top-end power loss

[doodles526]

So, Summer finally came to us in Oregon and I tuned up the carbs, adjusted ignition advance, getting the car ready for the warm weather... Once I got the car on the road she ran beautifully, quick off the line and decent power all the way through the rev-range. I arrived at my favorite twisty road and decided to have a little fun around the corners, keeping rpm's high and in the power band. But after about three miles of decently hard driving I went to the gas out of a corner and right when the car normally seems to get its most power there suddenly is none. It almost feels like it redlines at a much lower rpm now, the engine noise also changes to be harsher at that rpm. I was able to drive the car home no problems, and it drives fine until you hit that point. I'm not sure on the exact rpm's that it hits when it happens as my tach is broken, but it's around 4600-5000. I thought it might be the timing chain, but as I'm researching that it seems that just wears over time and it wouldn't have been instant as in my case.

I haven't messed with it or driven too much in case I just mess it up more, so I wanted to see if you guys have any suggestions of what to look for? Could it be as simple as the carbs just went out of tune again or the dizzy rotated a little on its own? Basically I just want to make sure it isn't something obvious that I'm missing that will seriously compromise other engine components before I start experimenting with the simple stuff like tuning.

BTW 260z w/ l28 and dizzy from a 280zx, l26 intake, with 4 screw SU carbs

[Zedyone_kenobi]

Well start with the simple stuff first.

check your timing.

check your fuel pressure

Check your cap and rotor

report back.

[SteveJ]

If all of those check out, you could always go the route of installing a wideband O2 sensor and datalogging. It could tell you if the mixture is off on the top end.

[Zed Head]

High RPM ignition breakup could be the ZX ignition module. Module problems quite often go away when the module cools down. If you take it out again and the problem is gone but comes back after things get hot, that would be one thing to think about. It's been suggested to take some sort of cooling spray in a can and spray the module when it happens to get a better diagnosis.

Not a cheap fix though. Verify timing and fuel before getting carried away.

By the way, the 260Z already had electronic ignition. Did you install the ZX distributor or did a PO?

[clayton 260z]

The engines sound changes? Is it loss of power due to fuel related isues or ingnition breakdown? It sounds fuel related...

FWIW