Hi all,

I've been looking at ways to reliably automatically switch a mixer bypass on when I swap from LPG to petrol.

I've looked at things like grey water divirters, electronically switched reticulation valves from an orchid and various other similiar things.

In the end I serendipitously found the answer. I tripped over an old carby that was half stripped in my shed.

Then it hit me.. the old stromberg single barrel downdraft carbies had the big butterfly at the bottom.. The carby butterfly is perfect because:
1. nearly perfectly airtight.
2. easy to open and close, most of the other valves I looked at were not easy enough.
3. Has linkages on the outside to hookup an actuator to.

So I started thinking about how to open and close the butterfly when needed, and so I started looking at an old sierra carby I found in the shed and it had a big a** vacuum actuator bolted right to it.

So in essense, I have a big butterfly valve pipped to either side of the mixer ring, spring loaded shut by default, connected via standard linkage to a vacuum actuater hooked to the cars vacume tree and somewhere in that vacuum line is a solenoid that switches based on their being power to the LPG lockof soleniod next to the mixer. (ie when the LPG is turned on, the vacuum to the butterfly actuator is cut off allowing the spring to close the valve and force all air though the mixer ring. When on Petrol, the vacuum is allowed though to open the actuator and allow a shedload of extra air get around the mixer ring.

The beauty of this is that the fail safe is always though the mixer, so if something goes pairshaped, the system will default to not bypassing and thereby not damanging your engine by leaning out too much.

The only bit I've not sourced yet, is an 12v way to open and block the vacuum hose.

I might be able to find something in the heater controls of an EL I have here..

any thoughts?

Last edited by frankieh on Sun Sep 18, 2011 8:04 pm, edited 1 time in total.

well it seemed like a good idea to me

12v way of controlling a vacuum source?

BBM switch?

AU falcon, remove the washer bottle, under it there is a valve with 2 wires and 3 vacuum ports.
most wreckers i've got them from didn't know they were there and only wanted a few dollars.

One port is common, one vent to atmosphere, the other goes to your vacuum actuator.
The only other thing you need a small one way valve to hold vacuum when a full throttle.

It's the same thing that opperates the vacuum lift on sprintgas new gen mixers. I could probably find a diagram here some where to show you how to set it up.

I don't know if it's me, but it would be nice to see some pics of your setup - then we might be able to better advise you.

Im pretty sure he's using the secondary diaphram from the zook carby to operate the butterfly in the base plate of the stromberg carby to act as a bypass around the mixer ring.

Yeah, I was picturing something similar - I'm only familiar with the strombergs from my former holden life - I trust he's using the bigger basebody of the BXV-2, rather than the smaller BXUV-2.
They're the only one's I've played with, other than the twin barrel WW2.

I suppose he could've used a climate control blend door motor to control the butterfly, if he didn't want to use vacuum.

I was thinking about taking this a step futher and seeing if I could find a way to trick the computer into advancing the timing a couple of degrees when on gas..

like figure out what signal the knock sensor gives when it detects knocking, then set the timing manually significantly advanced so that when the computer retards it, it is retarding it to where it would be normally at most.. the idea being that when you switch to petrol, the computer retards the timing, when it is on gas, the computer leaves it advanced.... or something along those lines..

With the air bypass, and a timing adjustment, you might just be able to get both the petrol and gas systems more optimsied and therefore better performing.

I will take some photos of what I have and plan.

I did toy with electronics and even the blend motor, but I decided against them because the blend motor wasn't designed to be in an engine bay and the carby bits are. also long term the carby bits are likely to be more reliable.

As for the stromberg, I had one on my persuit 170 XP falcon engine many many years ago.. the main selling point is that the whole base with the butterfly detaches from the rest of the carby.

AEB do a timing advance unit, call sprintgas.

effalcon and EL_tickford.. I shall investigate the vacuum switching methods you have mentioned.

I'll also check out the AEB thing too... ta

I assume you mean these puppies..

http://www.aeb.it/products/timing-advance-processors

Wonder which one suits a TFI ignition....

OK.. photos.. firstly, this is the stromberg I dug up in my shed.. no idea what model it is, but I'm pretty sure I pulled it from an XB or XC 6cyl years back.




Secondly, This is the butterfly segment off the above Stromberg. It doesn't look that big (I have size 16 feet and hands to match so the scale is deceptive), but remember that it used to feed a 250ci engine by itself, whereas in my application, it's just supplementing the airflow that goes though the mixer ring (which is about the same size so I'm doubling the air flow that normally gets through the mixer.)


Lastly, is kind of a layout photo:


Where the hole is in the rubber TB neck is, is where my mixer ring usually goes. My plan is to bolt the butterfly segment to the back of that and plumb it into the airflow both before and after the mixer ring. Then use the vacuum diaphram and some relays etc to open and shut the butterfly when the gas is on or off... if I do it properly, I should be able to swap to petrol any time I like and not suffer power loss because I have a mixer in the mix. seems like a plan.

Would it be better to move the mixer out of the intake path and add it into a secondary path and use a throttle body from an E series to block the primary path when on LPG. Otherwise move to a GRA carb for what would probably be a better overall result.

mine sorta does this...impco 300 - the whole thing lifts up out the way via a cable setup allowing air to flow around it

Gas injection is the ultimate solution with no air intake restrictions.

Only $575 at your local eBay!

Cheers
BenJ