Gasoline, LP, NG Scrubbers

Foley Environmental

Foley Environmental is a division of Foley Industrial Engines. We are the oldest engine distributor in North America.
With almost 104 years in the engine business we have extensive knowledge of exhaust scrubbers and purifiers. This makes us the ideal supplier for your company’s needs.

Foley Environmental serves both the public and private sectors. Our customer base includes Boston’s Big Dig, California public works projects, Brown University, Bucknell University, Hyster Forklift Co., Narragansett Electric Co, IBM, and many more public works projects and companies. Many OEMs, such as Yale and Hyster Forklift Co, now include our Foley Environmental purifiers as standard equipment on new machines. These companies are a testimony to our effective solutions to exhaust emission problems.

As the only U.S. based exhaust purifier specialist, we pride ourselves on shipping within 24 to 48 hours of the receipt of an order.


Foley Goes GreenOur exhaust scrubbers allow you to work indoors with a propane or gas engine without any health risk. These air purifiers install easily and come in different styles, depending on the application. Here in the East, purifiers really came into their own on Boston’s Big Dig. This was the largest public works project since the Tennessee Valley Authority. Foley Engines supplied most of the purifiers used on this project. Because of the experience gained during the Big Dig, Foley Engines is now an OEM supplier to Hyster and Yale for their forklift purifiers.

  • Clip-On Style. The easiest to install is simply a clip-on style purifier that installs at the end of the tail pipe. We supply the purifier with the appropriate sized muffler clamp and it installs easily. Depending on the horsepower of the engine, the scrubber is typically the size of a coffee can. Scrubbers are physically larger for a high horsepower engine such as a 1000 HP engine in a generator. When the purifier is no longer needed, such as in a rental application, it can be removed and stored.
  • Combination Muffler/Purifier. The other style purifier or scrubber is a direct fit combination exhaust
    purifier/muffler. This style is most appropriate where there is no room at the end of the tail pipe for a clip-on purifier. These applications include skid steer loaders, and zero tail swing mini-excavators. These combination muffler purifiers are exactly the same shape and spatial dimensions as the OEM muffler and the installation time is similar to changing out a muffler. Typically, once installed these are not removed. These muffler/purifiers usually cost up to twice as much because they are both a muffler as well as a purifier.

To keep you up and running, we stock here in the US over 400 scrubbers, both the clip-on style and the combination muffler/scrubber version. Since we are the only U.S. based exhaust purifier specialist, we are able to ship these units quickly, often the same day as the order is placed, and without any customs delays.

We have scrubbers for gas-fueled engines, such as Honda and Wisconsin. The scrubbers for the Honda’s are combination muffler/purifiers that are identical to the OEM Honda muffler in size and shape. For Wisconsin engines, we supply a clip-on purifier. But because Wisconsin engines are inherently “dirty,” we recommend that you change the carburetor jet size and install new spark plugs and premium spark plug wires such as Accel. See Tech Tip 56, Spark Plug 101, for more info on Wisconsin spark plugs. The Tech Tip 26, Foley Engines Clean Air Tip, has more info on exhaust scrubbers for gasoline fueled engines.

What They Do & How They Do It

Simply put, our exhaust purifiers allow you to work indoors close to a gas or propane fueled engine without any health risks. They do this by using catalytic exhaust technology to make the exhaust emissions safe to breathe. Each purifier houses a catalytic core, which eliminates harmful emissions by collecting gas particles and burning off dangerous pollutants. These include particles such as Carbon Monoxide (CO) and Hydrocarbons (HC). The harmful emissions of gas or propane engines are converted into water (H2O) and Carbon Dioxide (CO2), which makes it safe to work in close proximity with your machine.

Attached you will find engine exhaust emissions test data for Honda, Kohler, Clark, and Wisconsin (single and multi-cylinder) spark ignition gasoline/propane fueled engines. These engines are typically horizontal shaft and vertical shaft engines such as the Honda GX160 (5.5 hp), Honda GX200 (6.5 hp), Honda GX270 (9.0 hp), Kohler command 11 (11 hp) and the Wisconsin W4-1770 (35 hp). In a typical exhaust gas purifier application (where the engine carburation jetting is correctly adjusted) the following average exhaust gas emission reductions can be expected.

Carbon Monoxide (CO)=70% - 82%+
Hydrocarbons (HC)=55% - 88%+
Oxides of Nitrogen (NOX)=80% - 85%+

These average exhaust gas emissions reductions are dependent upon using a well maintained, relatively new engine operating with moderate to heavy load which is consuming a regular unleaded on-highway gasoline or liquid propane fuel. In addition the engine carburetor main jet or propane needle jet(s) has been changed (slightly leaned) to provide additional oxygen for increased catalyst activity. The lean jetting change will optimize catalyst performance and minimize CO, NOX and HC emissions. The exhaust gas purifier is a combination purifier/muffler replacement mounted directly to the engine exhaust manifold or an inline exhaust gas purifier.


Test Data for Foley 3SXT Catalytic Purifiers for Gasoline/Propane Engines

  • Test Dates: Various test conducted from 1994-1997
  • Test Equipment: Horbia Mexa 534GE 4 Gas analyzer, exhaust gas measured = CO, CO2, HC, O2
  • Test Engines: Honda GX160, Honda GX200, Honda GX240, Honda GX270, Kohler Command 11
  • Test Fuel: Regular Unleaded
  • Test Load/Speed: Full engine load and governed speed
  • Purifier Models: Foley model 3SXT-GX160/200, 3SXT-GX240/270, 3SXT-Kohler Command 11 purifier muffler

Test Results

Test Engines

Before Purifier

Raw CO Raw HC

After Purifier


Honda GX160

-Stock main Jet = 72

-Lean Jet = 70

6.5% 100PPM1.2% 30PPM
Honda GX200

-Stock main Jet = 74

-Lean Jet = 70-72

5.5% 80PPM1.0% 30PPM
Honda GX270

-Stock main Jet = 88

-Lean Jet = 82-85

7.0% 100PPM0.9% 10PPM
Kohler Command 11

-1 ½ turns out in main stock

-1 to 1 ¼ turns out in mains lean

6.2% 60PPM0.5% 10PPM


Test Data for Foley SXT Catalytic Purifiers for Gasoline/Propane Engines

  • Test Date: March 17, 1994
  • Test Equipment: Horbia Mexa 534GE 4 Gas analyzer (CO, CO2, HC, O2)
  • Test Engine: Honda GX240/270, 9 brake horsepower, spark ignition naturally aspirated engine, powering a concrete trowel machine
  • Test Fuel: Gasoline, regular unleaded
    Please note that all of the tests were conducted at full engine load and speed.

Raw Emissions With Leaner Main Jet Changes

Main Jet SizeCarbon Monoxide (%)Hydrocarbons (PPM)Engine Operation
#88 (stock)7.0% CO100 PPM HCGood
#855.2% CO80 PPM HCGood
#801.8% CO20 PPM HCSlight Misfire

Raw Emissions With Main Jet Changes and 3SXV Purifier

Main Jet Size & PurifierCarbon Monoxide (%)Hydrocarbons (PPM)Engine Operation
#88 + 3SXT Purifier2.5% CO30 PPM HCGood
#85 + 3SXT Purifier0.9% CO10 PPM HCGood

By using leaner carburetion jetting the raw CO and HC emissions will drop as noted. However, if the carburetion jetting is too lean a misfire may result, engine power levels will drop and cylinder head temperature will increase (with leaner jetting). We currently believe that the #85 main jet may be the ideal carburetion jet (for Honda GX240/270) and will reduce raw CO and HC emissions, maintain engine power levels (with minimal increases in engine cylinder head temperature) and provide adequate oxygen for the catalytic purifier. As noted the Carbon Monoxide (CO) levels dropped from 5.2% to 0.9% (an 88% reduction) by using the #85 main jet and the 3SXV catalytic purifier.

We believe that a #82 main jet should also be considered and will test this jet to determine if we can reduce CO/HC further without hindering engine power.

Test Data for Foley 5SXT

Exhaust Emission Results

  • Equipment Type: Concrete Saw
  • Model Number: Correct Cut CC3500 (manufactured by Diamond Products)
  • Engine Type: Wisconsin SI Gas 35 HP 4 cylinder (model W4-1770)
  • Fuel Type: Gasoline
  • Equipment Owner: Stephenson’s
  • Ambient Conditions: Outdoor – 65°F / Sunny – June 19, 2003 – 1:30-2:30pm EST
  • Test Equipment: SPX/Horbia S54371 5 Gas Analyzer (Bar 97)
  • Measurement Ranges: CO – 0 to 10.0% Volume
    HC – 0 to 5000 PPM HC (N-Hexane Equivalent)\ CO2 – 0 to 20.0% Volume
    O2 – 0 to 20.0% Volume
    NOX – 0 to 2000 PPM NOX
  • Repeatability: 2% of reading
  • Duration: Approximately 60 seconds of sampling time at test point

Test With Stock Jetting and No Purifier

Test ResultsTest 1 (Idle)Test 2 (High Idle No Load)Test 3 (Full Load)
HC771 PPM598 PPM430 PPM


Test With Lean Jetting and Purifier

Test ResultsTest  1 (Idle)Test 2 (High Idle No Load)Test 3 (Full Load)
HC303 PPM268 PPM209 PPM


Exhaust Emission Test Results

  • Equipment Type: Fork Lift Truck
  • Model Number: Clark C500-70
  • Serial Number: 685-0123-7419K OF
  • Engine Type: SI Gas/LP engine-duel fuel
  • Fuel Type: Propane
  • Equipment Owner: Ryco
  • Ambient Conditions: Indoor – 45°F/Sunny – February 26, 1997 – 48% Humidity
  • Test Equipment: Horbia Mexa 534GE 4 Gas Analyzer
  • Measurement Ranges: CO – 0 to 10.0% Volume
    HC – 0 to 5000 PPM HC (N-Hexane Equivalent)
    CO2 – 0 to 20.0% Volume
    O2 – 0 to 20.0% Volume
  • Repeatability: 2% of reading
  • Duration: Approximately 120 seconds of sampling time at test point

Baseline Test - Stock Clark SI Engine

Test ResultsTest 1 (Idle)Test 2 (High Idle No Load)
HC150 PPM127 PPM


After Addition of Purifier Test – Stock Clark SI Engine + Purifier

Test ResultsTest 1 (Idle)Test 2 (High Idle No Load)


Exhaust Emission Test Results

  • Equipment Type: Crane
  • Model Number: Broderson Crane IC-80-3 E-SP
  • Serial Number: #285187
  • Engine Type: Continental TM27 (52 hp)
  • Fuel Type: Propane
  • Equipment Owner: High Reach Inc.
  • Ambient Conditions: Sunny/Partly Cloudy – 76°F
  • Test Equipment: Ferret Instruments Model 14-5 gas Emissions Analyzer
  • Measurement Ranges: CO – 0 to 10.0% Volume
    HC – 0 to 10,000 PPM HC (N-Hexane Equivalent)
    CO2 – 0 to 20.0% Volume
    O2 – 0 to 21.0% Volume
    NOX – 0 to 5000 PPM NOX
  • Repeatability: 2% of reading
  • Duration: Approximately 60 seconds of sampling time at test point

Baseline Test – Stock Continental LP Engine

Test ResultsTest 1 (Idle)Test 2 (High Idle No Load)
NOX104 PPM1371 PPM


After Addition of Purifier Test + Stock Continental LP Engine

Test ResultsTest 1 (Idle)Test 2 (High Idle No Load)


Foley SXT Exhaust Gas Purifier and Purifier Muffler Installation Instructions

The Foley SXT Purifier is supplied in a kit form with the following items:

  •          SXT Catalytic Purifier
  •          Oxygen Sensor Port with Plug
  •          Exhaust Clamps
  •          Heat Installation Wrap
  1. The gasoline/propane exhaust should be in a very good state of condition with respect to tuning, repair and maintenance. All engine components and component tolerances should be will within the engine manufacturer specifications. The engine should not be consuming an unusual amount of lube oil. The ignition and carburetion systems should be operating properly and should be set to the engine manufacturer specifications. A complete tune up prior to installation of the gas purifier is recommended to minimize harmful exhaust emissions. It also provides good purifier operation and life. Ensure that the engine spark plug(s) are new and that the air cleaner element(s) is new and/or clean. See Tech Tip #56 Spark Plug 101 for more information.
  2. If you are installing a purifier/muffler simply remove the stock OEM muffler. Using a new exhaust gasket, exhaust clamps, bolts and nuts (if applicable) install the purifier/muffler in the same manner as the stock OEM muffler. Torque all fasteners to manufacturer specifications.If you are installing a “plain style” purifier (SXT-P), avoid installing the purifier to close proximity to electrical components, fuel lines, fuel tanks, hydraulic oil lines, hydraulic oil tanks, plastic components or any other combustible items. These purifiers are designed to slip over the outlet pipe of the stock OEM muffler. Or they are designed to be installed inline in the exhaust system tubing before the muffler. Use new exhaust clamps for a “plain style” purifier. The purifier should be securely mounted. Avoid installing the purifier on badly rusted muffler, weak exhaust piped or muffler with weak tailpipes.If you are installing a “plain style” purifier before the muffler on a gasoline or propane engine, locate the exhaust gas purifier as close to the exhaust gas manifold outlet as possible. Cut out a 7.5” to 12.5” (depending on the exhaust gas purifier model as required) long section of the stock exhaust pipe. Install the exhaust gas purifier into the exhaust pipe. Use the supplied muffler clamps or weld the exhaust gas purifier directly to the exhaust pipe. If you are welding the exhaust gas purifier to the exhaust pipe use a #309 filler rod as filler material. Is using muffler clamps torque the nuts and bolts of the exhaust clamps to the correct specified torque. Ensure that there are no exhaust leaks.
  3. Drill an 11/16” diameter hole into the exhaust pipe as close to the engine exhaust manifold as possible (within 12” is ideal). The 11/16” diameter hole must be drilled before the catalytic purifier. Fully weld the supplied steel oxygen sensor port (18mm X 1.5mm port) on top of the 11/16” diameter hole. The oxygen sensor port and plug are supplied with the exhaust gas purifier. Purchase one wire or 3-wire oxygen sensor from your local automotive parts store. Apply a high heat anti-seize compound to the threads of the oxygen sensor port. Start the engine and allow the engine to fully warm up for at least 15 minutes. Attach the voltage meter set to millivolts (mV). Measure the millivolt signal from the oxygen sensor while the engine operates at a steady idle speed and at a constant load.Use this table to interpret the oxygen senor voltages:
    Millivolt Voltage (mV)Interpretation
    Less than 250 mVToo Lean
    250 mV to 410 mVLean
    410 mV to 580 mVIdeal for Purifier Operation
    580 mV to 800 mVRich
    Over 800 mVToo Rich

    Adjust the engine carburetion (richer or leaner as required). In most cases engine will have to have the carburetion slightly leaned to produce and oxygen sensor voltage of 410 mV to 580 mV. This range will produce the best carburetion setting for proper purifier operation and will result in the lowest Carbon Monoxide (CO), Hydrocarbons (HC) and Oxides of Nitrogen (NOX) pollutant levels. Alternately you can use and automotive exhaust analyzer (4 gas or 5 gas model) to measure the CO, HC, and NOX after the exhaust purifier. Adjust the engine carburetion (richer or leaner, usually slightly leaner than the stock jetting) to obtain the lowest CO, HC, and NOX emissions. Take extra care when adjusting the idle fuel air mixture or high-speed main jet size. Engine failure can result if the engine carburetion setting is adjusted to a lean setting. If a sudden miss-fire occurs the air fuel ratio is probably too lean or too rich. Use a cylinder head temperature gauge (for air cooled engines) to determine if the engine is running at the correct operating temperature. If the engine is running too hot a richer air fuel ratio will be required to keep the engine cool. In general (based on tests conducted on the 2002 model year Honda single and tin cylinder engines) we have found that reducing the carburetion main jet size by one or two jet sizes leaner produced the lowest CO, HC, and NOX emissions. Minor jetting changes (1 or 2 jet sizes) to leaner or possibly richer carburetion main jets will not affect engine performance and cooling. On propane fueled engines simply adjust the mixture screw to adjust the air fuel ratio. Remember to take extra care when adjusting the air fuel ratio so as to prevent the engine from overheating and misfiring.

    On newer EPA or California specification engines the engine carburetion may have adjusted to a leaner (or possibly) richer calibration at the factory. If this is the case carburetion re-jetting and adjustment may not be required. Alternately only minor jet leaning (typically only 1 jet size smaller) may be required. Test the Carbon Monoxide (CO) emissions to determine the stock CO emissions before the catalytic purifier is installed.

  4. When the carburetion is properly adjusted the model SXT catalytic purifier is ready for service. In order to ensure long purifier life, avoid using the choke when the engine is warmed up and operating under load. In addition we recommend that the use of any engine shutdown mechanisms (for example a water tank level kill switch on a concrete saw) be disconnected. If the engine ignition system is shutdown while the engine is under load, raw fuel will collect on the catalytic purifier core. The raw fuel will burn rapidly and will melt the catalytic core and automatically void the warranty. In addition keep the engine well tuned and equipped with new air cleaner elemental at all times.
  5. The purifier has very high surface temperature (1300 F degrees +) and may produce a red/orange glow or small flames from the outlet cone. Insulate the purifier with the supplied heat insulation warp after the purifier has been installed. Secure the heat insulation wrap after the purifier with hose clamps or wire. Cover the heat insulation wrap from oil or fuel contamination, if the purifier produces excessive flames from the tailpipe; double-check the engine carburetion to determine if the air fuel ratio is too rich. Leaning of the engine carburetion may be required. If the engine carburetion is correct, set the correct air/fuel ration, consider adding a section of tailpipe to the purifier outlet. This section of tailpipe should reduce the flames at the purifier outlet cone.
  6. During engine operation avoid all personal contact with the purifier and or purifier/muffler. After engine shutdown avoid all personal contact and do not allow the purifier to come in contact with any combustible objects. When re-fueling, adding lubrication oil, adding coolant, adding hydraulic oil or during any periodic maintenance, ensure that the engine is shutdown and that the surface temperatures of the purifier and/or purifier muffler have cooled to ambient temperatures. Avoid re-fueling and avoid any contact of any form when the catalytic purifier or purifier muffler is hot.


If you have any questions please call us toll free at 1 800 233 6539, or simply e-mail your inquiry to

Foley Environmental is different: we are a three-generation, ninety-seven year old family firm that wants to help.



in the U.S. 1.800.23.FOLEY

Dr. Diesel

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