Odd noise on deceleration GS 750

[jknappsax]

I replaced the manifolds and O-rings on my 1978 GS 750, and now I get an odd noise on deceleration. It was a real bear changing the 0-rings because you need to remove the air/filter box and the rack of carbs. This is all I did. Nothing else was disturbed, except I had to temporarily remove the hoses to the oil cooler/ thermostat so I could get everything back in. It starts and runs well, except the deceleration noise. I didn't button all the hoses and thermostat down with cable ties, like they've been for years since I installed the oil cooler. Any ideas on what might be causing the noise? I torqued the Allen screws for the manifolds to 5-6 ft./lbs as my Clymer manual, but maybe air is being sucked by the o-rings on deceleration? Any other thoughts?

[Dave8338]

There should be no air "sucked in" on deceleration...if there were and it was that noticeable, you would have running issues to say the least. What sort of noise are you hearing? Can you determine where it is coming from? Does the bike run fine otherwise?

[t3rmin]

Yeah I'd like to hear a more detailed description of that noise...

[jknappsax]

Kind of hard to tell while moving

It sounds like something rattling rapidly, like maybe the thermostat against the frame, or maybe the cam chain adjuster needs work. Hard to tell while moving, and doesn't seem to happen when the bike is stopped, and I roll on and off the throttle. I should check the cam chain, but nothing there was disturbed, all I did was change the o-rings. It runs fine, in fact starts and idles better after the o-ring replacement. When I put her back together after the job, I somehow lost frame ground to the starter relay, which I didn't realize right away, as I have a KICKSTARTER!!! which I usually use to initially start her up. I added a ground wire right to the negative battery terminal, and all was good. The thought crossed my mind that the starter relay was kicking in briefly, but the noise is not the horrendous one I would expect if the starter ran while the engine was running, so that doesn't make any sense. I haven't had much time to troubleshoot it, as I'm working on the hull of a sailboat on the Chesapeake every day off I have (with the GS 1000 project waiting in the wings!). Any thoughts any of any kind would be greatly appreciated.

[chef1366]

I would remove and clean the cam chain tensioner. On these automatic tensioners on deacceleration they give the chain a moment of slack. If it isn't working properly I would worry about bent valves.

[Dave8338]

I noticed on mine the other day, that the chrome piece that holds the fork reflectors on, when at just the right RPM/load, would vibrate to the point that it sounded like a loose baffle in the exhaust. Took me a few minutes to locate it (while riding) 8-[ but a little silicone spray when back home took care of the problem.

You never know, it may be something easy / simple. Go with Chef on the cam chain tensioner...make sure it is working correctly.

[jknappsax]

Probably is the cam chain adjuster

Luckily, I have only heard this noise ONCE, so I think the valves are fine, but I definitely need to work on it. Thanks for the opinions!

[gasmanstl]

Identical noise 93 GSX-1100g: "rattle" on rolling off throttle

Luckily, I have only heard this noise ONCE, so I think the valves are fine, but I definitely need to work on it. Thanks for the opinions!

Did you work on the tensioner, and did it go away?

I'm totally thinking that it sounds like something slightly loose and rattling, JUST LIKE a reflector...or my windscreen...it doesn't seem to happen at higher speeds, but is that just because I can't hear it? Hard to fish around with hands up there while riding the bike...

But the thought of the cam chain tensioner is scary. Just curious what you found, if anything.