twin carb conversion

[bravekozak]

Runs fine. I have another twin carb setup, but it's not rebuilt. The carbies need a little cleaning.

Today, I was walking through Miller's junkyard in Fort Erie and happened to glance at the open engine bay of a Honda Oddysey van. The vacuum booster hose with the integral internal check valve was oriented almost like the Laser manifold. I just cut a little off both ends and slipped it in.
Perfect. Best of all, he gave me the hose for free at 5 p.m. closing.

[bravekozak]

The end of the full length laser air cleaner snorkel is 1.75" X 2.5". I am currently using a cut off version because the 88-89 Festiva snorkel tube is too small ( plus it has a semi circle for the vacuum diaphram). I just noticed that the Mazda 121 DB has what appears to be a larger snorkel tube. I am going to ask what the dimensions are and report back.

[bravekozak]

I don't believe there is a second port for a oil pressure safety switch. In the absence of a VAF, I am looking for a substitute safety for the electric fuel pump. I found this box that measures the tach signal. It is expensive and not as good as shutting down the engine in the event of low oil pressure.
I will just continue with a direct ground to that wire on the fuel pump relay and trust myself to shut the engine off if the oil pressure plunges.

[Christ]

1 - Look up circuitry (if you know how to make circuits) for a low-pressure cutoff using the readout (ohms) from the OPS.

2 - Tee off the OPS hole and install a cutoff switch if you can't feasibly accomplish (1). Use black iron or aluminum fittings, brass will work harden and crack in time, causing oil leaks and funky readings.

[Movin]

Maybe I am missing something ? The chevy TBI engines had a fuel pump circuit
in the oil pressure light sender, and I think a gauge sender with pump switch
was used too. A stock efi crash switch would work to add safety in the event
none of us want, a crash.

Nice project, you have put a lot of quality thought and work in this,
and made a nice interesting pictorial, I enjoyed reading it.

[bravekozak]

I have a new double vacuum distributor that I want to install.
The question I have is concerning the vacuum signal. Do I need a Y fitting on the upper vaccuum port, to hook up the upper vacuum from both carbs? Or, should I only hook up the distributor to one carb? The lower barb (below the butterflies) is only on the farthest carb. Should I only use the upper barb (above the butterflies) on the closest carb? or on the farthest carb?

The shop manual says:
"The larger diaphram chamber is connected to the the spark port on the carburetor, just above the throttle at the idle setting. The smaller diaphram chamber is connected to the the intake manifold below the throttle."

The barbs are 0.200" (for hose sizing).

[FestYboy]

provided both carbs are balanced, it doesn't matter which port you use, signal is the same. technicaly speaking if you want a quicker responce, use the carb closest to the dizzy: less mass to move in the line.

[bravekozak]

Thanks FestyBoy, I will do exactly as you say.

New question.
Has anyone ever taken the stock EFI fuel pump to pieces?
What can I do to slow it down so that it will be quieter and only put out enough pressure for a carb? Maybe I need to modify the vanes?
What about just reducing voltage to the pump? Would that cause excessive amp draw? If I have to operate, I will. Nurse, pass the scalpel please.

[Movin]

Thats like asking a 300 hp turbo to work excellent and make 70 hp max with less boost..

[bravekozak]

Yes, that's what I want. No room for a mechanical pump.
Does anyone know what the amp draw on the stock electric fuel pump is?

[navdoc101]

Don't know, but can't you use Matt Dickmyer's FPR?

[zoe60]

It may be easier to get an aftermarket electric fuel pump that puts out 3 - 5 psi and mount it in the engine bay.

[FestYboy]

^ this, or as suggested in post 56, an FPR to lower the pressure to the 3psi needed for the carbs. i suggest the FPR method to make sure you'll have the volume of fuel required to feed those two carbs.

i would call Matt to see if his unit is stable at such a low pressure or see if he has a better suggestion.

as far as pump noise goes, factory units are quiet. once the engine fires, you can't hear it. but if you want to make it quieter, you can add mass to the tank and the area around the tank with tar paper or flashing sealer (self adhesive).

[greywolf200]

^ this, or as suggested in post 56, an FPR to lower the pressure to the 3psi needed for the carbs. i suggest the FPR method to make sure you'll have the volume of fuel required to feed those two carbs.

i would call Matt to see if his unit is stable at such a low pressure or see if he has a better suggestion.

as far as pump noise goes, factory units are quiet. once the engine fires, you can't hear it. but if you want to make it quieter, you can add mass to the tank and the area around the tank with tar paper or flashing sealer (self adhesive).

You can get the FPR for carb applications from Summit, JEGS and especially VW suppliers. You see a lot of them on VW's (Superbugs) that have been converted from FI to carb. We have one in the back yard now. Works fine.

[Zanzer]

Check out the Holley red and blue electric fuel pumps. You can buy them on Ebay with the regulator included for anywhere from $40-$75. Plus they are rebuildable so if it ever goes out you can get a rebuild kit for $15.