About a week ago my 85 s started shaking bad when I reach speeds above 25mph. The car eventually stops accelerating and dies. Thought it was a vac leak in the air control valve which I blocked up in hopes of a temporary fix. Not so I am pretty much out of guesses other that fuel pump failure or some other electrical problem.
Any help is appreciated.

 

More details of the car and mods would be great....

I had the same issue a few days ago. My friend (RW-7) asked me if I ran in low on gas lately, which i did, and that it could just be a clogged fuel filter. I took off the filter, shock and cleaned it out and it solved the problem. Does it shake because one rotor isn't firing or are they both misfiring?

It wouldn't be a fuel pump because if those go, they go completely.
All assuming its a 12A and no mods....
So check the fuel filter
check the fuel lines
Make sure the carb is getting fuel (see if fuel squirts from the primaries in the carb)
This should be a good start for ya...

 

More details for sure. At speeds above 25 mph? In any gear? Or is it an above x rpm, which.

Does it feel like you are hitting a wall (bogging) if so it *could* be your secondaries arent opening (depending completely on rpm not speed).

Change your fuel filter, they are like 4 bucks.

Do a pressure test for fuel pressure. Can also do a flow test on the fuel pump.

But really we need alot more info that will help us (more likely the carb experts not I) to help you diagnose your problem.

Search through the faqs (welcome to the forum btw), there is probably something there.

The shaking is definetly an issue though, that does NOT sound like strictly a fuel problem. Do a compression check for sure, or take out the plugs and turn the engine over by hand to feel/hear if there is compression