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UTV Massimoto 500


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  • 2 weeks later...

T/S to the basics required for motor to run




SPARK PLUG------pull spark plug.....check plug condition at electrode.....looking for WET, SOOTY BLACK---all bad.  Want a dark TAN electrode insulator color.  A FOULED plug or internal damage will not let the spark jump the electrode gap....NO RUN.

SPARK TEST.....plug out......You want a NEW plug if any question of condition.....this will create an ignition source (spark) for any fuel spills, loaded cylinder what blows a spray of raw gas---very exciting, etc.  Pull the ignition coil low side primary connector.  Spin over engine and check for blowing fuel.  If mess, blow off fuel with air hose and blow into the spark plug hole also.  Vent out fumes from shop.

Actual spark test-----reconnect the ignition coil connector.  Put known good spark plug in cap and place plug on metal frame or engine case.  Spin over the motor....2 things  happen......hiss of air thru spark plug hole AND the snap of the spark arc.  Now put finger over the spark plug hole like using a thumb on a garden hose.  on the COMPRESSION stroke, the escaping air will "blow off" your finger if engine mechanicals solid.  Should have a nice POP.  The spark should fire at this time......about 8-12 Deg. BEFORE the piston hits TDC on Compression stroke.  If you have the above conditions go to next test.

COMPRESSION-----finger pop test is a quick and dirty check.  It takes air to make air....open the throttle to allow air into the intake unrestricted.  Use of a compression tester is needed to get a hard number like 120 PSI or better.  Not a testers are created equal......use one that has the valve core in the spark plug hole screw in end.  use of a hose extension will lower the compression value indicated.  Also engines with auto compression releases will be lower also.  use manual spec'd value in these cases.

Other causes for low compression....valve adjustment clearance too tight.  Carbon under valve face/seat.  Burnt exhaust valve.  "birds beak" plasma gas jet erosion of valve face.  Worn out cyl/rings.  Cam chain jumped timing or broke (mechanical problems)


FUEL/AIR MIX---------For the problem of run/no run depending throttle setting:

CARB....shut off fuel to carb......drain bowl......you will manually supply the fuel later

THROTTLE BODY......you are FI so disconnect the fuel pump connecter UNDER the Pass side seat.  Lift out the seat.....fuel tank is right there.....remove clip and then part the connector halves....result on new fuel introduced for testing.

FUEL TEST--------everything from above reinstalled, spin over engine...should NOT run but might if raw gas is in air box.  here is where you supply the fuel to the air intake....starter fluid short bursts.....if engine fires and runs then dies after a few seconds after the fluid runs out, give another burst.....runs....dies...do again but then try to time the bursts to keep running for at least 10 seconds.

If it works with the starter fluid boost.....you have a fuel problem.

The problem could be any of the following:

Fuel delivery supplier mixed DIESEL and GASOLINE in tank

Corn gas has too much water added and syrup won't burn----phase separation

Water in fuel tank....rain or flood water or pressure wash tank vent.

Low fuel pump pressure-----40 to 45 PSI normal for these FI systems

Fuel filter got water in it or sediment clogged


ANY CONDITION FOR FUEL CONTAMINATION......start with draining the fuel tank....have to go thru the fuel pump lid and lock ring which may be too much or more than you want to tackle.  Basically the tank drained, fuel pump drained, lines drained between fuel pump and injector.  REFILL with new gas NON-CORN (recreational gas) is best to run anyways for these machines.  Cycle  pump  to fill lines all the way to the injector body....pull injector and crank engine (KILL SPARK) and look as spray mist as injector fills and then fires....bad spray sometimes means a new injector after everything else is cleaned up.

Try above----post back findings


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