Topic: [Video] Weird clacking noise from engine at idle

[NastyNip]

Hey there,

So my 1974 CB550 runs fine and dandy just after cold startup, and performs great for around the first 15min of riding, but after about 20min of fairly normal city riding, it starts acting up and the engine starts producing a noticeable mechanical "chugging" or "clacking" noise during idle. I have uploaded a video here, taken just after I got back from a ride:

Does anyone have any idea what this noise could be? After riding for 20 minutes, the bike sometimes feels like it wants to die at stoplights unless I give it some throttle, and I feel that I have to goose it extra when I come off the line. Any ideas?

The only thing non-stock is the MAC 4-1 exhaust which I have rejetted for. (one size up, now 40 105 jets)

I have recently adjusted the tappets and sync'd the carbs.

Thanks for any tips!

[toolguy]

should run a lot smoother at idle than that. .  Yours is missing at times, skipping a beat. .  may just need carb sync.  noise sounds like primary chain slap. .

[flybox1]

Revisit the major maintenance items....set the valve lash, cam chain tension adjustment, timing/advance, and finish with a vacuum sync of your carbs.

[NastyNip]

Revisit the major maintenance items....set the valve lash, cam chain tension adjustment, timing/advance, and finish with a vacuum sync of your carbs.

  I just did those three last weekend, maybe take another pass at it? Adjusting valves is such a hassle...

[Tews19]

sounds like chain slap. you stated you sync'd the carbs right?

[NastyNip]

Yep I vacuum synced the carbs, adjusted idle mixture, adjusted valve clearances. Maybe I did a crappy job?

When you say chain slap, you referring to the cam chain right? I believe I adjusted it last week, but the adjustment knob didn't move too much.

[Tews19]

You can adjust while running too. To me that sounds like primary chain if not cam. Or did you pull in clutch while running to see if it quiets?

[NastyNip]

Ah, I didn't know you could adjust the cam chain while running, good to know.

I found this thread from a few months ago, and the guy posted a video very similar to mine:

http://forums.sohc4.net/index.php/topic,139999.msg1585399.htm

Seemed to point to a carb sync issue, so maybe I just need to take another pass at it.

[heyitsrama]

How is compression across the cylinders?
My old motor sounded like that when it had around 70PSI in cylinder 4. I posted a video of mine a while back its somewhere in my profile.

[NastyNip]

How is compression across the cylinders?
My old motor sounded like that when it had around 70PSI in cylinder 4. I posted a video of mine a while back its somewhere in my profile.

Compression is good, I checked last weekend.

You can adjust while running too. To me that sounds like primary chain if not cam. Or did you pull in clutch while running to see if it quiets?

So I pulled the clutch in, and indeed the sound goes away. Does that mean it's the primary chain? ...Do I have to split the case?

[Tews19]

Nope. Sound is normal. You can swap out the clutch plates if you want. Do a search for clutch basket noise. Nothing to worry about though.

[NastyNip]

So you're saying it's the clutch (worn out) and not the primary chain? Is there any way to verify this before I pull the basket?

Regardless, I'd be way happier to replace the clutch than the primary chain.

[Wobbly]

If the noise goes away after pulling the clutch, then it's the clutch basket. It's very common for the SOHC 4 Honda bikes.

[Retro Rocket]

If the noise goes away after pulling the clutch, then it's the clutch basket. It's very common for the SOHC 4 Honda bikes.

+1, also, when the carb sync is out, these engines sound like they are full of nuts and bolts, they rattle their heads off...

[NastyNip]

Thanks for the great advice guys. 

I'm picking up plates, springs and a gasket today and will put it on my to-do list for this weekend (along with another pass at a carb sync)

I'll report back with results!