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L30 stuttering/machine gunning issues during acceleration

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Hey guys, I'm having some trouble getting my '72 240Z to accelerate without "machine gunning". I've searched all over the site and have not found suitable answers. It's a 3.0l race motor, 13:1 CR, triple Weber 45s, ported head that flows 227/155 CFM, 280zx distributor, summit racing ignition box(per Dave Rebello), new coil, carter fuel pump, Rebello road race cam grind. I had my timing set around 15, 35 advanced. I advanced and retarded it from there and the problem remained. As I accelerate, it doesn't have full power and makes stuttering/machine gun sound. It's not a mechanical sound, like a rod knock or broken rocker arm, but sounds more like ignition or fuel related. Also I am running ngkbr9 plugs and 110 leaded fuel. Any help or suggestions as to a cause would be greatly appreciated.

Thank you in advance, Andy

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Thanks madkaw, I also am starting to suspect that it is ignition related. It all worked a couple months ago, but I've had fuel issues since then. (Rusty tank, clogged fuel filters, now that's all fixed) So now I guess wires, cap, rotor, and plugs need to be examined.

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I had an issue with my MSD ignition box when I first wired it up. The trigger leads from the distributor aren't marked + or - and I had them hooked up backwards. If you are using those try switching the magnetic trigger leads around.

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With high energy ignitions "they say" it's possible for a wire to arc to another wire and cause the wrong cylinder to fire. And spark blowout is when there's too much cylinder pressure for the spark to jump the gap on the spark plug. So you tighten the gap a little. I had it on my L28et. At 15psi it would start missing. I closed the gap to .025" and cured it.

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So, number 5 plug was wet fouled. I hope fuel and not oil. I'll check lash tomorrow (left my feeler gauge at work). Valvetrain looks healthy. Possibly a compromised plug wire?

 

Could also be a faulty injector. Run some good injector cleaner though it. CRC One Tank Power renew is very good. Or better yet, send them out for ultrasonic cleaning, testing and calibration. InjectorRehab and Injectorman ( Motorman ) are two excellent  sources

 

You should also have local places that do Ultrasonic cleaning and testing of injectors. 

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