and your ready to go

Yes, but not at the same time. To be done one after the other. The gauge is a mechanical device and the drums will interfere.