rattling on left side (with pictures)

[nezzer]

My 81 xs1100 had been expierencing some problems misfiring at low rpm recently. I replaced my very cracked carb boots with a set of new ones and that seems to have fixed the problem.

Now I have a new problem. Below approximatly 3k RPM my engine is making a rattling noise I had never heard it make before. At first I thought it was the cam chain so i adjusted it. That was not it. I then checked my exaust pipes to make sure they were secured to the the engine with no loose bolts. They were fine.

After listening to all the different parts of the engine I narrowed it down to a part by the timing marks. Perhaps this is the pickup, I'm not sure.



Bottom line is that the vertical shaft shown in the next picture is moving up into the cylinder looking thing. I may be getting to technical for some people but this all seems like normal operation to me, except for the fact that it is rediculously loud (and it was not that loud before)



Any ideas on why this thing is all of a sudden making such a racket?

[DiverRay]

Check on the vacume line from the can to the carb. It should be going to the #2 carb BODY, not the carb boot. That should clear the noise.
Ray

[TopCatGr58]

Rattle, and Hmmmmm? U, too!

Hey there Nezzer,

That thing is the vacuum advance module/diaphragm. It rotates the timing plate to advance or retard the timing under varying throttle loads as sensed by the amount of vacuum applied to it.

Some folks have found it rattling when they inadvertently attached it's vacuum line to the wrong port, putting it on the Intake Manifold port instead of the #2 carb body port!

Also, the vacuum diaphragm may be wearing out and leaking, causing it to move to easily back and forth. Remove the hose from the #2 carb port, apply suction to it, and then stick your tongue into the hose end to keep it sealed off without having to apply additional suction. The vacuum plunger should have retracted into the unit, rotating the timing plate, but it shouldn't move again until the vacuum is released. IF the plunger slowly or quickly releases returning the plate to it's original position, then the diaphragm is broken/leaking!

Sadly further still, is that it is a discontinued part! SO, either you'll need to find one on Ebay, a local wrecker, or do lots of research at your local auto parts shop, and try to find a similar unit amongst the auto vacuum advance modules? If you do find one that works, let us ALL KNOW!
T.C.

[andreashweiss]

I have a good used one in case there is a need. andreas

[strom]

Change the vacuum line, like Ray said... grease themoving parts a bit, if it still continues, don't worry bout it. Rev the engine with the cover off and you will see what rattles. But it's no biggie.

LP

[nezzer]

The vacume was indeed connected to the carb boot rather than the carb body. I connected it correctly and the noise has dissapeared.

I still have one question though, carbs 2-4 have a rubber cover on the carb boot metal nipple. Carb 1 does not. Should it? When the engine is still warming up there seems to be sort of a backfire coming out of that carb #1 nipple. It only occurs about once every 4 seconds and stops happening once the bike is warmed up. Is this normal operation that the rubber cover is supposed to address?

Here is a picture of the ruber cover on carb #4:


And here is a picture of the metal nipple with no rubber cover on carb #1


Thanks.

[LoserShoes]

Yes its supposed to be plugged. Make a temporary plug from a piece of tubing and a screw, then see if Yamaha still has them.

Might find something to fit at a good autoparts store.

Steve

[randy]

They're still available from Bikebandit. Or, any vacuum plug that fits snug will do the job.

[John]

Go to any auto parts store and buy a 3/16 in vacuum cap. Get four, they're cheap. Besides, the old ones are probably hard and brittle may leak a little because of it.

[chevy45412001]

az

auto zone has a real nice kit of all sizes for 10 bucks. i thought it was a good deal.

[Meatloaf]

Just did the same thing. Almost had a stroke. Been working on my bike for a year (never had it on the road) put it together and hear this awful rattle. It didn't sound like valve-train or bottom end so I jumped on here and found the solution in this very thread.

Thank God for XS11.com

[Ken Talbot]

Originally posted by nezzer
And here is a picture of the metal nipple with no rubber cover on carb #1

metal nipple with no cover = vacuum leak

Not good!