Home > Personal, VW > When you’re a Jet…

When you’re a Jet…

May 27, 2006

It’s a basic truth in life; little things matter.  I just rejetted my VW carb to better account for alcohol in the gas. Both jets together probably weigh about a quarter of an ounce but it made a HUGE difference in the drivability of the car. The engine is much smoother and has a lot more power at low speeds.

Details:  It’s a Bocar 34PICT-3 carb, and I just 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.  The engine has a Brazilian 1600DP longblock with stock cam and crankshaft, standard intake manifold, and a SVDA distributer from aircooled.net.  Electric fuel pump and separate fuel pressure regulator set and tested to 2 lbs.  The fuel pressure regulator was wildly inaccurate by the way, so be sure to actually measure the pressure and not depend on the setting.  I recommend locating all filters, pumps, and regulators outside the engine compartment.  My car has one filter under the gas tank and another above the transmission between fuel pump and regulator.  The tank has Shell regular gas in it right now (15% alcohol) but it runs the same on Citgo or Wal-Mart gas for that matter.  (Jets shown slightly enlarged for detail)

UPDATE- I have consolidated this post and all the other fuel and carburetion related posts into one: 34PICT-3 Carburetor Final.  That post will also be updated when new information comes in.

Categories: Personal, VW
  1. May 28, 2006 at 20:16 | #1

    I have read that vehicles made now in Brazil will run on 85 percent alcohol and some on pure alcohol. Will your VW do that or would it need a conversion? Brazil is energy independent I hear mostly due to ethanol. Might be an answer for us to look into.

  2. May 28, 2006 at 22:35 | #2

    That would be really cool to run on homegrown ethanol but I’d have to do a conversion – rubber fuel system parts are iffy enough with 15% but with 85% they’d corrode pretty fast.  Also different jets again for it to run right, and change the timing, etc.

    Some fuel-injected engines can switch back and forth because they can change their fuel mixtures and ignition timing by sensors and the onboard computer.  Carbureted engines don’t have that flexibility so they have to be used for one or the other.

    Back in the ‘50’s my dad and his friend converted a CHP cruiser to propane for a pilot program.  It ran great, officers liked it, and when they tore it down after 180,000 miles it was clean as a whistle inside.  Don’t know why state cars didn’t all end up with propane tanks, must have been some reason.

  3. zilch
    May 29, 2006 at 09:06 | #3

    I would be curious to know the fossil fuel efficiency of producing ethanol.  Last I heard, agriculture in First World countries was running at a net caloric loss- that is, it took more than one calorie of fossil fuel to grow and bring one calorie of plant material to the consumer.  I don’t know what the figures are for ethanol, however.

  4. May 30, 2006 at 09:53 | #4

    I would also like to know the fossil fuel efficiency of ethanol production, if anyone knows of an objective study.  Even if the balance is negative, obviously a wider range of fuels is becoming available at the pump, which means technology will begin to improve and it may become a positive balance in time.  I hope so.

    The effect of politics on engine tuning, what fun.

  5. zilch
    May 31, 2006 at 04:13 | #5

    Here are the first two articles I could find on the efficiency of ethanol production: one says it uses up more, and one says less, fossil fuel calories than are produced.  Obviously, this is not easy to calculate- how far do you go evaluating things like farm equipment maintainance, road construction to factories, etc?  But I agree that experimentation is a good thing- as long as it’s critically vetted for pork barrels.

  6. interested
    June 1, 2006 at 13:20 | #6

    From what I understand the calorie deficit in producing ethanol is mostly due to the dependence of agriculture (corn specifically)on petrochemical fertilizers.  Energy concerns aside, this is reason enough to question ethanol as a fuel source.

  7. June 2, 2006 at 22:51 | #7

    I hadn’t considered the petrochemical component of producing ethanol, but that is indeed a concern.

    While not a scientist, David Olive’s recent column in the Toronto Star regarding the current Canadian government’s affair with ethanol fuel is pretty interesting.  I’m betting ethanol is a net loss in terms of the whole energy equation.  Reduction of pollutants is important, but a net loss in efficiency is a loss in the long term.

  8. June 3, 2006 at 07:58 | #8

    I’m not terribly worried about it.  Ethanol, like hydrogen, can be produced in many ways and new ways can be found.  This is a fundamental difference from oil, which can only be produced by finding underground deposits of fossil carbon, and pumping or digging them out of the ground and processing them into gasoline.

    In the ‘kill two birds with one stone’ department, cellulosic production of ethanol looks very promising.  If that happens, the price of newsprint will go up and recycling paper will suddenly become a paying proposition.  :coolsmile:

  9. Jack
    September 22, 2006 at 22:16 | #9

    I have three 34PICT-3s apart on my workbench right now. I’m trying to find one whose idle rpm reacts the way the book says it should to adjustments of the volume and mixture screws. So far, no luck.

    Can you tell us what idle and main jet sizes you had originally before replacing with the 55 and 130?

  10. September 23, 2006 at 14:40 | #10

    Jack – Alas i don’t remember the size of the original jets but they were visibly smaller than the new jets.  What you describe sounds like my engine was acting when the needle valves were overwhelmed by fuel pressure and failing early.  I’d turn the air idle screw and it really wouldn’t make a difference because the carb was slobbering fuel into the manifold.  (Eeeuwww!)

    Just this morning I compiled everything I’ve done with the 34PICT-3 into a single post that may help.
    34PICT-3 Carburetor Final.  That will be the post I will continue to update with fuel issues from now on.

    After a bit of tweaking later I’ll make that post into a .pdf for people to print out who want it but it is up to read today.

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