We have tried almost every thing & i am losing my patience fast! To the point where i will sell the bloody thing!!
Maybe a new petrol tank is a possible?!
marc
Best plan is to work through this systematically rather than just go off on a scatter gun approach. Take a step back and work through things one by one.
First of all is it running stock parts? Or have things been changed already? Is the carb the original one for example?
You say that this jumping (hopping) happens under load and when things get warm.
If the engine's demand for fuel suddenly increases, and unless the engine receives fuel in the correct amount to the desired fuel/air mix then problems will occurr.
So you need good fuel delivery.
Is the pump working? If you take the tank line off and put a fuel line feeding it into a jam jar of fuel, and run the engine does the pump empty the jam jar. If yes Pump is OK.
Is the line feeding the carb blocked or leaking? If you disconnect the fuel line from the pump to the carb and put the fuel line into a jam jar and turn the engine over with the ignition off does the jam jar fill up with fuel? If yes then line is OK. If the fuel comes out in a dribble and has rusty flakes in it, your tank is buggered. Change it and the line at the same time.
Is the tank allowing fuel to pass freely. If you are getting rusty flakes in the fuel then the tank has internal rust and is blocking up the filter at the end of the sender unit.
Is the inlet filter to the carb blocked? Take the carb off and take a look. If the gauze is blocked clean it out.
Is the well in which the gauze sits in the carb clean or full of aluminium corrosion? If the car has been sat for a long time unused then the carb will corrode and block passageways with corrosion. To clean it out removing the carb degreasing it, soaking it in vinegar for a couple of hours and then cleaning it out with carb cleaner will clear the corrosion.
Is the needle jet sticking or blocked preventing the float bowl to refill quickly?Unless you know when the carb was last serviced spend £17 on a carb kit and replace the needle valve. Think of the carb as a toilet. If the valve jams then the toilet won't fill with water and you can't flush. The carb is the same. The needle jet and float bowl are the cistern on the carb.
Is the float punctured and not reacting to the fuel level? Again this is like the ball cock in a toilet. If it doesn't float it won't work. Check it. Also make sure this float is at the correct height, see the haynes manual for this.
Is the carb sucking in too much air, though failed gaskets or leaking O rings?Is the carb sucking air when it should be sucking fuel? Make sure all seals are replaced and are good.
Is the carb not getting enough air? Is the air filter blocked? Likewise if it gets no air then it won't work either. Check.
Are carb to cylinder head isolator blocks in one piece and not broken/cracked.
Is Carb bolted down to head tightly? Again see my comment on too much air.
2) If temperatures increase the likelihood of the fuel vaporizing also increases. This is much more common with modern fuel which is more unstable. If the fuel vaporizes in the fuel line then the pump can't pump it as the pump is only designed to pump a liquid not a gas.
Temps will increase if the fuel air mix is too lean. An aircooled engine can cope better if it is running too rich better than if it is running too lean. It will run lean if it gets too much air in the fuel air mix.
Re route fuel lines away from sources of heat see my comment about pump trying to pump a gas rather than a liquid.
Make sure that the engine is running at the correct temp (No air leaks on carb)
Tappet gaps set correctly? Always to good to ensure that they are not too tight to allow for expansion.
Make sure that cool air duct is present and in good order no splits etc. If the engine is sucking in hot air instead of cool air it will get too hot.
Check that thermostatic flap works. This is the device that allows the engine to dump heat.
Try these things first. These problems will happen on a VW as well btw.
