"Bosch Distributor part numbers"
VW used a lot of different distributors over the years. The original working engine, carburettor and distributor combination that came with each VW worked really well. But as these aircooled VWs have been around for many years, parts wear out or fall out of spec, and owners have had to replace, and make do with what is available.
All too often this has meant slapping a 009 on their engine. The 009, unfortunately has become standard, and is the distributor we see most often in the engine bays of our customers. It is also the worst distributor for an aircooled VW engine. Its such a shame that owners are driving their dubs around not knowing what they are missing. The flat performance, and hesitation off idle, the worst fuel economy is just an accepted reality.
If its not a Chinese copy of a 009 causing problems, then its a Chinese copy of a Bosch "034" falling well short.
The aftermarket 034 (copy) distributor is not to be compared with the original Bosch "034" model. This Distributor is essentially a "009" with a Vacuum Advance assist, to help prevent hesitation in all of those Stop-n-Go situations in city traffic. In practice this aftermarket distributor is very hit and miss due to build quality. A strip down of the internals quickly reveals the difference in the quality and strength of the springs. On quite a few occasions when timing a customers engine, we have noticed that the max amount of mechanical advance of these 034 copies can be in excess of 35 degrees! Dangerously high when you consider that the vacuum canister when connected can deliver up to an additional 12 degrees of advance.
The more recent 034 copies are fitted with rev limiting rotors to counter this issue. But this only prevents over revving. It does not address the fact that the advance curve is obviously completely different to the original Bosch "034" distributors.
Here are what the numbers and letters mean on the side of your distributor. Shown here is an example of a typical distributor code: JFUD 4 (left arrow).
Here is how to de code it:
J - 1st Position [Housing Diameter]:
J, JG, JH, JN or JGN = up to 70mm
P, PG, PH, PN, PGN = from 71 to 83mm
T, TG, TH, TN or TGN = from 84mm
FU - 2nd position [options]:
F = Mechanical advance
U = Vacuum advance
Y = additional mechanical advance (e.g. butterfly linkage)
M = shielded (for radio interference)
D = RPM limiter
R = Rotor with resistor
Z = Distributor with dual points
S = Sport
X = Special (e.g. impulse pickup, tach-hookup)
4 - 3rd position [# of cylinders].
Left arrow - last position [direction of rotation].
Below is a table with most of the distributor part numbers and specs over the years. Use the search to identify your distributor.