PMO Carburetors
Sizing, jetting, fitment and install — how to pick the correct triple-throat kit for your flat-six the first time.
Spec'd to your engine, before the order goes in
Washburn's supplies all eight PMO Induction kit configurations — 40mm, 46mm and 50mm, street through big-bore — along with the syncrometer, float gauge, jet sets, rebuild kits and air cleaners that go with them. Every kit is built to order against a PMO Carb Setup Sheet, so the work that matters happens first: we confirm your displacement, cam, compression and exhaust before the order is placed.
Triple-throat carburetion, built to hold tolerances the originals never could
PMO has built its reputation since 1997 as the specialist brand for triple-throat, IDA-style carburetion on air-cooled Porsche flat-six engines. PMO Induction is an EMPI brand, and every carburetor is machined, hand-assembled and finished at PMO's facilities in Anaheim, California — aerospace-grade billet held to tolerances the original 1970s-era Weber IDA carburetors were never built to hold.
Every PMO kit is a matched pair of triple-barrel carburetors — three throttle bores per carburetor, one throat feeding each cylinder, six throats across the pair. That layout is what gives a properly tuned flat-six its throttle response and even cylinder-to-cylinder fueling, but it only works if the carburetor holds its tolerances over time.
The upshot for a shop or an owner: less chasing an idle that won't hold, less rebuilding worn shaft bores, and a carburetor built to be re-tuned as the combination changes — cam, compression, exhaust or displacement.
- Brand
- PMO Induction
- Style
- Triple-throat, IDA-style, one throat per cylinder
- Bore sizes
- 40mm, 46mm, 50mm
- Manufactured
- Anaheim, California — an EMPI brand, machined and hand-assembled from billet
- Sold as
- Matched pair, triple-barrel, for flat-six engines
One-piece stainless throttle shafts
Machined and micro-polished to .002" tolerance — the single biggest failure point on an original Weber IDA, where shaft wear creates vacuum leaks, an inconsistent idle, and a tune that drifts over a season.
Sealed bearings & Belleville pre-load
Sealed ball bearings and Belleville spring pre-load keep the throttle shaft radially and axially located, so the bore stays round and sealed instead of slowly wallowing out.
Integrated fuel sight glass
On each carburetor — verify float level at a glance instead of partially disassembling the carb the way you have to on an original Weber.
Redesigned fuel inlet
Replaces the Weber's leak-prone banjo-bolt fitting with a higher-flow, better-sealed connection.
A true 50mm throttle bore
The largest triple-throat Weber ever built, the 46 IDA 3C, stopped at 46mm — and it was a racing part, not factory fitment. PMO's 50mm exists for big-bore, high-compression and stroker flat-six builds that outgrew it.
Built to a setup sheet, not a shelf
Displacement, cam, compression, exhaust and elevation all feed the final jetting — which is why the same 3.0L can correctly take two different kits.
Spec'd against your engine, not your title
Built for the air-cooled Porsche flat-six family.
911
The core PMO application, from early 2.0L cars through the 3.0L SC era and beyond.
914-6
Six-cylinder 914 chassis running the same triple-throat induction layout.
964
Carbureted conversions and built engines moving away from factory injection.
993
The last of the air-cooled cars, typically on race and heavily built combinations.
Chassis year is a starting point, not the answer.
The correct carburetor size is a function of displacement, camshaft, compression ratio and exhaust. Two owners of the same 3.0L 911 SC often run different kits: a mild cam at stock compression may be correctly sized at 40mm, while a performance cam and higher compression needs the 46mm to keep up with the airflow demand.
Same carburetor family, two entirely different jetting curves. What separates them is cam, compression and exhaust — exactly what the Carb Setup Sheet asks for, and exactly what the year on a title cannot tell you.
Budget for the job, not just the kit. Air cleaners are ordered separately (standard, or short-body for A/C cars). Cars built after 1974 generally need an exhaust suited to open velocity-stack induction. Vacuum-advance distributors — roughly 1971 onward — typically need re-curving, sometimes rebuilding. Setup and upkeep want a syncrometer, a float level gauge and a jet set. Installation and final tuning are done by your engine builder. We would rather walk you through that list before you order than have any of it be a surprise later.
The exhaust and distributor points are worth settling first, not after: open velocity-stack induction changes both backpressure and vacuum signal versus the factory setup, so flag your current exhaust and distributor before you order and the kit gets spec'd around them.
Kit & jetting calculator
The same three variables PMO's own Carb Setup Sheet asks for, plus elevation.
Street = stock or mild cam at stock compression. Performance = a hotter cam and/or raised compression. Not sure? Choose Street and we'll confirm it with you before anything is ordered.
A ballpark starting point, not a final tune. Interpolated from published PMO factory baseline jetting and standard altitude-correction practice. PMO builds every kit to order using its own Carb Setup Sheet — your exact cam, compression, exhaust and elevation. Use this to walk into that process informed, not to set final jets at home.
Eight factory configurations
By throttle bore and displacement. Two variables decide your kit: bore size tracks how much air the engine needs to breathe, tune tracks how you actually run the car.
40mm
Stock through mildly built engines, roughly 2.0–3.0L.
PM-O801-0
Stock-spec drivers wanting a factory-correct, tractable street tune.
PM-O802-0
Engines with a performance cam and/or bumped compression.
PM-O803-0
Stock or mild-cam SC-era daily drivers.
46mm
Performance cams, raised compression and Carrera-class displacement.
PM-O804-0
Performance cam and compression that outgrew the 40mm street tune.
PM-O805-0
Stock-spec Carrera-class engines, street driven.
PM-O806-0
A performance cam and/or raised compression.
50mm
Big-bore and stroker builds that outgrew the largest Weber ever made.
PM-O807-0
Big-bore builds still tuned for street manners.
PM-O808-0
Stroker and big-bore engines needing maximum airflow.
Six throats. One per cylinder.
Three barrels per carburetor, two carburetors, one throat feeding each cylinder. It is the layout that gives an air-cooled engine its throttle response — and the reason tolerance, not displacement, separates a good set from a worn one.
What has to be right before the carbs go on
Confirm exhaust and distributor compatibility first
Open velocity-stack induction changes both backpressure and vacuum signal versus the factory setup — sort your exhaust and distributor curve before you bolt carbs on, not after.
Set float level using the sight glass
PMO's integrated sight glass lets you set and verify fuel level on the bench and again once the engine's warm, with the tank at a realistic level — no partial teardown required. A float level gauge makes this a one-minute check.
Synchronize all six throats
Use a flow-balance (Unisyn-style) gauge at idle and again at a steady 2,500–3,000 RPM — we supply a PMO syncrometer for exactly this. An out-of-sync bank shows up as a lopey idle and uneven cylinder temps long before it shows up on a dyno sheet.
Dial in idle mixture warm
The idle jet controls roughly idle through 1/8 throttle — adjust only once the engine is at full operating temperature.
Read plugs across the range
Main jet governs roughly 3/8 throttle to wide open; air correction jet shapes the transition and top-end enrichment curve. A few heat-cycled full-throttle pulls followed by a plug read is still the most reliable way to confirm the main jet for your exact combination and elevation.
Re-check sync and mixture after break-in
Linkage settles and gaskets seat in the first few hundred miles — plan a follow-up sync and mixture check, not just a one-time setup.
For the job
Everything above is easier with the right tool on the bench. These are the PMO service items we supply alongside the kits.
PMO Syncrometer
The airflow gauge for step 03 — balances all six throats at idle and at cruise RPM. Made in Germany; works on PMO and Weber carburetors alike.
View product →
PMO Float Level Gauge
Turns step 02 into a one-minute check. Sets and verifies float height against the sight glass without pulling the carburetor apart.
View product →
PMO Jet Set, 40mm
Spare mains, air correction and idle jets across the range for your bore size, so you can chase a plug read without ordering one jet at a time.
View product →
Fuel Pressure Control Unit
Adjustable regulator with barbed fittings. Carburetors want low, steady fuel pressure — an unregulated pump is a common cause of a float level that won't stay put.
View product →
PMO Rebuild Kit
Gaskets, seals and diaphragms for 40mm, 46mm and 50mm PMO sets — the refresh that goes with the post-break-in re-check in step 06.
View product →
PMO Air Cleaner Element
Standard 3.25" element. Open stacks look the part, but a filter is what keeps grit out of precision-drilled jets.
View product →- Lube throttle shaft linkage and cross-shaft bushings at every service interval.
- Re-check throat-to-throat sync any time idle quality or fuel economy changes.
- Replace the inline fuel filter on schedule — jets are precision-drilled orifices and don't tolerate debris.
- Clean jets with carb cleaner and compressed air only — never redrill or probe a jet with wire, which permanently changes its calibrated flow rate.
- Check sight-glass fuel level periodically, especially after any fuel pump or regulator work.
We spec it before we sell it
Because a re-order costs more than a phone call.
Washburn's Metal is a shop of air-cooled Volkswagen and Porsche owners and specialists based in Orange, California. Sheetmetal restoration and fabrication are what we do with our hands — we're not an engine shop, and we don't turn wrenches on your motor. What we bring to PMO carburetion is what we bring to everything else we sell: we live in these cars, and we make sure you're ordering the right kit before it ships.
As air-cooled owners ourselves, we know the questions a parts counter won't think to ask: whether your distributor needs re-curving, whether your exhaust will support open velocity stacks, and whether your "3.0L" is really making the compression and cam profile you think it is.
- Range
- All 8 PMO Induction kit configurations
- Before you order
- Free fitment check — send cam, compression and exhaust
- Who we are
- Air-cooled owners and specialists, not a general repair shop
- Based in
- Orange, California — nationwide shipping
Before a kit ships
How do I know if I need the 40mm, 46mm, or 50mm kit?
Bore size follows your engine's total displacement and how much air it needs to move, not the model year on your title. As a starting point: 40mm typically covers 2.0–3.0L, 46mm covers 2.8–3.4L, and 50mm covers 3.5L and up or heavily built engines. Use the calculator above for a specific recommendation, or send us your displacement, cam, and compression and we'll confirm.
What's the real difference between the "Street" and "Performance" tune of the same bore size?
Same throttle bore, different jetting curve. A Street tune is calibrated for a stock or mild-cam engine at stock-ish compression — tractable idle, good part-throttle manners, daily-driver friendly. A Performance tune assumes a hotter cam and/or higher compression that needs more fuel at wide-open throttle to stay safe. Pick based on your actual cam and compression, not your ambitions.
Do I need to change my exhaust to run PMO carburetors?
In many cases, yes — especially on cars built after 1974. Open velocity-stack triple-throat induction changes backpressure characteristics versus the factory intake and exhaust, so it's worth confirming your current exhaust is compatible before your kit ships.
Does my distributor need anything done to it?
If your car has a vacuum-advance distributor — common from roughly 1971 onward — it typically needs to be re-curved, and sometimes rebuilt, to match the vacuum signal of a triple-throat carburetor setup correctly. Plan for this alongside the carburetor install, not as an afterthought.
Does elevation actually matter for jetting?
Yes. Less oxygen per unit of air at altitude means a sea-level jet will run rich once you climb — main jet and air correction jet both typically need to come down to compensate. It's one of the inputs on PMO's own Carb Setup Sheet, and it's built into the calculator above.
Are PMO kits jetted out of the box, or do I still need to tune them?
PMO builds every kit to order against your Carb Setup Sheet — displacement, cam, compression, exhaust, and elevation — so it arrives close to correct for your specific combination. Expect to fine-tune idle mixture and confirm the main jet with a plug read once the engine's broken in and fully warmed up; that's normal for any carbureted induction system, not a sign anything's wrong.
What does a PMO kit include, and what do I still need to source?
Each kit is a matched pair of triple-barrel carburetors, pre-jetted to the configuration you order — chokes, main jets, air correction jets, emulsion tubes and idle jets — with PMO crossbar throttle linkage, a PMO fuel pressure regulator, carburetor isolators, fuel hose and hardware. Intake manifolds are not included and are required — stock manifolds will not support the 46mm or 50mm carburetors. Air cleaners are separate as well (standard, or short-body for A/C-equipped cars). Tell us your engine and we'll quote the manifolds and air cleaners alongside the kit so nothing is missing when it lands.
How long does a build-to-order kit take, and who installs it?
Since every kit is built to your Carb Setup Sheet, lead time varies with current order volume — contact us for the current estimate on your configuration. Washburn's specializes in sheetmetal restoration and fabrication, not engine work, so installation, exhaust prep, and final tuning are handled by your engine builder or installer of choice.
Spec it first.
Tell us your displacement, cam and compression and we'll confirm the right PMO kit before you order.
Jetting figures on this page are reference starting points derived from published PMO Induction factory baseline specifications and standard altitude-correction practice. They are not a substitute for PMO's official Carb Setup Sheet or for tuning verification on your specific engine. Prices shown are those listed on each kit's product page at the time of publication. Specifications are subject to change.