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Smoking 71 Roadster



I have a 1971 roadster with an original factory 350 4 speed Rock carb. When I accelerate or downshift there is smoke that comes from the exhaust. The driver side more than the passenger side. I have had a compression check and the cylinders are consistently 165-170 and I also went ahead and installed new valve seals. I have replaced the plugs, wires, cap, points, rotor, timed the engine and ran through a tank of carb cleaner. I have been advised it may be a fuel problem where the car is running too rich but that the Rochester carb is not adjustable in this way and should be rebuilt. If that is the case then why would the driver side smoke more than the passenger side?

Can anyone advise on what this could possibley be?


Well-known member
Jul 3, 2001
Auburndale, Florida
1969 Killer Shark
What color is the smoke?

If it has a blue tint, it is oil. You could have a bad oil ring and not have a compression problem.

If it is grey/black it is fuel.

If it is white it is coolant getting in there and burning.

Tom Bryant

Well-known member
Nov 9, 2000
Edgerton, Ohio, United States
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)

Welcome to the Corvette Action Center Community. In addition to what Chris said I feel the Rochester Q-Jet gets a bad rap all too often. The fact is that they are very tunable and after you play with one for awhile you will appreciate them. First off there is a secondary well plug that is in the bottom of the secondary fuel bowl. It is prone to leaking in these older Q-Jets. This allows raw fuel to run down into the intake manifold. There are kits that fix this problem and it should always be done if you have the carb off for rebuild.

Overall richness is calibrated with different sizes of both primary and secondary metering rods. The tapered end determines the amount of fuel that flows through the jets. There are different metering rod hangers that control the rate that the rods rise controlling the enrichment rate and even the accelerator pump arm has 2 holes so you can change the ratio if you need a bigger shot to eliminate a stumble on acceleration. The secondary air valve, the big flapper in the back side of the carb, acts like a vacuum diaphram on a Holley to open the air flow to the secondaries. The only differences are that the butterflys open with the gas pedal and the air valve opening rate is fully adjustable right on the car. No diaphrams or springs to buy.

You simply loosen the set screw and turn the preload screw, located on the bottom of the shaft boss, until it opens the air valve all the way. Then add 3/4 turn more to preload it. Make a few runs. If it bogs add 1/8 turn more preload at a time until the bog goes away. If not back off the pre load until it bogs then add 1/8 turn. I would recommend moving the accelerator pump arm pin to the outside hole first to eliminate that as a possibilty. If it stumbles before you get into the secondaries get a new accelerator pump.

Sorry for rambling but I just know that someone will blame your Q-Jet for all of your problems when it probably isn't it or if it is, it can be easily fixed.




Thank you for sticking up for the q jet. I was beginning to think that I was the only one that liked them!!

I still think that the q-jet is superior to most carbs on a street driven vehicle . . . if one knows how to tune it . . .


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