High RPM miss?

[70z4fun]

Greetings all,

I have a series one 240z with a L28 with 240z head and carbs. I did install the Petronix Series II electronic ignition. It seems to want to stop power past 5K and I get an occasional exhaust backfire. I am thinking I need to recheck the timing,, as I have been running it at 10 degree before TDC.  Have not done the valves for a bit, so was thinking of checking that too.
I did just check the carbs for float level and sync them. If I keep the rpm done, it seems to run fine, which is fine for general driving. But it's just not right at higher rpms 

Any other suggestions would be greatly appreciated

[Mark Maras]

 At 5000 rpms does the engine cut out (misfiring cylinders) or just run out of power?

[70z4fun]

Feels more like a misfire, which brings on the loss in power.......

[Mark Maras]

 I've experienced running out of power (no miss) when the fuel filter was dirty. The only time I've experienced a high rpm miss was cured with a new set of NGK plugs.

[dutchzcarguy]

22 hours ago, 70z4fun said:

Petronix

To say it mildly.... i'm not a fan..   I still have the orig. points and renew them every 20000 km (last time was even more) and my engine does not want to stop rev'ing.. i'm always surprised how easy it go's into the red.. (1971 240z orig.engine no revision yet!)

[jpc3006]

70zfun,

Reading your post made me recall my experience last year with a similar engine "miss" at high speed and high load. My engine is the original L24 rebuilt 3 years ago with Ztherapy carbs, Pertronix II, and 0.6 Ohm Pertronix coil (ballast resistor bypassed). I may be running a bit more advance than you as I have 35 degrees total (static + centrifugal) at 2800 rpm. At full throttle in 3rd going uphill merging onto a limited access highway I would get a miss that would not let it rev above 5000, it did not backfire but just wouldn't pull. Never noticed anything in 1st or 2nd gear. Everything on the engine was new or in the case of the carbs, rebuilt. The problem was resolved with new set of NGK spark plug wires. It turned out that the wire to the number one cylinder on the other wire set was defective. As a test, this morning it revved to 6000+ with no issues.

I think you are on the right track, set the valves, timing, and perform a general tune up to see if there is any improvement, if not, look at your coil and wires.