Re: [T3] Update on fuel pump adjustment

["Steven Ayres" <comwest@att.net>]

BigAl=> is the need for the T3 pump
=> pressure due to the fuel injection?

We're talking about carb pumps (FI pumps furnish *much* higher pressure, of
course), and specifically the pump-spec change from 3.5 to 5psi, as noted in
'Without Guesswork'.  In checking this reference, I notice a few interesting
details I hadn't thought about before.

There are two different specs for both Types 1 and 2 engines. For all 1500
engines, max delivery capacity -- flow rate, as Jim has been saying -- was
increased from 300 to 400cc/min (up 33%!). Max pressure on these engines
stayed at 3.5psi. This held for the 1600 Type 2s (all single carbs through
'70, where this book ends).

For the T engines -- Type 3, 1600 dual carbs -- flow rate was also set at
400cc, but the max pressure spec goes up to 5psi +40%). The footnote to max
pressure may provide a clue as to why:

"Via 1.5mm (.059in.) diameter float needle valve (1.2mm (.047in.) diameter
on Type 3 / twin carburetor)"

(There's no special pressure spec for 1500S engines because the pre-'66 Type
3s are not covered in this US handbook. I'd like to hear from European
sources on that.)

So, assuming that these specs are accurate (and this is an official VW
handbook), the PDSITs are apparently supposed to get smaller-diameter
valves. Does the higher pressure spec make more sense with that difference
in play? Are these valves supplied with rebuild kits today, or are we
normally getting Type 2-sized valves, say? Further, flow rate is indeed a
factor, and it's different between 1300 and 1500 Beetles as well. Are most
aftermarket pumps set for 400cc? Does this cause any problems for smaller
engines? Seems like there's more info to be mined along this vein.

It's looking to me like, just as with the FI engines, there are subtle
differences in fuel-system parts for carbed engines, and we have to look
closely at them to be sure our systems are correctly tuned for proper
performance.

Steven Ayres, Prescott AZ
'66 KG1600



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