Author Topic: was: thump, thump, thump at idle-CB550 cam chain?now: electr ignit (Read 4832 times)

locostbamboo · « **on:** May 04, 2009, 02:56:25 PM »

I have a loud thump, thump at idle and a friend says it is my cam chain tensioner. I tried adjusting, but not any real change. Does it sound like cam chain to folks here? Sorry if this has been asked a million times.

Rob (former CB750 owner, now CB550 owner) in Oregon

Johnny5 · « **Reply #1 on:** May 04, 2009, 03:24:53 PM »

Cam chain rattle sounds more like a box full of junk shaking around. It's definitely not a "thump" sound.

Is the noise at idle or during a ride? Does it change with the engine speed?

locostbamboo · « **Reply #2 on:** May 04, 2009, 03:31:03 PM »

only at idle-around 1100 to 1300 RPM.

heffay · « **Reply #3 on:** May 04, 2009, 03:56:07 PM »

carbs are probably out of synch... things don't keep running smoothly so the engines start making more noise, as described.

Duke McDukiedook · « **Reply #4 on:** May 04, 2009, 04:00:02 PM »

Yeah, cam chain is more of a rattle.

locostbamboo · « **Reply #5 on:** May 04, 2009, 04:38:40 PM »

OK, thanks.

locostbamboo · « **Reply #6 on:** May 08, 2009, 09:09:53 AM »

Went to see if local shop had carb adjustment tool. Explained what it was doing to them and they said I need electronic ignition, not carb sync. Anyone have experience with this?

Thanks.

heffay · « **Reply #7 on:** May 08, 2009, 09:32:13 AM »

did they look at your points?
just slapping on an electronic ignition won't magically fix the problem... points are just as fine tunable as a dyna... they just go out of adjustment while electronics don't normally.
my opinion... they're trying to sell parts

locostbamboo · « **Reply #8 on:** May 08, 2009, 09:49:08 AM »

They didn't look. I think I will still try the carb sync first. I got the parts to make my own manometer, but am having issues figuring out both the adjustment screw for each carb (where) and where the connection is for the vacuum line on each carb. I have seen several write-ups on making the manometer (thanks) and a few on how to sync, but none that show the actual connections. I will keep seaching the forum, but would be happy with a pointer as well!

Thanks. Great forum. Was a member years ago with a couple of CB750's (unfortunately sold/gave them away when we moved) and am glad to have the assistance now with the 550.

heffay · « **Reply #9 on:** May 08, 2009, 09:55:52 AM »

the attachment holes on my cb350f are actually on the intake manifolds that attach to the motor... not on the carbs.

look for a screw on the top portion of each of those... should just be a screw in each one.

locostbamboo · « **Reply #10 on:** May 08, 2009, 10:07:53 AM »

Cool. Will look there. Thanks!

Popwood · « **Reply #11 on:** May 08, 2009, 10:12:14 AM »

I get this sound at idle on my '75 550, too, and it gets more pronounced in neutral than in gear with clutch in, although you still hear it plainly then. I've done everything but carb sync but that's my next step.

By the way, got a Carb Tune Pro, ordered from England. Have used it on a '73 BMW 75/5 and '74 cb360 with very good results. The online purchase from England was easy and efficient. Was on my doorstep in less than 10 days.

upperlake04 · « **Reply #12 on:** May 08, 2009, 10:21:56 AM »

Quote from: locostbamboo on May 08, 2009, 09:49:08 AM

I got the parts to make my own manometer.

You can make the connectors easily yourself too with a some M5 bolts, a piece of tubing, a hacksaw, file, drill and solder, braze or JBWeld.

TwoTired · « **Reply #13 on:** May 08, 2009, 12:11:18 PM »

Does the noise change when you pull in the clutch?

Nix on the electronic ignition requirement.

I bet they had one to sell you.

You should do a complete and thorough tune up, though. Finishing with a carb sync.

The whole gear train can go into "clack" mode if the crankshaft doesn't maintain constant rotation speed. And, if some cylinders are firing stronger than others, the crank constantly changes speed. The clutch assembly mass can change the harmonic strength of the sound.

Cheers,

locostbamboo · « **Reply #14 on:** May 08, 2009, 02:31:43 PM »

Noise is the same with or without clutch. It goes away at higher RPM's though.

heffay · « **Reply #15 on:** May 08, 2009, 02:32:45 PM »

if i had money i'd wager it on the carb sync.

locostbamboo · « **Reply #16 on:** May 08, 2009, 02:43:16 PM »

So at lunch I found the screws on top of the intake manifold. I am still looking for where to hook the vacuum tubes. On the bottom of the manifold maybe?

heffay · « **Reply #17 on:** May 08, 2009, 03:04:09 PM »

take those screws out and put the vacuum lines there... other ends go to the carb synch.

locostbamboo · « **Reply #18 on:** May 08, 2009, 03:33:45 PM »

OK, I see. I am learning. Thanks!

masonryman · « **Reply #19 on:** June 17, 2009, 04:53:54 PM »

I just noticed the same problem, on my 76 550 SS, just before the carb over flows started dumping gas every where.

I thought it was going to be a simple cleaning but the carbs turned out to pretty much junk. They were very pitted in side, once they were disassembled and cleaned, I don't think any part inside will seal ever again. So I did what anyone wanting to ride would do I took the carbs off my project bike. These carb had been gone through and polished but the project has yet to be rode and the carbs have not been synchronized.

The SS runs better than ever but still has the rattle. My job has been shut down till next Tue So I think I will use the time to change the points and sync the carbs.

I update with the results

Thanks
Mark

HondaMan · « **Reply #20 on:** June 18, 2009, 08:13:03 AM »

I vote for timing: check the points, gap, and put a timing light on it to see if the spark is steady and on the timing marks. A bad condensor on one side can make weak spark for that pair, too. It can even make one half of a coil not fire (i.e., one cylinder will be cold), a very interesting side effect.

tlbranth · « **Reply #21 on:** June 18, 2009, 09:15:19 AM »

One carb slightly ahead of the others will make a pretty nasty noise. Sort of a thump - slightly higher pitched.

masonryman · « **Reply #22 on:** June 21, 2009, 07:09:29 PM »

After new points, plugs and some adjusting on the carbs the bike is running much smoother and much quieter at idol. It still has the familiar clutch noise but you can't adjust away everthing

The wife and I went for about an hour ride and the bike performed flawlessly

HondaMan · « **Reply #23 on:** June 22, 2009, 07:18:16 AM »

Have you checked the timing? If one of the sets of points is off, it will make for a lumpy idle.

Joksa · « **Reply #24 on:** June 22, 2009, 08:56:54 AM »

Quote from: upperlake04 on May 08, 2009, 10:21:56 AM

You can make the connectors easily yourself too with a some M5 bolts, a piece of tubing, a hacksaw, file, drill and solder, braze or JBWeld.

And if you wan't save some time, go to hardware store and get some M5 mig/mag nozzles

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Author Topic: was: thump, thump, thump at idle-CB550 cam chain?now: electr ignit (Read 4832 times)

upperlake04

masonryman

masonryman