Tuning the Weber 38 DGAS Carb

When i purchased ME196 in May 2005 it had done just 4000 miles and i though it rather strange that an engine with such low milage ran very rich, so rich that i would soot up plugs. The first thing i did was try to adjust the mixture. On the Weber 38DGAS 3C carb fitted to ME196, the mixture screws are set back in an alloy housing which is part of the carb that is difficult to see inside.

So i thought it best to remove the carb and give it a good clean inside and out. As we would say over here in Lincolnshire there was "enough muck inside to grow tates" (Potatoes). So a good clean and blow out was the order of the day. The gaskets and seals were all suffering from petrol rot and needed changing but now came the strangest part of the strip -

THERE WERE NO MIXTURE SCREWS AT ALL............

If i recal correctly on the last of the 3.0ltr Capris the carb came factory set and in the end of the housing there was a plastic plug which had a tiny hole in the end so adjustments were made with a tiny (Thin) screwdriver, but they always fitted a mixture screw. I ordered a carb kit and the missing screws from Anthony Boshier-Jones via Fastroadcars.com and these were here the next day.

The parts were fitted and i thought visitors would like information on the correct way of setting up the 38DGAS carb.

Firstly, once eveything is clean you must check the float level within the carb, if this is set wrongly you will have fuel excess fuel or starvation when you use the car hard.

Holding the top of the carb at 90deg so the float can hang down, measure from the flange (Without Gasket) to the bottom of the float and adjust it to 40mm. To make an adjustment, bent the small flap that pushes the float needle until its is correct. Check the other side float and bend the float until it is also 40mm so that both floats are parallel.

Now turn the body so the float can hang down and adjust the small tab at the side of the float so it stops the float going more than 50mm.

As the Essex V6 gives such great torque many off road racers use the engine with the 38DGAS carb fitted. To stop fuel starvation the change the 50mm to just 44.5mm so if your car suffers from high speed cornering starvation this adjustment should be tried. Now fully assemble the carb and refit it to the manifold replacing both gaskets on the black spacer block that is between the Carb and manifold.

Once everything is reconnected you MUST check that all linkage and levers are free and do not bind in any way. With the engine switched off check the linkage opens to full throttle and closes to the Idle Speed Screw.

VERY IMPORTANT
The number one reason for problems with setting up any Weber carb is improper linkage installations binding or an over tightened linkage nut, causing the linkage assembly to bind

Poor running is not always a badly adjusted carburetor. One of the major advantages of the Weber 38DGS carburetor is the ease of adjustment and tuning. Check the timing and vacuum pipes for leaks before you start. These notes assume you car is standard with a standard carb that has factory jets.

Set up prior to tuning

First of all you must set the carburetor to the correct base line settings. Do not depend on the existing settings.

All settings are done with choke disengaged so that the choke is fully opened. Most cars are fitted with an automatic choke, so in this case you can either warm the engine up until the choke is fully open or by opening the choke butterfly fully by hand while the linkage is operated through its full movement so it clears the choke cam. You should hear a metallic click as the choke cam is released. You should also check the choke fast Idle screw under the choke assembly to confirm that it is not in contact with the choke fast idle cam

1. Set the Idle Speed Screw by undoing it until it is no longer in contact with the throttle stop lever. Snap the linkage again to be sure that the linkage comes to a close without any assistance and is not binding. Now screw the Idle Speed Screw back into contact with the lever and then continue screwing in 1/2 a turn.
2. Set the mixture screws by turning each screw in until it lightly seats. DO NOT FORCE AS THIS WILL CAUSE DAMAGE TO THE SCREW AND IT’S SEAT IN THE BODY OF CARBURETOR. Back out the screw 1 full turn.

BE SURE TO FOLLOW THE NEXT SET OF INSTRUCTIONS IN SEQUENCE, DEVIATION WILL CAUSE THE CARBURETOR TO NOT FUNCTION TO ITS IDEAL SPECIFICATIONS AND MAY NOT PROVIDE THE PERFORMANCE AND FUEL ECONOMY AS DESIGNED.

1. Start the engine, the engine will run very slowly more like a tractor. As long as the engine stays running idle speed is not important at this point.
2. The first thing, do not set the idle speed, set the Idle mixture screw to lean best idle setting. First, turn in the mixture screw until the engine dies or runs worse, then turn out the screw turning 1/4 turn at a time. The engine should pick up speed and begin to smooth out. Back out 1/4 turn more, or until the screw does nothing or runs worse then turn back in to the point where it ran its best.
3. Repeat on the other mixture screw and by listening adjust both to the best, fastest and smoothest running point.
4. Now that the mixture screw is at its best running location, you can adjust the Idle speed the screw. The idle speed screw will be sensitive and should only take ¼ turn to achieve the idle speed you like.
5. Check and set idle to your driving preference. Put the car in gear and apply slight load, and set the Idle as you like it. Don’t set it too high, as this will cause excessive clutch and brake wear. The Idle only needs to be 650 to 800 RPM under light load.
6. Recheck mixture screw to lean best idle again. If all is still best and smoothest idle you are finished.
7. For information clockwise (in) weakens the mixture and anti-clockwise (Out) richens the mixture.

If things are still not right

Although the carb is factory set if the mixture screw is more than 11/2 turns out turns then the Idle jet is too lean (too small). When the mixture screw is ½ turn or less, then the Idle jet is too rich (too large). and confirms the need to change the jet size. Jet Kits are available but if you need to change them its best to take your car to a rolling road and let them set it up. Standard jets will not be correct for cars with fast cams Etc.

And Finally

If you open your engine cover and the carbs look like this...

the best of luck....
but you can always email me and i will do a swap......