GENTLEMEN

I HAVE A 1971 CAPRICE 2DR HT W/402BB/TH400 4BRL Q-JET. THE PROBLEM I AM HAVING IS THAT WHEN I GO TO WIDE OPEN THROTTLE THE ENGINE DOES NOT RESPOND, THE ENGINE DOESNT DIE AT ALL, BUT IT JUST DOESNT DO ANYTHING FOR AT LEAST THREE SECONDS. AFTER THAT THE ENGINE SEEMS TO KICK IN. THE CAR HAS ONLY ACCUMULATED 600 MILES IN THE LAST 5 YEARS SO MAYBE VARNISH AS GOTTEN AHOLD OF THE CARB.
THANKS FOR ANY HELP.

NICHOLAS

You need to adjust the seconday plate at the top, the spring is losing it's tension and opennig just a little to early, tighen the screw very very little at a time then test drive etc. Marty

try adjusting the accelorator pump

It's definately your upper secdondary butterfly valve that needs adj as Marty mentioned above.
It's opening too fast and without a secondary accelorator pump to enrich the mixture for a few seconds the motor leans until fuel is pulled out of the carb into the motor then it picks up and takes off after that.

Also have a friend floor the gas pedel and then open the upper secondary valve and look in carb to ensure it's opening all the way which many q-jets are not adj correctly to do so,
adjust as needed to get full open. The car must be off and warmed up to do this because there is a secondary lock out on the carb for when the motor is cold that stops the lower secondary throttle plate from opening..

There is a small allen head screw you must loosen 1st to allow you to adj the screw that goe's into the side of the valve shaft.

Get a hold of a q-jet book or ask someone that's familiar with q-jets to help you dial it in,it will take 15-30 mins doing a couple road tests toget it right.

Scott

I have a similiar problem only my car actually dies for a second , just like you turned the switch off, then it jumps to life. I have a Holly carb. can anyone tell me if it is a simular situation?

Freshayr,what carb are your runnig,a vac or dbl pump holley,auto or std trans?

If your running a stock carb on your ls6 it's a vac secondary holley and if it bogs down for a second or two when your floor it then picks up it's usually due to too light of a spring in the secondary diaphram. This allows it to open too fast giving the motor a big gulp of air with no fuel for a couple seconds (due to no secondary accelorator pump) then the fuel reaches the motor and it picks up.

You need to get a secondary sping adjustment pkg from summit or jeg's for your holley and install a stiffer spring to slow down the secondary opening rate to correct the bog. The springs are color coded as to their relative tension which is included in the inst with the kit.
Thie is a trial and error thing to do and can take and afternoon to get dialed in but is well worht the effort to do so. Holley also offers a quick change secondary diaphram/kit in case your interested so check that out too.

A dbl pump carb shoots some fuel into the secondaries as they are opened to avoid this.

The holley vac carb that was stock on the LS6'S was decent but if your car is a 4spd i would opt for a holley dbl pumper for faster/crisper throttle responce when going from partial to wide open throttle on a moments notice like when you want to blow off a pesky 5.0 stang or a rice rocket. Yeh the vac secondary is a little better on fuel but no matter how you look at it any LS6 is eats a lot of fuel,so bad to really bad fuel consumption is not much different to me.

If you do decide to swap holley carbs some day dont forget to check the jet size and pwr valve rating (in primary&secondary) in the old carb you removed . This is so you can check the new carb to ensure it's calibrated the same as the old one and if it's not make it right before you install it to avoid tuning issues later on. This is assuming your current carb is working well with the exception of the momentary secondary bog and the fuel calibration (jets & pwr valve/s) for primaries & secondaries are correct for your application at this time.

Scott