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 Post subject: fuel passages
 Post Posted: Mon Oct 01, 2012 9:53 am 
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Hey guys I was thinking :- .......Yea now I have a headache #-o ...We try to keep the fuel passages to size and the smallest one is usually the restriction and we are talking main well up to the banjo.. So what affect does it have if you have a larger banjo hole than what the angle passage is...Another words say you have a angle passage that is .150 and you have a banjo pin and passage to the booster that is .170 is there an affect to that? I would assume that the restriction is the angle passage only being 160..Kind of like a 4 inch pipe going into a 6 inch pipe only so much can get into the six inch pipe and there would be a lot of area in that pipe that is not full..Get what I am saying???

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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 11:15 am 
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http://en.wikipedia.org/wiki/Bernoulli's_principle :-k :-k

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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 11:32 am 
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Beretta wrote:
Hey guys I was thinking :- .......Yea now I have a headache #-o ...We try to keep the fuel passages to size and the smallest one is usually the restriction and we are talking main well up to the banjo.. So what affect does it have if you have a larger banjo hole than what the angle passage is...Another words say you have a angle passage that is .150 and you have a banjo pin and passage to the booster that is .170 is there an affect to that? I would assume that the restriction is the angle passage only being 160..Kind of like a 4 inch pipe going into a 6 inch pipe only so much can get into the six inch pipe and there would be a lot of area in that pipe that is not full..Get what I am saying???


Add to that the fact that the combined area of those holes in a booster is somewhere around 40% LARGER than the hole in the banjo that feeds them? :-k


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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 12:24 pm 
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The trick is to make sure the jet is the restriction in the path, if it's not the emulsion doesn't work as it should. I try to make from the angle channel to the banjo progressively larger, at least a few thousandths larger at each step. Chamfer the entrances where you can.


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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 2:58 pm 
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If you keep steeping up the size wouldn't that slow down the Velocity? causing it to be more of a dribble and not covering the whole pattern?

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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 4:38 pm 
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We are talking small amounts, the idea is to avoid turbulence at the transition points and to maintain the jet as the control for the circuit.


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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 7:12 pm 
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Mark what your saying is not the case with my E-85 carb as it's got .233 main wells with .187 exit channel with a .200 booster pin and banjo passage...Not enough to worry about?? Or should I open up that exit channel as the new banjo's are .213..

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 Post subject: Re: fuel passages
 Post Posted: Mon Oct 01, 2012 8:12 pm 
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My 1250 has the same blocks and pins, should be fine. You should have gone through the banjo with around a .205, drilling the end for the pin, but I 'm not sure it will be an issue.


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 6:25 am 
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Dont forget there is a kill bleed above the emulsion bleeds that is feeding air into the angle channel or the feed outlet. That air has to be considered with the flow of the outlet to the booster, that's why its the biggest drilling (or its supposed to be).


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 6:37 am 
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ALSO that anti siphon air bleed; the kill bleed; doesn't have to push fuel out the way to flow its air so it flows more air than the lower emulsion bleeds do. The fuel thats present in the well behind the kill bleeds is at lower pressure than the bowl level so it's easier for the air from that bleed to enter the well compared to the air from the lower emulsion bleeds. THATS why its important to have the optimum size main jet. You have to have the right size well drilling and booster outlets etc so that the main jet is the main restriction and its clearly defined within the flow physics to be the main restriction. That allows the emulsion bleeds to work more effectively. When carby guys make the drilling smaller the main jet can be changed and not much happens so its difficult to tune it, because the emulsion bleeds dont function properly. The standard Holley is not far off correct, it just needs a tweak that's all.


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 7:21 am 
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Bruce, From what your saying how much larger should, lets say the main well,cross channel etc compared to the MJ size?

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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 8:06 am 
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That question doesn't have a definitive answer. Its so interlocked I'll try to explain it this way.
The channels could all be the same size if they start off large enough.But it would require a different emulsion well arrangement. The Weber style with tube emulsions enables spreading of the air around the tube and keeps the bubbles separated whereas the Holley puts all the air in on the one side of the well. If the channel is made large all the way the bubbles stand a pretty good chance of coalescing when the velocity is slow. The other issue to solve is when the channel is large the transition point from laminar to turbulent flow occurs at greater flow rate than in a smaller drilling. The transfer circuit of a normal design, say a Holley, is capable of around 40hp from 2 barrels of a carby (like on a normal progressive linkage setup). That point coincides nicely with the turbulent flow beginning in the main well so the transitions to the booster are seamless and the booster flow doesn't have a lean spot in it. If you drilled the main well large all the way then the transition point would be higher up in the Fuel flow rate so there would be a period during the engines low load range that it would be too rich because of the amount of fuel exiting from the booster (remember laminar flow is more efficient relative to the vacuum than turbulent flow is). So do you blame the transition slot or do you blame the booster circuit or the emulsion bleeds? Ohh we can lower the float level and try that! NO you have to have a balanced system otherwise you just lower the float and it works fine until the engine power starts to pull the bowl dry. It's just like you have to have a balanced T-slot, you can put a T jet in it but ask yourself are you covering up a slot thats too long?

When you correctly balance a carby which is what I try to do for my customers, you finish up with no holes in the butterfly's, a shorter transfer slot, a wide enough transfer slot, minimum emulsion bleeds and fairly ordinary looking stock main well specs with near stock jets on any size engine you stick it on. But geez does it take a long time to get them right. And not a lot of people want to pay for that. The ones that do amaze their mates with their cars docility with performance.


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 8:55 am 
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What I'm trying to get across is people seem to concentrate on drilling the main well this size or that. But in reality you can get the AFR you need on gasoline from a stock Holley. You gotta clean them up and clean up the corners etc but they can run richer than you need.

There is not one single thing in a carby that stands out as the first priority to modify. Every engine I do either, a Holley or a Smartcarby, has a different design carby on it at the end. there all unique.

Anyway there is no set rule what the size increase of the well sections should be. Some tuners concentrate on the main well as a magic thing they understand and charge for, others like me basically ignore it. The sizes just have to be enough to not step it backwards thats all there is to it really. If you drill the upstream too large then you step the flow backwards into the previous flow zone and you might get a change in AFR at low power levels that you dont want. Some carbys I'm sure are like that and people just fiddle with the pump shot to cover it. There is a totally different objective for a road car compared to a drag car, the drag car tuner can get a lot of things not optimum and no one complains. Driving a road car with those manners is a totally different problem. You learn things from road carbys that make differences to drag carby performance. And the main thing I have learnt is the problems are not in the Holley well.

I have never had to change the main well, I work on the t-slot and IFR and emulsion. Thats about all you need to concentrate on. If you need to go drilling the main wells then I think your running out of fuel in the bowl so I fix the fuel system. I never drill butterfly's I'll do machining on the base plate and totally alter the slot then I dont need holes. I get the right size carby for a start. I never forget the importance of ignition control.

Dont rush to blame the carby, its never the carby.


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 9:32 am 
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Shrinker, this carb isn't gas, it's E85. It needs about 30% more fuel, add to that it's a 1250. When I tried to run a gas #2 mainwell the jet size approached the size of the bottom of the mainwell, so we went larger and jet size dropped. With the 1250 I even went to methanol booster pins,boosters, and banjos to get the jet size down.


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 Post subject: Re: fuel passages
 Post Posted: Tue Oct 02, 2012 7:51 pm 
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Well E85 is a different matter then isnt it. Of course it will need larger well size but the principles of getting larger after each bend is still the same. The problem with E85 is it holds laminar flow way longer than gas and you cant get correct control of laminar flow by using only emulsion. If you try to reduce the well size so that it turbulates then the main jet is no good, just as you have found out. Emulsion carbys are perfectly designed for low viscosity fuels, nothing else. For higher viscosity fuels you need a needle to obtain accuracy.
E85 may be a cheap fuel for racing but its really only good for that, to get an accurate carby for E85 road driving emissions control etc would be quite difficult, so just use EFI.

Hey what emission control laws do you guys have, here we have any car made after June 1973 can be modified but it must pass its original emission test standard. What the law in USA?


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