Topic: 550k Knocking Sound

[Vintage Esquire]

I couldn't get my bike to start for a long time and many of you provided some key advice.  I replaced my pilot jets with new #42 from Sirius and it started right up.  Since I had already bench adjusted the carbs, it runs pretty well.  Since it hadn't been started in 13 years, I did all of the usual pre-start things mentioned in other threads.  After taking it around the block at 4k RPM's or less, it has now developed a deep sounding knocking sound in the bottom end at idle.  When I give it a quick rev to 3K, it goes away, then returns when back at idle.  It doesn't sound like valve tap because it's a deeper sound which goes with the speed of the crank.

After letting run, I pulled the tappet covers and saw oil - good.

What do you think?  I still need to really sinc the carbs and put the factory air box back on.  Is it possible that the carbs being out of sinc would cause that noise?  Simple timing issue?  What about crank bearing(s)?  I don't want to take the bottom end apart if I don't need to.

Thanks for the advice.

[domer]

sync the carbs, she'll make all sorts of fun noises when they aren't synced!

[number13]

2nd that thought. Synch carbs and points, then
see if the noise persists.

[Roach]

what they said and do a plug chop after you synch those carbs

[Vintage Esquire]

Thanks for the advice.  I will let you all know how it goes.

[Hush]

Yep synch carbs, I thought my pistons were trying to climb out of the barrells when I first got my bike going, had the carbs synched and runs like a quiet sewing machine once warmed up.
When cold these 30+ year old girls can be quite noisey so don't be too worried unless that noise remains once the bike is well warmed.

[Duanob]

The theory goes for the 550 that when the cylinders aren't firing exactly the same as when the carbs are out of sync, they fight against each other at idle. This causes slack in the primary chain and it slaps around quite a bit. The 550 didn't come with a P chain tensioner. When the carbs are synced the cylinders are working together and this causes tension in the primary chain which is what Honda designed into that motor. When you hit the throttle there is always tension in the primary chain so it doesn't knock around except at idle.