Air-Cooled VW Bug, Bus, Sand Rail & Dune Buggy Weber IDF Jetting Guide
Weber IDF Carburetors and EMPI HPMX Carburetors are popular performance additions to vintage air-cooled VW bugs, buses, sand rails and dune buggies.
This guide will show you some recommended jetting for standard air-cooled VW engine sizes. It will show jet sizing for everything from a VW 1600 CC engine to a VW 2332 engine.
Please note that this jetting guide is meant as only a guide and not a strict rule.
Your engine may have different characteristics than what this guide accounts for based on cam choice, compression or another factor. This guide should get you close to what you need, but you will have to do your own testing to make sure your VW bug or dune buggy runs the way you think it should.
Recommended Jetting For Weber IDF & EMPI HPMX
|Weber & HPMX Single 40 IDF Jetting||Venturi||Main Jet||Main Air Corrector Jet||Emulsion Tubes||Idle Jet||Pump Jet|
|VW Type 1: 1500 - 1600CC||28mm||145||160||F11||65||75|
|VW Type 1: 1600 - 1835CC||28mm||150||160||F11||65||75|
|VW Type 1: 1835 - 2000CC||30mm||155||160||F11||70||75|
|Weber & HPMX Dual 40 IDF Jetting||Venturi||Main Jet||Main Air Corrector Jet||Emulsion Tubes||Idle Jet||Pump Jet|
|VW Type 1: 1500 - 1600CC||28mm||130||200||F11||55||50|
|VW Type 1: 1600 - 1835CC||28mm||140||200||F11||55||50|
|VW Type 1: 1835 - 2000CC||28mm||145||200||F11||65||50|
|VW Type 1: 2000 - 2332CC||28mm||155||200||F11||65||50|
|Weber & HPMX Single 44 IDF Jetting||Venturi||Main Jet||Main Air Corrector Jet||Emulsion Tubes||Idle Jet||Pump Jet|
|VW Type 1: 1500 - 1835CC||34mm||160||175||F11||60||80|
|VW Type 1: 1835 - 2000CC||34mm||165||175||F11||65||80|
|VW Type 1: 1500 - 1835CC||36mm||160||165||F11||60||80|
|VW Type 1: 1835 - 2000CC||36mm||170||165||F11||65||80|
|Weber & HPMX Dual 44 IDF Jetting||Venturi||Main Jet||Main Air Corrector Jet||Emulsion Tubes||Idle Jet||Pump Jet|
|VW Type 1 1500 - 1600CC||36mm||145||200||F11||60||50|
|VW Type 1 1600 - 1835CC||36mm||150||200||F11||60||50|
|VW Type 1 1835 - 2000CC||36mm||155||200||F11||65||50|
|VW Type 1 2000 - 2332CC||36mm||160||200||F11||70||50|
Links to Jet Tools:
We recommend checking your carburetor to see what jets you have before ordering. The jets usually have a number stamped in them that says their size.
It is never a bad idea to measure the jets in your VW Bug, Sand Rail or Dune Buggy. It is possible that they have been reamed for more flow.
Keep in mind a jet's function when deciding on jet sizes for your air-cooled VW.
Jets meter air and fuel entering your air-cooled VW engine through the RPM range. They are responsible for the air-fuel mixture that will enter your engine and be burned inside the cylinder.
Idle jets supply fuel from idle to around 2000 RPM. Main jets supply fuel from 2000 RPM on. If your car has a bog or hesitation note where in the rev range it happens.
Air-cooled VWs in general like running richer than leaner. These engines experience higher head temperatures than many vehicles and more fuel leads to cooler running. Many carburetor related stumbles can be traced back to a lean condition in the rev range.
However please note that too much fuel can cause engine wear due to thinned oil. If your spark plugs are black and fouled or you see lots of black smoke coming from your exhaust after installing new jets you are probably too rich.
Air correction jets work the opposite of fuel jets. The larger the air correction jet the more air it lets into your air-fuel mixture. This will lean out the mixture. The larger the fuel jet the more fuel it lets in, which will richen the mixture.
You can look at your spark plugs to get clues on how your engine is running. Light grey plugs or a plug with a melted electrode typically indicate hot running lean conditions. A dark sooty plug usually indicates a rich condition. A brownish plug with a clean electrode typically indicates the engine is running clean.
A wideband oxygen sensor is a great way to measure your VW bug or sand rail engine's air fuel mixture. Often these are installed during engine dyno sessions or for performance applications.
When looking at air fuel ratios 14.7 parts of air to 1 part of fuel (14.7:1) is considered "Stoichiometeric" or the ideal optimized mixture of air and fuel. This number is an indicator from which lean and rich are measured. Numbers greater than 14.7:1 are considered lean. Numbers less than 14.7:1 are considered rich. That is more air or less air respectively mixing with fuel.
For air-cooled VWs it is usually ideal to have your air-fuel mixture somewhere between 13:1 and 14.7:1 at idle. Under full acceleration this mixture should richen up to around 12:1. When cruising some dial this mixture back up to around 14:1. In general you want your engine to be in this range at all times. Remember lean is hot so it is not recommended to set your engine on the lean side of these numbers. Also please note air-fuel ratios will constantly change during driving and testing. The only way to get an accurate map of your air-cooled VW engine's air fuel ratio is to data log readings in a controlled environment like an engine dyno.
Please let us know if you have questions about your engine or application!