Seafoam with every fill up?

[charbot]

Hi all,

The reason Im asking about the Seafoam is...is my '77 GS 400 makes an intermittent knocking noise at low RPM (under 1400) that sounds like its coming from the front left cam. The noise is worse when the bike is leaning to the left side and goes away when it is tilted on the right side. This guy's seems to have the same issue (but no real diagonosis/solution): http://www.thegsresources.com/_forum/showthread.php?t=98537&highlight=noise+leaning+left&page=2

Anyway, it comes and goes, kinda mysterious.
There is really no performance issues, just the noise. Runs great... This was an abandoned bike that sat for a few years and Ive done all the tune up stuff - clean/ sync carbs, valves, etc. I periodically add a little Seafoam to the tank for good measure.

Recently I noticed something.... Im fairly certain that the knocking noise seems to start sometime after filling up the tank (low-octane, usually at BP station) -noticeable only at idle, under 1400, in neutral, or with clutch pulled and in gear.
... but, if I add some Seafoam to the tank it eventually goes away, till the next fill up.

I guess this isnt really a problem, Seafoam is relatively cheap... and if Im right, it does the trick. Just wondering if this is may be an indicator of some serious problem looming "over the horizon"?
or is it just bad gas/ weird additives?
Any ideas?

 

[Nessism]

Sounds like a mechanical noise related to the cams and/or cam chain. I don't understand why the fuel system, and Seafoam, could have any effect.

There is a thread here, and a tutorial hosted by basscliff, related to cam walk noise, and eliminating it. Noise of this type is not damaging, just annoying to some people.

 

[charbot]

I don't understand why the fuel system, and Seafoam, could have any effect.

me either... except that it does seem to eliminate the rattle.
When I did the valves I tried to check for any cam-play. Everything seem tight. There was no indication that the actually cam was moving around on the shaft. Since the noise goes away/gets worse depending on how I lean the bike, I would assume, if it is cam walk, the sucker would be fairly loose.

When it is rattling, the noise is clearly coming from the left exhaust cam, unless its telegraphing through from somewhere else.
...and like I said 1 ounce of seafoam per gallon appears to to clear it all up....?

 

[Guest]

Gremlins.

 

[Nessism]

Maybe your points are messed up, advancing the timing? Seafoam can not effect an engine noise, expect for maybe detonation.

 

[twotimeGSr]

I think Nessism is on to something...

I think Nessism is on to something...

Maybe your points are messed up, advancing the timing? Seafoam can not effect an engine noise, expect for maybe detonation.

If there is a difference using Seafoam... Would the "correction" be noticed over the long term... or rather immediate? If it got better after many many miles... then maybe it would be because Seafoam cleaned up the valves or something... but I think this is very doubtful. It sounds more like a detonation issue.. and if the Seaform causes the fuel to ignite quicker.. then maybe that change in detonation puts force on the cam (assuming that is the noise) at a different time and shuts up the noise. If so, I would think advancing the timing a bit might do the same thing. Worth a look see.

 

[charbot]

It sounds more like a detonation issue.. and if the Seaform causes the fuel to ignite quicker.. then maybe that change in detonation puts force on the cam (assuming that is the noise) at a different time and shuts up the noise. If so, I would think advancing the timing a bit might do the same thing. Worth a look see.

So I should advance the timing on the L cylinder?

The points have been done by eye, not strobe, so they may be just a hair off...but that would be a constant factor- havent messed with them in a few weeks.
They were off a bit before but no theyre really really close. I've checked and reset them a few times because I first thought that they were the culprit.
when I fill up the noise does not start immediately. maybe on the next ride. Same with adding the seafoam. Like the next day, I realize it no longer rattles.
I suspect it is a detonation issue- low compression on a valve, maybe(only thing I wasnt able to check)- only thing that makes sense....other than the gremlins, of course. This bike definitely has a few.
like, for example...
at idle, applying the choke always floods it- sometime fouling the plugs. The strange thing is that the PO put on a modified airbox and 2-1 exhaust with no rejetting.
Even with it being a bit lean throughout the throttle and at idle (screws needed to be about 3/4 richer than the stock settings)- its still too rich with the choke. -? If I give it a little throttle with the choke, then it is fine.
Ive since rejetted within the ballpark, and the choke still behave exactly the same. If I tighten the fuel screws way too lean, (to when bike starts to back fire), then I can get it to chug along with the choke. ...I guess this is another thread.