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Thread: Over-boring a Weber 32/36 dgav

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    Rolleyes Over-boring a Weber 32/36 dgav

    Hi guys. Can anyone please show me the proper way to bore out a Weber 32/36 dgav carb from 26/27 to 27/28? I read an article in Hot Rod Magazine (USA) quite a few decades ago that off-roaders from California tweak their Webers that they use in their air cooled VW engines. Cheers!!

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    Re: Over-boring a Weber 32/36 dgav

    theres loads of ways to do it, if you carefull you can do it by hand with a die grinder and drum roll. its better done in a milling machine or lathe though, as you ideally need to maintain the original cross sectional shape

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    Re: Over-boring a Weber 32/36 dgav

    Overbore 1mm in first step, 2mm (max) for second and they will flow a lot more power (I'm not talking about air, it's just not working this way). With this mod it should flow enough "air" (power) for any Pinto engine. The rest of the engine (single carb manifold setup) will not be much better so extra air will not make extra power.

    You can "round" it all up with Dremel at the entry, same on the other side. Best way to do the part between choke and throttle plate is using a lathe but centering is difficult because it's all "cast" on top, it is not correct center. This way you can make the exit of the choke correct at the right angle but don't worry too much, it will work as it is too. I regular build this kind of carbs (also 38 DGAS for V8 engines where I use a larger turned out choke). Only little extra makes already good results. Going too large and the carb will be a pig to tune on the road.
    Last edited by onyd; 12-01-2020 at 15:17.

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    Re: Over-boring a Weber 32/36 dgav

    Quote Originally Posted by onyd View Post

    You can "round" it all up with Dremel at the entry, same on the other side. Best way to do the part between choke and throttle plate is using a lathe but centering is difficult because it's all "cast" on top, it is not correct center. This way you can make the exit of the choke correct at the right angle but don't worry too much, it will work as it is too.
    just like parallel boring dcoe chokes, technically bad, but most people do it that way and they still work!

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    Re: Over-boring a Weber 32/36 dgav

    Correct, as long as you don't bore 30mm to 36mm it is working. And even if you do it, with some funny jetting it will still work.

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    Re: Over-boring a Weber 32/36 dgav

    Sir Onyd, could you show me, precisely by drawing, how to bore out the Weber DGAV carb properly? I am new at this and any wrong instruction I give the machine shop will just destroy the carburettor.

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    Re: Over-boring a Weber 32/36 dgav

    Sir Graham, Is it correct to say that I can only bore out 1 mm on each of the primary & secondary barrels? If I bore them both 2 mm, would my carb still be tuneable? What is the proper size Auxiliary venturi to use in each barrel after over-boring them 1 mm? Thanks.

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    Re: Over-boring a Weber 32/36 dgav

    For not having any tuning problems, just bore first step max 1mm en second max 2. Even 1mm is enough in most cases. If flow a lot more power. Please note, it will only help you further if the engine can use the extra air, otherwise it is a waste of time.

    For a standard engine, 1mm in second stap will be all what is needed, leave the first step standard.

    Just drill it out straight 1mm. Milling machine is most easy to center. Use a Dremel and some abrasive paper to round off the corners and it will work just perfect.

    The most important part to keep your carb tunable is the camshaft. If you add to much valve lift at TDC or too much duration, the carb will be very difficult to be tuned.

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    Re: Over-boring a Weber 32/36 dgav

    Okay, sir Onyd. Thank you for the information again!! One more inquiry, if you don't mind. I plan on using my china-made 38 DGES on my 1600 SOHC 8 valve Mitsubishi engine. Will it work or will it be overfed? tnx again!

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    Re: Over-boring a Weber 32/36 dgav

    If your engine is 1600 cc, I suggest not to overbore the 32/36. Or at least not the first step. 1 or max 2 mm at second step if the engine is really high tuned. For standard engine and road use, I would not touch the chokes.

    38 DGAS on a 4 cylinder. This was a popular tuning add in the early "day's of no knowledge at all". It is the worse move you can make. Specially on a 1600 cc. You will loose all the good things the 32/36 can give you and only get bad ones in return. If you really need a bigger carb (but I feel you don't) start from 32/36 DGAV and enlarge the chokes. It will flow all the air you need.

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    Re: Over-boring a Weber 32/36 dgav

    As ONYD says, back in the day, the 38 DGAS was a 'supposed hot mod' but they were virtually untunable and proved not good at all - and that was with 2.0L engines but they did work acceptably on the V6's. I'd have thought a 32/36 would be plenty big enough for a 1600 unless head work / a cam is in the mix?

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    Re: Over-boring a Weber 32/36 dgav

    Correct Katana, 38DGAS do work brilliant on V6, 6 inline, and small V8 engines (with or without enlarged chokes). You can play with the whole setup like full load enrichment, high speed enrichment, and of course, the jetting. But not on small 4 cylinders. They are just not designed for them.
    Last edited by onyd; 20-02-2020 at 20:20.

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    Re: Over-boring a Weber 32/36 dgav

    Quote Originally Posted by katana View Post
    As ONYD says, back in the day, the 38 DGAS was a 'supposed hot mod'
    absolutely, and there was almost no evidence they actually gave more power, might of felt faster when you gave the throttle pedal a small shove, but that was most likely down to the synchronised throttles. with only a 1mm increase on dia on one choke there cannot be a huge power gain

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    Re: Over-boring a Weber 32/36 dgav

    Quote Originally Posted by onyd View Post
    Correct Katana, 38DGAS do work brilliant on V6, 6 inline, and small V8 engines (with or without enlarged chokes). You can play with the whole setup like full load enrichment, high speed enrichment, and of course, the jetting. But not on small 4 cylinders. They are just not designed for them.
    So what is actually so different on the 38DGAS that it will not work properly on a 4 cylinder?

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    Re: Over-boring a Weber 32/36 dgav

    i thinks its mainly the idle bleeds, which leaves then dead rich at light throttle

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    Re: Over-boring a Weber 32/36 dgav

    That's the only thing we changed many moons ago on a 38DGAS before fitting it to a Pinto.
    Fastroadcars have a 38DGMS suitable for a Pinto, they fit a 145 idle air bleed think we used a 150 .

    https://fastroadcars.co.uk/store/ind...product_id=589

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    Re: Over-boring a Weber 32/36 dgav

    The first and most importante problem with the 38 DGAS on a small 4 cylinder engine is the fact both valve open at the same time and feeding 4 cylinders where it was original designed so that 3 cylinders where sucking on each barrel. Which means in most situations, a 1500 cc 3 cylinder has a 38mm carburetor with 27mm choke.

    When fitted in a Pinto, a 2Ltr see 2x 38 and 2x 27mm choke direct. Not one after the other. The original 32/36 opens progression first after the other. It does make a big difference in jetting the engine from idle over light load to full load. A lot more variables to play with. By fitting the 38 DGAS you just loose all these advances. Further more, the full load jetting and full speed jetting is also not very good for this setup. It can be altered but even then you stick with a carburetor worse as original fitted. It is just not designed to work in this situation. I only got disadvances, not a single advance.

    About the progression opening of one valve after the other in the 32/36. Today the sell a kit so you can change this and have both first and second step opening at the same time. More like a 38 DGAS. I believe Weber is selling this kit. Honest, this is the most stupid thing you can do. It does not change anything at full throttle (both valve are open anyway) but you loose the whole progression what makes this carb so interesting. I can't believe someone was so stupid to do this and they even sell it. It is every clear, not a lot of people have a real understanding of carburetors and setups.

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    Re: Over-boring a Weber 32/36 dgav

    Wery interesting read this! I`we been trying to learn more about the 32/36 so I can keep it on my Pinto in stead if EFI. So if I`m correct in my thaugts the 32/36 works best on a 4 cylinder because it sucks only trough one barrel on light load and therefore the airspeed is much higher trough it than two barrels on the 38?

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