Topic: stock cb500 running rich after rebuild

[kurtkarram]

Hi everyone,
I just did a top end rebuild on my cb500. Just new gaskets, rings, and lapped valves.
Now after about 100 miles on the bike since, my plugs show I'm running a bit rich.  Plugs looked perfect before the rebuild.

I have done all the 3000 mile tune-up procedures, including carb sync. Bike is 100% stock.  1973 cb500, needle at 3rd, air screw 1 turn, stock jets.
I'm not sure if it's just a down low issue or not. Bike rides perfectly after 3k rpm, but stumbles a bit going from idle up to that point. I also have to crack the throttle open a tiny bit just to get it started (while warm), and then releasing the throttle it will idle at 1400rpm. I didn't change any setting on the carbs before/after the rebuild other than syncing them.

[denward17]

What's the carb float levels look like?  They all within limits?

[TwoTired]

Do the carbs still have the stock Keith in brass in them?

What air filter do you have?
What exhaust do you have?

Once the center electrode insulator on the spark plugs gets a carbon coat, the spark becomes erratic, requiring replacement or cleaning by blasting or burning.

Do all the plugs show the same deposit pattern?

Do check for fuel level in the float bowls.

Also verify that the emulsion tubes in the carbs are clear.

[kurtkarram]

All stock brass, just replaced o-rings. While I had the carbs off for the rebuild I double checked all the brass parts and passages were clean

Stock paper air filter from 4into1
stock 4-4 exhaust baffles all in tact.

I checked plugs 1 and 4, I can try to upload pictures. They looked almost identical.

I had checked the level about a year ago when I first got the bike. Used an external clear tube just mashed in the bowl. They were all in limits then, but I see I might want to check again. I can print an adapter that threads in to make it less....messy.

[newday777]

When you pulled the plugs, did you do a plug chop or did you pull them after idling a bit??

[kurtkarram]

I pulled them after 100 miles on the rebuild

[newday777]

I pulled them after 100 miles on the rebuild

But was it after idling?
Do you know how to do a plug chop to properly read the plugs?

[dave500]

check the spark plug cap resistance.

[RAFster122s]

Trim about 1/4 inch off the wires before replacing the plug caps to give the caps fresh copper to bite into when reassembling.

[Scootch]

But was it after idling?
Do you know how to do a plug chop to properly read the plugs?
[/quote]

I would like to hear about that...

[dave500]

if all the bike is stock jets etc something else is up?if you got the stock airbox is the filter good?get that ignition squared away first and spot on before you attempt repeated "plug chops"even with a 4/1 pipe all the stock jetting works fine,dont use any ethanol fuel if you can.

[newday777]

But was it after idling?
Do you know how to do a plug chop to properly read the plugs?

I would like to hear about that...
[/quote]

As with anything regarding our bikes if you want to get details, do a Google search,( I just did it on this, so I wouldn't have to write it out) "SOHC4 How to do a plug chop" and this came up 1st choice..... (add the SOHC4 to your search)

http://forums.sohc4.net/index.php?topic=92318.0

I learned how to do it in the 70s from my friends out back when I was parts manager.
As I traveled across the country and got into east Colorado where it's still flat just out of Kansas on I-70, I noticed my bike was lacking power when I twisted the throttle at speed so I did a plug chop and found I was running rich at that 4,000' plus elevation so I went down on the main jet size(I carried 3 sets of jet sizes with me, being forewarned before I left NH, at sea level). Each time I'd change the jets I'd do another plug chop to see the difference. I used the same plugs not new,  so I wouldn't strip the threads.

[newday777]

But was it after idling?
Do you know how to do a plug chop to properly read the plugs?

I would like to hear about that...
[/quote]

And this is the result of adding the SOHC4 to a Google search, a multitude of information to read and watch videos....

https://search.brave.com/search?q=sohc4+how+to+do+a+plug+chop&source=web

[HondaMan]

Hi everyone,
I just did a top end rebuild on my cb500. Just new gaskets, rings, and lapped valves.
Now after about 100 miles on the bike since, my plugs show I'm running a bit rich.  Plugs looked perfect before the rebuild.

I have done all the 3000 mile tune-up procedures, including carb sync. Bike is 100% stock.  1973 cb500, needle at 3rd, air screw 1 turn, stock jets.
I'm not sure if it's just a down low issue or not. Bike rides perfectly after 3k rpm, but stumbles a bit going from idle up to that point. I also have to crack the throttle open a tiny bit just to get it started (while warm), and then releasing the throttle it will idle at 1400rpm. I didn't change any setting on the carbs before/after the rebuild other than syncing them.

When you had the head off, and like the intake manifolds, did you install new intake manifold O-rings? They are the same size as those in the valve-adjuster caps. The old ones were/are hard as plastic and don't seal any more, especially once disturbed. This will leak air in at idle, raising engine speed and making all mixtures lean until about 1/8 throttle, then rich. This will darken plugs while raising idle speeds.