Throttle Sensitivity

[Bob Bidonde]

Throttle sensitivity is the response time of the engine to changes in the throttle. In the Zenith carburetor, the Venturi establishes the throttle sensitivity. Does anyone have a different outlook about this?

 

[Kurt in NJ]

Spark advance is a big factor also

 

[cadillac512]

So is compression ratio and weight of the rotating parts like a lightened flywheel. The throttle linkage ratio of an A is also a factor...it's a pretty quick ratio thus the need for the foot rest next to the throttle.
If strictly thinking about the carb, then yes venturi size and air speed will make a difference.

 

[Jim Brierley]

Whatever made you think of that???

 

[Phil Brown]

Whatever made you think of that???

Early snow this year ?

 

[BRENT in 10-uh-C]

Whatever made you think of that???

I agree with Jim. The Venturi is what creates the vacuum to draw the fuel upward and then create the turbulence to mix & atomize the fuel into the air. A Zenith will run without the Venturi installed, so just the vacuum from the intake manifold is sufficient to get the fuel in the bowl to move however it does not create the needed turbulence to get the fuel mixed into the air.

 

[KMBeers]

Brent, were you able to drive the car without the venturi installed? Or did it just idle?

 

[nkaminar]

Modern cars are controlled by an engine management computer. The fuel injectors and throttle plate are all controlled by the computer. The computer controls the throttle response. I have to anticipate the need to rapid accelerate in my 2016 Chevy truck because the throttle response is slow.

Kits are available to reprogram the engine management computer in cars and trucks. That way the throttle response can be changed to suit the owner's needs.

I have found that the Zenith carburetor on a Model A car is quite responsive and is nice and smooth throughout the throttle setting. It is actually a very good design. If you are not getting the throttle response that you should then the carburetor may need rebuilding or there may be other problems such as a vacuum leak or timing or the GAV is not set correctly.

 

[jeepguy1948]

I don’t think Bob has a problem. He likes to start conversations about various topics. I have learned quite a bit from reading (and occasionally contributing) to his threads.

 

[BRENT in 10-uh-C]

Brent, were you able to drive the car without the venturi installed? Or did it just idle?

Actually it started and idled. I took it for a drive and it was sluggish and gutless, but it did drive. When I tried to adjust the GAV it did nothing when adjusted. We brought it back and we pulled the bowl off of the Carb to blow some air thru the jets. That's when we noticed there was no Venturi. I asked the customer, and he admitted he had been in there but did not recall ever seeing it. So yeah, they will run, but they are slug.

 

[ModelA29]

The A would be more responsive if it had an accelerator pump.

 

[Bob Bidonde]

Jeepguy has it right. I like to stimulate conversations. In doing so, I also learn from you all.

 

[gdmn852]

Hello, in the linkage itself, the strength of the spring would be a variable,and if any binding in linkage.SU carburetors use oil for the slide valve and the weight of oil will affect throttle response, on MG sites this is much discussed.

 

[Bob Bidonde]

There are 2 sensitivities in discussion. On is fluid mechanics and the other is mechanical. My stimulating post was about the fluid mechanics. I love this forum. You all are great!