Home > Personal, VW > 34pict-3 carburetor final

34pict-3 carburetor final

September 23, 2006

UPDATE: 22 November 2008
This post has attracted a lot of comments, and I’ve added new information in the comment stream that does not appear in the main post.  The result is a bit jumbled and hard to read for reference purposes.  At this time, I am closing comments on this thread, pending a complete re-write that will integrate all information from both the main post and the comments into one.  Then I will re-open comments. 

In the meantime, please be sure to read through all the comments.
- George

This post is everything I’ve learned about the 34PICT-3 carburetor, all pulled into one place.  Warning: long post with lots of pictures.  It is intended to supplant previous posts on the subject and I will update it rather than make new posts when new information comes along.

In the early sixties, VW had a 1300 engine with single-port heads (both cylinders shared an intake port), coupled to a Solex 32PICT carburetor and a Bosch vacuum-advance distributor. (Mind you, this is my memory talking, so don’t bet the rent-money on it.) It was a very successful engine if you weren’t in a hurry, but American buyers wanted more power.  VW responded with the 1500 and then 1600 dual-port engines, for which the super-reliable 32PICT carburetor was too small.  In many stages thus was born our nemesis, the 34PICT-3 carburetor.

This larger carb was far more complicated and was almost big enough for the engine.  Really, VW should have gone with a 2bbl carb, but I was ten years old at the time so for some reason they didn’t seek me out to ask my opinion. 

I currently have a 1600 DP engine with a 34PICT-3 carb, and it has been a challenge to get it running right.  Fuels have changed (15% alcohol has less oomph per volume, so needs to be mixed differently) and modern fuels tend to clog the jets with lacquer condensates.  My car ran very badly and I was determined to correct it. 

The 34PICT-3 really needs a longer advance curve, so you can begin with a dual-advance distributor (having both a mechanical- and vacuum-advance component.)  This is broadly known as a ‘Mexican taxicab distributor’ and Aircooled.net has a modified one they call the SVDA.  They have the advance cam reground to their own specs and specify a different timing setting that eliminates the flat-spot on the 34PICT-3.  It’s a good distributor.

Be sure to use a fuel-block (shown) to connect the vacuum outlet on the left side of the carb to the vacuum advance.  This is simply a metal tube bent in such a way as to prevent fuel from ever running down into the vacuum-advance can on the distributor and ruining the diaphram therein.

Also, get rid of your points.  Install a Pertronix or Compufire and forget about the crappy Bosch points adjusters.  (I always liked GM’s system – you could adjust the points using a dwell meter and a hex wrench with the engine running.  So simple!) 

Notice the bright red intake manifold section boots.  I think they’re made of silicone or polyurethane or something besides rubber.  They are far more resistent to cracking than the old rubber ones.

I use copper ignition wires with Bosch 1K ohm plug ends, but that’s just me.  You might do fine with fancy fiberglass-core wires.  I assume you are using the right spark plugs for your engine – the ones that came with my engine were wrong.

Next the jets in the carb need to be changed.  They are a bit lean to begin with, even assuming pure gasoline.  Your boxer engine likes the fuel mixture a bit rich.  I couldn’t find a new Solex carb, so I’m using a Bocar 34PICT-3 carb, and I installed a 130 main jet, and a 55 idle jet.  Remember on the 34PICT-3 the idle jet affects drivability and power up to about 2,000 rpm when the main jet takes over.  In other words, it’s extremely crucial for in-town driving. This helped a lot.

I think the original idle jet was a 50, but the replacement jet orifices (orifii?) were visibly larger in the new jets than the old ones.

One repeating problem I had was blown needle valves.  If you turn the carb upside down you should not be able to blow air (lips on fuel intake – do NOT use compressed air) into the float chamber.  I’d adjust the fuel pressure by stacking gaskets under the fuel pump (which is the official method from the VW service manual) but the needle valve would still go.

The symptom was that the car would run rough, smell of gas, plugs would foul, and adjusting the air idle screw would make little difference.  (This is very bad for the engine, by the way.)  Gas mileage was terrible.  I finally reckoned that the nominal fuel pressure was probably going sky-high when the engine compartment got hot.  Between the fuel pump and the filter, that’s a lot of volume to expand and alcohol has a high coefficient of expansion.  I carry a spare needle valve now – they’re only about five bucks.

The pressure solution was two-fold.  First, get all unnecessary fuel components out of the engine compartment.  You don’t want a large reservoir of fuel inside there getting hot during operation.  There is also a safety reason for this.  Once in a while the weight of the filter bouncing along on the line will work the brass fuel intake out of the carb, with flaming results.  This has never happened to me, but I have seen pictures. 

In this picture, you are looking straight down behind the left side of the engine between the oil cooler exhaust and the #3 cylinder. The steel fuel line enters the engine compartment (wrapped in an insulating cotton sleeve made from the hem of an old t-shirt) and turns upward along the front of the engine shroud, and bends across.  It is best to use a tubing bender for this operation.  Just four inches of rubber flex line remain between the steel line and the carb.  The steel line is held in place by a magnetic network cable clamp, which works great.

Notice at left there is an elaborate pass-through for the steel line through the front tin.  I enlarged the hole to accomodate a rubber sleeve around the steel line, and it is held in place by fender washers and clamps.  Maybe I am just being overly fussy, but I don’t want the sheet metal rubbing through the steel fuel line.  I don’t want it rattling, either.

I suggest two fuel filters; one under the gas tank, and one in the transmission compartment.  You don’t want any crud going in the carb.  (There is another source of jet-clogging; we’ll get to that in a minute). 

Second, regulate the fuel pressure to about 1.5 lbs/in2.  I tried one of the old Ford-type adjustable regulators, and it worked fine until it sprung a leak and blew gas all over the place.  This was corrected by retorquing the screws around the circumference but it was unnerving all the same.  Also note that the markings on the regulator are completely inaccurate.  Use a fuel-pressure gauge to adjust your pressure.

After the gas-spewing incident (and calming down, no harm was done), I got a Holly low-pressure regulator.  (Specify low-pressure: it also comes in a higher-pressure model that you don’t want.)  It is well-made and has two outputs which is nice if you ever decide to go with dual carbs.

The regulator comes with a mounting bracket which can be screwed to a firewall, and then you screw the regulator to the bracket.  I made a little secondary bracket out of some sheet metal and riveted it into the transmission well, then simply hook the regulator bracket in (with a piece of inner-tube to prevent rattling) and put a zip-tie on to hold it in place.  Anytime I want to service the regulator, I can just cut the zip-tie and slide it out.

The Holly regulator is set with a hex screw at one end opposite the intake; the farther in you screw it, the higher the pressure.  Notice in the picture how far out I had to screw it to get a low enough pressure.  Then you lock it in place with the locknut.

I gave up on mechanical fuel pumps.  It was so easy to mount an electric pump.  This one was rather cheap – someday I’ll get a totally silent rotary pump to replace it.  One nice thing about an electric pump is that it will fill your float bowl in a few seconds without having to crank the car.

In this picture you are looking up into the transmission well (with the driver’s side heater-duct removed).  The clutch lever is visible at lower-right.  At lower-left is the cheap electric fuel pump.  Fuel from the frame fuel line (large loop of flex line) enters the pump at bottom – mounted as low as possible so if I am parked pointing downhill and am low on gas the pump will ‘grab’ OK).  Then to the fuel pressure regulator at center, and out to the fuel filter at right and into the engine.  If any of these components malfunctions, they will leak fuel onto the nice, cool, non-sparky transmission rather than onto the hot, electrically sparking engine.  Not visible in this picture is a plastic mud-guard fashioned from a plastic jug and held in place by strong magnets.  The wires and hoses have been neatened up a bit since this picture was taken – I don’t like stuff flopping around, but I don’t like it held too rigidly either.

The second fuel filter is mounted in place with a ‘bracket’ consisting of a bit of plastic from a 2-litre bottle, molded with a heat-gun around a filter, and secured by two powerful magnets from an old computer hard drive.  This makes it easy to swap out the filter anytime (except for the inconvenience of crawling under the car).  I use ramps for that – they are safer than jacking up the car.

Note that with an electric pump, and with the Pertronix magnetic pickup, you don’t want to sit there with the ignition on but the engine not running for more than a few seconds.  Wire your radio accordingly.

To adjust the 34PICT-3 is different from previous models.  On earlier carbs, the adjusting screw on the throttle arm set the idle speed; on the 34PICT-3, it only sets the butterfly valve closing clearance.  You want about four thousandths of an inch clearance along the outer edge of the butterfly valve when it is in the closed position.  Do this by backing out the throttle arm screw until it just touches the lowest part of the choke cam, then turning it back in about ½ turns.  The main thing is so the butterfly valve doesn’t “stick” in the closed position.  Once this adjustment is made, you never have to set it again.

Engine running, valves adjusted, timing set: now adjust the idle speed using the great big screw on the left side of the venturi.  This is the ‘air-idle adjusting screw’ and it passes air, not fuel.  Set your idle to about 850 rpm.  Then turn the little fuel-idle adjusting screw below it clockwise until the rpm just begins to drop, then back it out about ½ to ¾ turns.  Then fine-adjust the idle with the air-idle screw again.  Repeat three or four times with the engine really warmed up to get it perfect.

A word about air cleaners.  I really like the oil-bath cleaner that VW used to use.  If you live in a volcano zone (like my brother does), it’s really the only cleaner to have and generally I just think they’re neat.  But for some reason my oil-bath cleaner wouldn’t clear my Scat powder-coated shroud – go figure; German car, Chinese shroud, 40 years apart…

Anyway I got a new Mexican VW air cleaner with a paper element and it fits perfectly.  It is an original VW part and well made but notice how it sits at a goofy angle.  I’m always wanting to straighten it out.  I still miss the oil-bath cleaner.  Damn modern innovations… 

Now on to the other cause of clogging.  I tried every gas under the sun but the jets would still clog.  A friend of mine who knows about fuels explains: modern fuels are formulated for fuel-injected engines.  The fuel is piped to an injector under tremendous pressure.  The injector is screwed into a blazing-hot cylinder head, so the fuel doesn’t evaporate until it is well clear of the injector.

Now put that same fuel in a carbureted engine.  The fuel is under zero pressure in a float bowl.  The venturi effect sucks the hot fuel through tiny jets, which are ice-cold (sometimes literally).  So in the confined space inside the jet the fuel drops 80 degrees in a fraction of a second and the additives precipitate out as lacquer just inside the jet.

My car would get to idling crappy and performing badly; I’d remove the jets and soak them in carburetor cleaner and ‘Vroooom! it would run great… for about a week. (Be sure not to neglect the tiny little trim jet just to the rear of the idle jet on the right-hand side of the carb – it has a really small opening.) Using an old product called “Seafoam” – as needed – fixed the clogging.

Heat management; notice the heat risers on the intake manifold are wrapped in fiberglass.  I want them to warm the intake manifold, not the engine compartment.  I also wrapped the muffler in fiberglass which reduces the heat in the engine compartment considerably, and I put a cotton sock (secured with bailing wire) over the oil pump filter to insulate it from the heat of the muffler and blowing off the left 2 cylinders’ fins. 

Obviously a lot of the stuff in this post is beneficial no matter what carby you have.  I’m sure there’s more and like I said, as I try new stuff, I’ll come back and update this post.  I’ll start a new fuel post only if I go to dual carbs, and there’s lots of other stuff I want to do before messing with that.

Categories: Personal, VW
  1. September 23, 2006 at 17:38 | #1

    Oh, I remember fond (and not-so-fond) days of tenderly ministering to ony one of the several VW’s I’ve owned.  Last one was a 70’s vintage Kombi with the “Porsche” engine:  Dual carbs.  When they crapped out, I replaced them with an aftermarket header that let me install a Pinto carb…


  2. Jack Dinan
    September 24, 2006 at 21:51 | #2

    George: A most informative post. Please do add to it as you get more information. Some questions:

    oYou mention that your jets would clog in less than a week. How did you determine this? By looking through the hole at a light bulb? If yes, was the hole entirely closed?
    oYou show a photo of two jets. Is the larger jet sthe idle jet? If so, then this is the jet that Bentley refers to as the pilot jet.
    oOn a carb, next to the idle jet and slightly to the rear of it is another jet. I have seen this referred to as the auxiliary fuel jet.  Do you know the function of this jet? What size do you use for this jet?
    oCan you get an adequate flow with the fuel pump pressure set to 1.5 psi?

  3. September 25, 2006 at 10:56 | #3

    The larger jet is the idle jet or pilot jet, and goes in the right-hand side of the carb.  It looks like it has a ball-bearing stuck in the outside of it, and has the biggest effect up to around 2500 rpm so it’s really important for driving around town.  The “smaller” jet next to it (it has a much larger opening) is the main jet, and goes in the bottom of the float bowl.  Those are the only two jets I changed.  Later, I may experiment with the other jets – these had a big effect.

     align=right Then there’s the teeny jet just to the rear of the idle jet; I’m darned if I know what it does – probably trims the fuel mixture at certain vaccuum levels – but it sure does affect how the engine runs.  What is visible on the surface is a plug; the actual jet is behind it and takes a very small screwdriver with a rather fat blade (I wound up grinding one special) to remove.

    I determined a clogged jet first by the engine beginning to run very badly.  Then a laser pointer would not shine through the jet, or only a little (don’t let it shine into your eye).  Finally, putting a small piece of rubber hose on the end of the jet, I couldn’t suck any air through it.  After soaking in carburetor cleaner (the really agressive aerosol type) for an hour, a laser would shine through it, I could suck air through it, and the car ran great.

    Here’s a wonderful article from Rob Boardman about carburetor jets.  Boardman’s site is a gold mine, as are the ACN technical pages.

    1.5 to 2 lbs is a good safe setting – might be able to go a bit higher by removing the pump and filter from the hot engine compartment where expansion after shutoff affects the float valve.  Fuel pressure gauges are inaccurate enough that you’ll want to experiment a bit to make sure you don’t fuel-starve.  If you drive at very high speeds, you probably wouldn’t be using a 34PICT-3 anyway. For this carb, figure 3 lbs max.

    Thanks for writing!  And if you find out anything else that helps, let me know.  Eventually I’ll update the main article with new material from the comments.  :coolsmile:

  4. dennis
    January 13, 2007 at 03:23 | #4

    My mechanic says I need to screw out – counterclockwise – the volume screw on my 34pic carb so that my plugs don’t continue to be fouled with black soot

    I read on the net I needed to turn the screw the other way

    Which is correct?  My plugs are black and mileage about 18mpg ( less than normal)  on my 74 superbeetle.

    Does turning the screw in add or subtract fuel   or air?

    Turning it counterclockwise adds air and subtracts fuel or????

    I’m Sooo confused.


    Dj,  Los Angeles…

  5. January 13, 2007 at 12:19 | #5

    34pict-3-idlescrews.jpg align=right In this view of the left side of the 34PICT-3, above is a large screw about 1cm in diameter.  That’s the air idle screw and it meters air to regulate idle speed.  Turning the screw clockwise is less air, for a lower idle speed, and counterclockwise is more air for a higher idle speed.

    Right below it is the fuel metering screw.  Clockwise is less fuel for a leaner idle mixture, counterclockwise is more fuel for a richer idle mixture.  Basically you adjust idle speed with the air idle screw, then turn the fuel screw clockwise just until idle begins to drop, then back out a half turn or so.  Then recheck idle speed (should be about 800) and trim back and forth between them.

    The screw on the main throttle lever should not be used to control idle speed the way it was in previous Solex type carbs. With the 34PICT, it only controls the resting position of the butterfly valve, which should be almost but not quite closed.  The specification is .004 inch clearance around the edge of the butterfly valve but I just turn it until the valve is just closed, and then inward a half-turn to open it again.

    Sooty plugs as gas mileage in the 12mpg range can also be caused (are more likely to be caused, IMHO) by fuel flooding past the needle valve up in the float. The needle valve stops the flow of fuel from the fuel pump when the float is full.  One other thing that can cause sooty plugs is if the heat riser tube on the intake manifold is plugged.  This causes fuel to condense out of the intake mixture on the inside of the intake manifold for very uneven results.  Notice my heat riser tubes are wrapped in fiberglass to keep them hot, to heat the intake manifold a little better and let less heat into the engine compartment.

    For some reason I had terrible trouble with needle valves failing until I put a fuel pressure regulator in the circuit between the pump and the carb.  Since then, no serious fuel problems.  Of course this assumes your ignition is good, etc.  I use a Pertronix magnetic points replacement kit so no points in my distributor. 

    Also your carb could be worn so air leaks in past the butterfly valve shaft, which makes tuning very difficult.  Hope that helps.

    Even though things are running pretty good right now, I am thinking about dual carbs this summer.  More power, cooler running, so I’m told.

  6. January 13, 2007 at 21:48 | #6

    Dennis replies;

    Thankyou Mr Wiman,
    I could not read the security word so Im writing my reply here! Thankyou so much for the information on carb adjments.
    Can I therefore just turn clockwise, my volume control screw a turn to lean out my sooty plugs?
    And when will I know I have turned in the screw enough?  Will I hear the rpms go down?
    I do have a petronix in the car with rebuilt carb too about 4 mo old..
    Thankyou again
    Dennis, Los Angeles..

    Sorry about the security word – sometimes it is difficult to read but I can’t turn it off lest I be slammed with spam.

    You can make your idle mixture leaner by turning the fuel screw clockwise but that probably won’t fix the sooty plugs problem.  From your description it sounds like fuel is flooding into the carburetor.  Try turning the idle fuel screw clockwise – gently so as not to damage the screw seat – until it seats, then back it out three turns.  Start the engine and slowly turn it clockwise until the engine rpm’s drop a bit then back out a bit. 

    If turning either screw makes no difference on the engine, look for fuel flooding problems.  You might need to add a fuel pressure regulator, a new needle valve (once they fail you need a new one) or the idle fuel screw seat may be damaged and unadjustable.  You might need a new carb.

    I suggest re-reading this entire thread and making the adjustments and if that doesn’t help, you should find a (nother?) classic VW specialty shop – LA is probably full of them – and get them to analyze the problem.  Good luck.

  7. Michael
    May 6, 2007 at 19:55 | #7

    I am about to install a new Bocar 34 pict 3 in my 1600 DP. It came with what appears to be a 55 idle jet and 127.5 main. In your post you didnt mention what the value of the air jet under the carb cover to be. I am having a hard time reading the number on it.

    Where is a good source for these jets?
    Thanks, Mike

  8. May 6, 2007 at 20:11 | #8

    I think you’re talking about the air correction jet, which comes in a wide range of sizes.  Here’s a great article on jets on Rob Boardman’s site, and I have found aircooled.net a reliable source of jets.

    Right now my bug is in the shop for a throwout bearing.  My hands are getting too arthritic to handle an engine – and I’m only 50! – so I’m paying someone else to do it for the first time.  But when I get it back, I am thinking about experimenting with dual carbs.  The 1600 is an under-aspirated beast and could benefit from more air.  But that would also mean a different distributor because the SVDA that I have is curved for the 34PICT-3.  Such fun!

  9. Michael
    May 10, 2007 at 23:34 | #9

    I seen a low pressure Holly regulator on ebay for 18.00 plus shipping, it says 1-4 psi. Is this the one you used? Also, have you thought about or tried runnig a webber progressive on a 1600? I have a new intake setup and heat risers, I was thinking of going that route someday….Will a weber off a Pinto late 70’s adapt, I wonder….much less money….
      For now, I will run the new 34 pict 3 Bocar I just got in. Ordered a 130 main and will be here Fri…all comes together this weekend. Wish me well! Thanks for all the tips!

  10. Richard
    May 17, 2007 at 22:15 | #10

    My ‘73 Super Beetle needs a little help commuting up the hills in this thin air.  Would changing the jets on the 34 PICT-3 help?  Would I need smaller or larger jet sizes?  Thanks for the site!

  11. May 17, 2007 at 22:23 | #11

    Hi Mikey – Yes, the 1-4 psi would be a good choice.  The 34PICT-3 should never exceed 3 lbs and I’m running about 2.5 lbs.  Be sure to read the whole thread including comments as there are some cautions.

    Many people use progressive carbs on the 1600 to good effect.

    Richard, if you’ve got a thin-air problem (such as perhaps you live in the mountains) you should consider going with a progressive carb because the 1600 is under-aspirated.  Or (as I might do this summer) switching to dual carbs. 

    As to smaller/larger, be sure to read Boardman’s site.  I don’t know what size you have and some experimentation is in order.  Note: if you are using a mechanical-advance-only distributor, you probably need a vacuum advance.

  12. hadi malakwi
    September 8, 2007 at 15:52 | #12

    i have a 75 beetle car…and i dont know how to adjust the solex car….???
    the engine runs so fast….??

  13. September 8, 2007 at 18:42 | #13

    Hi Hadi!  I suggest reading this entire post, and all the comments, as it contains everything I know about the 34PICT-3 (which is probably what your car has) The fast running could be due to mis-adjustment (such as the butterfly valve adjustment on the throttle lever), but it could also be due to excess fuel flowing down the carb (from a pressure-overwhelmed needle valve) or it could be due to a damaged fuel screw.

    Also there are some links here to technical articles on Rob Boardman’s VW website and on Aircooled dot net. 

    Hope that helps

  14. hadi malkawi
    September 9, 2007 at 10:58 | #14

    hi..i have a 75-old beetle…with SOLEX 30.PICT-3

    this morning after i had cleand the carb>>?
    i didn’t knew how to make the propper adjustment>>..i went to specialist technician to the adjustmen..?he did his work very well ,but i feel the car not fast enough as it used to ..
    sometimes..when i push on the breaks…the engine stops..(at the time the carb is still feeding with 12 v)>>>…?
    also..i noticed that there is an upnormal fuel consumption…
    so, what can i do??

  15. September 9, 2007 at 11:27 | #15

    Hi Hadi, the 30PICT-3 is very different from the 34PICT.  I am trying to remember how to adjust it but it is not the same and I have not handled one since 1982.

    Here is an article on Rob Boardman’s site on the 30PICT series that will probably have the information you want.  I hope that helps!

  16. Ian
    January 6, 2008 at 19:09 | #16

    Just wanted to drop a note and say thanks.  I was the complete idiot to knowing anything about engines.  With the help from Muir’s book I pulled my 1971 VW camper engine to replace seals, muffler, fuel line, tune up, etc… After successfully getting all together and back in, it ran perfectly other than one thing, it wouldn’t idle.  Finally after finding your site I was able to pull the main plug and jet and adjust the air intake valve to make her purr like a kitten.  Thanks again for taking the time to make the site, you saved me some bread. 
    Galveston, TX

  17. H
    February 7, 2008 at 05:28 | #17

    An absolutley superb article.

    Keep up the great work

  18. Elmo
    May 18, 2008 at 07:39 | #18

    I just found this site this morning (5/18/08) and I have to commend you.  It’s a wonderful site.  Now I have a progressive carburetor on my 73VW type 1, 1600cc and it’s not adjusted correct.  It is running too rich.  Does anyone know how to adjust and jet this thing correct?  All suggestions are welcome.  Thanks.


  19. GIAL8R
    June 13, 2008 at 13:57 | #19

    I’m interested in how that Progressive Carb setup is going???  Any luck getting it running well and if so, how’s the performance and mileage?  I have a 34 PICT-3 on my 74 Ghia and I’m thinking about a little performance boost.  I don’t think a dual setup makes a great deal of sense with today’s gas prices, but there are some single setups that might???? 

    Awesome write-up !!

  20. June 13, 2008 at 14:24 | #20

    Thank you!  The setup as described here runs very well indeed.  Be sure to read through the comments and responses.  But I am selling my Beetle because my hands are getting too arthritic for auto work.

    Dual carbs have the potential to get very good gas mileage and much better performance though.  All progressive carbs are by necessity a design compromise – do away with the long, relatively cold intake manifold and you can get closer to optimum.  But you will need a different distributer than the one shown here.

  21. July 11, 2008 at 17:01 | #21

    Great article..Keep up the good work. I just discovered your blog today and I must add that I am enchanted by this post..

  22. Punch buggy
    September 1, 2008 at 12:50 | #22

    I have a 1972 superbeetle that has a Solex34 Pic 3 carb on it. The problem is I can’t get it to idle warm. I have checked for vacuum leaks with come carb cleaner seeing if the idle speed would pick up. It did not. I also reset the points and timing just to eliminate them from the equation. So back to the carb now. I also noticed that the mixture screw does not have an affect on the idle speed at all. I’m thinking the cut-off valve might be stuck or not retracting when it is started. Is there other things to check. The only way it will idle is with it slightly choked and that means it is lean obviously. Any help would be appreciated thanks.

  23. September 1, 2008 at 13:52 | #23

    In the 34PICT-3 the idle speed is regulated by the air idle screw – see picture above – and the idle mixture by the idle mixture screw.  You might also have a clogged jet – read the section about SeaFoam for unclogging it.  Also the sections about regulating fuel pressure, about the Pertronix magnetic pickup (made a big difference) and check your butterfly valve for correct adjustment and wear.  If it is worn a new, rather than rebuilt, carburetor, is your best bet.  Good luck!

    I guess it is getting time to re-write this post and incorporate everything from the comments into the main body.  Lots of good conversation has come in from readers.

  24. Punch Buggy
    September 2, 2008 at 09:18 | #24

    I was lucky and found the real problem with this car.
    See link the carb and distributor are not compatible. The exact symptoms described in this article are what I have. I am going to be performing this change soon I will let you know the results.

    Thanks for the reply.

  25. C
    September 29, 2008 at 13:07 | #25

    What a great site! I enjoyed reading through everything.  I need some advice, Mr. George, if you don’t mind… I’m a 26 year old woman who just lived a year in Africa.  I came home and traded my old Wrangler for my dad’s newly restored bright yellow ‘74 Superbeetle which I love to pieces.

    I’ve come across a few problems (the latest being what I think is a clogged heat riser) and I’m hesitant to go back to the shop (especially since I’m low on cash).  I think I can fix them, with the help of Muir’s book, but I have little automotive experience.  I’m a little concerned that time/money in the upkeep of my little bug might be beyond what I can do or afford, and I’m hesitant to jump in and start tinkering with something that could potentially be life threatening…  Do you have any advice?

  26. clyde
    November 13, 2008 at 11:35 | #26

    Where can I locate for purchase a copy of afore mentioned Muir’s book?

    I am not a mechanic, but enjoy tinkering. I have a 1972 s. beetle that I can only get to run on two cylendars. It is getting fire to all four, but it is getting gas to only two cylendars. Any helpful suggestions.

  27. November 13, 2008 at 11:44 | #27

    You’ll like that book – it’s a wonderful example of clear technical writing for the non-technician. I try to emulate his style when writing instructions for people where I work.

    Muir, John, How to keep your Volkswagen alive, A Manual of Step-by-Step Procedures for the Compleat Idiot.

    Looks like the new edition is paperback instead of spiral bound, but otherwise the same.  Also think about getting the Bentley shop manual, which is excellent but written for mechanics.

  28. Rich
    November 23, 2008 at 16:38 | #28

    On the vw-resource web page writes the opposite of what you say the volume control screw does:

    “Next set the volume of gas available at idle speeds. This is done using the Volume Control Screw. Please note that the Volume Control Screw controls the AIR volume, not the fuel volume. Screwing it in reduces the air and makes the fuel/air mixture richer. And of course turning the Volume Control Screw out increases the concentration of air and makes the mixture leaner.
    Note: The Volume Control Screw is the smaller of the two adjusting screws, located on the left side of the carburetor just above the Idle Cutoff solenoid (which has a black wire from the positive side of the coil attached to it). The Volume Control Screw is NOT used to set the idle speed – that’s the job of the Bypass Screw

    How is correct?

  29. November 23, 2008 at 18:57 | #29

    Both are correct, though we used different focus and nomenclature.  That’s a fairly common problem in technical writing.  See comment #5 for clarification.

    Turn the air-idle screw (the big one) clockwise (in) to reduce air.  This will have the secondary effect of a richer mixture, but its primary effect is to reduce the amount of air that passes into the manifold, and the engine slows.  Turning counter-clockwise (out) allows more air, and the engine speeds up.  Once you have the desired idle speed, you trim the mixture with the fuel screw – the small one.  This will affect the idle speed, so repeat both steps in smaller increments until both are in perfect balance.

    It should be obvious why the air-idle screw is so much larger than the fuel screw; they approximate the air/fuel ratio.  Relatively minute quantities of fuel are required compared to the amount of air.

    It is a bit confusing scrolling up and down through main text and comments.  At this time, I am closing comments on this post, pending a re-write that will aggregate everything into one article with all illustrations in place.

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