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I've been experimenting with my Predator for a couple of years and finally have it running pretty good. Some of the info is my own discoveries, some is from this site, and some is from other sites such as the Old MiniBike forum.

Carburetor
You can buy miniature drills from Harbor Freight. Item#62379. They tend to drill oversize.
ALWAYS check the results with a wire gauge and calipers, or a wire-type spark plug gauge.
Enlarge main jet from the stock size to 0.030 - 0.032.
Enlarged idle jet to #75 (0.021").
If the exhaust is smelly and burns your eyes, you are running too rich.
You can solder the jet closed with plumbing solder and try again if you mess it up.
Disassemble the fuel shutoff valve and check for debris. The gasket can be turned around and re-used.
Cut metal away to make idle mix screw adjustable. It may not need adjustment.

Fuel System
If the gas tank vent line won't pass enough air, the motor will quit. The tank vent is very restrictive. Disassemble and take guts out of the rollover valve, enlarge hole in black plastic cap to about 1/8”.
Run a perforated metal screen instead of an air filter for snowblowers.
Check fuel flow out of the fuel tank hose where it attaches to the carb. Predators have a filter where the hose attaches to the tank. There should be plenty of fuel flow.
The Predator engine can have a ½ inch of fuel in the bottom of the tank and be out of fuel.

Ignition
The spark plug tip should be light gray if the mixture is right.
Replace the junky factory plug with an NGK BP6ES gapped to .028".
Disconnect the low oil switch if it is too sensitive (trips going over a curb).
I don’t have a spec, but the factory ignition coil had about 9900 Ohms resistance. A replacement one was about 4800 Ohms.
A standard paper business card makes a good coil gapping tool.

Tuning
Remove the gas tank and move the spring on the governor lever to next hole to increase tension. This may stop surging.
Set the engine to run 1800 RPM idle and 3900-4000 full throttle.
Buy a digital tachometer and install it where you can see it. The ignition fires on every stroke, so set the tach for 1 cylinder 2-stroke.

Mechanical
The Predator seems like it puts out more power at higher RPMs.
It supposedly will live a long time as long as you don't go much above 4000 RPM.
The Predator 212cc flywheel breaking is more of a danger than breaking the connecting rod. The stock flywheel is unsafe over 5000 rpm. Running over 4000 rpm you should change the flywheel to a billet aluminum flywheel.
Stock valve springs will float at around 5200-5500 rpm. High rpm valve springs are cheap and are 26psi vs the stock 18psi compression rate.
The stock connecting rod seems to be able to withstand high rpms as long as the engine oil level is full.
 

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I don't own a Predator engine but those little Toro 521 blowers are wonderful machines.
 
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Great info, The idle jet to .021 is what I have been doing to all the 208cc engines I get to fix the pulsing on, Works great and I just use a pin vice and go slow.
 
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