Some of the reasons to convert your Jeep from its stock Carter BBD:
- Bad BBD performance (rough idle, stalling)
- Outright failure of the BBD
- Higher reliability
- More power/ better performance
- Improve fuel economy
My Carter worked fine, following a thorough clean up to cure rough idling and stalling problems. I converted for the last two reasons. I kept my Carter and its connection hardware as a backup, and made the conversion without destroying the ability to revert if necessary.
I had had some problems which were actually unrelated to the Carter per se; napthalene granules in the float bowl causing idling and reliability issues.
Reasearching cures to those problems turned up articles and suppliers for Weber conversions touting them as cure-alls for many Carter issues. I have to say that after cleaning up my Carter, it performed like new. *Like new* is not all that great for a Carter, however, and I decided to switch to obtain Weber’s legendary smooth and power enhancing performance. I also hope to see increased fuel mileage provided by the Weber progressive throttle setup; the Carter throttle is not progressive -- both throats are operated by the same throttle butterfly shaft.
The kit I chose was the $289 WK551 34 DGEC, from Quadratec.com because it was the newest, applied to my year, and was the least expensive.
The 34 DGEC is a true Weber having dual 34mm downdraft throats with progressive throttle linkage and automatic electric choke on the primary throat. There is a vacuum pull-out to open the choke after starting. It gets its vacuum from a port into the float bowl vent. At low throttle openings, the carb is essentially a one-barrel. At about 40% throttle the second throat begins to open and rapidly catches up to the primary, until at full throttle, both plates are fully vertical.
Was the conversion painless? Almost -- I did have to add some 3/4-inch holes to the top of the air cleaner for two lines. The kit was complete, although I was glad I had some extra 5/16 inch fuel line. I had to make some slight configuration changes to the carb, and these are described below.
Am I happy, now that it is done? The answer is a resounding YES! It starts easily in winter or summer, idles smoothly, accelerates rapidly without hesitation to over eighty miles an hour in a quarter-mile, and the throttle is very much more responsive than the Carter’s. I recently had it climb my 150-foot 4% grade driveway, idling in high range 1st gear! Initially, going by the Weber specifications for a maximum of 3.5PSI fuel inlet pressure, I installed a cheap ($22) Spectre fuel pressure regulator. It failed -- it repeatedly just shut off completely while the engine idled. I then removed it and my Weber performs fine with the stock fuel pump, which is rated at 4--5 PSI. The Weber specifications do not tell how to measure the fuel pressure. With the line connected to the carburetor or not? Engine running or not running?
Do you have to do a “Nutter Bypass” with a Weber conversion? It should not be necessary, since that modification involves the Carter idle stepper motor, which goes away, and also the vacuum advance modulator, which we do not use, either. My method permits reversion to a working stock Carter configuration if necessary to resell the Jeep YJ, for instance.
Although I bought it from Quadratec.com, the carburetor kit is one produced by Weber: V1000-43536 or K551 kit. The conversion takes about 3.5 hours, depending. I cannot stress this enough: READ ALL THE REMOVAL AND INSTALLATION INSTRUCTIONS FURNISHED WITH THE KIT! Study them, and go through the motions by pointing to or touching each item in each step. Do it several times to get a feel for where things are, what tools you will need and maybe predict needed configuration changes and extra hose, clamps, etc. The Weber kit DOES NOT include the following items you may need:
- Carburetor cleaner
- Gunk Liquid Wrench
- Teflon tape
- Pressure regulator (I did not use one)
- New fuel filter (place it in the line at the INLET of your fuel pump)
Refer to the vacuum system diagram at the bottom of the page for rough locations of the elements you need to reconnect or plug.
Carter BBD Removal
- Park on the level in a place sheltered from the weather, overhead trees, etc.
- Remove and set aside the original equipment air cleaner assembly, inlet air duct, and plug its attached vacuum lines. Retain the lines that go to the pulse-air valves and the rocker cover.
- Place rags under the fuel line attachment to the rigid pipe and carefully detach the flexible line and any fuel filter you have between it and the carburetor. I recommend installing a “visible” paper-type fuel filter upstream of the fuel pump on the other side of the engine.
- One-by-one, remove and label the vacuum lines, breather lines and electrical connections from the Carter BBD. If your distributor vacuum advance line goes to the carb, I recommend you re-attach it to the factory connection at the manifold. Remove the float bowl breather hoses -- the Weber breathes internally. (I used the longest one to connect the Decel Valve to the new adapter plate, below.)
- To gain access to the carburetor mounting nuts, remove the low-idle solenoid assembly by unscrewing two philips head screws on the carb top.
- Unclip the throttle link from the throttle arm of the carb.
- Remove the carburetor mounting nuts, and lift the Carter off of its mounting studs. Keep it level -- fuel remains inside and can leak out. Drain the fuel from the carb by tilting up the inlet side while holding the carb over a can or bucket.
- Remove the adapter plate/spacer below the carb by prying it up with a screwdriver. Be careful not to score the intake manifold mounting surface.
- Stuff rags or paper towels into the intake manifold holes to prevent dirt or pars from falling in.
- Clean the mounting surface with a soft scraper (wood or plastic), rags and solvent.
- Apply some Gunk Liquid Wrench to the base of the mounting studs and let sit for 15 to 20 minutes. Using two of the original mounting nuts as jam-nuts, remove the original mounting studs from the manifold: put on one nut, put on the second nut, unscrew the bottom nut up against the upper nut with a 7/16 inch open end wrench until the stud breaks loose and can be removed. Failing this, use a small pipe wrench to remove the studs -- there are new ones in the Weber kit.
- Dismantle the throttle linkage bracket and crank assembly from the intake manifold and unclip/dismount the throttle cable from the assembly. The cable head can be dismounted by squeezing the ears with channel-lock pliers to back it out of the square hole in the bracket.
- Install the brass barb fitting from the adapter bag using teflon tape into the side hole in the edge of the top adapter plate.
- Using the other multi-hole gasket, install the top adapter plate onto the bottom plate with four sockethead allen screws.
- Using a length of 3/8-inch hose (I used a piece from the old Carter breather hose), connect the Decel Valve to the barb fitting (the old hose there is too short to reach.) Clamps are not required on this hose.
- Place the last gasket (4 holes only) over the studs and install the Weber 34 carburetor on the studs with the furnished hex nuts and washers. I found that I had to install the nut by the throttle linkage first, holding the carb up a little so the nut would clear a boss in the casting.
- Tighten all nuts in a criss-cross pattern.
- Using 5/16-inch fuel hose, connect and clamp your gas line to the Weber fuel inlet barb fitting.
- Cover the small brass vacuum port fitting with one of the plastic covers from the connection fittings bag, or relocate your VAC (vacuum advance line) here. Some claim to get better performance from this, although I was unable to tell much difference. I used the original manifold vacuum source. It allows me to measure manifold vacuum at the distributor end of the line.
- Install the air cleaner bottom plate. Notice that the valve cover breather port goes towards the valve cover. I found that I had to shorten the 10-32 screws by about an 1/8-inch because they bottomed out in the casting holes. There was no air cleaner gasket in my kit, so I made one from some sheet gasket material I had on hand.
- Connect a length of 3/8-inch hose between the port on the bottom of the plate to the valve cover breather (rear of the engine).
- Attach the electric choke wire to the pin on the choke cover. IMPORTANT! If the connector does not grab the choke electical lug firmly, replace the connector. If this connector comes off while driving, the automatic choke will cool, and cause the engine to race at high RPM.
Pull your coil wire (center) on the distributor, and crank the engine a few seconds to pressurize the fuel line. Check for leaks and correct any problems before proceeding. There should be no fuel going into the primary throat of the carburetor. If there is, you may have to perform a float level adjustment, or install a regulator, or both.
The Weber 34 DGEC supposedly arrives 'pre-adjusted.' But I had to adjust the idle mixture and idle speed, which are interactive, as well as the choke vacuum pull-out and fast idle speed. I screwed the idle mixture screw in until just seated and backed it out one and a half turns. I subsequently turned it more in by about a full turn. I suspected this meant my idle jet is too rich for my altitude (2100 feet.) The jets are a one-piece fuel metering only design. Air correction must be done somewhere else. I could not find an exploded parts diagram for the 34 DGEC at the time of this conversion. The primary jet was 65 (.065mm), secondary 47.5 (.0475mm). I sent for five more jets, ranging from 60 down to 45. With some experimentation, I ended up with 47.5 in the primary side, 45 in the secondary. The idle mixture screw now peaks RPMs at about one and a quarter turns out.
I had originally set the idle speed by the instructions (all the way out, then back in until it touches), but it idled at about 700 RPM, so I had to turn it in a little.
The fast idle was low -- Jeep recommends 1800RPM, I set mine for about that.
I found that the choke pull-out adjustment was almost all the way out, keeping the choke butterfly closed and rich after starting. Left this way, the engine eventually choked to a smelly stop (so much for 'preadjusted'!) To open it up, I turned the screw in about 4 or 5 turns without touching the linkage so the choke opens enough to smoothly run at fast idle of 1800RPM. This adjustment is interactive with the fast idle speed. As you turn it in, the choke plate opens, raising the fast idle speed. On my 34 DGEC, the fast idle screw is a 6mm hex head with a 7mm locknut.
Replace the coil wire and start the engine. Use the pictures in the kit instructions to locate the idle speed, idle mixture and fast idle (choked) screws, and adjust accordingly. Mine idles smoothly at 700 RPM, just where I like it for all-weather reliability, and 1800 RPM when cold and choked. After the electric choke warms up the choke butterfly releases automatically when the pedal is tapped, and the idle-step cam rotates to the low idle position.
I also checked the timing while I was under the hood. I set the initial timing at 9 degrees advance with the vacuum line at the distributor disconnected and plugged, the Vac. Sw. unplugged, and idle speed cranked up at 1600 RPM. My Vac. Sw. plug is located on the firewall above the rear of the valve cover. To measure intake vacuum, you have to connect your gauge to the original manifold tap, where the brake booster attaches. This should also be where your distributor vacuum line connects. Do not use the carb throat vac port as recommended in the carb kit instructions.
After timing the engine, it's a good idea to re-adjust the carb idle speed and mixture at 650 to 700 RPM with the vacuum line reconnected. There is a carb idle adjustment procedure online at RedlineWeber.com that you can use if you need to.
Addendum: The Weber throttle shaft coil spring is too weak to reliably return to full “off”, because of the somewhat radical bend you get in the throttle cable in this installation. I retrieved the old spring and hooked it between the attachment point on the linkage and a home-made bracket.
I fastened the bracket to the nearest bolt on the brake booster. Dismounting and reconnecting the EGR TVS (round yellow plastic thingy in the original air cleaner housing) helped reduce the noxious NOX fumes in the exhaust. I just tucked it into the mess of vacuum switches at the rear top of the valve cover.
Warm Restart Fix
I had some problems with warm restarts after driving for a few miles -- it required a half minute of cranking to get it to restart. Black smoke — flooded I guess. I tried re-installing the original 3-line fuel filter ahead of the carb, but that didn't quite do it. I got a 3x3/8in brass barb tee and soldered a cut-off head of a brass philips head screw into the branch opening. In this screw head I drilled a 7/64-inch hole and connected that to the fuel to tank return line. The result is a no-moving-parts pressure regulayor! See the final configuration picture above for the location and hookup of the tee. This has improved warm restarts, even on hot summer days. It also successfully functions as a pressure regulator, bringing the carb fuel pressure down from 5 or 6 psi to 3.5 psi required by Weber. Just remember to NOT press the accelerator pedal before warm-restarting. If you do, the carb will flood the intake manifold.