I have changed the sparkplugs and bogy cords and the firing module but the golf still wount start.there is spark and gas.the engine turnes but wount start.

terminology- bogie cord?? Is that harness or coil high tension wire

1) you need to check if there is enough gas in the tank
2) check for spark in the sparkplugs
3) make sure the gas is clean and has no water in it

change faulty sparkplug or ht lead,check lead by holding sparkplug end near to engine nearly touching,have someone turn engine over whils checking for spark jumping,if spark present then not lead,change spark plug,if sparkplug ok then check pressure in cylinder, poss piston damage

Check the coil. This sends tdhe spark to the Distributor.

could be a number of possible faults.1/crank sensor not working when hot,trace this and pour cold water on it(dont do this if it is not by crank pulley as water isnt good for modules etc) and retry.2/sparkplugs worn,but usually they would fault more on cold start.3/fuel pump cuts out when run,try wacking tank from underneath and retry.though I would concentrate on nil spark caused by a faulty ignition module or crank sensor.
Next time it fails to start.pull off a sparkplug lead,make a quick test plug with an old(but working)sparkplug.pull the side wire away from the center electrode 5mm and insert into plug lead.earth ground the plug on its thread against metal on the engine.crank and check for spark visually,don't be tempted to hold the plug while cranking.if nil spark we will have to test further which is faulty sensor.if it sparks ok we will need to test for fuel.
testing for fuel is easy.
when it fails,unclip air filter housing,while engine is being cranked,spray an aerosol based carburettor cleaner into air duct to engine,it should start and run while spraying and stop when you stop spraying if fuel delivery is the fault.fuel pump will then need testing/replacing.
be careful not to spray onto ignition or any areas of spark

If it will turn over check to see if its fuel or fire. To check for fuel, spray quick start for a few seconds into intake. If it starts and stops. its fuel. Change fuel filter and check fuel pump. If it does not start its fire, Could be distributor cap, rotor, coil, spark plug wires or spark plugs. If it does not turn over it could be battery or starter. Check battrey connections, ground strap from motor to body and ground wire from battery to motor and body.

This could be a number of things...
Crank sensor, cam sensor, coil, PCM, spark control module, ect.
Start with the sparkplugs, make sure they are firing if not work your way back from there spark pligs, wires, coil, control module, cank and cam sensors, PCM this is what i would do if this rolled into my shop.

check your spark plugs. on older machines, overtime are neglected and are rarely changed.
Also, if your sparkplugs arent the issue, check the Gas Line. a common problem with this is your gas lines may incur crystalization inside and hence looks like a Cancerous Lung. Filling up with more and more only is harder on your engine.
Hope that Helped! -Jordon :)

As far as the engine cover, is this what you wanted?

could you give me more info plz