my motor starts to stumble around 4000 rpms. It gets worse the higher i try to to take it but it runs pretty much fine below 4000. I just changed the fuel filter and spark plugs. Also it has pertronix installed. What could be the problem? please help me figure this out. Summer is almost over and I dont wanna put it on jack stands yet.

Is is missing, or just lacking power? If it just runs out of power, I would suspect a fuel problem, but I would check the plug/coil/ timing just the same.
Mark D.

It sounds like its mis-firing. but it only happens after the car has warmed up a bit. When its still fairly cool i can rev to red line with no or very little stumbling. once it warms up though it has a hard time almost exactly at 4000 and then up from there. I also replaced the cht last year.

valve adjust?

Im gonna double check the timing tonight and if thats not it I will try that tomorrow.

the timing was on. Im starting to rethink even checking the valves because its been less the 1000 miles since i checked them and why wouldthe valves let it not stumble when fairly cool and stumble when warmed up? ALso it revs all the way up in neutral no matter what but has a hard time when in gear.

Valve adjust would be the first place to start for sure. If the timing is right on and the pertronix is working properly it probably isn't iginition related. Have you checked the TPS setting? It's kinda a wild card idea but it is the piece that tells the FI system how much fuel to give under different positions in the throttle. Could be shot, I would check the setting first. Pelican has a procedure for checking it on their website. Wish I could be more help. Good luck!
Eric

I think the TPS adjustment just sets for closed throttle. TPS tells the ECU the throttle is closed so it can go into overrun shutdown, if it's an ECU with that feature.... Otherwise, TPS sends pulses that tell ECU throttle is openning, as in acceleration, so it can richen....

I have a '76, and try as I may, I can't get to to run right without a 270 ohm ballast resistor in the CHT line. Supposedly, '76 did not originally have one, only '73. Anyway, does yours have the resistor? It plugs directly into the CHT, and then the other end plugs into the harness. If not, you might try it.

Your old TS2 may have stabilized hot to a higher resistance, leaving you with a richer mixture than you're getting with your new one. You should try measuring your CHT in the morning- should be around 2500 ohms. After a run, try again- should be down to 50 or so. Why did you change TS2 anyway?

The other thing RPM-related is your EFI breaker points in the distributor. How new are they? I suppose they could bounce around at higher RPM and cause some strange things, but it doesn't explain the fact that it runs OK when cool...

Jim

Cylinder head temp sensor loose or malfunctioning. Any time you have a problem after warm-up, I think head temp sensor. The presentation is a little unusual, but....

Thanks ever one for your input. Im gonna check the CHT and make sure its in properly. Im sorry I dont know what a ts2 is. ? I will keep trouble shooting this. thanks.

the "ts2" as they are refering to is what you are calling the CHT. It is the temp sensor that is in the head above #3 cylinder. In the haynes manuals, and probably other books, it is called a temp sensor 2(ts2). I would also check there. If there is a bad connection or broken wire, it will erratically change the mixture. I have a '73, so I have the resistor. I had a broken wire on that, and that is what was giving me problems at first. Not sure what else would be your problem though. Maybe Fuel pressure???