I recently installed a DGV in my wife's 1275cc RWA Midget. Before starting
with the carb work make sure the ignition system is in good order and the
timing is correct. I found an O2 sensor and A/F gauge along with a color tune
to be helpful. I live at 8,000 ft. The nice guy at Pierce Manifolds sold me a
pump jet with a long snout. The short snout pump jet that came with the carb
just dribbled the fuel out instead of spraying it. Next, my idle jet was too
large...so I silver soldered it shut and started drilling it out with a #80
bit. Once the idle circuit worked (see Visard) I started in on the primary
circuit. Same story...silver solder the jet shut and slowly drill larger and
larger holes until the mixture was 13:1 or so. (I like it a bit rich ;-) Next
find the optimum size air corrector. With the engine under load...secondary
circuit wired closed...does the carb lean out ? If yes, silver solder air
corrector closed and drill out smaller. Too rich...increase air corrector hole
size. Same scenario for the secondary circuit. The next piece of the puzzle
drove me crazy. After I had everything just right the @$%! carb still had a
flat spot at the progression circuit. Right after the idle circuit cuts out
but before the primary circuit takes over. It turns out that the butterfly
valve was too far open at idle and was exposing the progression ports drilled
into the carb body itself. By drilling a small hole in the butterfly valve
(opposite from the progression fuel ports) I could close the butterfly valve
and get the progression circuit to overlap the idle and primary circuits. Once
I got everything tuned well the exhaust manifold developed a crack. So I
installed a LCB header I had laying around. With the LBC installed now I will
have to tweak the jets again. If this reads like a bad novel the good news is
that a DGV can be made to work and all of this experience should help me when
it comes time to tune the 45DCOE on my 1380cc Bugeye. Stay tuned ;-)
Mark Hanna (Colorado)
|