Timing L28E/SU

[Guest jurven240z]

Howdy,

 

Done the above engine swap using the European distributor with L24 mounting into L28E/MSD 2 coil(no ristor)/mild cam. SUs with SMs set at 2 1/2 turns on fuel knob/tuned and time set at 10 degrees before. Problem is that I still get knocking at shutoff and I can not turn the distributor any further to advance the timing to see if this will help. Does anyone know if I showed change the distributor mounting or should I just cut back on the fuel knob? It is running good at idle 800 rpm but will be torn down early next year(burning some oil). Anyone want an L24/E31 from 5/70 240Z. $50.00 you pickup LA area.

[Z-Gad]

Hey JB,

I know when I leave my choke on and turn the car off, it makes that knocking at shut off. Try leaning out the mixture another half to a full turn and see where it gets you.

[Pop N Wood]

If the engine keeps "running" after the key is turned off, that is called dieseling. It is typically caused by carbon build up in the compression chambers. The carbon build up increases the compression and allows the engine to run without spark just like a diesel.

 

This was a very common problem with late 60 cars in the 70's. The late 60 cars were built with high compression ratios and needed high octane gas. Unleaded gas killed cheap high octane. When I was in high school it was not uncommon to see cars dieseling for several minutes after they were shut off.

 

If your current engine is the 5/70 L24 with the E31 head, then you have the highest compression ratio engine Datsun put in the Z. These engines were rated for 93 or 95 octane gas to begin with. The fact you are burning oil makes carbon build up highly likely.

 

IF this is your problem adjusting the timing probably will not help. Once the key is off there is no more spark. (I say probably because incorrect timing can make the engine run hotter, inturn heating up the carbon.) Important to note that turning the key off kills the spark, but as long as air is being sucked through the carb the flow of gas continues. This is why having the choke on makes the problem worse, more fuel to the diesel. This is also why FI engines don't experience this problem.

 

Try using higer octane gas or octane boosters to see if the problem persists. You can also leave the engine in gear when turnining it off to make the rattling stop a little quicker.