i own a 75 vw bug fuel injected new tune up new tranny throttle body cleaned, etc but i have a problem losing all engine power after its been rain for about 20 miles and is hot, very rare when cold. when you give it throttle it will accelerate all of a sudden it will cut out and act as if it has stalled but sounds very weak and gets weaker. the way i counteract this is by playing with the clutch and gas, then slamming it into the next lowest gear then it will run fine. something will squeal in the back like a belt on metal but that's. besides the usual leaks it has one in the cooling tower. i cant figure this out. i can think maybe the compression is is being lost after its hot or the spark is failing at the coil. I cant duplicate it for my mechanic to look at because its so infrequent. anything that you can offer would be great thank you.
Update:The wires are new put in yesterday could the throttle position sensor be a problem?
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VW bugs are bad for moisture problems with the ignition. Replacing the plug wires might help. Check the ballast resistor for the coil (it have something collected there that is absorbing moisture). I can't remember if we RTV'd those old distributors or not to keep water out.
I agree with air cooled but would add this- Re-torque the heads and rocker arms before you re-adjust the valves. Be sure to adjust this all with the engine cold.The fuel pump on this is electric and does not have a little ball and is not cheap to replace. I doubt it is related. Generally the coil is good or not but check this run it in the dark and look at the engine just to be sure you don't see any leakage of current any where. If there is an issue you will see sparks around the coil or wires.
the squealing belt is slipping. the squealing belt operates the cooling fan. the cooling fan is not spinning properly when belt is squealing. the cooling fan not turning properly is causing the engine to run too hot after 20 minutes of driving. you lose compression when it's too hot. if you are lucky you may get away with adjusting belt tension. if not lucky you may have damaged the heads, pistons and cylinders from running to hot. if you don't know how to adjust belt tension on an old vw get a manual.
re-check the valve clearance. to me it sounds like the valves are too tight. as they get hot (the exhaust valve can get red hot in certain climates, which is normal). as the valves get hot they expand, this is why you give them "free play" in movement, which is .006 inches. sounds like the valves are too tight and are closing up