. I have a 1974 L18 620 with stock hitachi carb.
My troubles began over a year ago now. I had gotten this truck running from nothing to running like a dream. I was using it daily with only some minor fiddling necessary to keep it happy. One day while getting off the interstate it basically stopped wanting to accelerate at all. I was able to limp it along in idle letting the clutch out slowly. I have not since been able to get it to run smoothly. I have been worried that an internal engine part broke but can't seem to diagnose what. The best i can tell is that the engine is running incredibly rich. All the spark plugs were fouled out with thick black soot. I had already done work on the internals of the engine and rebuilt the carb when I first got it. Everything worked fine for over a year so i don't think any of that work was a direct cause of this. I have since tried to thoroughly check and clean systems of the engine. It now will idle but not smoothly accelerate. There is a white smoke in the exhaust that smells sometimes like gas. when I do accelerate I can get the engine to rev as high as I want but get a lot of black smoke. Not getting back firing. plugs are getting black and wet now, seems to be gas and maybe some oil. Now that it will idle I am also noticing a gassy smell to the oil.
I have taken the carb off cleaned it thoroughly,
I have checked the entire electrical ignition system,(previously put the pertronix induction system on instead of the original points) found a resistor was only allowing about 9 volts into the main ignition coil, got that taken care of and now have 12v. The cleaning and new part has helped but still getting really bad combustion.
I am wondering if it may be the carb still or if I should look at other parts.
A compression test showed equal pressure on all cylinders but I don't know that the actual pressure should be.
I want my datsun to rise from the ashes again.