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Sun May 25, 2025 4:20 pm

Thanks everyone, below is my engine's build specs, could the Gurus here please advice if there's anything I should change or improve with my carbs which I am having rebuilt...The 'Carb Guy' said my engine is running too lean and hence the plugs keeps getting fouled. We want to start from scratch with the carbs so your worthwhile expert advice would be sincerely appreciated!

2180cc VW ENGINE SPECIFICATIONS:
DRD H Beam Rod 5.4 VW Journal
DRD 4340 Crank / 82 mm Stroke VW Journal
Chromoly 8mm Stud Kit/Nuts/Washers
Silver Line Main Bearing Set (STD/STD/STD)
New AI Pent Roof Case/Full Flow and Filled Behind #3/94mm Bore
Dual Thrust Cam Bearings
Type1 Rod Bearings
AA 92mm Thick Walled Piston & Cylinder Set
KEP 8 Dowelled 215mm Flywheel
OEM Scat Rockets 1:1
DRD L5 CNC VW Heads 40x35.5 Dual Springs-Pair/92mm Chamber/94mm Bore
8.5 Compression
Engle 110 Cam
Derale High Performance Rotary Inline Fuel Pump
CB Performance Magnaspark Ignition System
CB Performance Thin Line 1.5 Quart Sump
Twin Webers 40mm IDF = air correction jets 200 / F11 Emulsion Tubes / Main Jets are 145 and Idle Jets .60

Sun May 25, 2025 4:36 pm

I'm not a Weber guru, but have worked with/installed a few IDF sets in the past 30 years. Your statement from the carb guy is contradictory: If the carbs are set too lean, your plugs would not "foul" (with a dark oily residue from a rich mixture) but would have signs of the center portion overheating.

What are the venturi sizes on your IDFs? That's another essential stat which we need. You can usually view the size along the top rim of the venturi when looking down from the top of the carb with the air cleaner off. The numbers are usually cast into the top curved portion, though clone-style IDFs may not have the numbers. You're looking for numbers such as 28, 30, 32 which are the millimeters of the narrowest part of the tapered inner bore of the venturi.

Sun May 25, 2025 7:06 pm

Start with reading up on Weber carbs and things will come together a lot smoother than relying on other people to advise you on the basics. Making a want list will not get anyone a good running engine - it will simply empty their wallet. John Passini's book on theory is an excellent book to start with.

Sun May 25, 2025 10:50 pm

Common weber 40idf-70 carbs not really large enough for that engine.
Why not use 44idf or at least 40hpmx with 32mm vents?

Mon May 26, 2025 2:24 am

Thanks everyone but any chance if anyone knows if my existing idle jets/sizes are okay? Moreover, anyone running 2180 with 40 IDF's and if so, curious what sizes you have. Thanks!

Mon May 26, 2025 9:54 am

If your carb guy stated what he stated he is incorrect, if your plugs are fouled with your existing setup and jetting it wouldn't be running lean it would be running rich, let's assume that you have 28 mm venturi's that comes stock with your 40 idfs, your main jet and idle seem a bit too big, your idle judge should probably be dropped down to 55 in your main jet I would probably start between 120 and 125, so the jetting that you have now to me would seem a bit big and would be running rich and most likely failing the plugs, and that's assuming that that is the actual size I run across all the time that would have stamped on the Jets are not what they are a lot of people drill or ring them out so your car guy needs to check them which a get gauge and not rely on just a number stamped on them, that's where I would start.
Also verify proper fuel pressure.

Mon May 26, 2025 12:11 pm

Your jet sizes are about right to work in 40idf-78/79 with 32vents

But all the jet sizes would be far too large in model 40idf-70 with 28 vents

So you need to know what model of carburetor you have, and what size venturi you have in them.