In the top metering block, the idle jet is at the bottom of the main jet well (red arrow). We can help you choose the best carb that will work for your vehicle and how you plan on driving it. Engine size, cam, cylinder heads, ignition system, compression ratio, exhaust system, type of fuel, the vehicle and type of driving are all key elements in final calibration. main jet: 98 . This larger jet sizing may foul your spark plugs, but that's better than burning up your pistons. main jet: 96 . : Needle Taper Diameter Dimension Chart The taper of the needle determines the amount of fuel. By drilling out your stock main jet to larger sizes you will be able to narrow down what jet size your carburetor needs. Screw the new jet size into the jet mounts within the metering block, with a screwdriver or pair of pliers. Correct carburetor jetting is important for proper combustion. A Pilot jet is effective at idle speed up to 1/4 throttle(low-range). Check the diameter of the carburetor throttle roller. making a jet change. If you decide to test the engine by experimenting with different jet sizing, always start with a larger jet size than you deem necessary. Part way down page are needle specifications. Jets are threaded and have a small orifice through their center that varies based on the size of the jet. 01-26-2013, 09:38 PM #10. dirtdigger. Screw the new jet(s) into the jet mount(s) in the metering block and press the fuel bowl gasket and bowl to the metering block. IDLE SYSTEM FIGURE 2 (1) Main Jet and Metering Rod (2) Primary Well (3) Idle Jet (7) Transfer Slot (8) Idle Screw Port (4) 1st Idle Air Bleed (5) Idle Channel Restrictor (6) 2nd Idle Air-Bleed 2 SECTION 1: THEORY OF OPERATION Save the gasket that was pressed between fuel bowl and the carburetor's metering block (what the fuel bowl is bolted to). What size carburetor is correct for my engine? Carter YF & YFA carburetor jet sizes. In essence, when an engine's performance level is increased, more air is required to run the engine. Replace the Pilot Jet with one size larger. If either happens, make adjustments to the jet sizes again until the plugs do not appear excessively dry or filled with black carbon, indicating burning and fouling respectively. I decided to increase the size slightly and see if the scooter performance improved, so I replaced it with a "115" jet (1.15mm diameter). Carburetor Jet Size Calculator. Year 1995-2004 Engine 1200 – Jet Size 170 (California 185) Running the correct ratio of fuel and air makes your dirt bike run optimally. A Pilot jet is effective at idle speed up to 1/4 throttle(low-range). For example, a jet may be stamped (on its head) with the number 30. When the throttle is opened on a carburetor, the amount of fuel that flows into the main circuit is controlled by the carburetor’s jets. What jet size did you end up going with? As mentioned in step 1, you'll need to increase the jet size for lower altitudes, while a smaller jet size will be needed for higher altitudes. Kids' Footwear Size Chart. Thanks . The jet(s) are now exposed and can be identified by their center orifice, screwed into the metering block. Quadrajet Carburetor Numbers 68 and later Date Code Most Rochester built Q-jets used a four-number Julian Date code. Mk I Concentric . As a general rule, your engine tuner or engine manufacture should preset the taper. Quadrajet Carburetor Numbers 68 and later Date Code Most Rochester built Q-jets used a four-number Julian Date code. Open pipes? Doing this will allow you to access the jet needle. Installing jets of different sizes helps increase/decrease the fuel/air ration depending on what your bike requires. An electronic micrometer is a better measuring device, it can get that third digit. A leaner needle taper will use a richer main jet than a comparable engine/carburetor combo with a richer needle taper. Every engine responds differently, and final jetting changes are most often determined by the engine builder or tuner. FBO/Quick Fuel Carburetor Size and Series Chart. A needle jet is effective from 1/4 throttle to 3/4 throttle(mid-range). This is probably to avoid engraving “.5” on the jets If your plugs do foul, you'll simply need to reduce the jet size and continue testing until the correct jet sizing is reached. Keihin Jet Identification Chart. Faulty one will be about 3/16" dia. Search. In the lower plate, it is at the top of the down leg passage (yellow arrow) to the idle mixture adjustment screw. Call for current pricing on any Quick-Fuel product. As a very rough guide, for single carburetter installations on four cylinder engines it is normal to use a 1 1/4 in. Unscrew the jet(s) with a screwdriver or pair of pliers and note the size stamped on the jet's head. The brass main jets are easy to drill so you can get by with one of these inexpensive drill bit sets. Note that the thread and the external size of the jet depends of its location in the carburetor. The jet needle controls the fuel mixture in the mid range throttle position which is approximately 1/4 to 3/4 throttle opening. Please confirm if the jet kit I currently have (referenced above) is the correct kit for the Cobra pipes. Spares by Carb Type. 12/1/00 Courtney Hook For those of you who don't know it, you can drill your jets out for larger sizes instead of spending big bucks to acquire a vast selection. This Jetting Chart provides a base line starting point. Replace the jets with a larger jet sizing by two to three sizes. these are just a guide. Order by selecting the jet size from the drop down list. Carburetor Jet Tips. 37-119: 37-933 6-506: 122-62 N/S: 125-85 0.025: Plain 108-83-2: 108-89-2 108-90-2: 108-27-2 N/A: 134-105 1-3/16: 1-1/4 1-1/2 a Calibration Reference Chart for your model of carburetor has been included. Select your AMAL Carb Type below. Enter Engine Displacement Size CI / CC Enter Maximum Safe Engine RPM Enter Volumetric Efficiency Of Engine % VE Calculated Results Required Carburetor Size In CFM CFM Required Stock heads average 80- 85%: 100% VE CFM Required: User % VE CFM Required (Rounded) 100% VE … Install a smaller jet size if the ambient temperature dips below 35-degrees Fahrenheit. 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