Alternator/Accelerator Pump Linkage Interference

See the end of the article for difference between the
German and Brazilian carburetors.

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Dave's '73 Super Beetle has a 1971 1600cc dual-port engine. However, a previous owner (or perhaps the mechanic who rebuilt the engine) installed an alternator in place of the generator (which were used on VW engines up until the mid-1973 model year). The alternator, of course, is "fatter" in diameter at the rear, whereas the generator is the same diameter over its entire length. This increased diameter at the rear alternator caused an interference problem with the accelerator pump linkage in Dave's setup. Dave replaced the alternator, but the diameter of the new alternator was the same as the old one, so he had the same interference with the new alternator.

Specifically, Dave found that the accelerator pump linkage on the right side of the carburetor was rubbing against and hanging up on the alternator body, causing the throttle to be abnormally open and the idle speed too high. The situation made it impossible to tune the carburetor properly -- a big problem, and an odd one, according to Rob.

Dave found that he had to grind the body of the alternator away a little bit to provide clearance for the accelerator pump linkage so the throttle lever would close all the way and the screw at the top of the lever would rest properly on the stepped throttle cam on the left side of the carburetor.

Dave found that a PO had left out the two bottom bolts where the alternator attaches to the fan housing, probably to shift the alternator over to the right a bit so it would clear the accelerator pump linkage. When removing the fan shroud with the alternator attached, Dave found that he had to take the top off of the carburetor to provide the necessary clearance.

A number of "fixes" to this interference problem were suggested:

  • "Speedy Jim" wrote to say that "VW used a carburetor linkage that was "flipped" up-side down to clear the alternator body. You can also increase the height of the carburetor using a spacer between the intake manifold and the carburetor."

    Rob commented on this -

    This intrigues me - I've never heard of it. Maybe "Speedy Jim" is saying that when VW started using the alternator (in '73) they modified the link on the carburetor. Your's might have had the earlier form of link if that's the case ('71 carburetor). Since you say that this new carburetor (Bocar) is exactly identical to the old one in every respect (except for the size of the main jet), I don't know what he means by "turning the linkage upside down."

  • Rob suggested that Dave put his hand into the fan opening (front of the fan shroud) to see if there is a gap between the rim of the fan, and the shroud. He said, "The gap should be very small - not more than a mm or two. It's a faint possibility the PO used the earlier fan and mounting plate with the four bolts. The mounting plates are different, so the wrong fan would show up as a large gap (5mm or so) between fan rim and shroud. THAT would put the alternator off I'm sure (though I'm not even sure if it's possible to mount the wrong mounting plate.)"

  • John Connolly (Aircooled.Net) suggested -

    You have three choices:

    • Flip the linkage over on the throttle shaft (you can do this on some carburetors).
    • Bend the linkage (I have done this with no ill effects).
    • Use a spacer under the carburetor as "Speedy Jim" suggests.

Dave wrote regarding "bending the linkage" - It's actually the bolt head on the adjusting bell that impacts the alternator body; I'm not sure how flipping or bending the linkage would change that.

John responded - Because the bolt is then on the TOP of the alternator, not hanging down. Late model carburetors did just this! Just see if you can invert the linkage that actuates the accelerator pump so it's on the top. Then, make sure it works. :-)

Dave was unable to find a spacer to raise the carburetor -- Rocky Mountain Motor Works (now Mid-America Motor Works) had one for '61-'70 single-port Bugs for $11.95, but their catalog doesn't show one for the dual-port carburetor/intake manifold interface.

Someone wrote about his success putting a spacer under his 34PICT/3 carburetor. He purchased some gasket material and cut out five gaskets using the regular one as a template. Then he "pasted" the five gaskets together, coating them with Indian Head lacquer gasket sealant. He also coated the outside of the bundle with the sealant and let it dry overnight. This "spacer" raised the carburetor about 3/8 of an inch and solved the interference problem. "HOLY COW!" he wrote. "This thing is like a brand new car! It accelerates like a rocket now ... well maybe not a rocket... But a whole lot faster than grandma with a baby buggy!" :-)

Dave resolved his interference problem (though not completely) with a little judicious bending of the accelerator pump linkage and slight grinding of the alternator body. A more expensive resolution is replacement of the carburetor. Aircooled.Net sells three 34PICT/3 carburetors: a Brazilian Bocar ($179.95), a Pierburg model ($185), and a German model ($250). The latter two models clear the alternator; the Brazilian Bocar carburetor will not. The Brazilian carburetor requires alternator grinding, which Dave learned the hard way. Dave purchased a Pierburg 34PICT/3 carburetor from Aircooled.Net, which resolved the interference problem. Later Dave replaced the carburetor again with a rebuilt German 427-1 model from Keifernet (keifernet@hotmail.com).

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