How much is the stock carb holding you back?
Engine output on a stand — there is no drivetrain and no chassis in these numbers, which is the same basis Harbor Freight rates the engine on. Simulated at 800 ft and 75°F; thinner air makes less power and wants less fuel, so both the horsepower and the jet move with them. Governor removed. Compression 9.06:1.
Where each one wins
| RPM | stock 18mm carb | Nibbi PWK24 | diff |
|---|---|---|---|
| 1500 | 2.50 | 2.83 | +0.32 |
| 2000 | 3.44 | 3.88 | +0.44 |
| 2500 | 4.41 | 4.99 | +0.57 |
| 3000 | 5.43 | 6.13 | +0.70 |
| 3500 | 6.51 | 7.36 | +0.84 |
| 4000 | 7.73 | 8.73 | +1.00 |
| 4500 | 9.02 | 10.19 | +1.17 |
| 5000 | 10.38 | 11.72 | +1.34 |
| 5500 | 11.81 | 13.29 | +1.48 |
| 6000 | 12.55 | 14.17 | +1.62 |
Horsepower at each rpm. Everything except the part named is identical between the two runs.
A built engine — big cam, race pipe, rev coil, stainless valves — asked to breathe through the carburettor it left the factory with.
This is the clearest illustration on the site of why parts have to be matched. The engine is capable of considerably more, and one 18mm restriction is enough to hide most of it.
It works the other way too. Fitting this carb to a stock engine buys very little, because the carb was never the restriction there. The right part depends entirely on what else is fitted.
The build
| Engine | Predator 212 Hemi (Gen 2) — 27/25mm valves · 5.5mm stems |
|---|---|
| Governor | Governor removed (full rev range) |
| Piston | Stock flat top — Hemi OEM (ARC DJ-1285PH · .550" CH) |
| Head | Stock Hemi head — as-cast factory |
| Head gasket | Stock HEMI — fiber .045" (ARC DJ-1310TP) |
| Camshaft | DynoCams 335 — .334" · 259.8/264.7 @.050 · 36 lb · 8,500-9,000 rpm |
| Valve springs | 34-36 lb open/race |
| Retainers | Billet w/ keepers, 36 lb — ARC DJ-1046 ($11.00) |
| Valves | Stainless kit, Hemi 27/25mm — GPS KDVALKIT27-25 · ARC DJ-SSVALVE HKT |
| Rocker arms | Stock rocker arm — 1:1 ratio |
| Connecting rod | ARC 6256 Billet — Hemi (+.020" raises CR) |
| Flywheel | ARC 6696 Billet — Hemi Speedway (32° BTDC) |
| Ignition coil | ARC rev limiter coil — 9,000 rpm |
| Carburetor | Stock Mikuni clone 18mm — Hemi factory |
| Air filter | Pod / cone filter — GPS / OMB angled filter kit |
| Exhaust | DynoCams race exhaust pipe |
| Fuel | Pump 87 octane |
The other one
| Engine | Predator 212 Hemi (Gen 2) — 27/25mm valves · 5.5mm stems |
|---|---|
| Governor | Governor removed (full rev range) |
| Piston | Stock flat top — Hemi OEM (ARC DJ-1285PH · .550" CH) |
| Head | Stock Hemi head — as-cast factory |
| Head gasket | Stock HEMI — fiber .045" (ARC DJ-1310TP) |
| Camshaft | DynoCams 335 — .334" · 259.8/264.7 @.050 · 36 lb · 8,500-9,000 rpm |
| Valve springs | 34-36 lb open/race |
| Retainers | Billet w/ keepers, 36 lb — ARC DJ-1046 ($11.00) |
| Valves | Stainless kit, Hemi 27/25mm — GPS KDVALKIT27-25 · ARC DJ-SSVALVE HKT |
| Rocker arms | Stock rocker arm — 1:1 ratio |
| Connecting rod | ARC 6256 Billet — Hemi (+.020" raises CR) |
| Flywheel | ARC 6696 Billet — Hemi Speedway (32° BTDC) |
| Ignition coil | ARC rev limiter coil — 9,000 rpm |
| Carburetor | Nibbi PWK24 — 24mm flat slide |
| Air filter | Pod / cone filter — GPS / OMB angled filter kit |
| Exhaust | DynoCams race exhaust pipe |
| Fuel | Pump 87 octane |