Hey there. I recently purchased a 7/71 240Z, this being my first Datsun.
Heres the situation. When i first received the car, it ran super rich. Fuel smell all the time, smoking from exhaust. Pulled plugs, they were BLACK. Picture of plugs below indicates about 40-60 minutes of actual running time on brand new plugs.
Did a compression check, got 225-235 PSI across all 6 cylinders. Seems a little high to me, no? The engine, from what I can see/know, is a L24 block, E88 head combo. The head has obviously had some work done, since it is alot cleaner than the block, looks like its been hot tanked and possibly milled.
The camshaft has E30 cast on it, looks stock.
Changed the plugs. It fouls them literally in one week, not even driving the car down the road. Just starting it in the garage, moving it in/out, etc.
Start and let it run maybe 5 minutes each time, plugs come out BLACK once again. If i start it, and give it gas slowly, the engine revs up quite nicely, aside from the rich smell and smoke filled garage. If i try to give it a sudden burst of throttle, the carbs seem to backfire, and fuel actually comes out of the carb intake. Also makes like a hissing or spraying sound, not like a BANG backfire as if the mixture was ignited.
The SU carbs, early ones, have the stock N27 needles, move up and down without any problems, i have balanced them with a Unisyn, etc.
The choke cables are not stuck, etc. , even disconnected them one time to make sure.
Thought it may be a weak coil, ignition system, bought a Pertronix Ignitor and coil, FlameThrower 3.0 ohm. Noticed a difference after install, but did not solve this problem.
There are a few marks on the crank pulley, one is highlighted with white paint, i would assume that its TDC? I took a pic of the pulley at this point, along with cam gear position and camshaft lobe position.
When i do get it idling with little to no smoke coming from the exhaust, once i do try to drive it, its fine under 2500 RPM, but once I get around 3-3500 rpm, with anything over 50 percent throttle, it loses power and the smokescreen exiting the rear of the car is smoking out my neighbours down the street.
If anyone has any insight, or things i should check, pics i should take for more info, please let me know. I like to think that I have good knowledge of how motors work, I have built over a dozen motors for other people, but they were all Honda/Acura motors so somewhat different than the L series.
I have tried to explain this as best as i can. Sorry if I sound like an idiot at all in this post LOL. The previous owner was a young kid, and he didn't even touch the car, so I can't even ask him for any input. The motor work was done a few owners ago i think.
Thanks in advance!
Jay