Blocking secondaries

[flapdoodle]

The quote about the Opel on this thread...
http://www.gassavers.org/showthread.php?t=8613&page=2
renewed my thoughts that blocking the secondary would help FE.

I have wondered for some time how much air leaks past the secondary butterfly, and how much gas "leaks" past the secondary float valve.

Has anyone tried blocking the secondary off completely to make a small 2 bbl carb?

This is what I am considering on my Holley 4160...

1. A rectangle of aluminum flashing sandwiched between two gaskets to block the secondary bore.

2. A plug for the gas tube connecting the front and rear float bowels.

These modifications are reversible if it produces undesirable results.

[R.I.D.E.]

In the Opel they were only trying for a specific power level under very controlled conditions. Pulse to 45 MPH EOC to 15 MPH and repeat. This was not attempted on any public streets in any kind of traffic.

I don't think it would make a large difference in your Buick Flapdoodle. On the other hand (assuming your carburetor is fairly simple (not very familiar with yours), it should be fairly easy to disable the secondaries. Disconnect or disable the actuation part. I would not worry much about the fuel supply because the secondaries only deliver fuel when the butterfly starts to open. They don't have an idle circuit (at least I think they don't).

If there is an external linkage, just unhook it and make sure it can not jam the throttle in an open position and see if it makes a significant difference.
Remember, you won't have much emergency power, especially at higher speeds, so please be careful until you are comfortable with that kind of modification.

regards
gary

[Jay2TheRescue]

What year/model Buick are we talking about? I did a lot of research years ago on what was available when I was considering switching the stock setup on my Buick to one of the optional setups from various years. I was so close to putting a 1980 Pontiac 301 V8 with a Rochester 4bbl carb as was available on the 1980 Regal.

-Jay

[flapdoodle]

On other forums I found that the Holley 4160 has a history of leaking secondaries, sometimes enough that idle adjustment becomes impossible.

I blocked off the vacuum secondaries last night and found it had a major effect on the idle. (I.E., would not idle without major adjustment). This means every change I made testing HHO and trying to optimize it will have to be done over, since they changed the vacuum with every tweak, which in turn changed the amount the secondaries were open. It also means the vacuum advance and main jets need to be reevaluated.

Manual linkage will be needed.

Will keep this updated.

[flapdoodle]

I had to turn the idle stop screw in 1 1/4 turns, that is an indication of how much secondary leakage there was. The idle mixture had to be richened 3/4 turn each screw. Idle is the smoothest since I have owned the car. I have my fingers crossed that means better FE.

Previously I had re jetted for altitude minus one number on the primary, but left the secondary jets alone thinking they were rarely used.

A slight tap of the pedal chirps the tires at a traffic light, and flooring it at 45 MPH still pushes me back in the seat, so not much was lost in power. I topped off the tank and should have mileage figures soon.

[blownb310]

I am interested to see what the result is of this modification is [in FE]. I would not have thought the secondaries would leak like you describe yours did. Is it an old carb with worn throttle shaft bushings?

[flapdoodle]

Originally Posted by blownb310

I am interested to see what the result is of this modification is [in FE]. I would not have thought the secondaries would leak like you describe yours did. Is it an old carb with worn throttle shaft bushings?

Nope. It is a new carb, not rebuilt.

[Lug_Nut]

A slipped accelerator cable was keeping the secondary (Holley 5200 series two bbl square choke Weber copy) on my Sonett from opening. Since most of my driving was moderate and with a light weight car it mattered little, until I wanted some power.
On the dyno with the primary only I had 22 hp peak. With the cable re-adjusted to allow the mechanical secondary to open fully I had 66 hp peak.
Daily fuel economy didn't change since my driving seldom tipped into the secondary anyway.
Would completely disabling the secondary improve fuel mileage? Don't know.
Don't care either.

[flapdoodle]

I looks like 1/2 MPG savings so far (on my test circuit through town), but will keep a close eye on it. A secondary mechanical linkage might be a wise purchase for me.

Since the idle stop had to be opened, and the idle mix increased I believe that the secondary main jets were providing a little gas before I blocked the secondaries. I wonder if the idle circuit gives better mixing. Anyhow, the smooth idle and smooth low speed around town alone made this a worthwhile experiment.

[maxxgraphix]

Just slap on a single brl TBI with a fuel management system.