>>Peter Burgess's book on powertuning recommends taking the
>vacuum on the upstream side and very close to the butterflys. His comment
>is that if the take off is on the engine side of the butterflies-so the dist
>receives vacuum signal at all times-it will create the wrong advance
>characteristics for the engine. How important is this vacuum location? Do
>I need to invest in a centrifigal advance carb like the Mallory dual point
>dizzy?
You can temporarily run the distributor with the vacuum advance disconnected.
You will have a drop in fuel efficiency, because a vacuum advance causes the
spark to happen sooner BTDC during high vacuum situations, ie: cruising &
decelerating. The only way to get vacuum out of a side draft weber that is
correct for vacuum advance is a little scary, but I did it, so hey, it can't
be too bad. You have to drill a small hole into the weber carb located so
that when the throttle butterfly is closed, the hole is just on the
aircleaner side of the throttle, but as the throttle is opened, the hole is
exposed to intake vacuum. I then pressed a vacuum hose fitting into the hole
that I drilled & sealed it in place with liquid solder, Making sure that none
of the liquid solder, or the fitting protrude into the airstream of the
throttle body.
throttle
_______________________
| / / \
Engine | / | |
Aircleaner
| ________/o________\____/
^
^...drill hole here and hook
vacuum line to distributor
I hope this comes out as drawn. I borrowed a vacuum gauge and about 4' of
hose routed into the passengers compartment, and tested several drill
locations before choosing the one that provided the correct vacuum for the
distributor.
Good Luck
David Riker
69 Midget
|