Weber 32/36DGV verses the Weber 38DGES

(carpal tunnel)
Thu Feb 24 2005
01:12 AM
dok33
(addict)
Thu Feb 24 2005
02:12 AM
yodta
(pooh bah)
Thu Feb 24 2005
06:09 PM
Two things cause idle problems with Webers . Ok, maybe three or four but here they are:
Fuel pressure-excessive fuel pressure at idle or a high pulsation from a fuel pump can cause the carb to idle high and irratically.
3psi is the rule, 2.5 works about the best.
Vacuum leaks- #1 cause of high idle problems . No offense, but the Redline adapter plates are known to be a problem. I've made
a business out of modifying the stock intakes and adapters for the Suzuki engines . The base of the plenum on the intake needs
to be ground flat first. The bottom of the base plate also needs to be ground flat to match and a 1/16" gasket used instead of the
1/8" supplied gaskets. After that plate is installed and torqued, the top of it needs to be milled flat again as well as the bottom of
the carb adapter if it uses the 2 piece design. Then, lastly the top of the carb plate should be milled. I've had to repair a bunch of
DGV series carbs that were brand new and bent at their bases due to the plates being warped from excessive torque used to
seal them. The gaskets are way too thick and cause a problem with the plates bending . Once the whole stack is built, an
accumulative error builds up and bends the carb as well . $100 later it can be fixed...
Throttle shaft seals-some of the newer Spanish built DGV DGAS series I've had here have had a problem with the throttle shaft
seals being installed backwards. They are nylon and are broken off a "casting tree" much like model car parts . That little bump if
installed into the sealing bore results in a pretty good vacuum leak and will raise the idle speed .
Throttle plate synchronization- the 38DGAS series has a synchro adjustment on the primary throttle shaft gear. That screw allows
the gears to be meshed and fine tuned to close both throttle valves at the same time. Over time the gears wear a bit and cause
the secondary throttle valve to be left open a bit raising the idle. It's just an air leak and air leaks are just like vacuum leaks .
Some of the problem units I've had through here were not set up properly new . This timing procedure must be done with the carb
off and is a real pita but not impossible .
Another problem of note with the 38DGAS is idle jet sizes . Both idle jets have to be the same size , not drilled or different brands.
Genuine Weber idle jets are flow metered then stamped for sizing. Everyone else just stamps their sizes according to the hole
drilled. Jet sizes with Webers are very consistent , you can swap out jets that are 20yrs old and the engine don't even change
note as long as the numbers are the same. Also, lean best idle settings and calibration are very critical to the DGAS and a bit
different too .
With the carb warmed up and the choke verified to be off drop the idle as low as possible, preferrably down around 400revs or
less. To properly calibrate idle jet size the lean best idle must be set with the throttle valves shut so you are adjusting only the idle
circuit without getting into the transition circuit . The idle jets in these carbs meter the amount of fuel in volume that is available to
the transition , very important for driveability. 32/36's usually respond their best with around 1-1.5 turns out on the mix screw. Any
more turns than that and you need a larger jet . 38DGAS models usually run their best at .75-1 turns out on the mix screws . Both
should be as equally balanced as possible . Excessive number of turns on either model should indicate a need for a larger idle jet
. All the DGV series (32/36 & 38/38) place the transition circuit at the outer edge of the bores. On some manifold designs this is
not optimal due to the flow pattern of the plenum. Don't be surprised if you have to run a seemingly large idle jet to get good
driveability. Some of the Suzuki's 1.3L engines run 65-75 idle jets due to this problem. No real effect on fuel mileage but the
driveability goes way up. A great way to guage the idle jet size is to very slowly increase the idle speed screw up into the
transition stage and see if there are any flat spots. A flat spot will indicate a lack of fuel in the transition or bad spot in the timing
curve . Not sure how you guys handle the dual vacuum advance system of the 20/22r , would like to hear some info on that as
well . Hope all this makes sense....
Sarge
Re: Weber 32/36DGV verses the Weber 38DGES
bah... carbs are too complicated, I think if I get the celica I'll just throw a 7mgte in there
Re: Weber 32/36DGV verses the Weber 38DGES
Sarge, good writeup, and I agree with most of what you said, though I have to disagree slightly with a few things.
I absolutely agree that vacuum leaks are the #1 cause of inconsistent and poor idling. your plan for milling the plates flat is a must
if you decide to keep the adapter plates as your mounting solution. best route to take, however, is to go with a one-piece adapter
if you can find one, or the offy intake; do away with the adapter plates altogether. these adapter plates are cast and not machined
flat prior to distribution, so the mating surfaces are crap. milling them removes the irregularities in the mating surfaces.
right about the gaskets, too. I learned that one way early on. you DO NOT want a layered paper gasket here. the intake produces
a fair amount of vacuum and all concentrated at that little carb throat. layered paper gaskets here are just another point of failure,
so you need either a single layer, thin gasket, or forget the gaskets altogether. I understand gas-ga-cinch is the way to go.
one other common mistake is over-tightening the adapter plates. once you get the lower one installed, it's best to thread in those
four studs to where you want them, just short of contacting the lower plate, mark 'em, then pull them out and crimp the crap outta
the threads above that mark for about 1/4" or so. this will help prevent the studs from screwing further into the lower adapter plate
as you tighten the four carburetor mounting nuts. if they go in too far, the upper plate will start to lift off of the lower one, and it'll
leak. use loctite here, too, then threaded the studs in and snugg them down. the other thing to consider is to make sure you don't
over-tighten the carb mounting nuts because one of two things can happen -- 1.) you can cause the upper adapter plate to lift up
slightly, introducing a vacuum leak, or 2.)force the studs to thread in further, and if they go through the upper plate and start to
contact the lower plate, the upper plate will lift, not to mention if you crimp the threads, you can toast your upper plate.
excellent information on making sure the throttle plates are closed completely at the time you are adjusting idle circuit. they're not
very clear about this in the basic tuning instructions, are they? there's no "why" to anything they tell you in the instructions. you
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