Topic: Unnerving Engine Clang Noise - Vid Inside

[550Resto]

Hello all, recently I've noticed a metal clanging coming from my motorcycle at slower speeds and also at highway speed. I recently had issues with high idle which I think have been fixed, but now after 10 mins of riding and warmed up she doesn't want to stay running when I pull the clutch in and dies and the only way to start her up is to pull the choke full on. I didn't have this issue before and am seeking any guidance or advice.

It's a 1978 CB550, stock airbox, 4into1 delkevic, new carb boots and manifold Orings. Timing is good both static and dynamic. Carbs were bench synced and also checked with vacuum gages and look good. I'm kind of at a loss for what's going on.

[Hondawggie]

"high idle" + "banging" sounds like an air leak causing detonation.
Pull all 4 plugs and look for golden brown.  If you see whitish like it was super hot, could be detonating.

I think I heard the clanging towards the end of the video.


Another thing to check would be:
- correct spark plugs?  This is a real 'edge case' because if a spark plug is incorrect and is too long and the piston is hitting it, the mechanical sound would be constant I believe

- check valves -- could hit the piston if way out of adjustment


But 'high idle' to me sounds like an air leak, *assuming* the idle adjust knob on the carbs is adjusted for 1000rpm idle.   If you have an air leak you could have an overly-hot cylinder leading to detonation.


It's pretty surprising how 'mechanical' detonation sounds.

[mj1176]

Sounds like valves but what do I know?

(the answer is "not much")

[550Resto]

I forgot to mention that when I pull the clutch in the noise goes away. I though valves but it's like a clanking sound, valves were adjusted. I won't rule it out though. Thanks! I'll probably pull the carbs as I want to go up a jet sizero on the mains. I'll give the boots a look and make sure they're on good.

[DaveBarbier]

Since it's only while the bike is moving I'd say it's not valves or cam chain. Does it go away if the bike is in neutral and not touching clutch?

[robvangulik]

It's only heard while riding, and goes away with the clutch pulled?
Try the drive chain....

[550Resto]

Went for a ride after replacing the plug caps to work on a different issue. I parked and got off and it hit me, I know where the noise of clankiness was coming from. Behold!

It only was heard at slower speeds. Is there a fix for this? It's a new chain and sprockets. I also heard it before changing out the old chain.

Would tightening up the chain do it?
   I was able to set my foot on the stand while moving and the noise went away! I can't recall the min or max chain slack at the moment. Anyone know? CB550 1978. Thanks!

[scottly]

You lost the stop for the center-stand when you switched to the 4-1 exhaust. You need to fabricate a new stop that prevents the stand from hitting the chain.

[DaveBarbier]

I could see a craigslist add stating, "Custom automatic chain tensioner."