Spark Knock

[JHBMX5]

I have a 79 sreet tracker, engine rebuilt, .020 over, pod filters, mac 2 into 1.
When the bike is good and heated up, cruising at 60 mph plus, I hear what sounds like spark knock, if I let off the gas a little it stops, accerate a little it gets worse.
The carbs are re-jetted, pilot 30 - one up , main 145 - 4 up, the needle I forgot to document the postion , I think it was set to fact. # 3 postion.
Bike still has points, all ignition parts are new, coils, plug wires, caps all new, new advance springs.
I re-tarded the timing on both sets of points , seemed a little better, running premium fuel. The bike runs really good , idles great, no flat spots or hesatations.
What would raising the needles one notch do ?
Maybe it just something rattling and it sounds like spark knock ??????

I'am at loss here guys, any ideas ?

LATER

JIM

 

[shotgunjoe]

You should DL and read the carb guide.

If its NOT spark knock and just a rattle, you should be able to duplicate it by reving the engine to the same RPM while the bike is sitting. If it IS knock, then it should disappear because theres no load on the engine.

 

[ReycleBill]

Excess heat can also cause spark knock. May not be an issue in Kalamazoo but down here in the Southland it's a big concern. I made some fins that I bolt to my crashbars to put more wind on the engine.

 

[retiredgentleman]

If the engine is running well, I wouldn't change the needle clip. These engines don't ping, with the timing set correctly, and regular gas works fine.

What do the spark plugs look like?

Make sure the timing does not go past the full advanced mark at greater than 3000 rpm.

Is the camchain tensioner set correctly, and valve clearances OK?

There have been reports of the drive chain set so loose that it slaps the chain guard and makes noises

 

[JHBMX5]

I haven't checked the plugs yet, I'll do that next and re-check the timing, probably do a carb sync. while I'am at it. The valves and cam chain are set fact. spec.
I have had several XS's a 70 XS-1 , 72 SX-2, 79 SE, this one runs and carbuerates so good good I hate to change anything.

Thanks guys.

JIM