Have you checked your compression or done a leak down test lately? A weak valve
spring, or bad valve could be causing your low vacuum as well as poor ring seal.
If every thing checks out ok try adding another vacuum canister.
ROGER.
Lib596@xxxxxxx wrote:
> Here is a technical question I hope someone can help me with.
>
> I am always trying to improve the way my dual fuel system (LPG/Gasoline)
> operates.
> For best performance on both fuels I have made a vacuum operated gate which
> closes to restrict the air flow through the air cleaner when operating on
> LPG but stays open for gasoline. This system works like a charm on my Caddy
> but there is hitch with the Imperial (413 engine). There is not enough
> vacuum generated while I am cranking the engine to operate the vacuum motor
> that closes the restictor.
>
> So far I have tried taking the vacuum off every different source on the
> manifold and carb. I have closed off all other vacuum take offs and just
> connected the restrictor motor. I have checked for inlet manifold leaks, I
> have fitted a non-return valve in the line to the restrictor. In addition, I
> can't use the vacuum reservoir because it still won't hold a vacuum
> indefinitly and besides, each time I switch to gasoline or turn off the
> engine, the vacuum solenoid would dump the reservoir vacuum. Whichever way I
> try, the vacuum motor still won't operate unless the engine is already running
>
> I know I could just use a cable to close the gate, but the idea is to have a
> completely automatic system with no extra levers, buttons or switches inside
> the car. I could also try to find a 12 volt vacuum pump, if such a thing
> exists, just for starting the car but that seems unnecessarily complex.
>
> Is there a reason why the cranking vacuum is so weak on these engines? Is
> there a way to increase it?
>
> Hope someone has some ideas, I'm right out
>
> All the best,
>
> Tony V.
>
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