🔧 Jetting Finder
Select your carburetor, build level, altitude, and temperature to get a recommended starting jet.
▸ RECOMMENDED JETTING
Main Jet Size Reference Chart
| Carburetor | Build Level | Sea Level | 2,000 ft | 4,000 ft | 6,000 ft | 8,000 ft |
|---|---|---|---|---|---|---|
| OEM Stock | Stock | 70–72 | 68–70 | 66–68 | 63–65 | 60–62 |
| Mild | 78–82 | 76–80 | 74–78 | 71–75 | 68–72 | |
| PZ19 (19mm) | Stage 1 | 82–86 | 80–84 | 78–82 | 75–79 | 72–76 |
| Stage 2+ | 88–92 | 86–90 | 84–88 | 81–85 | 78–82 |
OEM carb numbers reference the common AGK-style replacement jet scale — measure your stock jet's thread pitch (.194"/4.9mm or .154"/3.9mm) before ordering, since both versions are in circulation.
Pilot Jet, Needle & Air-Fuel Screw Settings
| Carburetor | Build Level | Pilot Jet | Needle Clip | A/F Screw (turns out) | Notes |
|---|---|---|---|---|---|
| OEM Stock | Stock | N/A | N/A | N/A | Fixed-jet carb — no idle mixture screw, no adjustable circuit |
| OEM Stock | Mild | N/A | N/A | N/A | Main jet is your only tuning point after a filter/exhaust swap |
| PZ19 | Stage 1 | #17 – #20 | Clip 2 – 3 | 1.25 – 1.75 | Verify stamped pilot number — richen slightly if it bogs off-idle |
| PZ19 | Stage 2+ | #20 – #22 | Clip 3 – 4 | 1.5 – 2.0 | Pair with 18lb valve springs and billet flywheel for sustained high RPM |
Altitude Correction Quick Reference
Thinner air at altitude = leaner mixture. Drop jet size by approximately the amount shown below from your sea-level baseline.
| Altitude Band | Approx. Jet Correction | Air Density vs. Sea Level | Tip |
|---|---|---|---|
| Sea Level – 1,000 ft | Baseline (no change) | 100% | Sea-level jet is your reference point |
| 1,001 – 2,000 ft | –1 to –2 sizes | ~97% | Minor correction; most skip this band |
| 2,001 – 4,000 ft | –3 to –4 sizes | ~93% | Noticeably richer — correction required |
| 4,001 – 6,000 ft | –6 to –7 sizes | ~87% | Significant correction; re-tune A/F screw too (PZ19) |
| 6,001 – 8,000 ft | –9 to –10 sizes | ~81% | Full retune; consider needle clip adjustment too (PZ19) |
| > 8,000 ft | –10+ sizes | <78% | Full retune recommended; stock power drops 20%+ |
Temperature also affects mixture: add ~1–2 jet sizes for cold weather (<45°F), subtract 1–2 for heat (>90°F).
Carburetor Quick Guide
OEM Stock Carb
Stock & Mild Builds
- Bore Size Small fixed venturi
- Stock Main Jet ~70–72 (AGK scale)
- Pilot Jet N/A — fixed, no circuit
- A/F Screw None
- Best For Stock, Mild builds only
- Note Two jet thread sizes exist — measure first
PZ19 (19mm)
Governor-Removed & Full Builds
- Bore Size 19mm
- Typical Main Jet #82–#92
- Pilot Jet #17–#22
- A/F Screw 1.25–2.0 turns
- Best For Stage 1–2+, gov removed
- Note Stud pattern is offset — needs adapter manifold
Lean vs. Rich Symptoms
🔴 RUNNING LEAN (jet too small)
- Engine overheats quickly
- Flat or hesitant acceleration
- Popping / backfire on deceleration
- Engine surges at steady throttle
- White or light grey spark plug tip
- Loss of power, especially at WOT
- Piston / valve damage risk if ignored
FIX → Install a larger main jet (go up 2–3 sizes and retest)
🔵 RUNNING RICH (jet too large)
- Black smoke from exhaust
- Wet, black, or sooty spark plug
- Sluggish low-end, poor throttle response
- Fuel smell at exhaust
- Fouled spark plug; hard to restart
- Engine loading up or blubbering at WOT
- Increased fuel consumption
FIX → Install a smaller main jet (go down 2–3 sizes and retest)
Jetting Tips & Best Practices
Plug Chop Method
Most reliable jetting check: run the engine hard at WOT for 10–15 seconds, instantly cut the ignition, and coast to a stop. Pull the plug — tan/light brown = correct, white = lean, black = rich. Always read it before the engine cools.
Main Jet Comes First
On the OEM carb, the main jet is your only adjustment — there is no pilot circuit. On a PZ19, start with the main jet for WOT behavior, then dial in the needle clip for midrange, and finish with the A/F screw for idle.
Temperature & Humidity
Cold dense air acts like lower altitude — go up 1–2 jet sizes below 45°F. High humidity also affects tune. Hot weather (90°F+) requires going down 1–2 sizes. Re-jet when seasons change significantly.
Ethanol Fuel Factor
E10 gasoline (10% ethanol) runs leaner than pure gasoline. If switching to non-ethanol or E0 pump gas, you may need to go up 1–2 jet sizes. Always note your fuel type when recording a tune.
A/F Screw Baseline (PZ19 only)
Gently seat the A/F screw (do not force it), then back out 1.5 turns as a starting point. Adjust in 1/4-turn increments at idle — out = richer at idle, in = leaner. The OEM carb has no equivalent adjustment.
79cc Parts ≠ 212/301 Parts
The 79cc runs a fixed-jet OEM carb with no idle circuit — a completely different design from the numbered jets on the 212 or 301. Once the governor comes out, most builders move straight to a PZ19, which needs an offset adapter manifold to bolt up. Always use 79cc-specific numbers.
Frequently Asked Questions
What is the stock main jet size on a Predator 79cc?
The Predator 79cc uses a small fixed-jet float carburetor rather than a standard numbered jet like the 212 or 301. Stock orifice size is typically around .027 to .029 inches, and there are two different jet thread patterns in circulation (.194"/4.9mm and .154"/3.9mm), so always measure your stock jet before ordering a replacement.
Does the Predator 79cc have a governor, and should I remove it?
Yes. The 79cc ships governed to about 3,600 RPM. Removing the governor allows 5,000 RPM or more, but the tiny stock carb quickly becomes the bottleneck, which is why most governor-removed builds pair the change with a PZ19 carb upgrade. Stock valve springs are good to roughly 5,500–6,000 RPM; go past that and budget for 18 lb springs. The 99cc big-bore version shares the same 37mm stroke, so if you have bored out to 99cc, jet slightly richer than the numbers on this page.
Can I use Predator 212 or 301 jetting numbers for the 79cc?
No. The 79cc is a much smaller platform with a completely different OEM carburetor design — a fixed-jet unit with no idle mixture screw, unlike the numbered jets on the 212 and 301. The absolute jet numbers, thread patterns, and tuning approach are all different. Always use a 79cc-specific reference.
Related Calculators
301 Jetting Chart
The 301's jetting reference for OEM 26mm, PZ27, and PZ30 carbs.
224 Jetting Chart
The 224's jetting reference — different absolute numbers, same tuning principles.
212 Jetting Chart
The original 212 jetting reference for smaller-bore builds.
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