engine chatter

[brock]

Hi folks.

I just took my somewhat new xs1100 on a trip, 300 miles up, 300 home, for the weekend. On the way up, I noticed what sounds like a little bit of chatter at higher rpm's coming from the engine. while up there, i changed the oil (with mobile 1 red cap) and the plugs. on the way home, i noticed that same chatter, and it would start just over 4000 rpm's. in pretty much every gear, which made it easier to spot. on the highway i'll get down by the tank to try to hear it, but down there it just sounds like engine noise. also it seemed that if i brought it up to 4k really slowly i could get it over without the chatter, which made me think its the clutch making the noise? I dont know.

Then on another (hopefully unrelated) note, just at the top of the hill from the house, the rpm's dropped at idle to about 500, for a block or so, and then stalled out, almost as if i ran out of gas. stopped, looked around. gave it a sec. started it back up, and then it runs fine. that was two days ago, and havnt tried anything since.

any ideas?

[skids]

Re: engine chatter

Here is something to try: Open the gas cap and see if repeats itself. If it does, close the gas cap and put the petcocks on Prime to see if the problem quits.

[brock]

ok, i'll try that. but why? you think at the high rpm's its starving for fuel? then what's the source of the noise i hear?

[dntemp_ca]

Hey, Brock. Welcome to the world of XS ! Your engine chatter noise could be one of many things...cam chain needing adjustment, valve noise, but the way you describe it sounds like what my bike does. I've attributed the chatter on my bike to the pulsating vacuum advance mechanism. Reason I say this is because I've disconnected the vac advance hose (under the left side engine cover) and took the bike for a spin. Guess what? No more chattering noise! Anyway, I reconnected the vac advance hose again and am riding it despite the noise. I'm going to clean and lube the whole advance mechanism again to see if I can reduce the chatter. This may not be your problem, but thought I'd share what I suspect is the cause on my XS.

[skids]

OK, I'll let you in on a dumb thing that I once did. I once had a petcock that was leaking on occasion. This was on a standard at the vacuum control. I suppose that the vacuum control for the special works the same way. Anyway, I was rebuilding the petcock and I thought that I could stretch out the spring a little to have it exert more force against the diaphragm plunger when it is not running. I think I must have stretched it just a bit too much, or maybe the O-ring that I installed was a little thicker than stock. As a relult, when I hit the highway, two of the cylinders begin to run out of fuel and at first, it runs lean and vibrates and pings, then two cylinders drop out, unless I turn that left petcock position to Prime.

The thing about the gas cap: If your breather is a bit restricted, the tank will build a vacuum and interfere with gravity flow into the carbs. The same sounds will be heard with that condition. I believe that you might want to check for plugged in-line fuel filters if you have them installed (and you should install them if you don't have 'em).

Of course, there are other things that will cause rumbling vibrations, like the problems with bad pick-up coil wires in the 78 through 80 models.

These are just trouble shooting ideas that might help, but do not cover the whole gammit.

Originally posted by brock
ok, i'll try that. but why? you think at the high rpm's its starving for fuel? then what's the source of the noise i hear?

[brock]

you know, i did notice some noise around the fuel cap after i shut it off. the sound of there being a vacuum in the gas tank. i could release the presure in there by opening it. maybe it is starving. what solves that, replacing that rubber bit under the gas cap?

also, i've never seen a bike with two petcocks before. what's the point of having two? and what would be the result of me just shutting one of them off, and running off of only two cylinders?

[TopCatGr58]

Hey there Brock,

There's a vent in the gascap, it's a small little hole in a little round piece, and it can get clogged. You'll need to take your cap apart to get to it, and clean it, and that should fix it allowing it to vent properly as to not build up a vacuum inside the tank.

Each petcock is designed to supply fuel to 1 pair of carbs! So, shutting one off will shut down a side pair of cylinders, not good for the crankshaft and bearings!! Some folks have hosed their's together, and so with some "T" type connectors, supply both pairs of carbs from 1 petcock!

As others have stated, chatter could be many things, even the vacuum advance hose connected to the wrong port!? HTH.
T.C.

[ratbyk]

Engine Noise

A few weeks ago I had an engine noise that was driving me nuts trying to find. In the end discovered that the fuel cap was not pulling down tight enough to compress the rubber ring that seals the cap/tank. It was vibrating where the hook part of the cap locks onto a bar. At certain RPM it sounded just like it was coming from the engine where in fact this small vibration was being magnified and sounded like engine noise. By pushing down on the cap with my hand it would disappear. Take the pressure away and back came the engine noise.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[prometheus578]

BROCK: also, i've never seen a bike with two petcocks before. what's the point of having two?
Topcat was correct in that each petcock feeds a pair of carbs but many other makes of bike have one petcock feeding a bank of four carbs. The difference lies in the design of the gas tank. Other tanks are flat underneath at the back of the tank, allowing gas to flow from both sides to the petcock. 1100's have a main frame member running down the middle of where the tank sits, with the tank over-hanging it on both sides. With only one petcock you'd have half a gallon or so of fuel sitting on one side of the tank that you couldn't get to.

[D. P. Larmee]

The other alternative is what honda used on my little cb350. It has one petcock but it has a hose that connects one side of the tank to the other so that fuel from both sides of the tank make it to the petcock. The only problem is that this hose runs under the frame bar and has to be disconnected everytime you take the tank off. Always results in your arms getting covered in gas.

[strom]

two petcocks....
1. you can drain both sides, since there's a ridge in the middle. OK, you can drain em more....

2. one isn't enuff, since it gobbles up gas.

3. It looks cool

4. more gaskets to replace, more money to make

5. something

LP

[scalded dog]

I have been getting a little engine noise, but a lot of vibration. this just started recently. When I bought the bike ( 79 xs11 standard) a year ago, it had 12,900 miles on it now I have 31,000 miles on the bike, I have never had the valves adjusted, the clymer manual says this should be done every 4000 miles, as well as retorqueing the heads, Is this maybe part of my vibration? The bike still runs great, and now the stock mufflers are getting a little more of the deep throatier sound to them. Just curious as to wheather anyone does this regular maintenance on their xs 11. Thanks. Later 'Dog

[skids]

Well, now...have you checked fuel economy letely? When the baffles go, your economy will go to hell in a hurry. Also, if that is the problem, the torque may feel "mushy" at certain rpm ranges (middle?). If the baffles are shot or you have a broken exhaust system, usually under the foot peg heat guards, get it fixed. Pound on the muffler with a fist to see if it rattles...

Originally posted by scalded dog
maybe part of my vibration? The bike still runs great, and now the stock mufflers are getting a little more of the deep throatier sound to them. Just curious as to wheather anyone does this regular maintenance on their xs 11. Thanks. Later 'Dog