Edelbrock, one of the leading manufacturers of high performance bolt on parts for automobiles introduces a high performance off-road/dual-purpose carburetor for the Honda 400EX and Honda XR motorcycles.

We met Jason Rayburn from the research and development department and Mike Price, the lead technician at Edelbrock. Edelbrock has a large facility located in San Jacinto, California.

We brought a 2000 Honda 400EX, basically stock except for a Yoshimura full race exhaust and a K&N Filter to be fitted with the new Qwik Silver carburetor. Our goal was to improve throttle response while increasing overall torque and horsepower, which we did!

The Edelbrock Qwik Silver carburetor is 100% American-made and available in chrome or ball-burnished finish. It features a unique patented Dual-Venting System, which is designed to minimize the effects of altitude changes. This eliminates the constant tuning that other brands require. The bowl has external vents to eliminate flooding in the event of a roll over, which also allows for quick and easy restarts.  

The Qwik Silver carb also features a simple, externally adjustable, single fuel circuit. If you’re experiencing hard starting or a lag in acceleration then it’s running lean. You need to make a simple adjustment with the needle adjuster at the top of the carb. No changing jets in this carb, all adjustments are made by either adjusting or changing the needle. Very simple!

We put both the stock Honda and the Qwik Silver carbs side by side, with the throttle held wide open for comparison. The Honda carb has two butterfly valves; one in the middle (normal location) and one on the end; the slide (partially showing), and needle along with lots of other “garbage” that causes airflow turbulence which results in power robbing performance. The Qwik Silver carb basically has ONLY a .125” wide needle! This allows you to use a smaller carb and still get more torque and horse power. Other carbs need to be larger to flow the same amount of air and fuel as the Qwik Silver carb. The larger the opening, the slower the velocity, causing slower acceleration. If you compare a 38mm Qwik Silver carb to a stock 40mm carb, the Qwik Silver will out flow it by 10%!

We started the upgrade process by installing a set of street tires used for the dyno machine. We wanted to find out what the horsepower and torque were before we installed the Qwik Silver carb. We put the TRX400EX on the dyno machine securing it with tie downs on the rear and a chain wrapped tight around the front bumper. A scissor jack was also used to get the front wheels slightly off the ground. After the quad was secured, we attached an RPM Pickup to the spark plug wire to read the rpm’s and proceeded to take a measurement. We measured 28.5 hp with 23.2 ft-lbs of torque. After removing the air box lid we gained an additional 2 hp.

Then we rolled the quad into the shop to begin installing the new Qwik Silver carburetor. First we removed all the plastic and the fuel tank, then we removed the throttle cable (paying close attention to the routing of the cable). Next we removed the air box and air box intake tube, and then the stock carb. It’s a good idea to stuff a clean rag into the intake manifold to keep debris out of the motor.

Installation is not as easy as a common carb, but still simple. This installation is for a thumb throttle. Consult the detailed instructions for the twist throttle set up. First you need to use a razor blade to remove the rubber alignment tabs from the intake manifold, leaving a smooth surface on the outside edge on the manifold. Next you need to remove the existing pipe plug (in the cap of the Qwik Silver carb) and set it aside for future use. Install the provided metering adjustment tool on top of the carb, but do not over tighten. Then install the provided fuel line to the carb, remove the rag from the intake and install the carb into the intake. Do not tighten at this time. Next, install the cable in the 8:00 position of the cable wheel on the carb, then into the routing bracket just behind the wheel and secure it with the Phillips screw. The cable must be adjusted to allow for wide-open throttle pull. Check that the slide in the carb will go all the way up before continuing. You can make adjustments with the idle by adjusting the screw to the left of the cable wheel.

Next you have to remove some of the aluminum in the thumb throttle housing to allow for the pivot arm to swing farther than the stock set up. This is easily done with a dremmil tool. This carb does not have a longer slide, the geometry of the carb is slightly different than stock and needs to be able to move farther. The next step is to remove the stock air intake tube from the air box. Use a hack saw to cut about 1.5 inches off the end of the tube to allow the newly positioned throttle cable to function properly. In our case, we removed the tube altogether and plugged the hole. You can use a 2-inch engine freeze plug or make your own design for a plug. It’s not critical that this hole is plugged. Some people who ride in lots of mud may want it plugged. Re-install the air intake tube, tighten all clamps securing the carb to the intake boot and don’t forget to re-insert the crank vent hose into the air boot.


Install the fuel tank, cut the fuel line to the proper length, then install and secure the fuel line. Turn on the gas to check for any leaks. Fully open the throttle several times to prime the accelerator pump. This should only take a few pulls of the throttle, if it's done too many times you will flood the motor. If this happens hold the throttle wide open while starting the motor.

The Edelbrock Qwik Silver carb virtually eliminates cold starting problems because of the built in accelerator pump. Accelerator pumps are mainly used for four stroke motors where instant low rpm throttle response is needed. It’s also fully adjustable to fine tune throttle response for different combinations and riding styles. The pump adjustment screw is set to 2 ¼ turns out. By turning the adjustment screw to the left it will allow more fuel to be returned back to the float bowl resulting in less fuel being sent to the pump squirter to feed the motor. The further in the adjustment the less fuel is sent to the float bowl.

One push of the starter button and this 400EX roared to life! We test rode it in the parking lot to check throttle response. After minor adjustments of the accelerator pump adjustment screw, we put it back on the dyno machine to see how the Qwik Silver carb really helped. After the first run we noticed a huge difference in the torque curve. With the stock carb you can see 3 distinct dips in the torque curve between 3500 and 6500 rpm due to the carb switching from the needle jet to the pilot jet to the main jet. With the Qwik Silver carb it’s one continuous smooth curve between the same rpm’s. Torque is the main ingredient in having a powerful motor. Without torque you have no usable horsepower! In the horsepower department we gained an overall of 3.5hp, going from 28.5 to 32hp including removing the air box lid. This reading would have been greater if the motor had modifications like a high compression piston wilder cam and an after market rev-limiter.

So how does it run? It runs great! No more cold starting problems with better throttle response and more noticeable torque. We tested it on a large hill at Dumont sand dunes.

It was crisp off the bottom end and pulled considerably harder up the long hill. If you're looking to improve the power to your TRX400EX, the Edelbrock Qwick Silver carburetor should definitely be on your modification list!