Carburetor secondary diaphram spring reversal

[kitchman]

Viewed several YouTube videos where the spring located underneath the secondary diaphragm is reversed, placed between the outside of the diaphragm and the housing cover. This is said to get the secondary to behave more like a mechanical actuated one. Has anyone done this with success?

[irowiki]

On our cars, or on carbs in general?

[kitchman]

It is definitely for the Aisan two barrel carb, The carbs. in the various videos appear to be almost identical to ours. I initially discovered these videos as a result of searching 1986 Toyota Tercel carburetor rebuild, I believe. The idea of reversing the diaphragm to spring to assist secondary valve opperation sounds very compelling.

[xirdneh]

if it does work i would like to see a picture

[irowiki]

Why would you want to do this though?

[kitchman]

First reason is I don't believe my secondary valve ever worked when I purchased my car. Second it is noted on various YouTube videos that it is not uncommon for secondary valves on Aisan carbs. to either not open or not open fully. This being said, if reversing the secondary diaphragm does in fact work, what possible downside could there be in doing this? It is said that doing this make the throttle response snappier. When ever I punched the accelerator on my car I never got that secondary boost sensation. Have not done this spring reversal as yet nor have I re-installed the carb. just rebuilt. Was trying to get some board confirmation as to whether or not to modify the diaphragm, being easier to do on the bench.

[irowiki]

I have never felt a "boost" on any tercel I have driven. I think the effect is much more subtle.

You would probably kill your MPG doing that.

[dlb]

When ever I punched the accelerator on my car I never got that secondary boost sensation.

i think you're expecting too much from a 62 hp engine. i don't think anyone here would say they feel any boost when the secondary engages, or that they can even feel it at all. the same goes for the weber carbs, too.

[irowiki]

I'm not even sure what the secondary does, I think it might be a gradual effect, or something. I'll video my FWD Wagon going up a hill one of these days so you can hear it straining.

[Petros]

the secondaries allow more air/fuel mixture into the engine. With just a single barrel carb, to get good low throttle response and efficient running it has to be smaller than ideal for full throttle operation. so to get more power output and efficient low speed output, they use two venturies, one optimized for low speed/low power operation, and a second larger venturi optimized for wide open throttle operation, for passing, merging, going up hills, etc.

The secondary used to always be mechanically operated by the linkage, simple and reliable. But I guess to optimize emissions and economy, they went to vacuum operated secondaries in the 1970s or so, to get better control of fuel air mixture. Eventually of course the carb was abandoned all together for EFI, with superior control of the mixture over most all driving conditions.

[4wdEconoBox]

I've been looking into this too. It's a simple "mod" that early Corolla owners with the 4ac do in order to make the secondary valve open quicker. Supposedly you can actually hear the secondary open once you the spring flip trick. Also supposedly it doesn't harm fuel economy very much. I went and tried the other day and couldn't get it to run right so I changed it back and it still wasnt running right so I thought I had really messed up. Turned out that I accidentally left a vacuum line off, after I put the vac line on it ran good again. I'll probably try this again tomorrow and let everyone know how it goes!

[marlinh]

Can you post the links to these videos? I would like to be able to confirm that the secondary opens at all.

[4wdEconoBox]

http://youtu.be/D3JuA3Uvymk
Here's the one I seen!