>(1) The engine runs fairly well (as well as it used to) without the vacuum
>advance connected. When I connect the vacuum advance, any opening >of
the throttle produces a cyclic "surge" phenomenon, which consists of >the
engine
>cycling up and down in speed. (I didn't try to drive it that way, only
>blipped the throttle.)
Surge at steady speed is the result of either too much total advance or
lean idle/main metering (see carb stuff below). It's easy to get a tooth
off when installing the distributor. Or maybe the base timing is too high?
>(2) I only get about 13 psi vacuum (steady) at idle. I have done the
usual
>squirting of carb cleaner to try and find vacuum leaks and got no improvement.
> My timing is not late; if anything, I have it set a bit early. The cam
specs
> are:
>
> Isky 621262, Hydraulic 0.445" lift, 262 deg advertised duration,
> 208 deg duration @ 0.050
>
>I have heard I should have 17-22 psi vacuum; what am I doing wrong?
Seems a little low but I'm running 12 psi at idle with a 218/222 @ 0.050",
0.530"/0.530" lift, 110 LSA cam (on a Ford 351C), so you're not that far
off. Was the cam installed retarded?
>With regard to the carb, I have (somewhat systematically) varied the
>accelerator pump cam and squirter size, and the secondary spring, >ending
up pretty much with the out-of-the-box combination (i.e., every >change
made things worse or the same). Perhaps the Holley is not
>the way to go; if not,
>what's the right answer for this engine/vehicle combo?
The right answer is a stroker crank. 215 cubes isn't much for a 3000 lb
brick with a slush box :-). What intake manifold are you using? The
Offy Dual Port would be best for a heavy vehicle but the stock 4bbl
ought to be okay. Regarding cam selection, the Range Rover guys
might know what works well for a heavy vehicle.
As far as the Holley goes, you've also got the power valve and metering
jets to work with. I'm in the middle of the Holley tuning drill on the
Pantera. If you wait a few days, I working on a set of tuning notes.
While I prefer a Carter for your application, the Holley should work
fine, once it's tuned properly.
Later,
Dan Jones
|