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ok I am going to blow through a lot of questions here I have a 1971 240Z i upgraded the alternator and now my dash and running lights stay on anytime the key is on what could cause this? Second last monday i swaped a 79 280 f54block n42 head with the biggest cam you can get without going to larger valve springs i bought the motor this way i put my brand new ztherapy 4 screw su carbs on it with the msa 6to1 header and the orignal bosch distributer and e12-80 module but it wont run right it backfires through the carbs when you rev it  I did get it to run the other day long enough to set the valves at .012 exhaust .010 intake but Im not sure the coil is right it has a pretronix 3.0 ohm coil from the kit I put on the 240 motor when i got it i also tried a crane cam lx91 and it got worse so I switched back to the pretronix my plug gap is .042 i just need a starting place iv done everything i know how to do to no avail. what am I not seeing?

 

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Back at ya.  What is your idle ignition timing?  What is your mechanical advance curve, approximately?  Is your camshaft installed so that lobes open and close the valves at the appropriate times?

 

You're swapping parts, but don't seem to be setting them up to function properly.  Timing is more than everything with an engine.

 

Could also just be running lean.  That causes intake backfire also.

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Ok I get ya when setting up the timing it is set at approximately 10 before tdc no vacuum the diaphragm in the vac adv is shot I'm gunna get a new diaphragm for it the cam was setup professionally at an engine shop I used a color tune to set the fuel it is running a bit rich as I set it that way

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I would get in to the details.  You're looking for something big but it's probably something small.  Could just be a vacuum leak at a carb gasket.

 

Spend some time understanding what's really happening.  You said it backfires through the carbs when you rev it, but you also said " I did get it to run the other day long enough" implying that it won't even idle.  Won't idle and won't rev are two different things.

 

If you're using an E12-80 module use a coil that has specs. close to a ZX.  Like ~ 1.0 ohms primary circuit resistance.

 

Be careful with your cam swaps and lash adjustments.  The cams don't tolerate certain things and will wipe a cam lobe pretty rapidly.  Backfiring through the intake can also be a sign of a wiped exhaust lobe.  Make sure that your lobes are still lobes, and not cylinders.

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Regarding the alternator:

 

What did you upgrade...that is almost offensively vague, that pretty much just says you touched the alternator, your definition of upgrade could also be very different. Is it a one wire race alternator? Is it the common Zx alternator with 60amps and the voltage regulator delete, is it the high output alternator that requires a pulley change? Might as well go to a doctor and say, "I hurt." Not too revealing.

 

Regarding back fire through carbs:

 

Check timing order, remember the cam can be 180 out, engine rotates twice for each cam rotation. Take the valve cover off or look through the oil filler cap and see if the lobes on the cam is pointing up, check the timing chain is on the right link, check that the motor is at TDC and check that the distributor is pointing at the right cylinder. This should be basic stuff when swapping heads and ignition systems. 

 

After that is done, confirm spark by removing spark plug, placing it on valve cover and confirming actual visible spark if you don't have a spark plug firing indicator.

 

You can fire though the carb if your timing is off, or if it is really lean and detonating before the intake valves are closed. Lean can be caused by too much air or not enough fuel. Too much air can be caused from worn throttle valves, leaking gasket (or if it has blown through the carbs, then very potentially a blown out gasket). Not enough fuel can be plugged fuel filter, gummed up lines, rust gas tank, weak pump etc.

 

 

Also please make an effort to follow forum rules. Proper grammar, spelling, punctuation, and capitalization, or at least an effort will make posts much more pleasant to read and easier for someone to look up posts using key words. 

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Ok sorry it took some time to get back but regarding the alternator I bought an oreillys 71 replacement alt. As my old one had a bad bearing that's all I have done regarding it. I found that the new distributor had bad shaft bearings so replaced it now no pop out the intake but if you give it a quick rev it stumbles like a momentary lean condition but if I ease it up it does fine. I talked to the lady I got the engine from she said to put the stock 1.5 ohm 79 coil on it and replace the plugs and I'm gunna try that tomorrow.

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Does it stumble during the rev up or when you let your foot off the accelerator? Earlier you mentioned the vacuum advance was kaput. Its prime function is to advance the timing when you let off the accelerator with the engine still reving and high vacuum created when you close the throttle.

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