Carburetor Selection Guide SMALL BLOCKS Stock Appearing Can be used with or without filters. We offer composite or aluminum filter adapters, but the composite is best. We also have ARC adapters. Stock Honda: The stock Honda carb is .575 Venturi and will support up to around 10 HP. It typically takes a #95 jet. Stock Clone: The OEM clone carbs are .610 and will support around 11 HP. Use a #95 main jet. .625 Bored Honda: The best choice for stock appearing with high torque and good starting. Great throttle response. Up to 13 HP. .650 Bored Honda: Slight increase over .625 in HP with slight decrease in torque .650 Bored Clone: Good economy boost in power. Up to 13 HP. .670 Bored Clone: Some increase and low-end loss. Hard to start. Throttle response is not so good. Extreme (.680): Has large butterfly for maximum flow. Up to 15 HP. Although this is more expensive, it works well. Stage 4: A ported and polished extreme. Highest HP stock appearing. GX390 Stock Bore: Works okay and will get 16 HP. Terrible throttle response as there is no pumper circuit! Linkage is backwards. We don't make one, but the ARC throttle plates work if the arm is switched around. Normally, we don't recommend these. Bored 390 Carb: Do not use it on a small block; it's too big and hard to get working correctly. Tillotson Tillotsons make good power, but they are very hard to tune. Unless the customer knows Tillotsons, we do not recommend them. 304: Provides up to 20 HP Walbro PZ26 World Formula Carburetor: Nice carburetor that will support 18+ HP. It is equivalent in quality to the Japan PZ22. Easy to tune, but we only sell a jet kit (no individual jets). Mikuni Round Slide 22mm Small Body: Chinese Mikuni copy of a VM22. This is a huge seller and works great for the cost. Up to 16+ HP. We use these on most engines and hop up kits and recommend them. Take caution as there are a lot on the market in varying qualities. Also, there are two different thread sizes for the main jet. Most use the M5 x .8 (Keihin), and we do offer these. They use the Mikuni pilots, but we have found some that use Keihin pilots. Manifold length does not seem to matter that much. For the most part, they are great bolt-on kits. Use a #135 main jet to start. Does not respond well to methanol conversions. Always use an air filter! 22mm Large Body: Genuine Mikuni VM22. Better quality and easier to tune than the Chinese version, but costs more. 17 HP. Flat Slide 24mm Mikuni: Best carb for high HP gas. Takes a bit of tuning, but once right, it's awesome! Not for methanol. 20+ HP. Best for big bores and strokers. 28mm Mikuni Gas: Not recommended 28mm Mikuni Methanol: These make great methanol carbs that will support all big bore and stroker motors. Cannot convert back to gas. 28mm Black Carb (Nibbi): They seem to work great. They are based on a Keihin, built specially for racing. 20+ HP. BIG BLOCKS Stock Appearing Stock Honda: The stock Honda carb is 21mm Venturi and will support up to around 24 HP. Bored Honda: This 23.5mm carb works okay, but does not always make more power. Typically only 1+ HP. 24mm 3-Circuit: Good choice for stock appearing with high torque and good starting. Up to 26 HP, depending on the engine size. Extreme 390: Best choice if stock appearing is required! Tillotson We don't have these for GX390s. Mikuni 33mm Pumper: Best carb for GX390s-GX460s. Has a pumper circuit, so great throttle response. 35+ HP. Alky or methanol. Recommended for open builds. 34mm Round Slide: Nice bolt-on carb. We have seen this run as high as 35 HP. Use on GX390s or larger. This is our main seller. Recommended for economy builds! 34mm Flat Slide: Has the potential for more HP than the round slide and more options for tuning. 28mm Flat Slide: Use only on GX270s. 38mm Flat Slide: Good if you want a big carb, but we have not personally seen any power increases. Typically 33 or 34mm will support all the air the engine can use.