Hanging idle after load - 1973 CB450

[bh450]

The bike:

1. Honda CB450 1973
2. All stock except - Pamco Electric points with an electric advancer

Initial symptoms

1. Bike idled properly at 1200rpm and started from kick
2. After riding, the bike would sit at 3K rpm and white smoke would emit from the left exhaust.
3. Left spark plug was black and wet. (fixed)
4. Left exhaust leaks dark liquid (unclear if gas or oil or both). Right side is healthy. (fixed)

Current symptoms:

1. Right side exhaust is hotter than left.
2. Bike idled properly at 1200rpm and started from kick
3. After riding, the bike would sit at 3K rpm and white smoke would emit from the left exhaust.
4. After replacing the carb boots and the most recent test ride around the block, the bike starting at an 1200rpm idle successfully engaged the gears without the hanging idle. But a couple minutes in, the bike gear slipped transitioning from 2nd to 1st, getting stuck in neutral. After getting back in 1st, the bike would not hold idle and died. I pulled over and the bike would not start until after a minute with the bike fully off. Upon starting up, the idle jumped to 3k and remained. Worth noting, this was the first time i rode with the headlights on. After getting back home, I noted the left side was sluggish would only respond if i manually lifted the left side idle screw to flood that cylinder with gas.
5. The left side exhaust is popping.

Completed Maintenance (not in this order):

1. Reset cam chain
2. Set valves at 0.04mm (the manual states 0.03mm, but the smallest I own is 0.04mm).
3. Cleaned carbs (they were in good shape).
4. Reset float bowls to 20mm, they were around 22mm.
5. cleaned petcock and replaced incorrect O-ring,
6. Recharged battery.
7. Replaced both spark plugs and plug caps - running zero resistant plugs with 5ohm resistant caps
8. changed oil
9. Replaced gaskets at valve covers (these were clearly not removed by previous owner).
10. Rerouted clutch cable which was rubbing against throttle cables. Reset clutch cable.
11. Resynced throttle cables.
12. Resynced carbs by running on one cylinder at a time. left side first with air screw at 1 full turn out, lower idle screw until 1100 rpm, turn air screw up and down to find highest rpm. Repeat on right side. Then reconnect both spark plugs and run bike. Turning each idle screw an equal 1/8th turn at a time, finding the idle at 1100rpm.
13. Replaced rusty gas cap and seal.
14. Loosened clutch cable to 3/4” play per spec.
15. Checked air leaks by spraying carb cleaner on carb while bike running. No leaks found at the boot or carb.
16. Replaced carb boots.
17. Compression is 160 left, 162 right - engine warm

My understanding is the right side is running lean (exhaust is hot), the left side is not producing equal power. Replacing the plugs and plug caps removed the smoke from the left side and improved overall performance. I am starting to suspect there is some timing issue, but my understanding of electric ignition with e-advancers is they are set it and forget it….unless the guy who installed it did so incorrectly. Unfortunately I no longer own a strobe so I have not been able to check timing.

At this point, Ive read so many of the hanging idle and related threads and cannot seem to find an issue that speaks to the idle only occurring after the bike is under load. This sounds to me like an air leak, but not sure how that relates to the left side under performance. Please let me know your thoughts.


Thanks!

1973 CB450

 

[Ribrickulous]

As much as you may not want to do this - do you still have the original points?

Resetting everything to stock is a great way to eliminate uncertainty.

That said, I had a hanging idle on my 350 that was the result of a hysterically bad carb sync. It sounds like you’ve already completed that though.

The only other obvious culprit would be a vacuum leak. I’ve had that happen with bad aftermarket boots/intake gaskets. Check w/ starter fluid or carb cleaner around the intakes and see if there’s any change in idle speed. Check cold and hot.

 

[stl360+450]

A hanging idle can often be related to ignition timing, the mechanical advance (loose springs), air leaks, poor synchronization of the carbs, or issues with the throttle cable. In your case, the electronic ignition assumes responsibility for two of the usual culprits.

I think my dynamic timing light cost about $40 at Harbor Freight. Given that you haven't checked the function of the electronic ignition, that's where I would start. My understanding is that Pamco no longer exists, so there is no support available for that product. Were you given any paperwork on its function?

 

[bh450]

As much as you may not want to do this - do you still have the original points?

Resetting everything to stock is a great way to eliminate uncertainty.

That said, I had a hanging idle on my 350 that was the result of a hysterically bad carb sync. It sounds like you’ve already completed that though.

The only other obvious culprit would be a vacuum leak. I’ve had that happen with bad aftermarket boots/intake gaskets. Check w/ starter fluid or carb cleaner around the intakes and see if there’s any change in idle speed. Check cold and hot.

Hey, unfortunately, I do not have the original points.

I was thinking a vacuum leak too. Sprayed everywhere with carb cleaner and found nothing. Decided to swap the boots anyways, so now I have the those guys in Houston replacements. No change.

 

[bh450]

A hanging idle can often be related to ignition timing, the mechanical advance (loose springs), air leaks, poor synchronization of the carbs, or issues with the throttle cable. In your case, the electronic ignition assumes responsibility for two of the usual culprits.

I think my dynamic timing light cost about $40 at Harbor Freight. Given that you haven't checked the function of the electronic ignition, that's where I would start. My understanding is that Pamco no longer exists, so there is no support available for that product. Were you given any paperwork on its function?

Yeah, sounds like I need to check his work. He did not provide any info on the pamco. Not the most helpful seller I have to say. He had the bike for 6 months. I think he changed the points, changed the oil, replaced tires, polished the side covers and listed the bike.

I have no experience with e-points or e-advancers. My old 350 was points and had a similar issue fixed by resetting the advancer.

 

[stl360+450]

At least a dynamic testing light will help you see what the ignition is doing currently. If it's firing on the F/LF marks and the idle is high, then I would say you could look elsewhere for the cause of the high idle. If the high idle goes along with a greater advance angle, then it points to the ignition (no pun intended).

I have no idea if these instructions are correct to your unit, but found this on the 4-into-1 website.

If the Pamco unit is the issue, you could go to another electronic ignition or collect the parts needed to return to mechanical ignition timing, which it sounds like you've used previously with your old 350.