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I have a 1978 Datsun 280z. I rebuilt the engine last year. Removed the fuel injection and installed 240z SU carburetors. The car starts and runs great, I typically use it as a daily driver. The only problem I have, is that I hardly ever rev it above 4000 rpms. I watch videos of people driving Zs and they always take it up to 5000 or even 6000 rpms. But for my Z there seems to be no additional power or acceleration above 4000rpms. There doesn't seem to be any stumbles or misfires, it just seems like the power is flat above 4000 rpms. I thought Zs had power all the way to the yellow line. I've never driven another Z besides mine, so I do not know for sure. Any advice is appreciated! Thanks in advance!

Will the engine rev to 6000 rpm when there's no load on it? Years ago I was driving my 71 on I-5 when I found the engine wouldn't go any faster than 4000 rpm. I kicked in the clutch and found it would rev to 6000 but under a load it wouldn't go past 4000. The problem turned out to be a partially plugged fuel filter.

Thanks for the reply! So I just set the timing yesterday. Since I currently have a tank of 87 octane in the car, I set the timing to stock 10* BTDC. Once I'm through this tank of gas, I'll fill up with 91 octane and advance the timing. There was some backfire and popping on deceleration. So yesterday I pulled the plugs and there were a little white. So it was in fact running a little lean. I richened the carburetors a little by turning the adjustment on the bottom of the carburetors. This seemed to help with the popping. It now decelerates without popping, or at least significantly less popping. I synced the carbs when I first rebuild the engine. I've checked them once since then and there were still synced. Any further advice is greatly appreciated!