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-   -   knocking noise at RPM above 3000. (http://www.xs11.com/forum/showthread.php?t=44996)

tqs335 12-15-2015 01:58 PM

knocking noise at RPM above 3000.
 
Hi all.
My 81 Special has had a fairly loud knocking noise above 3K RPM for some time. It also seems to be affected by engine load. If I'm cruising at say 60 mph in 4th it is loudest but if I accelerate or climb a hill it seems to go away. If I actually knew anything about this engine, I would say it sounded like either a connecting rod big or small end or maybe a crank bearing. the nature of the noise doesn't really sound like the cams or rockers but I suppose that could be it. I did have one mechanic say he thought it was the vacuum advance mechanism. The thing runs great and has no unusual vibration or oil usage or leaks. Any suggestions are welcomed.
Thanks.

motoman 12-15-2015 03:31 PM

Vacuum advance hose plugs onto top frontside of #2 carb.

mack 12-15-2015 05:16 PM

Advance
 
Not enough info to really diagnos yet. When did it start? Suddenly or has it developed and worsened over time. With what we know to date. The advance seems a likely culprit and motoman has given you the most common cause. Ensure the small vac hose is not connected to the intake boot but rather the #2 carb.

BA80 12-15-2015 06:20 PM

Read this TSB on the Vacuum advance.......

http://i154.photobucket.com/albums/s.../partimage.gif

Bonz 12-15-2015 06:53 PM

Has the bike always had this noise? Have the carbs been off recently and vacuum advance hose is on the wrong place like Motoman said a few posts ago?

Ranger_xs1100 12-15-2015 09:36 PM

Knock Knock
 
Hi tqs335, and welcome to the forum.

I have 2 xs1100LG's (MNS)
One has the same knocking around 3 to 4k rpm.
The other one doesn't!

Disconnecting the vac advance seems to minimize the knocking but also
seems to have a negative affect on overall performance.

This problem has caused me to start knocking my head against the wall!
and that didn't help either!

Good luck tqs335..
Please let me know if you find a resolution...
I'll be watching this thread closely!

BA80 12-15-2015 09:46 PM

Quote:

Originally Posted by Ranger_xs1100 (Post 477990)
Hi tqs335, and welcome to the forum.

I have 2 xs1100LG's (MNS)
One has the same knocking around 3 to 4k rpm.
The other one doesn't!

Disconnecting the vac advance seems to minimize the knocking but also
seems to have a negative affect on overall performance.

This problem has caused me to start knocking my head against the wall!
and that didn't help either!

Good luck tqs335..
Please let me know if you find a resolution...
I'll be watching this thread closely!

If you read the TSB I posted the fix back in the day was a modified vacuum pod. A part that is no longer available. Some were fixed and some weren't that explains why you have one that does, and one that doesn't. Try swapping the vacuum pods and see if the problem moves from one bike to the other.

Also, in the TSB it says that the detonation is NOT damaging to the engine.

Ranger_xs1100 12-16-2015 05:54 AM

Knock Knock
 
I replaced that vacuum pod/canister/plunger unit (whatever it is called) with one from a 79 standard, which I believe used the same part number that the tech service bulletin recommends. There seemed to be some improvement but not an elimination of the knocking. I haven't swapped the one between my 2 LG's which will be my next step but it will have to wait til warmer springtime weather now.
Thanks BA80.

tqs335 12-16-2015 06:41 PM

Thanks gentlemen!
 
Thank all of you who generously responded to my post.
Im going to dive into the problem based on your advise and information. I really hope to make some progress on this. I love riding my bike but the noise gets a little annoying sometimes.
Thanks again!

mack 12-18-2015 01:00 AM

Ba80
 
You have any other service bullets? Are they available on this site?

BA80 12-18-2015 07:37 AM

No, sorry Mack. I have that one saved from several years ago when I still had the original 3J6 engine. I had the same knock at highway speed.

I believe that one came from TC.

MPittma100 12-18-2015 08:15 AM

Fuel
 
Have you tried different octane fuels? JAT

TopCatGr58 12-19-2015 09:59 PM

Quote:

Originally Posted by mack (Post 478070)
You have any other service bullets? Are they available on this site?

Hey Mack,

IIRC, I did post that one a while/years ago back when Yamaha had the TSB's on their Parts Fiche site, but since they revamped the site, they only show the parts lists, and so the TSB's aren't there anymore, and I didn't think to try to access and download ALL of them!? :rolleyes:

T.C.

mack 12-21-2015 01:01 PM

Tc
 
Yes when they revamped we lost fost of the models. However I found this site: It is very close to the fische but no FSB's:
http://store.speedandsportinc.com/

motoman 12-21-2015 02:30 PM

Quote:

Originally Posted by BA80 (Post 478074)
No, sorry Mack. I have that one saved from several years ago when I still had the original 3J6 engine. I had the same knock at highway speed.

I believe that one came from TC.

Vacuum can has to match year motor and initial static timing assembly. They go hand in hand;).


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