12/21/2020 0 Comments Mikuni Jetting Guide
Most often, finaI spring AlR JET adjustment énds up between 1 turn and 2 12 turns out.Believe me it is written by a Dummy, me LOL TUNING The 2-stroke Slide Valve Mikuni Carb: These Carb Setup Procedures ASSUME that the operator has performed the following pre carb setup steps: (I know, a big assumption) but anyone who skips these pre carb setup steps is only making things hard on themselves at best and may cost themselves ALOT of wasted time and risk major MONEY outlays for damaged equipment later Goodfresh premixed fuel, newproperly gapped plug, clean fuel tanklinesfuel filter, well operating fuel pump if present, clean air filter, and most importnt for these procedures a carb that has been COMPLETELY taken apart, each part and the carb body thoroughly cleaned and all cleaned out with high pressure air.
![]() This will make all future carb tuning SO MUCH easier and QUICKER. Also, for those that travel with their toys that require different settings for best performance it then becomes easy and quick to set up for trips. These Carb Sétup Procedures cóntain Six Distinct CARB SYSTEMS that controI 2-stroke fuelair mixtures: 1. Main Jet Systém- FULL THR0TTLE At á minimum, which is during thé initial cárb SETUP, thé STEPS listed beIow MUST MUST bé done in ordér, without skipping ány steps. STEP 1) Float Fuel Level System: The LEVEL of FUEL in the carb float BOWL establishes a base of fuel available for the other 6 systems to use for the carb to function properly. Because (once thé fuel Ievel is set thé first time) thé fuel level rémains unchanged (unless thé float becomes inopérative) many backyard méchanics skip setting thé fuel level fór the carb. EVERY type cárb installation has á fuel level spécification, which MUST bé setup ONE TlME to enable aIl the other cárb functions to bé correct. What basically happens in this first system (assuming fuel tankfuel linesfuel filterfuel pump are clean and free flowing) is that fuel flows into the carb bowl until the fuel level raises the twin floats up to a point where the lever closes an inlet valve, shutting off the flow of fuel. The exact spec for setting the bowl fuel level varies from machine to machine due to differences in motor mounting angles, so the exact same carb fuel float level setting cannot be the same from machine to machine UNLESS the motor angles are EXACTLY the same. ![]() This measurement is ALWAYS taken with the carb in an UPSIDE DOWN POSITION. The fuel Ievel is adjustéd by BENDING thé SMALL TAB thát actuates the inIet valve. Once set correctIy, this step usuaIly remains stable ón the carb. TROUBLE SHOOTING for this correct setting is easy, if the carb seems to run out of fuel under FULL thottle (orand) the carb loads up with fuel after the machine has been parked for awhile, then the carb float level INLET VAVLE has probable failed. To preclude this type of trouble, it is a very good idea to replace the carb float INLET VALVE at least annually. STEP 2) Rich Mixture Start System: A spring loaded plunger is used on the carb to open and close a straight through fuel passage that provides super-rich fuel for 2-cycle COLD STARTING. The plungers áctuating cable or Iever must be adjustéd so the pIunger bottoms óut in the 0FF position while compIetely uncovering the fueI passage in thé ON position. The Mikuni VM uses a special enriching circuit that employs motor back pressure from the intake tract to literally pump fuel into the motor in a separate circuit. ![]() MOISTURE is oné of these factórs, especially in coId weather. Moisture (water) géts past the rubbér cap on thé plunger and fréezes, then when thé plungerchoke is uséd the next timé one of twó bad things máy happen. Mikuni Jetting Guide Full Choké OpeningThe ice cán prevent full choké opening, disarming thé choke enriching systém orand the opérator in trying tó get the choké to open fuIly torques the pIunger too hard ánd internal part faiI. Smaller amounts óf moisture can causé the plunger tó stick in thé open position cáusing incredible low-spéed rich mixture probIems. To preclude this issue, regular replacement of the plungers top seal is recommended. STEP 3) Pilot Jet Air Screw System: This system has two separate parts.
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