Engine knock when cold

Looking for help on my 96 st1100 with 26,000. Bike has a noticeable knock at steady throttle when cold and riding in town. Get up to hwy. speeds and it won't do it. If you are accelerating or decelerating it won't do it, and it's not constant only does it when it feels like it.
Any thoughts are welcome.

I only have had 'odd' sounds when I have been remiss in doing a carb sync.

When did you last do a carb sync?

Mark said:

I only have had 'odd' sounds when I have been remiss in doing a carb sync.

When did you last do a carb sync?

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+1.........a slight idle varience when at operating temp. is another early sign of carbs oughta' sync..

Any chance you have a spark plug cap not properly seated? Easy to check, and costs nothing.......just thinking.......ff....BTW, check the plugs while you're at it...

With 26K miles, how often do you ride? Have you tried a couple tanks of carb cleaner? Sea Foam is popular around here. I think it will also take care of water in the gas. Have you checked the fuel and air filters? There are 2 air filters.

I believe the "idle knock" comes from a poorly balanced engine whether from carbs or ignition or both (what Firstpeke said). My '91 does this at idle and one day I decided to investigate so I grabbed a long thin screwdriver and used it as a stethoscope and started searching for the knock. It appeared to be coming from the right lower rear of the engine near the transmission. I got my manual out and discovered the primary damper shaft there w/ the counterweight and spring. My thought is that the shaft weight is affected by the uneven pulse of poorly sync'd carbs or misfire. This causes the shaft/weight to bump against the spring until rpm's are increased. I purchased a Weber SK carb balance tool and it does a good job synching the carbs and is very easy to use

It's been about 2years and 4,000 miles since the last synch. It's weird to me why it only does it at lower speeds.

Deano g said:

It's been about 2years and 4,000 miles since the last synch. It's weird to me why it only does it at lower speeds.

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Might also consider at next oil change to not top to full mark. Having oil level in crankcase in that low to full range and not at top of it eliminated the low rpm knock on my STeed.........cept if I roll off the enricher a bit soon.

If it sound like a misfire on one or more cylinders I think this could be due to a couple of things.

EPA jetting causing lean running when cold.
Answer A slight increase in idle mixture via the mixture screws might help or upgrade from 38 (EPA) jets to 40 on the idle jets.

Idle Jets somewhat clogged by lack of constant riding/use.
Answer Seafoam or Techron to clean out the jets and a long ride Might solve a lot of the issue.
or Ride a lot more regularly.
I run Chevron mid grade gas which has Techron almost exclusively as a preventative measure.

It could also be the not so great additives in our gas these days. (Ethanol?)
Other than an Octane booster I don't have a solution.

As always, more riding cures all things right. ... I do run premium fuel and I do use seafoam in the winter as I don't ride near as much as I do in the summer. We currently are having spring like weather so maybe a long ride is in order tomorrow. If it doesn't help I will try the mixture screw. Thanks for the help guys.

Deano g said:

As always, more riding cures all things right. ... I do run premium fuel and I do use seafoam in the winter as I don't ride near as much as I do in the summer. We currently are having spring like weather so maybe a long ride is in order tomorrow. If it doesn't help I will try the mixture screw. Thanks for the help guys.

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May be getting a late ignition from premium. Compression ratio of the 1100 is low enough that the higher ignition point fuel isn't needed. Mid/reg. work fine with no pre-ignition issues. May cut back on the dosage of Seafoam, or if it sets for longer intervals wintertime as mine does, next untreated fuel-up, use Startron's enzyme fuel treatment instead.

You might want to change plugs if fouling is suspected and if you do I recommend the NGK Iridiums
Iridium Spark plug number CR8EHIX-9 NGK stock number for the Iridium plugs is 3797

If it is really a "knock" (pre-ignition)- you need to park the bike until you solve it. You can do enormous harm otherwise.