Initial Start Procedure
To prime the engine, push the primer bulb on the carb until fuel shows in the return tube (yellow) - this ensures fuel is reaching the carb. Turn choke lever to vertical closed position (aka ‘choke on’). Pull starter cord until the engine tries to start – there will be a distinctive pop sound. Then stop. Open the choke (ie. turn choke off / aka ‘no choke’) – turn lever back to horizontal position. Pull starter cord – engine should start within the next few pulls. Do not turn the ‘choke on’ again and continue to pull – otherwise you may risk flooding the engine.
The above procedure is for a cold engine. Once the engine is warm (or in warm weather) – the choke should be left in the horizontal position (choke off), otherwise there may be a danger of flooding the engine.
Engine flooded
A common problem and easily done. These motors run on air/fuel vapour and any pooled fuel in the cylinder, as a result of; over pulling, excessive throttle use during start up procedure, choke left on during starting etc, will inevitably result in a flooded motor. The more the cord is pulled without it firing, the more fuel is being loaded into the lower end.
Remove spark plug – check if tip is wet. Plug may be fouled in which case it will need replacing.
De-flooding- With the spark plug removed, open throttle to max (WOT), no choke, pull starter cord 10-20 times to clear out any fuel that has accumulated in the engine (do this with care to avoid splashes to face etc – and of course avoid smoking / naked flames during the process). Turning the Baja upside down (with assistance if necessary) will aid in removing any fuel in the crankcase.
Also make sure any fuel that may have entered the pipe is drained out. Move the piston TDC, and tilt the Baja backward (wheelie style) to allow any fuel to drain out of the engine, through the exhaust port and out of the end of the pipe.
Leave the plug hole open to allow surplus fuel to evaporate from the cylinder. Leave for at least hour or longer dependant on temp (preferably overnight). Install a NEW plug and repeat start up procedure. Prime the carb. Remember to turn off the choke after the ‘pop’ otherwise you will just flood the engine again. Do not pump on throttle on tx. The car should start after a few pulls.
Holding the throttle at WOT during pull-starting may also bring the engine back to life, after all surplus fuel has been emptied / allowed to evaporate.
Turn the H and L needles clockwise to fully close. Then pull start until you hear the engine momentarily start (pop). Then set the needles back to stock settings and pull start again. Following the choke procedure (initial start notes above) may also assist, but use it with caution to avoid re-flooding the egnine again - Listen carefully for that 'pop', un-choke and pull start again.
A badly flooded engine can be a real pain to start – be persistent with the de-flooding procedure.
Loose bolts
Check that all bolts are tight, eg air filter/carb/manifold – exhaust. Loose bolts can easily result in too much air entering the fuel/air mix resulting in a lean seize (see below).
Checks should also include cylinder bolts and spark plug, ignition coil bolts (behind fan cover)
Air filter – Dirty or Wet?
Ensure air filter is regularly maintained. Clean and oil correctly and at intervals according to your terrain and frequency of use.
If you have hosed down your Baja make sure no water is clogging the filter and choking your engine of air. Always protect the air filter & carb with a suitable covering and remove radio box / electronics prior to a hose down.
Allow all parts to thoroughly dry, particularly areas such at the coil, flywheel which may have become wet. Also check the exhaust pipe for water.
Ensure the filter is not over oiled choking the engine.
Ignition Coil Gap / Flywheel
Check gap – should ideally be around 0.3mm /business card thickness.
After a hard roll, or knock the coil may have slipped resulting in a poor spark.
Loosen the two screws that hold the coil in place, slide a business card between the coil and the flywheel, carefully adjust the coil so it ‘just’ grips the card, then tighten the screws and remove the card.
Also ensure that the Woodruff Key (HPI#15431) is correctly seated in the crank shaft slot – it may even be missing after a rebuild and will affect timing.
Check coil is in working order and the plug wire is intact and connected properly (particularly if changed for an aftermarket one). If possible borrow another coil to eliminate this as a possible cause.
Gas Cap – blockage
Slowly open the gas cap, a hiss may be heard as the fuel vapour escapes. Leave the gas cap loose and try to start the engine.
If its starts - Check vent hole is not blocked.
An open vent hole is required to allow the pressure inside and outside of the tank to remain fairly equal.
A blocked hole will cause a pressure differential to form, and may lead to an undesireable rich or lean condition.
A postive pressure inside the tank would increase the fuel supply (by forcing more fuel through the lines), resulting in a rich condition, leading to potential bogging.
A negative pressure would result in less fuel supply reaching the engine, resulting in a lean condition - higher RPMs.
Clean out hole as necessary with a pin. Ensure all gas cap rubber internals are correctly seated.
Solution Option
Consideration may be given to eliminate the gas cap vent by installing an aftermarket kit such as the SnappyRc 'Ultimate Fuel Tank Kit'. Since the kit allows the tank to breathe through a check valve fitted to a third 'air' fuel line which exits adjacent to the exitsing fuel lines, the hole in the gas cap to be made redundant and suitably plugged. This of course also eliminates the potential for gas cap leaks.
Spark Plug Fouled / Check Spark
Replace plug with a NEW one. Can easily occur when fuel mix is too rich. New plugs can occasionally be bad out of the box – try another new one if in doubt and as a double check.
A spark plug check can be carried out in the following manner; remove plug from engine, reconnect the spark plug into the plug boot, touch the plug thread to the engine block or exhaust header, pull-start and check if plug is firing. NB. Even though a spark may be visible, it may not be strong enough to spark under compression.
Following a roof landing, check that the spark plug is not cracked/damaged. Aftermarket spark plug covers are recommended to give some measure of protection from such occurrences.
No fuel to engine
Check gas tank has fuel. Fill up as necessary.
Prime carb bulb by pressing (pumping) it a few times till you can see fuel in the return fuel line.
Check fuel lines for awkward bends/kinks blocking free low of fuel.
Ensure the fuel lines have been connected to the carb correctly. Black is the supply tube to be connected to the lower carb nozzle. The return tube connects to the top nozzle.
Check that the ‘clunk’ fuel filter is not clogged.
Carb issues
Check and maintain carb regularly. Disassemble, check for blockages, clean micro screen filter as necessary.
Replace carb – many issues that cannot be traced can be simply solved by replacing the carb.
It is recommended to keep a spare carb in your toolbox. Also check the stock carb intake manifold for cracks.
Carb Needle Settings
Return High (H) speed & Low (L) speed needles to factory settings. Close both needles (turn fully clockwise). Then slowly open (turn anti-clockwise) each needle as follows; H – 1.5 turns, L-1.25 turns.
Turning needles clockwise (close) will reduce the fuel, ie leaner. Turing them anti-clockwise (open) will increase the fuel, ie making the mix richer.
(Refer to the Tuning Guide)
Idle Screw
The idle screw, located below the H & L needles may require adjusting. Turn it clockwise to increase the rpm & vice versa. Set it to increase the rpms and repeat the basic start procedure.
Leaks / Gaskets
Is there poor compression? Are the rpms excessively high even after adjusting needles? Check for tears, leaks in gaskets. A gasket leak can result in a loss of compression and/or improperly mixed fuel and air (which may contribute to a lean seize – see below). More air (and less fuel) will lead to increased RPMs.
If the engine can be started, if only for a short while, spray carb cleaner or WD40 (preferably using a fine tube attachment for targeted use) around the gasket areas where a leak might be suspected, eg intake manifold. A sharp increase in idle speed may indicate a leak. Replace gaskets as necessary
Also inspect fuel lines for splits/leaks. Check the carb intake manifold - the stock mainfold material can develop cracks causing a leak
I found this here:
Link
