First off, I searched all weekend, and had no luck finding anything that solved my issue.
I'd like to not have to convert to mech secondaries, I just want the car to work as-is.
My car is an 84 GSL with A/C and 5spd.

Here's the deal.

Car accelerates fine up til about 3k rmp, then just flattens out powerwise. A couple of months ago, the secondaries would kick in SOMETIMES and the car felt great. Sometimes they woud stick open and I'd have the shut the car off. In the driveway, I revved the engine and the secondaries stay closed. I read that this is pretty normal because of a lack of load.

I have changed the fuel filter and had no change.
The secondaries will open easily when pushed with a skrewdriver.

My linkage and return springs all are in correct working order.

I suspect this is clogged or broken vacuum line, but don't know which ones to change / check.

thanks to anyone who can help.

 

The secondaries get their vacuum signal from internal passages, so there won't be any broken hoses causing them to not open.
On the rear of the carb, above the linkage, there is a rocker assembly with a spring loaded linkage going to it. Ensure this is positioned properly, as the secondaries cannot open if it is not correctly positioned.
After that, you may need to check the diaphram that opens them. It could be bad.

 

Good idea Rogue. Run a search on "teeter totter" and you'll find more information.

The way I remember it though, there is a vacuum "pod" on the carb that controls the opening of the secondaries. If the internal diaphragm is split, then it wouldn't work anymore. I might be totally wrong about this though, I've had mechs for a long time now...

 

That's the diaphram I was refering to
Located under the ~2" square cover w/4 screws, on the front (radiator) side of the carb.

 

Thanks a bunch guys, I'll check the diaphram tomorrow!