RPM Too Low

[smg1404]

I have a 1973 240z, Current setup is three webers, Motorsport headers, Malory dual point. (yeah I know obsolete) but I am an old guy and like tunning my engine. The car runs fine when cool to med warm and has no trouble getting to about 6500 rpm. But after reaching normal oerating temp it feels like I'm hitting a rev limiter at about 5200rpm. I'v tried timing changes, fuel octane changes, added a new fuel pump (carter electric) readjusted everything I can think of. I'm running out of new ideas.

Any thoughts?

[hmsports]

I'm not familiar with anything but early SUs, but what about vapor lock?

[smg1404]

I wondered about this also, I even constructed a heat shield to help ensure that this was not a likely cause. I also feel that the added capacity provided by the electric pump has lowered this as a likely cause. I ordered an aluminum radiator yesterday, this may not have been necessary, but it certainly will not hurt. I keep thinking that maybe it's a weak spark issue, but with a new coil, and distributer somehow that is hard to support.

[72zcar]

Have you tried adjusting the valves... I'm sure you have but you didn't mention it so I thought I would throw it out there...:sick:

[smg1404]

Yes I did, I will probably do it again this week end. I love that job, I don't know why but somehow it's very relaxing. I may also look into replacint the suply wire to the ignition circuit with something a little heavier.

[2ManyZs]

Well, one thing that could be a problem. Have you replaced the coil lately? It could possibly be the coil breaking down after it has run a while due to the heat of the resistance in the coil. Just though you might want to try another one if you hadn't already. If not that, it could be the ballast resistor if you are still running one. Secondly, have you checked your points out closely? The second set of points is there to retard the timing, could be it is being retarded too much. Just a random thought.

Only problem with adjusting the valve is this, if the valve springs are getting soft, you can adjust till your fingers bleed, and they won't act any different. If they are still the originals, they may need to be replaced.

[240znz]

I have to agree with 2ManyZ's. I'd check those valve springs, if they haven't been changed since new...now is a good time to recon that top end.