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Gordan

Vanguard manifold vacuum

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Gordan

I couldn't leave well enough alone and changed my LP regulator from a Garretson KN (with a high pressure regulator in front of it) to a Beam T60 (which operates on tank pressure, and has a built-in vacuum operated fuel lockoff.) My issue is that the lockoff won't open during cranking. I have the vacuum line connected to a port on the intake manifold that's just before the manifold bolts to the head. If I disconnect that line and suck on it, while covering the manifold port, the engine will start, and once it is started I can quickly reconnect the line and the lockoff will stay open and everything works fine.

So, the question: how much vacuum should I be able to expect? The specs for the regulator state that it should begin opening at .2" vacuum and fully open at .5". When I was cranking the engine with the vacuum hose disconnected I couldn't feel any vacuum at all. This is an LP engine so it has no choke.

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GregB

Sounds like at cranking speed the engine does not spin fast enough to generate required vacuum. I usually see that Beam regulator E-bay being sold for towmotor applications with a larger engine.

Aux elec vacuum pump that runs only when the switch is at start position?

If you know someone with a vacuum brake beeder some of those have gages on them, you could measure the vacuum at cranking speed to see what it is running. OR suck on a vacuum gage to see what you created. :D

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Gordan

Yeah, I'll probably rig up a manometer to figure out how much vacuum the engine is creating at cranking speed and at running speed. Worse come to worse, the whole vacuum lockoff is easily removable - it's optional on this regulator. I shut off the valve at the bottle every time, anyway. So it'll be functionally equivalent to my previous setup with the KN.

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Gordan

So... I'm not sure I understand that. The throttle cable indirectly pulls on the governor spring in order to force the throttle open, not closed, right? And it's the governor shaft that forces it shut against the governor spring/throttle. So what would close the throttle plate at RPM lower than idle?

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Gordan

I just confirmed that I was able to start it if I push the governor arm to hold the throttle plate closed as I begin cranking.

While the throttle plate is open with the engine open, I'd expect that how much it closes during cranking would be a function of how close the cranking speed is to the governed idle.

Well, between the previous paragraph and this one I went and adjusted the governed idle to 1100 RPM and now the engine will start without my intervention at the governor arm! Yay!

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Gordan

It just struck me that there's another way to go about increasing starting vacuum, even without choke: I could have rigged up the choke cable to close the throttle plate. Then I could just apply this "choke" while cranking. I may still do this eventually just to have a positive way of doing it.

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