Knock under load

[sidecarKev]

With my new floats my bike runs pretty good. I have noticed a knock in the engine when its under load. Especially when starting from a stop. I checked the valve clearances a couple months ago when I had the bike apart and made a few changes, should be still good. Fresh fluid changes. Could timing be slightly off? Its a pretty noticable knock.

[Geezer]

Are you using premium fuel?

Geezer

[sidecarKev]

No

[TopCatGr58]

Hey there Kev,

As Geezer suggested, you may need to up the grade of fuel you're using, especially since your bike is under a considerable heavier load than a NON-sidecar XS! Remember, the octanes of regular back in the late 70's and early 80's wasn't too far from our premium now, IIRC!? I use premium in mine, but I also have a big bore kit with higher comps!!

Don't "Knock it" till you try it, PUN INTENDED!!!
T.C.

[sidecarKev]

Is that really all it could be? Sounds almost to easy. Nothing can be that easy for me. More than likely it is a $0.69 crankshaft o-ring that requires a complete engine teardown.

[uk1.1s]

Uh-oh

Hate to admit it Kev.... but the only time my XS1100 engine 'knocked' it was the crank bearings (Big End).

Was worse under load and sounded at first as though it was coming from the cams....

Try putting a long screw driver tip against the engine cases in different places and put your ear up against the other (handle) end. Crude but effective way of tracing internal sounds to the right part of the engine... honest.

Best of luck

Graham

[Geezer]

Originally posted by sidecarKev
No

Try premium, you may be experiencing detonation.

Geezer

[sidecarKev]

Well it turned out that cyl #3 wasn't pulling its weight. Pipe was colder than others. Took the carbs off AGAIN, reset the float heights, and did a general cleaning. Put it back on, (getting faster and faster every time) and it had power like I never had before. I set the floats a little lean and fixed a rich condition I had at low rpm's. It worked. Now I have no problem from a stop. I'm hoping this is the last time I need to have those carbs out for a while. I also filled up with 92 octane just for good measure.