Help with engine problems – When the motorcycle does not run properly

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Help with engine problems - When the motorcycle does not run properly



Help with engine problems – When the motorcycle does not run properly

Error analysis in case of engine problems
50 reasons your motorcycle won’t run right

Blue smoke from the exhaust, misfires, uneven idle. Now just keep calm and go analytically to look for errors. In this workshop sequence you will find 50 tips on how you can crank up again powerfully.

Jorg Lohse


If the engine is cranked by the electric or kick starter but does not want to start

  • Old or contaminated petrol in the tank: before the next attempt to start the tank, empty the float chambers, check for dirt and run in fresh fuel.
  • Vacuum fuel valve does not open: Pull off the hose from the fuel valve, try to start. If there is no fuel, the vacuum membrane in the fuel tap or the vacuum supply line is probably defective. Try opening the lever on the fuel tap “Pri” put.
  • Filter in the fuel tap or hose blocked: Pull off the hose directly from the fuel tap and check whether petrol is running when it is opened. If so, the retrofit fuel filter is clogged and needs to be replaced. If not, the fault is probably in the fuel tap: remove and clean.
  • Engine flooded: remove spark plugs and dry them, close fuel tap, lights off. Crank the engine at full throttle a few times (electric starter) or kick it (kick starter with the ignition off).
  • Air filter tight: clean or replace.
  • No spark on the spark plugs: install new spark plugs, check spark plug connectors, ignition cables and ignition coils.
  • Ignition / engine electronics defective: check whether the battery is correctly connected and charged. Try installing a fully charged battery. Check the ignition system for dry connections, faultless cabling and a secure ground connection.
  • Compression too low: Either only the spark plugs are loose, or the piston rings are worn, valve seats are blown through, cylinder head gasket is defective. Then the cylinder head, piston and cylinder have to be overhauled.
  • No petrol in the tank: off to the next petrol pump.
  • Fuel tap closed: open or open “reserve” put.

Help with engine problems - When the motorcycle does not run properly


Note the position of the motor kill switch – this must not be on “Off” to stand.

If the electric starter does not spin

  • Motor kill switch is on “Off”.
  • Voltage too low: charge or replace battery.
  • Bad contact in the ignition lock or starter button: Open the switch and clean the contacts by sanding them.
  • Main fuse or starter relay defective: check and replace defective parts.
  • Defect in the starter z. B. by burned stator or armature winding or worn starter brushes. Remove the starter and have it checked and repaired if necessary at a specialist workshop or Bosch service.

When the electric starter cranks the engine slowly…

  • Battery too weak or cable badly connected: Charge battery, replace it, clean connection contacts, connect cable correctly.
  • Filled with oil that is too thick (e.g. winter oil with SAE 50 specification): fill in thinner oil with a viscosity that is adapted to the outside temperature.

When the electric starter runs but the engine does not crank…

  • Starter freewheel defective or runs backwards after overhaul due to incorrectly assembled housing or incorrectly connected terminals; Defective gears on the starter and / or engagement pinion: have them checked by an electrical specialist (e.g. Bosch service) while they are installed.

When the starter relay clicks but the engine does not crank…

  • Starter cable badly connected or short circuit due to broken cable: Check connections for tightness, eliminate corrosion, check for continuity with multimeter.

Help with engine problems - When the motorcycle does not run properly

Fresh petrol is often enough; the engine will not start well with dirty petrol.

If the engine starts poorly, only stutters or runs unevenly and often dies…

  • Petrol soiled: Dirt in the tank, in the petrol lines, in the carburetor. Drain gasoline, clean tank and carburetor, fill in fresh gasoline.
  • Idle speed too low: adjust speed and idle mixture.
  • Tank ventilation blocked: check whether the ventilation hole (in the tank cap) is B. is closed by a too tightly built tank bag, clean the hole if necessary.
  • Choke piston stuck, engine is running too richly: remove, clean, check Bowden cable runs smoothly.
  • False air is being sucked in because the carburetor or intake manifold are loose or cracked: screw tight, check the port for porosity.
  • Undervoltage in the ignition system: Charge the battery, check that all electrical connections are tight, eliminate corrosion, if necessary fit new spark plugs, plugs and ignition cables.
  • Incorrect electrode gap or ground connection on the spark plug: Check the spark plug heat value and condition, adjust the electrode gap, install new spark plugs if necessary.
  • Connection cable or connector of the ignition coils and spark plug connector damaged or broken, spark plug connector not properly attached. Pull out or unscrew the ignition cable, cut off a small piece and reinstall / screw it in again. Check whether the plugs in the clamp are corroded and whether the cables are correctly seated in their clamping points.

When the engine starts poorly and has little power at low revs…

  • Valves set incorrectly or too little play, valve adjusting screws loose, rocker arm worn; Broken valve springs or worn camshaft: Check valve clearance and adjust correctly, check valve clearance adjustment screws, lock nuts, rocker arms, rocker arm axles, valve springs and cam tracks for excessive wear.
  • Valve seats leaking, burned, valve guide worn, valve bent, stuck: have the compression measured by a pressure tester in a specialist workshop.
  • Cylinder head gasket leaking or cylinder head warped or torn: Visual inspection for oil leaks on the cylinder head, with the engine running, watch out for combustion gases escaping from the head gasket.

Help with engine problems - When the motorcycle does not run properly

When inserting the cleaned or new air filter, it is essential to observe the installation direction. Once the air filter housing has been reassembled, check the intake ports for proper seating or cracks. If the engine draws in secondary air, this leads to a leaner mixture. Consequence: engine damage.

When the engine has little power and needs a lot of gasoline

  • Air filter dirty, air intake system clogged: clean filter, replace if necessary. Check that all air intake openings are free and that the motor can draw in fresh air unhindered.
  • Ignition / motor electronics defective: check whether the battery is correctly connected and charged, check the ignition system for dry connections and faultless cabling.
  • Undervoltage in the ignition system: Charge the battery, check that all electrical connections are tight, eliminate corrosion.
  • Spark plugs defective: check spark plug heat value and spark plug pattern, check electrode gap and adjust if necessary, try fitting new spark plugs.

When the engine runs unevenly when idling

  • Valve clearance too wide or too narrow: set correctly.
  • Ignition timing incorrect: readjust.
  • Spark plug connector or ignition cable are not making proper contact with the spark plugs: Pull / unscrew the ignition cable from the component, cut off a small piece and install / screw it in again.
  • Defective ignition box: try to install an ignition box of the same type, ensure that the earth connection is clean.
  • Carburettor not synchronized: Adjust the synchronization of the throttle slide with a synchronous tester (e.g. from Bohm).
  • Adjusted idle: set correctly.

Help with engine problems - When the motorcycle does not run properly


Beware of unusual smoke from the exhaust.

When the engine doesn’t pull through and there is black smoke from the exhaust…

  • Rich mixture due to too large carburetor nozzles and too high float level: install smaller nozzles, adjust float level, adjust carburetor.

When the engine doesn’t pull through and there is blue smoke from the exhaust

  • If the level is too high, engine oil gets into the combustion chamber, is pressed into the air filter box via the engine ventilation system and sucked in again: Check the oil level, drain it if necessary, clean the air filter.
  • Cylinders and / or pistons are worn, have scoring or scratches, the running clearance from piston to cylinder is too large, piston rings or oil control rings are worn, broken, no longer tensioned or incorrectly fitted: measure compression. If the value is too low: dismantle cylinder, piston and piston rings and check installation dimensions, replace, grind cylinder.
  • Valve guides or valve stems worn, valve stem seal (s) defective: Dismantle cylinder head, check installation dimensions of valves and valve guides, replace if necessary. Install new valve stem seals.

When the engine doesn’t pull through and gets too hot…

  • Mixture too lean because the carburetor nozzles are clogged: Drain the fuel completely from the tank, dismantle and clean the carburetor, make sure to fill up with fresh gasoline.
  • Mixture too lean because the carburetors are set incorrectly or incorrectly injected: Set the carburetor correctly.
  • Wrong air is being sucked in: the carburettor is too loose, the intake manifold is cracked or porous.
  • Petrol line squashed, pinched, hose kinked: check whether all lines are routed freely. Also check whether a fastening strap from the tank bag is pinching the fuel hose under the tank.
  • Too little oil in the engine: create the correct oil level.
  • Oil pump defective or oil circuit blocked: switch off the engine immediately, contact a specialist workshop!

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