Does fuel movement in bowls during acceleration impact AFR?

[Stan Weiss]

Perhaps unrelated because Carter/Edelbrock carb aren't considered 'racing' carbs, but the long rammed engine in my '60 Chrysler loses power and occassionaly starts to run very rough during 'sporty' cornering. It's my believe one side of the engine goes rich while the other side goes lean.
The carbs are placed sideways on the long ram intakes, so different from their normal orientation.

One thing to remember is the difference in the direction the jet is mounted in the carb and its fuel opening between a Holley and a Carter / Edelbrock. One is vertical and the other is horizontal.

Stan

[BradH]

Even if the jets remain covered and regardless of what is happening with the float and needle and seats, wouldn’t the relative increase in fuel level at the front metering block and the decrease in the fuel level at the rear metering block directly affect the emulsion circuit. As well as provide a increase in fuel pressure on the primary jets and a decrease on the secondary jets due to inertia?

This is a more articulate way of asking my original question, thanks.

[Stan Weiss]

Even if the jets remain covered and regardless of what is happening with the float and needle and seats, wouldn’t the relative increase in fuel level at the front metering block and the decrease in the fuel level at the rear metering block directly affect the emulsion circuit. As well as provide a increase in fuel pressure on the primary jets and a decrease on the secondary jets due to inertia?

I would think that the G forces from acceleration / deceleration would have more impact that a small change in fuel column height.

Stan

[Mikej26]

Even if the jets remain covered and regardless of what is happening with the float and needle and seats, wouldn’t the relative increase in fuel level at the front metering block and the decrease in the fuel level at the rear metering block directly affect the emulsion circuit. As well as provide a increase in fuel pressure on the primary jets and a decrease on the secondary jets due to inertia?

I would think that the G forces from acceleration / deceleration would have more impact that a small change in fuel column height.

Stan

I agree with that. Just trying to wrap my head around all of the variables. After thinking about it’s bit more, while the g forces certainly have an impact, wouldn’t the carb be somewhat self correcting in the sense that the affects at the primary and secondary sides are equal opposites?

So sure on acceleration you’re forcing more fuel through a given jet size on the primary side than you would on a stationary level dyno, but you’re equally reducing the affect at the secondary side so it seems to me like the net effect might be somewhat mute. Same with deceleration.

[MadBill]

The inertial force is manifested in the change of fuel level, so there would be no additional effect on the fuel flow, but yes, the front barrels should richen by the same % as the rears lean, prompting some AFR maldistribution, but probably less than what happens with the mixture in the plenum.

[oldjohnno]

I've always been a bit sceptical about the effect of small changes in fuel level having an influence on AF ratios. When you consider that it's not unusual to have a signal of 20" H2O at WOT at the booster - and a similar drop across the main jet - then it's hard to imagine a difference of say 1/2" in fuel level having much effect on flow. Remember also that flow through the jet will be in proportion to the square of the pressure drop across the jet, so it takes quite a large change in the pressure gradient across the jet to make much difference in flow, certainly more than what's possible from a float bowl that only 1-1/2" tall. Of course all this presumes that the jet is always well covered.

[MadBill]

Here's one piece of data re same, more can be Googled:
https://www.allfordmustangs.com/forums/ ... at-afr.jpg

BTW, I think you mean't to write that flow varies with the square root of pressure.

[Geoff2]

And then there is the emulsion tube holes that might get uncovered/covered by fuel slosh...& how it affects the fuel curve.

[oldjohnno]

BTW, I think you mean't to write that flow varies with the square root of pressure.

Yes, thanks Bill. Or in other words it takes four times the pressure to double the flow, so a relatively small change in the pressure drop across the jet - as you'd get from a change in the fuel level in a float bowl - will result in an extremely small change in flow through the jet.

[Kevin Johnson]

Well, at least this inspired some rereading and I saw one of my favorite quotes again.

If you did that, it would only suck air from the fuel bowl and no fuel from the tank, just like if there's a hole in your straw you get air instead of milkshake.

[Rick!]

Here's one piece of data re same, more can be Googled:
https://www.allfordmustangs.com/forums/ ... at-afr.jpg

BTW, I think you mean't to write that flow varies with the square root of pressure.

That AFR graph looks bassackwards. The higher fuel level should be richer everywhere. At least that's the way it worked when I ran a chassis dyno back in the '80s. I'm pretty sure I couldn't get an engine to run right with a 1/2" low fuel level. The whole working principle of a carb is its sensitivity to very small delta P, is it not?

[peejay]

Even if the jets remain covered and regardless of what is happening with the float and needle and seats, wouldn’t the relative increase in fuel level at the front metering block and the decrease in the fuel level at the rear metering block directly affect the emulsion circuit. As well as provide a increase in fuel pressure on the primary jets and a decrease on the secondary jets due to inertia?

Yup.

I used to mess with a carburetor for which jets were not readily available. I tuned it strictly by messing with fuel pressure, which altered the fuel level in the bowl. Fortunately I was trying to go leaner, not richer.

This was not just a WOT effect, either, it was an across the board tuning change. I was able to get the plugs to stay clean and increase fuel economy by 25% just by dropping fuel pressure from 4psi to around 1.5. Quarter mile times also dropped by a little over a second, from 17 seconds to high 15s.

[MadBill]

Well, at least this inspired some rereading and I saw one of my favorite quotes again.

If you did that, it would only suck air from the fuel bowl and no fuel from the tank, just like if there's a hole in your straw you get air instead of milkshake.

Oooh, got the Wayback machine cranked to eleven this time Kevin!

[Kevin Johnson]

That AFR graph looks bassackwards. The higher fuel level should be richer everywhere. At least that's the way it worked when I ran a chassis dyno back in the '80s.

I think with the Autolite 2100 carb the wet setting is from the top machined surface down to the surface of the fuel in the bowl -- so a greater distance denotes a lower level of fuel in the bowl and the AFR would be higher ceteris paribus.

Float AFR.jpg