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Thread: Weber 38DGAS - Tuning

  1. #1
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    Weber 38DGAS - Tuning

    38DGAS Tuning

    CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT

    Base line Settings
    Speed Screw 1/2 turn in
    Mixture Screws 1 turn out
    Final Settings Engine Running
    Mix______
    Speed_____


    It is important to verify all linkage and levers are installed without binding and the linkage opens to full throttle and closes to the Idle Speed Screw. The number one and two reasons for tuning errors are improper linkage installations and over tightened linkage nut, causing a binding in linkage assembly.

    CALIBRATIONS MAY VARY DUE TO REGIONAL FUELS AND STATE OF ENGINE TUNE AND PERFORMANCE. POOR RUNNING DOES NOT ALWAYS MEAN A BAD OR POORLY ADJUSTED CARBURETOR. AN ADVANTAGE OF THE WEBER CARBURETOR IS ITS EASE OF ADJUSTMENT AND TUNING.

    SET UP ADJUSTMENTS
    1. Start set up by confirming carb base line settings. Do not depend on the existing settings.
    2. All settings are done with choke disengaged or warmed up so that the choke is fully opened and disengaged. This is done on automatic choke carburetors by first opening the choke butterfly by hand and inserting a wood block or wedge of some kind to hold open while the linkage is cycled (linkage operated through its full movement ) to clear the choke cam. (You will hear a metallic click as the choke cam is released. You can check the choke fast Idle screw under the choke assembly to confirm that it is not in contact with the choke fast idle cam.)
    3. Set the Idle Speed Screw by backing out the Idle Speed Screw until it is not in contact with the throttle stop lever. Cycle or Snap the linkage again to be sure that the linkage comes to close without any assistance. (Checking for linkage bind) Now bring screw back into contact with the lever and continue to open or screwing in, no more than 1/2 turn in, maximum.
    4. Set the mixture screws by turning each screw in until it lightly seats. DO NOT FORCE OR BIND AS THIS WILL CAUSE DAMAGE TO THE SCREW AND ITS SEAT IN THE BODY OF CARBURETOR. Back out the screw 1 full turn.
    TUNING:
    1. BE SURE TO FOLLOW THE NEXT INSTRUCTIONS IN THE PROPER SEQUENCE, DEVIATION WILL CAUSE THE CARBURETOR TO NOT FUNCTION TO ITS IDEAL SPECIFICATIONS AND MAY NOT PROVIDE THE PERFORMANCE AND FUEL ECONOMY AS DESIGNED.
    2. 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.
    3. The first thing, do not set up 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 back out the screw (recommend turning 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 to the point where it ran its best.
    4. Use your ear, not a scope or tuning instruments at this point. You want to tune the engine by sound. Adjust to best, fastest and smoothest running point.
    5. 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 turn to achieve the idle speed you like.
    6. Check and set idle to your driving preference. Put the car in gear and apply slight load, (AC on) and set the Idle as you like it. Dont set it too high, as this will cause causes excessive clutch and brake wear. The Idle only needs to be 650 to 800 RPM with light load or AC on.
    7. Recheck timing and vacuum hook ups. Recheck mixture screw to lean best idle again. If all is still best and smoothest idle then confirm and note the final settings.
    8. To confirm settings with the engine running. Start by screwing in the mixture screw and count the number of turns it takes to bottom out and note if the engine dies. If Idle Mixture screws are with in turn of base line setting then all is well. Also check the speed screw and note how many total turns from initial contact. You may have opened (turned in) the speed screw. Your final setting should be under 3/4 turn in. Reset the screws (back in) to the best final settings (Per your notes) and go on a test drive. If the settings are other than described then you may want to recalibrate the Idle circuit (low speed circuit) to your engines needs. This is done by following the rule of thumb BELOW.
    Simple Rules for low speed calibration
    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 turn or less, then the Idle jet is too rich (too large). These assumptions are based on the fact that the speed screw setting is not opened more than 1/2 turn in. If the speed screw has to be opened1/2 or more turns then this is also an indication of a lean condition usually requiring greater change. At times it may appear to be showing signs of richness or flooding it is really a lean condition. Please understand the need to keep throttle plate as near to closed as possible so as not to prematurely expose the transition holes. This is what causes the visible rich condition, and confirms the need to increase the jet size. JET KITS are available if needed.
    EXAMPLE With the idle speed screw set at no more than 1/2 turn in after contact with the stop lever; and the best idle occurring with the idle mixture screw set at 1 1/2 turns from lightly seating, indicates the need for a larger Idle jet. Achieving the best idle at less than 1/2 turn indicates the need for a smaller idle jet.

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    Re: Weber 38DGAS - Tuning

    Nothing about balancing the 2 chokes? Usually the lean mixture hunt is due to incorrect idle air bushes when the carb is fitted to a different engine than its intended.

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    Re: Weber 38DGAS - Tuning

    i just cant get mine working, ahhhhhhhhhhhhhhhhhhhhhh

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    Re: Weber 38DGAS - Tuning

    What's wrong with yours?

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    Re: Weber 38DGAS - Tuning

    The only thing i see the DGAS carb work 100% good on is a Oval Hot rod engine were its flat out from the off. Its not easy getting to work correctlly on a mild tune from idle cruising ect ect.

    Best of with a 34/36 DGAV all round better carb.

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    Re: Weber 38DGAS - Tuning

    I have to ask now- can a standard 38/38 DGAS/ DGS be made to work simply on a mildly modded pinto for road use or would I just be better off changing to a 32/36 ?

    When I bought my pinto engined kit car the PO advised me to change the 38/38 DGAS for a 32/36 DGV. He had one on it previously and thought it knocked the spots off the 38/38 for acceleration, smoothness and economy.

    I thought this was a bit defeatist so convinced myself it would improve by changing the auto choke to manual; well this tamed the occasional run away idle speed and improved cold starting but the idle/ low volume mixture was still impossible to get right - it always seemed to jump from too lean to too rich, there was always a flat spot coming off idle to a certain extent and it felt a bit asthmatic higher in the rev range despite swapping jets and adjusting to get the plugs the right colour.
    I then built up a slightly quicker engine, fr32 cam, vernier pulley, injection head with a 1 mm skim , a thinner Victor Reinz gasket and megajolt ignition. Unsurprisingly the carb behaved as before.

    I put it down to this particular example and found another 38/38 in good nick which I setup guided by the instructions at the top of this thread. Exactly the same result with this one.

    Plenty has been written about changing the pressed in brass tubes in a 38/38 to make the idle circuit work more predictably on a Pinto. That leads to 2 real world issues, there isn’t any information out there on how to safely remove and replace the tubes using basic tooling and no one sells the replacement brass tubes separately (vendors are keen to sell brand new 38/38s with the appropriate tubes in place but wont even discuss selling them as seperate parts).

    So, would I be best grasping the nettle now and just buying a new 32/36 DGVs with slightly upsized jets ? Is this the best way of getting a guaranteed outcome ?

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    Re: Weber 38DGAS - Tuning

    About 38DGAS and road use. Only think I can say, ignore. Don't even try, it's rubbish compared to the original 32/36DGAV (or manual choke, does not matters as long as your get the jetting right).

    Second thing I feel wrong, the FR33, rubbish again, to much valve overlap for a road car. Unless you never tried anything else it may feel like a good cam but there is much better on the market.

    Fit a nice BP134 from Piper and get you 32/36DGAV setup correct on a rolling road including a good ignition advance and it's the best money can buy. Idle like original, more power and same fuel consumption as original (as long as you ask for the same power of course).

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    Re: Weber 38DGAS - Tuning

    Cam choice is pretty subjective, I know others who have had good results with the Kent FR32 but with thats not the issue.

    The probs with the 38/38 were the same on the old standard engine as they are now. Its the carb I'm regarding as the problem i'm looking for advice on.

    Is there a sure fire available source of the modified brass tubes for a 38/38 or am I better off investing in a new 32/36 Dgv ?

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    Re: Weber 38DGAS - Tuning

    The reason you cannot get the idle mixture correct is because the idle air bushes need to be changed, this then allows the mixture to be set correctly and maintained.
    The best drivers have dead flies on the side windows.

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    Re: Weber 38DGAS - Tuning

    Anthony at Fastroadcars www.fastroadcars.co.uk sells a modified DGAS for a 2 litre engine, at least he did when I last checked his website.

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    Re: Weber 38DGAS - Tuning

    Quote Originally Posted by Miniliteman View Post
    Anthony at Fastroadcars www.fastroadcars.co.uk sells a modified DGAS for a 2 litre engine, at least he did when I last checked his website.
    I just make up my own idle air bushes.
    The best drivers have dead flies on the side windows.

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    Re: Weber 38DGAS - Tuning

    Quote Originally Posted by Miniliteman View Post
    Anthony at Fastroadcars www.fastroadcars.co.uk sells a modified DGAS for a 2 litre engine, at least he did when I last checked his website.
    Interesting site, does anyone have any opinions on his 32/36 DGV 5A for hot rod/ race/ rally? throttles synchronised and pump jet modified to inject fuel down both venturis? Thinking road rally use maximum two chokes?

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    Re: Weber 38DGAS - Tuning

    full throttle is full throttle, if you want max power put your foot flat to the floor so i dont see any point in synchronising throttles, it just makes part throttle driving more difficult.

    bore the chokes out a little, thin the throttle spindles , if your prepared to warm the engine before driving remove the choke flaps, as a halfway house you can just remove the secondary choke flap and its half of the spindle, most importantly for good intake flow radius the top of the inlet manifold runners where they join the plenum. having done that lot the 32/36 will do practically anything you need from it, the next step would be split 48's.
    Last edited by Graham; 24-03-2014 at 15:39.

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    Re: Weber 38DGAS - Tuning

    how do you get rid of flat spot on 38 dgas or would i be beter with 34 dgas

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    Re: Weber 38DGAS - Tuning

    if your talking about the just off idle flat spot when the carb is on a 2.0, with difficulty its going lean in progression, you need to reduce the size of the idle air bleeds which are not removable!

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    Re: Weber 38DGAS - Tuning

    a 34 dgas has small throttles and smaller still chokes, unless you have a 1300-1600 engine not a good move if your looking for performance!

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    Re: Weber 38DGAS - Tuning

    Best (and only) way to get rid of 38DGAS flat spot is replacing with 32/36DGAV. If the engine is highly tuned (as far as you can realistic tune with one carb) you can slightly overbore the chokes. Nothing more is needed, 38DGAS will not make more power.

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    Re: Weber 38DGAS - Tuning

    thanks

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    Re: Weber 38DGAS - Tuning

    what size are standered main jets for the 32/ 36 DGAV

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    Re: Weber 38DGAS - Tuning

    Quote Originally Posted by darren325 View Post
    what size are standered main jets for the 32/ 36 DGAV
    how long you got? depending on exactly which carb model yo have and what its for anything from 115 upto 150

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    Re: Weber 38DGAS - Tuning

    oh lol il have a look but going on pinto with a gts 2 cam

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    Re: Weber 38DGAS - Tuning

    how much is good amount to bore the chokes .

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    Re: Weber 38DGAS - Tuning

    1mm out of each, 2 tops. that might not sound a lot but its a big increase in cross sectional area, if you do bore the chokes try to reshape them so they retain the same cross sectional shape as origional

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    Re: Weber 38DGAS - Tuning

    ok thanks

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    Re: Weber 38DGAS - Tuning

    Formula Ford trick:

    To avoid a lean mixture at halve throttle block off the high speed enrichment and place bigger jets.

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    Re: Weber 38DGAS - Tuning

    wheres high speed enrichment . is that one in botton of float chamber ?

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    Re: Weber 38DGAS - Tuning

    Quote Originally Posted by darren325 View Post
    wheres high speed enrichment . is that one in botton of float chamber ?
    Yes

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    Re: Weber 38DGAS - Tuning

    great thanks

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    Re: Weber 38DGAS - Tuning

    This is essential reading; much applies..........

    http://www.turbosport.co.uk/showthread.php?t=109939
    Regards,
    Kevin

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    Re: Weber 38DGAS - Tuning

    running a gts2 cam in pinto when revs get to 3000 its sounds flat would that be to weak its had chokes made a little bigger

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    Re: Weber 38DGAS - Tuning

    if you havnt increased the main jet size it will definatly be weak

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    Re: Weber 38DGAS - Tuning

    running 170 /170 185 air correcters

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    Re: Weber 38DGAS - Tuning

    what size have the chokes been bored to?

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    Re: Weber 38DGAS - Tuning

    only 1 mm bigger on each

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    Re: Weber 38DGAS - Tuning

    i gave up jetting carbs a LONG while ago, but i think you will need to go up on the mains to get more fuel in in the midrange, then go up on the airs to stop it going rich as hell at the top end

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    Re: Weber 38DGAS - Tuning

    Quote Originally Posted by darren325 View Post
    running 170 /170 185 air correcters
    That is okay for a GTS2.
    What size are the idle jets?

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    Re: Weber 38DGAS - Tuning

    idle jets are 55 any smaller seems to cut out with out putting hand over air filter

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    Re: Weber 38DGAS - Tuning

    that setting is ok for gts2 ?? with chokes bigger. 170 170. 185 airs

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    Re: Weber 38DGAS - Tuning

    Can I pick your brains please

    autochoke Weber 38 dgas on Essex v6

    whats best way to set high speed jet? Is it a case of driving and keep popping bonnet adjusting? It was bogging down I've advanced timing a tad and it's improved just want to set carb now
    Last edited by apples24; 31-07-2017 at 19:30.
    southampton

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    Re: Weber 38DGAS - Tuning

    Oh my bad what a plumb they are both idle mixture screws lol
    southampton

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