I am hoping the racing community can help me out with this one…
I have a 1974 Land Rover which I just put a Weber dual-barrel DGV carburetor
on to get a bit more power out of than the stock super-restrictive military
carb. My question is this… nowhere can I find the general “theory” behind
jetting a Weber carburetor. So, unspecific to Jaguars or Land Rovers… can
someone tell me some “how-to’s” for properly jetting a carb to get the most
out of it. The Land Rover community tends to stick to the “if it is running,
it is jetted correctly” theory. I want some thoughts on when to move up a
jet size or when to move down an air corrector size. Are there any parts
which are specific to the baseline setup? It seems as if the emulsion tubes
come in all sizes and each car seems to have a proper setup.
Currently, the carb idles well. When driving with the only primary venturi
working, I get great throttle response, no pinging, great power, but a black
soot coming out of the exhaust during shifting, and the inside of the
tailpipe is coated with soot. When the second venturi opens, I get a slight
hesitation, then pinging, until the engine speeds up more and things are
fine. Under full throttle on the highway, I get two different acceleration
modes … if I am traveling 55 and floor it, I can go maybe 60. If I am
traveling 60 and then floor it, I can quickly accelerate to 70 or 72 which
is as fast as I can possibly make that truck go without losing my hearing.
There is a definite tendency for the engine to like higher RPMs.
How do I tune from here. I have tried lowering the main jets which seemed to
give a better power response throughout, but pings under heavy load. Can I
prevent the pinging by changing air correction jets? Emulsion tubes? There
are about 6 variables and I don’t understand what corrects what, nor can I
find any documentation on it other than baseline recommendations. Can anyone
in the racing community who knows the ins/outs of fine tuning a carburetor
shed some light for me on where to head?
Any help would be GREATLY appreciated. My girlfriend drives my XJR to school
4 days a week… so I am driving the Landy 160 miles a day on the highway.
PS… if anyone is interested in trading a 1974 military Land Rover for an
E-type… let me know. I am looking to sell the Landy!
PPS … scientific slants/explanations welcome!
Thanks,
Ryan
Cambridge, MA
1974 Land Rover
1995 XJR
Ryan Scott Bardsley
Systems Designer, Medical Simulation
Massachusetts General Hospital / CIMIT
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