Modified 30/31

[H2OSB]

I'm starting this thread as a result of a memory triggered by something Xevin said in Tim's "034" thread.

I recently met a semi-local well known, well respected VW guru who's been working on VWs for 46 years. He only builds DP 1600s for customers because that's the biggest factory size T1 (at least that's the impression I got from our convo. He may build other sizes). He asked me what carb I had on my '73 Super, which was the car I was driving when I went to his shop. I told him stock 34 PICT-3. He said, "factory junk!" He suggested you take a 30/31 PICT and drill out the main jet and emulsion tube with a number 54 drill bit. You then have a carb that responds immediately to trottle input with no hesitation.

I'm down to try this out, but my car is running well, and I don't want to screw up the Karma. Is this a known thing? Crazy old guy idea? I wanted to run it by those of you who know more about tuning a stock DP than me (i.e. most everyone).

H2OSB

[73SlowBug]

I'd buy another carb and try it on that one!
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Daily driven....Slowly.

[H2OSB]

The '73 I'm currently driving regularly, for some reason, had a 1600 SP with a 30/31 installed by the P.O. I swapped it out for the DP I have in there now. Then, some time after I removed it, my teenage son decided (without asking me) he wanted to see what the internals of a VW engine look like. In other words, I have a 30/31 on hand, that's not currently being used.

H2OSB

[allamaabroad]

I'm running a 30/31 carb on my 1679 DP. I've tried a really nice restored OG 34-3 on my engine, but ended up going back to the 30/31 because it just felt better. Its a good carb and plays nicely with an 009, so I could definitely see modifying it a bit to work better.

The shop I work at occasionally builds "super stock" carbs. You take a stock carb, pop the venturi out of it, then put the carb on the engine and keep drilling out the air jet and emulsion tube bigger until the engine runs right. I'd be interested to see this be done with a 30/31 to get a little more breathing out of it
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[ashman40]

What distributor are you running with the 34Pict and which distributor are you planning to run with the H30/31?

The 34Pict carb is a lean running carb and works well with distributors that "compensate" for this. This means running it with an SVDA or DVDA distributor. The vacuum advance port on the left of the car is "ported vacuum" which is what the SVDA/DVDA need for vacuum advance. If you try to run a 34pict w/ a 009 you will struggle as the 009 doesn't provide the needed timing kick just off idle to match the carb.

The H30/31 carb is smaller but probably more tolerant. The vacuum advance on the left side of the car is NOT "ported vacuum". It is "venturi vacuum" which is correct for the earlier SVA distributors. Matching an H30/31 with a 205T/205M distributor is a good match. If running with a 009 distributor, opening the jets as suggested would richen the mixture. This works to move the carb away from the lean running configuration found in the 34Pict models and makes for a richer running carb.

The downside of the H30/31 is the size of the carb throat (bore). The 1600DP can flow better than the older 1600SP or 1500SP engines. They can take advantage of the better flowing 34Pict carb. This means at upper rpms you could run into a point where the smaller H30/31 can no longer feed the larger 1600DP engine. But at all points below this the carb will be MORE responsive. This is the nature of a smaller throat bore (31mm is smaller than 34mm).

So, I don't doubt your mechanic's statement. You can tune a H30/31 to be responsive at all rpms... below the point where it will "run out of steam". This is fine if you don't wind out your engine or are looking for max performance. Also, matching the H30/31 with the correct distributor can be a night/day difference.
The stock VW Beetle design is for an economical car, not a performance car. If you seek performance you must understand you may need to throw economy out the window. The larger jets will likely impact economy. So while you get better response you could loose MPG. It is rare that you get better performance AND better MPGs.

I suggest you look at the carb + distributor as a matched set. Use known good combos and you will get good response, performance and economy.
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[Xevin]

X2 what ashman40 stated. IMHO There a lot of seasoned mechanics ( some buddies as well) that have “Good” success with the 009 H30/31. My feeling is because they had that combo ready to go off the shelf as an inexpensive and readily available option which was much easier to match up then sourceing out and rebuilding the proper combo. There are so many OEM combinations of the 205 distributor and 34-3 pict carbs. But only the correct matching numbers will play together as VW indeeded. When I bought my bug. The PO had the 30-31 009 on it. It ran fine except the hesitation of the line. I wanted better for my wife. So when I decided to build a 1641 DP engine I wanted everything matched up with all the proper preheat, and bits in place. When i bought my 034 distributor from Bill. He wanted to know what cam I was going to use and what specific (Flange numbers) Carb I indeeded to use. The 34-3 pict carb I had Tim at Volkzbitz rebuild had a slightly different vacuum signal (my technical term might be wrong) then the distributor so Tim was able to match it up. Those two talk to each other and know how to dial them in. Also, Tim recognized, because the throttle arm was bent I must be using an alternator. This carb was intended for a generator. So he replaced it with the correct one. I had no idea the same 34-3 carbs and 205 distributors have so many differences. My mechanic buddies didn’t either. At the shops my buddies grew up working in used new aftermarket stuff off the shelf or high performance aftermarket stuff that they could get to work “Well”

One of my mechanic buddies just bought a total stock 70 bus. He tows an Eriba trailer. He’s amazed at how well it performs and has a new appreciation for stock.

Full disclosure:
I haven’t run the stock setup yet as the engine is still being built. So I might just be talking out of my ass on the carb/distributor set up Good luck on your pursuit.
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[H2OSB]

Thanks guys! That's more help than I'd hoped for. The old guy only uses German parts, but I'm pretty sure he uses 009s with his modified 30/31. My car currently has a 009.

I'll give it a try.

H2OSB

[johnanddes]

[ashman40]

[glutamodo]

Ashman, I've posted before that exact same speculation. If someone offered a 34PICT-1 I'd queue up to get one! Even without some of the customizing elements you listed. Hell if someone just made a nice round-bowl carb with the pre-emissions idle circuit, but feeding a 34mm flange, I'd be happy. I think many others would be as well, so I find it rather strange that no one has tried to do so... despite Emissions Laws.
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[Tim Donahoe]

Latenightaircooled in Chico, swears by the H 30/31 009 combo, as long as the carb is “improved on”. By that, I assumed he meant drilling throttle plates and changing jets. Personally, I don’t really know since my 34 pict 3 with the 034 combination gets me off the line well, and accelerates fine in all gears (well, as much as a 1600 dual port can, anyway).

I get decent gas mileage with the original combination, too; although, I only tested the highway mileage once. It was 28 mpg. Not too shabby with our ethanol gas ....

Tim
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