This introduction is a compilation of a couple Motor manual introductions, the Haynes Rochester Carburetor rebuild manual, the Doug Roe Rochester Carburetor book, and some stuff that I researched.
Fuel economy standards enacted in 1978 forced the realization that smaller engines in downsized cars were a must. The Dualjet's utility was being stretched to the limit on medium-size, low-performance GM vehicles.
A new carburetor was designed for smaller engines. The two-stage carburetor, built almost entirely of aluminum, first came out on GM front-wheel-drive vehicles. The Varajet would serve all GM divisions (see usage chart at the end) using the 2.5-liter four-cylinder and the 2.8-liter V6 until throttle body and port fuel injection technology made conventional carburetors obsolete. It was also used on the 1.8L four cylinder engines, and by the Holden division of General Motors (Australia).
The first model (1979) 2SE didn't have a Computer Command Control (CCC) system with a mixture-control solenoid and electronic idle-speed control. It was introduced as a conventional downdraft carburetor. The electronics were added within two years.
Why did RPD (Rochester Products Division) go to the expense of designing a new model for small engines when they already had the Monojet with its good track record? For the same reasons the Dualjet replaced the 2G - the idle, off-idle and main system metering couldn't be controlled enough to meet emission and economy standards. If the Monojet were downsized enough, and the venturi made sensitive enough to meet emission and fuel-economy standards, It would have been too small to deliver adequate HP.
The Varajet models 2SE and E2SE, Figs. 1 and 1A, are two barrel, two stage, down draft design carburetors. Aluminum die-castings are used for the air horn, float bowl and throttle body. A heat insulator gasket is used between the throttle body and float bowl to reduce heat transfer to the float bowl.
The 2SE two-stage was designed with a triple-venturi 35mm primary bore for fuel metering control during idle and part-throttle operation. That bore was too small to expect any reasonable HP, so a 46mm secondary bore was added. This design supported the power requirements at heavy throttle.
An air valve is used in the secondary stage with a single tapered metering rod. Metering control is governed by the air-valve opening so a suitable power mixture prevails regardless of how far open the secondary is.
The float chamber is internally vented though a vertical vent cavity in the air horn. The float chamber is also externally vented through a tube in the air horn. A hose connects this tube directly to a vacuum operated vapor vent valve located in the vapor canister. When the engine is not running, the canister vapor vent valve is open, allowing fuel vapor from the float chamber to pass into the canister where the vapor is stored until normally purged.
An adjustable part throttle screw is used in the float bowl to aid emission control. This screw is factory pre-set and a plug is installed to prevent further adjustment or fuel leakage. The plug should not be removed or the screw setting disturbed. If float bowl replacement is required, the service float bowl will include a factory pre-set and plugged adjustable part throttle screw.
A hot idle compensator is used on some models and is located in the air horn. The opening and closing of the hot idle compensator valve is controlled by a bi-metal strip that is calibrated to a specific temperature. When the valve opens, additional air is allowed to bypass the throttle valves and enter the intake manifold to prevent rough idle during periods of hot engine operation.
The idle mixture screw is recessed in the throttle body and is sealed with a hardened steel plug to prevent alteration of the factory pre-set mixture setting. The plug should not be removed and the mixture screw readjusted unless required by major carburetor overhaul or throttle body replacement.
Another feature of the 2SE is its low-profile design. On modern cars, engine compartments are smaller and hood lines lower, so tall units are out of the question.
The E2SE carburetor, includes special design features for use with the Computer controlled Catalytic Converter System (C4) or the Computer Command System. An electrically operated mixture control solenoid mounted in the air horn, controls air and fuel metered to the idle and main metering systems of the carburetor. The plunger located at the end of the solenoid is submerged in fuel in the fuel chamber of the float bowl. This plunger is controlled by an electrical signal from the Electronic Control Module (ECM). The Electronic Control Module responding to signals form the oxygen sensor in the exhaust and other engine operating signals, energizes the solenoid to move the plunger down to the lean position or de-energizes the solenoid to move the plunger up to the rich position to control fuel delivery to the idle and main metering systems. When the plunger is in the lean position, fuel metering is controlled by a lean mixture screw located in the float bowl. When the plunger is in the rich position, the additional fuel is metered to the main fuel well through a rich mixture screw located at the end of the fuel supply channel in the float bowl. Air metered to the idle system is controlled by the up and down movement of the mixture control solenoid plunger. The plunger increases or decreased air supplied to the idle system which is further metered by the idle air bleed screw. The plunger cycles up and down approximately 10 times per second, controlling air and fuel mixtures.
On 1981 models with 4-151 engine and air conditioning and 1982 models with 4-112 (1.8L) engine, an idle speed control motor which is controlled by the Electronic Control Module is used to control idle speed, Fig. 1B. The curb idle speed is programmed into the Electronic Control Module and no attempt should be made to adjust idle speed using the idle speed control motor.
CAUTION: On 1980-83 units, use care not to remove the special friction reducing coating applied to the primary and secondary throttle shafts, the secondary actuating lever and lockout lever. On 1980 V6 units and on all 1981-83 units, a special graphite compound is also applied to the secondary throttle bore and valve.
EFE Grid EFE Grid (from How to Rebuild your GM 60 V6)
If your engine is fitted with a carburetor, An Early Fuel Evaporation (EFE) grid is probably used underneath it. This grid preheats the fuel as it flows from the carburetor to the inlet manifold, thereby improving driveablity when the engine is cold. Unfortunately, this grid has a tendency to disintegrate and cause driveability problems.
After sliding the EFE grid off the carburetor mounting studs, carefully inspect it. The bars forming the grid should not show signs of erosion, and the grid should be intact for the entire opening in the plate. If the grid has any problems, replace it.
Caption If you car or truck engine is equipped with a carburetor, and is a 1981 or newer model, and Early Fuel Evaporation (EFE) grid is used underneath the carburetor. Eventually, the EFE grid breaks up, causing a host of driveability problems. If yours is missing any part of the grid, replace it.
Stripped fuel inlet http://meltingpot.fortunecity.com/thurlow/858/rochprob.html
Most Rochester carburetors are made of "pot metal".
Karl not know what that means, but it is not as strong as steel.
As a result, a notorious problem is stripped threads on the inlet.
There is a solution for this, but it is not pretty. There is a part available from
GOOD auto parts stores. It is an oversized, self-tapping, inlet fitting marketed as a
"HELP!" or "Perfect Parts" product.
You install it by forcing it to cut new threads into the fuel inlet.
It has been suggested by Doug Kichener that these fittings not be removed as there are likely
to be small metal fragments held between the threads by the new fitting. Removing the fitting
could permit these bits to get into the carb and catch in the tiny channels which flow fuel.
This is a good time to install an inline filter into the fuel line.
A new line is probably necessary anyway as the new fitting can be more than an inch long, which will
be a problem for any factory original steel tubing!
Disabled EGR Disabled EGR system.
Neither Karl, Rochester Products Division, or anyone else contributing to this site advocates or in any way recommends altering or disabling your emission control equipment in any way.
That said, those whose EGR systems have "mysteriously" ceased to function have noticed that their vehicle runs differently when EGR is non-functional.
The reason for this is that the EGR pump operates on manifold vacuum.
The primary metering rods are raised/lowered into the jet orifices by a piston that responds to the manifold vacuum signal. When the EGR is inoperative, the manifold vacuum signal
available to the carburetor is very different from the conditions that the metering rods and jets were designed for! This typically results in a lean condition, possibly including "surging".
The only real solution is to fix the EGR system.
Those incorrigibles out there who refuse to do this have to have their carburetor re-jetted and re-rodded to correct for this. Best just to use rods and jets from a pre-EGR carburetor of the same displacement.
Hopefully, Karl will be able to provide the appropriate part #s here in the future.
On a similar note, if the ECM (computer) is disconnected from an appropriate-year
Quadrajet, a severely rich condition results. Again the only real cure is re-rodding.
Needle and Seat
This is addressing a problem that Karl has had with his 1965 Rochester 2GC.
The symptoms are a periodically terrible idle that may have coincided with an instance of WOT and may similarly go away after another instance of WOT. The motor will sputter and die at idle and in fuel will contimue to flow from the discharge nozzles after the engine has
died. Sometimes fuel will leak through the throttle plate hinge shaft holes to the outside of the carburetor and onto the manifold!
This has been diagnosed for me as contamination preventing the needle from seating properly and causing a flooding or overfilling of the float bowl.
The cure for this is to rebuild the carb and replace or adjust the needle and seat.
Remove any debris from the float bowl and check or replace the fuel filter.
Notes * Use the right gasket. It may not be an exact match due to changes in the design of the gasket, but it should still have the same holes blocked/unblocked the original one did or you WILL have problems.
* Clean the carburetor. Try dipping it in a can of carburetor cleaner and brushing it off. Then spray it with some spray cleaner. Then dry with compressed air.
DO NOT USE THE CLEANER NEAR OPEN FLAME. WEAR SAFETY GOGGLES. ONLY PUT METAL PARTS IN THE CLEANER BECAUSE IT IS VERY HARD ON PLASTIC (99% CHANCE IT WILL MELT PLASTIC). IF IT WILL DISSOLVE PLASTIC, IMAGINE WHAT IT COULD DO TO YOUR EYES, SO WEAR SAFETY GOGGLES. USE THE CLEANER IN A WELL-VENTILATED AREA. DID I MENTION YOU SHOULD WEAR SAFETY GOGGLES?
* If a vacuum line looks bad (cracked, dry-rotted, etc ) replace it.
* Make sure the float level is correct. Too low a level causes a lean mixture, resulting in late or hard starting, a flat spot in acceleration, or stumble. Too high a level causes a rich mixture, resulting in the engine racing after starting, percolation, and even fuel pouring out the bowl vents.
* Some parts need to be soaked overnight, brushed, and then sprayed off. You should wear safety goggles when you do that
* I have heard of two jet/metering rod sizes so far. #174 from high-altitude carburetors (I think) and #180 from others.
Varajet quick takes Motor Age, Jan 1983 v102 p28(2)
Full Text: COPYRIGHT 1983 Chilton Company; pictures not available
FIELD FIXIN' FINICKY FUELERS
On some of these Varajet secondary vacuum break diaphragms (circle), you have to grind off or cut off the cap on the end of the diaphragm before you can reach the adjustment screw inside it. Remember to find the air bleed hold in the diaphragm and tape the bleed closed before you pump it down for the ajustment.
Because we have gotten as many complaints about air horn screw location as we've gotten about the linkage on this carb, here (at left) is your own screw locator chart [chart not available]. Tighten screws in the numbered sequence.
Little one-use, throwaway clips adorn the Varajet's linkage. If the tip or end of the linkage points outward (arrow), the teeth or raised edges of the clip must point outward as shown here. If the end of the linkage points inward, clip's teeth point inward too. Don't press the clip on so tight that it binds up the linkage! New clips are included in carb overhaul kits. Instead of growing yourself a third arm, try taping the choke blade closed during choke linkage installation.
Oh horror! Secondary metering rod can fall out and sometimes does fall out of place. The stray metering rod may just create a severe bog or hesitation and then lay inside the secondary throat of the carb. Other times, it slips past the secondary throttle blade, falls into the engine, and creates a different kind of problem! When you install the metering rod, pull back the spring on the rod (circle) and be sure that the rod snaps firmly into the little bracket on the air valve.
Remember to dab some grease on that air valve spring where the arrow is pointing. Remember that some Varajets have a Q-jet style air valve adjustment screw and lock screw at the end of the air valve shaft, some don't.
If you are extremely careful, GM's procedure for hacksawing slots alongside the mixture plug and knocking the plug out with a punch words okay. But if you are slightly un-careful, you'll crack the throttle body--the base of the carb! Experience has taught us that the safest, easiest way to remove a mixture plug is to cut around the plug with a holesaw-type tool such as the Thexton 353 or the Borroughs BT-8211. Take your time, these carbs are expensive!
Whenever you get a Varajet-equipped engine that surges or runs poorly during light-throttle or part-throttle driving, check basic engine condition, check for fault codes in the computer control system, and then check the mixture solenoid dwell at 3000 rpm in neutral. Dwell at 3000 must average 35 |. Grab a Borroughs BT-7928 or a Kent-Mmore J-28696-10, the same mixture tools you use on the Dualjet and Q-jet. Remove the vent screen from the air horn and slide the tool into the lean mixuture/lean authority screw shown here.
Holden division http://www.uq.net.au/~zznweber/commodore/tech/
Holden division of GM
VB - VK Substitute Carburetter (Black and Blue Motor)
The most common cause of engine troubles with the 202 motors was the Varajet carbi. It made the engines work to well bellow their potential. A cheap substitue for the varajet is a small Weber (32-36) off of the XE falcons. They cost around $40 dollars (plus adaption plate) and are easily fitted to these motors with only the accelerator cable mount needing to be modified. They not only provide greater horse power but also increase your fuel effeciency. (N/B: With the black motor in the
VK the secondary throttle sensor must be disconected and the computer (EST) must be reset.
From: Kris Humphrys
VH (possibly) and VK 3.3L Carby's flooding
If your sitting at the lights and your VH/VK stalls on you and a strong smell of petrol is hanging around, more than likely it is a stuck needle valve in the carby. One solution is to dismantle the carby and rekit it, or another simple and less expensive option is to take the air filter off, and where VARAJET is written, tap on it with a screwdriver. This will move the needle so it sits back in its seat.
From: David Redmond