Spark Knock

1982 KZ550 LTD

I have been experiencing spark knock under heavy throttle (sounds like marbles rolling in a tin can.)

I have been using premium gasoline to try to prevent this - doesn't happen as much as with regular, but still occurs.

The timing advancer is free. I am confused as to why this would be happening on a stock 550 LTD (smallest cams, lowest compression 550 engine)

Just some thoughts from searching around:

I know you said the advancer is working, but what about the actual timing?
Do you have it timed at idle, or at full advance?

What about excessive carbon in the chambers?
Or perhaps your mains are too lean?

cjaldous wrote: Just some thoughts from searching around:

I know you said the advancer is working, but what about the actual timing?
Do you have it timed at idle, or at full advance?

What about excessive carbon in the chambers?
Or perhaps your mains are too lean?

I have a Dyna. It was timed with the engine off and a test light.

I have no idea about carbon in the cylinders. Have never taken the head off.

I have stock jetting (jets from K&L carb kits). I have retained the airbox and have a stock exhaust system with a couple leaks but not terrible.

If you have a strobe, you could try timing dynamically.
www.mpsracing.com/instructions/Dynatek/DS2-1_2-2.pdf

I hope someone else can chime in.

If it's knocking you need to retard the timing. Put a small mark on the adjuster plate and tweak it to retard and then go for a ride. You want the timing advanced as much as possible without knocking.

K&L carb kits are a crap shoot. Often times they come with generic jets that may or may not match your origionals. I'm not a fan and would much rather retain the stock jets for your bike. That way you know they are correct.

Not sure what kind of air filter came with your bike but make sure it's clean and doesn't flow too much air. For example, a K&N. If you have a high flow air filter you might want to oil it a little more to richen up the mixture to help reduce knocking.

With manual slide carbs it's easy to get knocking if you give it too much throttle while going slow on the highway. This is definitely more noticeable on a Gpz.

However, your advancer is likely advancing too early. That is normal as the spring wears out. You can fix it by squeezing one end of the spring loop a little to tighten it up. This makes the spring effectively a tiny bit shorter, and that is all it usually takes. Only do one end of one spring first as that is all it usually takes. The advancer should not start advancing until 1500. Be careful not to crush it too much. You can maybe do it while the spring is still attached to the post.

The other thing, that may happen is the rubber stops fall off the advancer arms so the total advance goes too far. Check for that. The rubber stops are tiny and they fall off sometimes. They end up looking like a piece of dirt. Patton has a photo showing the detail on the rubber stops.
There is a photo about 2/3 of the way down on this page showing the advancer and the stops.
home.comcast.net/~loudgpz/GPZweb/Ignitio.../PickupAndRotor.html

You really need to get a strobe on it to check your ignition timing and advance.
The early 550's can be prone to this.

shop.advanceautoparts.com/p/mr.-gasket-h...&utm_content=5021995

shop.advanceautoparts.com/p/mr.-gasket-d...god7NMHmQ#fragment-3

I wonder if one of these springs may work.

Guess I need to borrow a timing light.

No and yes.
Steve

swest wrote: No and yes.
Steve

Not sure I follow you

I think he means, no - the springs won't work, and yes - borrow a timing light.
Good luck!

Reviewing the Dyna timing instructions, I am now unsure if this could be an ignition timing issue as the Dyna is statically timed in the full advance position.