sharkthehunter77

Seems when i first start driving the gas pedal only wants to depress so far. Untill shes warm i can only push down on the throttle so much and she accelerates slowely. This problem, however, almost disappears when she up to about 160 degrees or so. Once warmer, I can push the pedal down all the way and hear the engine rev as the secondary barrels on the Q-jet ( rebuilt but not recently) open up but she takes a while to "jump" and accelerate. I assume this means the Q-jet is functioning improperly, but i know nothing about carburators. BTW, once the water temp reaches 180, throttle response is much much better. I have no idea what the connection is!?!?

lyonsh

It sounds to me like either a timing problem or sluggish throttle plate opening.

If the timing checks out ok, I would check the cable/linkage from the pedal to the carb - you may have some gummed up lube that's causing the problem until you get warmed up. Check it when it's cold to see if you can figure out where the sluggishness originates.

:cheers:

lars

This is normal. The Q-Jet uses a secondary lockout lever that will prevent the secondaries from opening while the engine is cold - obtaining WOT and peak cylinder pressure on a cold engine will cause engine damage, so GM put a lever on the choke linkage. Once the engine warms up, the choke makes the lever retract, and you get full throttle usage and normal engine response.

SanDiegoPaul

Is the heat riser/EFE opening right? The choke?

desi

Thanks Lars. That's exactly how mine works. I just needed to hear from a carb guru like yourself that mine is perfectly normal. I will be putting a 180 thermo to somewhat over come this issue.

:cheers:

Larry B.

There is a secondary lock out tang that won't let the secondaries open while the choke is on. This give a very stiff feel at about half throttle because you are winding an over ride spring, It's hard to explain but you can see the spring doing that on the drivers side of the carburetor on the secondary throttle shaft. The lock out tang is on the other side. It drops down when you set the choke. (Tripping the throttle) Q-jets are very smooth with no bogs or delays when they are properly set up.

lars

desi -
Changing the thermostat will not have any effect on the opening rate of the choke or how fast the secondary lockout lever is released: On early Q-jets, the divorced choke is heated by exhaust gas circulating through the exhaust crossover - opening rate is a function of how effective your heat riser valve is and your exhaust gas temperature. Later Q-Jets (1975 and after) use a hot air choke that also feeds off the exhaust gasses heating the crossover. After 1979, GM used electric chokes which open as a function of how long power is applied to them. None of the chokes respond in any way to water temperature.

However, if you want a water-temp reactive choke, the 2-barrel Holley-Weber carbs used on Ford Pintos (2-liter & 2300 engines) used engine block coolant water to heat the choke. These chokes opened quicker when the engine coolant heated up faster. We can do a tech article on how to adapt a 290-cfm 2-barrel onto a 350 Vette....! :lol:

Brettmc

Hmmmm, how bout 3 of em? Or even 4, if they are similar to the Webers I'm thinkin of. Didn't some 289s come with 4 Webers?

Brett :thumbs:

RATT7

I had the same problem to, thought it may have been the linkage, but once the car is warmed up, it works fine, thanks for the insight Lars :)

sharkthehunter77

Thanx for the responses all. Now to that pesky non working parking brake....