fuel tank level and carb seting

[bob miller]

i know as the fuel level drops the carb seting gets leaner...WHY ?...thanks...bob miller

 

[Speed Jr.]

i know as the fuel level drops the carb seting gets leaner...WHY ?...thanks...bob miller

I could be wrong, but I would attribute it to either less pressure from pressure line as the tanks air compartment gets bigger(as fuel decreases), or if the water flattens out, it will load the prop more and lean out the engine.

Larry Jr.

 

[Daniel's Racing]

i know as the fuel level drops the carb seting gets leaner...WHY ?...thanks...bob miller

Basically because there is less weight of the fuel helping to push fuel out and it has to be sucked up from a lower fuel level.

Even with exhaust pressure the fuel level does affect the ease of flow. If the lines are sized properly and a good designed fuel system

the fuel level affect on mixture is minimized.

Much the same as a well pump that is deeper versus shallow. The shallow that has to draw less height will prime faster and pump more.

Daniel

 

[Geraghty]

i know as the fuel level drops the carb seting gets leaner...WHY ?...thanks...bob miller

good old gravity........

The higher the fuel level in the fuel tank the higher the fuel outlet pressure being applied on the outlet of the fuel tank.....

as the fuel level drops in the tank, the less pressure is being applied on the needle valve resulting in less fuel flow and a leaner needle....

 

[bob miller]

a BIG thank you to every one who responded

 

[P THOMAS]

i know as the fuel level drops the carb seting gets leaner...WHY ?...thanks...bob miller

good old gravity........

The higher the fuel level in the fuel tank the higher the fuel outlet pressure being applied on the outlet of the fuel tank.....

as the fuel level drops in the tank, the less pressure is being applied on the needle valve resulting in less fuel flow and a leaner needle....

Rod, what about the setup with the pressure line to the bottom of the tank and a top vent to use when filling for a overflow, capped off when running.

Used to set up tanks that way and it seemed to give a more constant fuel draw as the fuel level when down.

Dont do this any more just one more thing to mess with.

 

[ken stang]

Phil

Been using this set up for many years. Works great for me.

 

[tnrcboatracer]

Gravity only cares about the level in the tank up stream from the carb. Hence a float chamber as used is FSRV works very well at eliminating needle change with fuel burn. The FSRV float chambe is level controlled without pipe pressure to the carb. There is pipe pressure forcing the fuel from the main tank to the float chamber, but the float chamber is vented to atmoshere.

This is not the same as our small hopper tanks on the pipe pressure system. Our hopper tanks are more like an accumator or bulge in the fuel line; the fuel level in the main tank still affect the fuel draw in a hopper tank setup. Same principle as a siphon. The pressure required to draw the fuel to the carb depends on hte height of the fuel in the tank.

 

[Raymond Bonenfant]

Great Stuff Here, Thanks.

Pressure is pressure right? So the size of the source pressure line from the pipe in a nitro set up to the tank should not matter; am I correct?

The ‘hopper’ idea is intriguing to me. I have often wondered if the bubbles in my tank at less then full levels crated by engine vibration being transferred through the hull (Stock Miss Vegas) are the source for some of my performance inconsistencies. One of my ideas was to put in a hopper (as you called it) to keep my main tank in an ‘always full’ condition; although I am concerned about the added weight.

Thanks

Raymond

PS: what does FSRV stand for? For that matter while I am really showing my ‘greenness’ and experience, what does SAW stand for in reference to rigger hydros?

 

[Andy Greene]

Great Stuff Here, Thanks.
Pressure is pressure right? So the size of the source pressure line from the pipe in a nitro set up to the tank should not matter; am I correct?

The ‘hopper’ idea is intriguing to me. I have often wondered if the bubbles in my tank at less then full levels crated by engine vibration being transferred through the hull (Stock Miss Vegas) are the source for some of my performance inconsistencies. One of my ideas was to put in a hopper (as you called it) to keep my main tank in an ‘always full’ condition; although I am concerned about the added weight.

Thanks

Raymond

PS: what does FSRV stand for? For that matter while I am really showing my ‘greenness’ and experience, what does SAW stand for in reference to rigger hydros?

If I'm not mistaken FSRV is a sanctioning body in Europe simular to NAMBA or IMPBA here in the states.

SAW= Straight Away racing-

2 Timed passes in a straight line for an overall average speed record attempt. Fun stuff- but very addicting with a never ending quest to go faster.....

Hope that helps, If I'm wrong on the FSRV thing, I'm sure some of my pals will let me know.

Andy

 

[bob miller]

Gravity only cares about the level in the tank up stream from the carb. Hence a float chamber as used is FSRV works very well at eliminating needle change with fuel burn. The FSRV float chambe is level controlled without pipe pressure to the carb. There is pipe pressure forcing the fuel from the main tank to the float chamber, but the float chamber is vented to atmoshere.
This is not the same as our small hopper tanks on the pipe pressure system. Our hopper tanks are more like an accumator or bulge in the fuel line; the fuel level in the main tank still affect the fuel draw in a hopper tank setup. Same principle as a siphon. The pressure required to draw the fuel to the carb depends on hte height of the fuel in the tank.

SAW stands for straight away speed trials

 

[Raymond Bonenfant]

Thanks.

Raymond

 

[Tall Fella]

Hello Raymond .

This is a reply from Australia . As Jon says - ( FSRV ) is a class that uses a mono hull with the prop and rudder under the boat . They run around a M or W course for a minimum of 15 minutes per race . At State or National race meets the time may possibly be increases to 30 minutes or 1 hour . They are eligible to run in regular mono class racing over here in Australia . Many years ago at my old race club where we ran a seperate Oval and ( Multi Boat - FSRV ) competition , I won the overall Club Championship with a Multi Boat . There is not much Multi Boat racing happening over here any more . They begin the race with a Le Mans start and are allowed rescue and refuelling during the race. I hope this helps with your enquiry .

Regards

Ian Baas

Tall Fella Racing

Australia

 

[Raymond Bonenfant]

Yes Sir it does,

Thank you

Raymond

 

[tnrcboatracer]

Raymond, you are right on the mark with the purpose of a hopper tank. It is to ensure consistent fuel flow at lower main tank levels. They are usually very small, and best if made with a vertical orientation to let the bubbles accumulate at the top. They aren.t heavy at all. There is altleast 1 thread on here regarding hopper or surge tanks. Most of the custom metal tanks have a hopper tank built into the inside of them.

 

[Raymond Bonenfant]

Thanks Jon,

Looking for a place to put anouther tank. Size? Just enough for a heat plus milling time right?

Raymond

 

[P THOMAS]

Thanks Jon,
Looking for a place to put anouther tank. Size? Just enough for a heat plus milling time right?

Raymond

What size motor? usually a hopper tank is a 1 oz, or 2 oz if you have room. a 20 motor only needs 6-8oz, 40 motor 12-14 oz, 60 and up 16-18 oz of fuel to make a race. Plan on finisihing your race on the main tank.

 

[Raymond Bonenfant]

Phil,

My initial thoughts were for my .18 Miss Vegas but if this is a “best practice” set up I may want to engineer such a set up into my Dumas Miss Unlimited build powered by a .32 Dynamite.

So, help me to understand; the hopper tank “is” going to run empty before the end of the race? At the sizes you suggested this would occur early in the race. Would this not negate the positive aspect of the setup by allowing the main tank to become aerated? Or…..is this set up designed to prevent leaning out due to fuel aeration at low main tank levels?

In my case, I see lots of bubbles generated in the tank during dockside engine operations (such as starting) when the tank is less than full. Now you must understand that I have never ran in a sectioned race before, but I will this summer; god willing. If my research is correct each heat race is only 3 or 4 laps plus the 2 or 3 minute milling time all of which is well within the tank capacity of the stock tank with plenty left over. Maybe I am climbing up the wrong tree searching for the cause of my performance inconsistencies.

Raymond

 

[tnrcboatracer]

As Phil stated, you want the hopper tank to still be full at the end of a race. The hopper tanks should be as close to the carb as possible. The fuel will flow from hte main tank to the hopper tank, and then to the carb. The hopper tank acts like a 1oz. 'bulge' in the fuel line that allows any bubbles to rise to the top while the fuel is drawn from the bottom. In reality, there should be only the tiniest amount of air in the hopper tank at the end of a race.

FYI, most heat races are 6 laps, with another 4 laps or so for mill time before the actual race. The pit time is 2.5 minutes with no launch in the last 30 sec (2 minutes to start your boat and get ready to launch). Your fuel burn will depend a lot on the motor (and nitro%) you run. I have been know to wait out the first 90 seconds of clock time and limit myself to 2 laps of mill in order to have enough fuel to finish a heat. And even then it might run out of fuel before I could get it back to the pit. Then Walt (Tanks-2-U) started making the hump style SGX tanks with an extra couple oz of fuel for my SGX 67/84 with MAC power.

 

[Raymond Bonenfant]

Ok, I see now! I did not realize that the main tank was the first to go empty. Thanks. Now to find a place to locate it.

Raymond