I have true dual exhaust/Flowmasters (no cats) on my 1983 F150 with a 302 engine. I have noticed lately that the passenger's side exhaust pipe is running slightly richer than the driver's side. It is most noticeable when the truck is first started, and diminishes as the truck is driven some. The engine was rebuilt a couple of years ago and only has about 2K miles on it. Other than that, my truck runs the same as it always has - FANTASTIC!

I am still learning about carbs. What would cause one side to run richer than the other? Is this a choke issue?

 

The choke is common to both sides. I would pull the spark plugs on that side, and see if all of them are black. You can also compare them to the other side. If you have one or two cylinders that are black, then I would suspect a miss-firing plug or bad sparkplug wire.

 

Oops...wrong post!

 

Whew! That shouldn't be too hard to check out! When I got the truck, I tried to adjust the carburetor with a vacuum gauge, but being my first time, I couldn't get it right. I ended up running way rich at idle. With the help of my father-in-law ex-mechanic, we adjusted the idle mixture screws to correct the problem. If I remember correctly, on that side (the rich side) I had the idle mixture screw set a full 1-1/2 turns out more than the other side! Assuming that did foul the spark plugs on that side, would the plugs stay fouled, even if the carburetor was re-tuned?

 

Idle mixture screw on one side of carb feeds two cylinders on each side of the engine, so evenly affects each side.

Well, more or less... It will affect the side that it feeds the middle cylinders slightly more due to better fuel distribution to the middle two, the 4 end cylinders typically run slightly leaner with msot production dual plane intakes, but that's going beyond the scope of this post.

 

You didn't say how you know one side is running richer, but if you are going by the color of the tailpipe, and you think you have fixed the problem, make sure to wipe the tailpipe clean of the black soot and then drive it awhile and see what happens.

 

Franklin, the reason why I say one side is richer than the other is because I can actually "see" the exhaust wafting out of the passenger's side tailpipe, but hardly at all on the driver's side. It is most noticeable when the engine is first started, and lessens as the engine warms up.

 

See, as in black smoke? If it's lighter colored you're see moisture/water vapor that could accumulate more in one side for any number of reasons, inlcluding how you park the truck relative to the sun. If black smoke are you sure it's fuel and not oil? Could indicate bad valve stem seals or rings on one of the cyls on that side.

 

Pulling the sparkplugs should be your next move. By inspecting the plugs you can tell if the engine has a problem or not. If they look good and oil consumption is normal, I would not worry about what you see coming out of the exhaust.

 

the exhaust cross over is heating the carb from inside the intake. when first started, the choke being closed/partial closed, will make a rich condition on the passenger side.you would not notice this if you still had cats