Why on earth will not pull in 4th gear??

[MIGHTY 8]

Hello again,

Went through a loooooooooong run without any problems...but now not anymore!

Car has had two recent visits to the local mechanic for fuel/carburator related problems (dual Weber 40IDFs), and after driving around town, I've noticed once in 4th gear, it looses its steam and won't rev above 4,000RPM.

Only in this regime, does it seem to have this problem...

Any leads, please??

[azruss]

my first thot is fuel starvation. what were the issues that required shop work. also possible that you have a vaccuum leak, hose disconnected or other air leak issues around the carbs.
On the other end, you may have a clogged cat. how is the performance under full acceleration. If it is lack luster, that could be an exhaust restriction. if it goes like crazy then cuts out at the top, it is a fuel pump issue.

[majicwrench]

Test things. Is easy to test fuel pressure, "T" into the fuel line at carb, run a piece of fuel line and the gauge to the base of the windshield, go for a drive. Get it in 4th gear and see what happens. Fuel pressure should not be dropping AT ALL.
Keith

[chrisfiat]

an exhaust pressure before the can should be no more than two psi

[minimike]

Also slipping clutch?
clogged cat?
To test clutch, start engine, put in 4th gear, rev up engine keeping foot on the brake firmly and gas, and release clutch slowly.
Holding the car with the brake, the engine should stall immediately when you reach the friction point on the clutch. If it doesn't stall, your clutch is slipping.

If you can find a test pipe, remove the cat and install it. Test drive the car and see if you lose power in 4th again.
Does it have power in 5th?

[seabeelt]

Is the car de-smogged? There is a switch at the tranny 3/4 shift rod that puts the car in a "more efficient" mode, but I don't know if that has any effect on otherwise desmogged cars. Mine is disconnected altogether. Probably a red herring, but just a thought
r/

[MIGHTY 8]

Thank you everyone for taking the time to respond. I travel quite a bit, which leads to significant lag time between posting and also trouble-shooting.
I took a nice test drive yesterday and have good reports. I fiddled around with the aftermarket fuel regulator and found that the setting was too low. I deduced that the carbs where flooding and therefor causing the original issue. I noticed a lot of "popping" going on underneath the car in the exhaust while cruising in any gear.
Thank you all again.