6) Snap the throttle a couple of times to make sure the slides are setting in well, and tighten the cable lock nut and recheck.

7) Move your thumb to the center slide and your middle finger to the left carb.  Adjust the LEFT carb till it lifts exactly with the center.

8) Snap the throttle again and make sure the lock nut is tight (tightening the lock nut will change the slide height).

9) Open throttle until slide is even with top of carb throat.  Feel that all slides are at the same position.

10) Take out any extra slack in the cable, AND check the oil pump for correct setting.

The finger method can tell movement in thousands of an inch (just say very accurate).  Set the sync from idle, because that is where it is most important.

Sync Method 2:  

1) Find a smooth round pin about 3/8" or 10mm dia. (I use the shank of drill bit)

2) Remove air box/filters.

3) Back out slide stop (idle adj) screws.

4) Set throttle lock or set throttle adjuster at the grip so the pin will just lightly drag as it is inserted in the carb throat under the slide cutaway of one carb.

5) Set the other carbs so they offer the same resistance when the pin is inserted by setting the cable adjuster at top of each carb.

6) Release throttle lock or reset throttle adjuster at grip insuring that slides on all carbs will fully bottom out and throttle grip has 2-3mm play.

7) Set air & idle adj screws per topics following for best idle.

As a final check to insure all idle adj screws are set the same, insert a nail, spoon, or long toothpick under each slide without altering slide position.  As the grip is turned the ends of all three should tip at the same time.  Readjust idle screws as required.

Carb sync video by Darth
 

Meters

A manometer or Uni-Syn can also be used and may obtain better results IF used properly.

When using a meter for carb sync the sequence of procedures must be altered to achieve desired results.

- Air screw adjustment for highest reading with meter must be done first.

- Slide sync adjustment may then be done with slides positioned off idle screws.

- Idle screw adjustment may then be done.

Index

Tuning

Tuning Prerequisites

- Timing can affect performance.  Know where your timing is set before making carb adjustments.  A couple of degrees can make a big difference in acceleration characteristics.  Properly setting timing may cure ills without getting into carbs.  

- Gearing can also be a significant factor. Too tall gearing can cause bogging on takeoff when tuning is spot on.

- Exhaust pipes/baffles MUST be clean.  Clogged pipes can kill top end.

- Excess carbon on pistons can cloud tuning issues.

- Air leaks and/or bad crank seals can affect tuning.  A leakdown test is strongly recommended.
    http://kawtriple.com/mraxl/cranksealtest/cranksealtest.htm

- Float Height must be properly set.

- Enrichment (choke) cables must be set with approx 1/8" free play at carb.

- Low compression can't be compensated for with tuning.  Compression specs vary between models but anything less than 140 psi requires attention.

- Change in fuel grades or blends can make tuning requirements change.  It is best to use premium fuel.

- If premix is used, it can alter tuning characteristics, as can ratio changes.

- Before making any adjustments be sure the carbs and jets are clean.  That means ALL jets... pilot, needle jet, and main, are removed and inspected/cleaned.  Carb body passageways should be blown out with brake cleaner or soaked in carb cleaner for several hours and blown out with compressed air.  There is a very small air passage in the bell of the carb that clogs very easily and is a major cause of jetting problems. Disassembly video Part 1  Disassembly video Part 2

- Sparkplugs should be NGK B9HS (or B8HS) or equivalent, properly gapped.  Extended reach plugs are an absolute no, no, and resistor plugs are discouraged as being problematic, as are resistor caps and wires.

- Unless ALL these prerequisites are met, tuning can prove to be fruitless and frustrating.

- Mikuni VM carbs are designed with three main circuits..... idle, mid-range, full open. Tuning and diagnostics of these circuits is based on throttle position, not RPM.  It is a good idea to mark the throttle with tape at various positions when diagnosing problem areas to make it easier to know which circuit requires attention.

- Adjustments should be made with air filters intact as you intent to run.  Changes to pipes or air intake may require rejetting. Be aware that pod filters with metal backing can reduce performance and made tuning more difficult.

Index

Adjustment Screw Location

 
(Note: VM24 used on S1 & KH250 models are as shown in H1-VM28)

Index

Enrichment (Choke)

Check the choke cable slack by tugging on the cable sheath at the choke lever. There must be 1/16" to 1/8" slack in the cable with the lever released. If there is no slack in the cable, the enrichment plunger may be held off its seat, causing rich fuel mixtures and increased exhaust emissions, especially at low throttle openings. If the cable slack is excessive, the cold-start system will not work properly, causing difficult starting with a cold engine.

To adjust the choke cables, loosen the adjuster locknut at the handlebar lever, and then shorten the adjuster till the cable sheath has at least 1/4" free play. Pull up the rubber boots from the carburetors and loosen the adjuster locknuts. Turn out the cable adjuster if cable slack is excessive; turn it in if there is no slack. Tighten the locknuts and replace the rubber boots. Now lengthen the adjuster at the handlebar lever until the cable sheath has 1/16" to 1/8" free play. Tighten the locknut.
 

Tuning Sequence

Because of the overlapping of carb circuits it is highly recommended to perform tuning in the sequence shown here... LoSpeed, MidRange, then HiSpeed.

Low Speed

Adjust air screws (one carb at a time) for highest idle RPM with a warm engine.  It will require that idle screw is turned to increase RPM for the cylinder to be adjusted.  Air screw adjustment should be made at >2000 rpm.  Adjustment should be made in slow, small increments.  If air screw is out more than 1 3/4 turns for highest RPM, a smaller pilot jet should be fitted.  If air screw is out less than 1 1/4 turns, a larger pilot jet should be fitted.  Return idle to normal and repeat for next cylinder.  Idle RPM should be 1250-1400 RPM. 

The airscrew is a fine-tuning adjustment designed to allow the carburetor to be slightly adjusted for variances in atmospheric conditions. The air screw works with the pilot jet, mainly affecting the engines initial starting, idling and initial power delivery. Proper adjustment of the airscrew can offer direct feed back on pilot jet sizing.  When adjusting the air screw, tightening the screw is richer and loosening it is leaner.

If you get no RPM fluctuation when adjusting the air screw there is a good chance that there is something clogging the pilot system or the wrong size pilot jet is installed. In most cases, the pilot jet should be the same as original stock, ref: http://kawtriple.com/mraxl/carbspec.html  Clean the system thoroughly with carb cleaner and blow out with compressed air.

A lean setting will cause your engine to surge at very low RPM’s, bog or cut-out when the throttle is opened quickly and have trouble idling down.

A rich pilot setting will result in hard starting, plug fouling at low RPM’s, sputtering as the throttle is cracked opened.

    - Note: Kaw specs for air screw setting is just a starting point.  Adjustment is required for best performance.
Each carb must be ADJUSTED for optimum idle. That is done via AIR SCREW adjustment.... seeking the point where idle rpm for that cyl is highest. That is the point where the fuel/air mixture is optimum at idle rpm. Starting from scratch, unless you're extremely lucky, there is no "balance" between cyls or carbs.... one cyl will be pulling the other two. When this condition exists ONLY the carb on the pulling cyl will respond to adjustment. Setting the idle stop to insure that the "pulling" cyl carb is in control of idle rpm will then allow adjustment of that carb to be seen in rpm changes. An alternative is to pull the plugs of the cyls not being adjusted so it would be apparent which cyl is "pulling". If, using this method, an air screw has no effect on idle speed, something is wrong. On a new stock bike setting air screws X number of turns is "close". Changes in altitude, humidity, pipes, or filters and all bets are off.

    - Note: Once each carb is adjusted they then need to be SYNCed to deliver power equally at the same time. This is done in two steps... slide position and idle stop screw setting.

SLIDE POSITION must be adjusted so at any given throttle position the slide opening is the same on all carbs. It is accomplished with the cable adjusters on the carbs and should never change once set. It is a static adjustment.

The other SYNC adjustment is BALANCING the carbs at idle so each cyl has equal "pull". That is done by setting the IDLE STOP screws so that any clockwise rotation of any stop screw increases rpm.

Use of a mercury indicator is another way to setup carbs, but the same principles are applicable.
 

- The aforementioned settings will primarily affect idle and performance thru 1/4 throttle position.

Index

Idle

Idle screw balance should be set so that any clockwise movement of the idle screw from any carb increases RPM.

- Back out all except one idle screw.

- Set desired idle RPM with this screw.

- Screw in each of the remaining idle screws until rpm just starts to increase.

Index

Mid-Range

Adjust the needle clip position to affect performance in the 1/4 to 3/4 throttle position.  Raising the clip will lean out the mixture.  Lowering the clip will richen the mixture.

When the clip setting is lean the bike will be very zingy sounding . Lean in the midrange will rob  power and cause the machine to run hot and seize easily or even hole a piston.

When the clip setting is rich the bike will have a lazy feeling in the midrange. Exhaust note will be a little flat sounding. In more extreme cases of richness the engine will sputter or kind of crap out in the midrange.

Clip position is called out from the top groove down.  Clip in the topmost groove is in position #1, the leanest setting.  You raise the needle by lowering the clip.

The safest way to set the clip position is to richen up the clip position setting until the machine loses a little power (feels lazy/unresponsive) then lean it back one position. Ideally you like to run the needle setting in either the 3rd or 4th clip position, if possible. The needle clip jetting is especially critical to your bike's reliability because on average more time is spent in the midrange than any other part of the throttle. Most triples pull very hard in the midrange, putting quite a load on the engine. This makes a lean condition very detrimental to your reliability.
Difference in clip position will be most noticeable at 1/2 throttle.

Index

Hi-Speed

Main jet size affects 3/4 to full throttle performance.  Plug chops can help determine correct jetting.

The main jet does not effect the jetting for starting and idling. It plays no part on low RPM or mid RPM jetting either. The main jet is very important to your bike's overall tuning, but should never be over emphasized at the expense of needle tuning or other facets of your carburetion tuning.

When the main jet is lean the engine will experience detonation or "pinging". Exhaust note will be of a higher, tinier type note. Engine will over heat easy and can be down on horsepower. A moderately lean main jet can cause engine seizures. A severely lean main jet can cause the engine to burn a piston (hole in top).

When the main jet is rich the engine will be a bit flat or lazy at ¾ to full throttle, giving off a flat, dead sounding exhaust note. When the main jet is severely rich the engine will sputter in the high RPM’s and have a lot of trouble making power up top.

The safest way to get the main jet setting as near correct as possible is to richen the main jet setting up until the engine begins to lose power and sputters at WOT. Then reduce jet size in increments of two sizes until sputtering disappears and WOT is clean and crisp.  Then go back up one size.

Alternatively, Ivan's Performance Products provide custom jet kits that perform well and eliminate surging. These kits are also a good alternative to the unobtainable needles and needle jets for stock carbs.

Index

Surging

Surging is a common problem with H2's.  Surging is a symptom of a lean condition.  Lots of folks try to cure it with oversized pilot jets but the best fix is to use 2.0 cutaway slides and careful slide sync.

Slide cutaway- changing slides one size can lean/richen mixtures at 1/8 - 1/2 throttle settings.  The smaller the number, the richer the mixture, i.e. 2.0 is richer than 2.5.  Slides can be built up to reduce cutaway with JB Weld to richen mixture or by removing 0.020" from the bottom of the slide.

Index

Plug Chops

Plug Chops are a good way to test the jetting accuracy of your carb setup.  Simply pulling a plug and looking at the color after running through a variety of throttle positions can be misleading and possibly lead to disaster if jetting is too lean.

The procedure outlined below is intended to test main jet sizing at WOT.  It is strongly suggested to begin with overly rich jetting and work your way down in two size increments to avoid seizure.  The same procedure can be used at marked mid throttle position to test needle jet position.  The distance covered should be at least 1/2 mi, the farther, the better.  It may be best to perform the test in a lower gear to avoid excessive speed.  Throttle position is the critical item.  Variation of throttle position should be avoided and can taint results.

It is possible to examine plugs by using a good light and magnifying glass rather than cutting the threads away.  A single cylinder can be used to hone in on the right jetting to save the expense of new plug consumption, assuming all carbs are jetted and setup the same.

Be aware that changes in fuel type/grade and timing can change results.
 

1. Get new spark plug(s), but don't put them in yet.
2. Warm up motor to operating temp on old plugs.
3. Install new plugs.
4. Accelerate through all gears to top gear with throttle pinned.
5. When you hit the top of the top gear, hit the kill switch and
pull in the clutch.
6. Remove the spark plug(s) and ride home on the old plug(s).
7. Hold the new plug in a vise and use a hacksaw to cut the threads
away from the center electrode.
8. You should see a brown 2mm "smoke ring" at the base of the
white center electrode if the main jets are dialed in perfect.
9. if the smoke ring is darker than chocolate brown or taller
than 2mm, you're rich on the mains, but if it revs clean to full
throttle, you can leave it there and be on the rich side.
10. If the smoke ring is smaller than 2mm or lighter than chocolate
brown, you're lean on the mains, go up a size and try again.
 

Chopped plug Illustration:

Below is a series of plug chops ranging from extremely rich to slightly lean.

Index

Leaking Carbs

Fuel dripping or leaking from bottom of carbs (overflow) can be caused from only a few things:

- Defective/contaminated float valve

- Improper float height setting

- Leaking float

- Defective/improper seating of brass overflow tube in bowl

- Split/cracked overflow tube

- Float binding on side of float bowl

Defective gaskets are NOT the cause of leaking carbs, nor is a leaking petcock.  When the bike is upright fuel level should be below the gasket.

Leaking at side of carb (as when on sidestand) can be defective gasket and/or warped float bowl.

Index

Tuning Notes

- Needles can have washers added beneath the clip to raise the needle less than one full clip length.  Sudco carries special washers for this purpose.

- Sparkplug gap can be varied to optimize power output.

- Air intake to carb body can influence tuning.  Short air filters with blocked ends may cause tuning problems.  Foam UNI Filters have been known to cure some flat spot tuning ills.  Stock inlet tubes smooth air flow and are sometimes better than aftermarket pods.

- UFO's have reportedly improved tuning performance.  It will drastically affect pilot jet size.

- Polishing intake ports is NOT a good thing to do.

- Machining intake adapter ID to match cylinder intake port IS a good thing to do.

- Giving a little "choke" at various throttle positions can help determine if you need to be richer at that throttle position.

- Altitude, humidity, type fuel, premix, filters and pipes can alter jetting requirements. 

- Note that use of "kits" will many times cause problems.  Usually, gaskets and float valves are the only parts worthwhile in the "kits".  Jets may or may not be what you need and needle taper is not stock.  Retain stock needles as they are not readily available from any source.

- The float controls fuel level in the float bowl at the bottom of the carburetor. It has no effect on jetting but can cause some symptoms that can be easily confused with a jetting problem. If the fuel level is too low for example, it can cause a bog similar to a lean condition.

- Make sure engine has passed a pressure test. It can be virtually impossible to tune an engine with an air leak. It is imperative that you establish a solid baseline with proper assembly and an air leak free engine. *Note: On a 2-Stroke engine there is absolutely no way to be sure your engine DOES NOT have an air leak without properly performing a pressure test.

- Establish that the engines compression is not weakened. Any loss of compression for whatever reason will give off signs that engines jetting is rich.  Any loss of compression on a 2-stroke engine should be followed by a top end disassembly and inspection of piston, rings, cylinder liner etc.

- Compression Test How To: Always use a quality name brand gauge (SNAP-ON Best Choice). Note length of threaded probe in relation to spark plug length. Perform test with engine cold, throttle wide open. Kick machine over until needle quits moving (10-15 kicks normal). Perform 3 separate tests, record results.  It is always a wise idea to perform a compression test on a fresh engine right after break-in to use for future reference.

- Spark Plug: To properly tune a 2 Stroke engine it is imperative to have a good quality spark plug that is functioning properly. This means that the plug cannot be too old or partially fouled. Spark plug gap is essential; an improperly gapped plug (or partially fouled one) can cause the engine to run poorly, sometimes appearing to be a jetting problem when in reality the problem originates at the spark plug. Also make sure you are using the correct heat range. Use of resistor plugs is discouraged!

- Weak Spark: Weak spark is not only detrimental to your engines performance but can make tuning your engine a nightmare. Weak spark will make the engine run rich. When an engine is running rich due to weak or poor spark the machines performance will slowly continue to deteriorate. Some common causes of weak or poor spark can be a failing or faulty coil winding, faulty plug cap or plug wire, failing coil, improper ground etc.

- Plug Color: Ideal plug color is a chocolate brown. A rich plug will be a darkish brown or black. May be oily and sooty. A lean plug can be a light brown, or gray (some severe cases can be white). Plug color must be checked after a plug check has been run. To perform plug check run engine at specific RPM that reading is desired for at least 5 seconds, then turn off engine without letting RPM’s fall. This test is very difficult to perform at any RPM other than wide-open throttle.

It can take years to learn how to accurately and precisely read spark plugs. For amateurs, plug color should not be the only piece of evidence used to adjust jetting. Plug reading should be evaluated with other jetting evidence to achieve a proper conclusion on tuning.

- Fuel: The fuel used in your triple is very influential in tuning your engine. Premium grade fuel is recommended.  Various grades, brands, and ethanol levels can cause inconsistent jetting feedback and make your engine run hotter than normal.

- Baffles: 2 Stroke baffles must be functioning properly. A clogged, poorly maintained, baffle can cause the engine to run funny making tuning difficult. An excessively packed baffle can also cause a tuning difficulty, making the engine lose power and run rich.

- Exhaust Pipe: Check your pipe for severe dents in head pipe section or end cone area, dents in these areas may affect tuning. Also check for carbon build up inside pipe. Any carbon build up at all is not desirable. Heavy build up will hamper engine tuning and rob power. Pipes with these problems should be replaced.  Pipes must be used that are designed for the engine.  Just because they fit does not mean they are "tuned" for your displacement, etc.

- Air Filter: It is highly recommended to do your initial engine tuning/jetting with a new air filter. A used filter will never quite work as perfect as new one. Old, dirty, improperly serviced filters will severely hamper proper engine performance and tuning. Some aftermarket clamp-on filters can make tuning difficult.  When performance is critical use a new filter.

- One Change at a time: When tuning a carburetor, only make one adjustment at a time. This is a good rule to follow so the tuner will not get confused or mislead from false information. Keeping to one adjustment at a time will help ensure that you will always know what effect each adjustment had on the engine.

- Unresponsive?: If during the jetting/tuning process you have made a number of adjustments (especially main jet or needle clip) to the carburetor and the engine has not changed. There is a strong possibility that something other than carburetion jetting is causing your engine to perform incorrectly. Jetting is a constant. When adjustments are made to a machine with all components working properly the engine will respond in some way. Depending on the adjustment made the bike will either run better or worse, but there is almost always some form of change. When changes are made without any response it is a sign of other problems. Things to check out would include; low compression, weak spark, fouled plug, failing reeds, air leak, clogged air filter, clogged or over packed baffle, etc.

- Proper Slide Throw: It is always a good idea to confirm that the carburetor slide opens and closes all the way. This should be done with carburetor hooked up but not attached, as to physically see slide travel thru its complete stroke.
 
- Flat spots often result from the type air filter used.  Many times, a chamber or channel type intake (similar to stock boots) can resolve these problems.  Stock intakes can work quite well if not restricted.

Index

Carburetor Specs

Note: Carburetor I.D. marks are on the front (Facing engine) of the channel for the choke mechanism.  

Index

Needle Information