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Jets for YF Carter Carburetor; How to identify and where to find.
Topic Started: Oct 1 2012, 10:12 PM (1,228 Views)
M606
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I live in Brazil and the gasoline we have here is 22% ethanol blended (E22). Differently from the pure gasoline, which has the stoichiometric air/fuel mixture ratio of approximately 14.7, E22 fuel has stoichiometric air/fuel mixture ratio of approximately 13.1. Such difference of air/fuel mixture ratio between pure gasoline and E22 fuel requires that the jets in the carburetor be enlarged, so the carburetor will meter a specific amount of E22 to provide the correct air/fuel ratio and the engine will run as originally designed. Thus, compared with pure gasoline, the carburetor must deliver 14.7/13.1 = 1.12 times more E22, in other words, 12% more fuel.

According to my calculations, I need to get jets with orifice sizes 5.6% larger in diameter than standard jet orifice sizes. Does anybody know any source or manufacturer of Carter YF carburetor jets?

The jets I'm looking for have orifice sizes near to:
- Low Speed Jet - size: .029" diameter
- Main Metering Jet - size: .098" diameter

By looking to my carburetor low speed jet, I noted that its part no. is 11-212S instead of 11-163S, which is the standard part no. for the low speed jet described in the part list for the YF-938SD carburetor.

According to the service manual, the orifice size for the 11-163S low speed jet is .028" diameter. What is the orifice size for the 11-212S low speed jet?

I have also found for sale the following Carter low speed jets: 11-108S, 11-161S, 11-162S, 11-186S. However, I haven't got any information regarding their respective orifice sizes. Is there any Orifice Size x Part No. Table for Carter YF carburetor jets in order to check such orifice sizes?

Thanks,
Felipe
Luiz Felipe Santos
1965 Kaiser M606
1951 Willys M38
Rio de Janeiro, RJ
Brazil
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oldtime
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My compliments...It appears that you have done your homework.

I'm afraid that specific information can only be gained through individual parts analysis or through a copy of the
Carter Master Parts Catalog.
I believe the going price for a Carter Master Parts Catalog is probably around $750.00 U.S.dollars.

I'll see if I can dig up any of the requested data.
You may need to size your own jets or you might also consider contacting Jon Hardgrove of the Carburetor Shop L.L.C.
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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M606
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Ken

Take a look at the link below.

http://www.google.com.br/url?sa=t&rct=j&q=...I_cVhZcuGROAyHQ

It shows a .pdf table where you can see the low speed jet part no. 11-186S, which appears for both Studebaker and Willys, however it shows different orifice sizes (.02925" for Studebaker and .026" for the Willys) despite having the same part no. Why does it happen? Are they really different or the information for the Willys is wrong? I say that because I also looked at the SM-1002-R6 and at the page 111 you can see that the low speed jet for both Carter 596S and 636SA carburetors has .029" diameter. Do you think such jet can fit the YF-938SD?

I have found a low speed jet 11-186S for sale, but the seller doesn’t know the orifice size for it. By looking at the photo, the jet is the same shape as the used in the YF carburetor.

I have already contacted the Carburetor Shop, but they are close for inventory control until October 8th.

I will be waiting for any information you can dig up.

Thanks,
Felipe
Luiz Felipe Santos
1965 Kaiser M606
1951 Willys M38
Rio de Janeiro, RJ
Brazil
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oldtime
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What you are attempting is a recalibration of the fuel metering.
Technically speaking you are delving into the science of fuel burning.
AKA Rocket Science

Yes you need a 1.122% fuel to air mix increase.
This is commonly termed as an enriched mix.
Therefore certain orfice restrictions need to provide a 1.122% area increase.
May I ask ...How did you figure a diameter increase of 5.6%

Quote:
 
What is the orifice size for the 11-212S low speed jet ?

Unknown to me...Can you measure it with a wire gauge ?
Consider that it is likely a current a problem for your carburetor.
Mis matched components taken from various carburetors without full knowledge of each specific function is fully innappropriate.

Quote:
 
It shows a .pdf table where you can see the low speed jet part no. 11-186S, which appears for both Studebaker and Willys, however it shows different orifice sizes (.02925" for Studebaker and .026" for the Willys) despite having the same part no. Why does it happen?

Not sure whats going on with the various figures priovided.
Apparently the orfice may have been re-calibrated and therefore it was superceded ?
Note that many times the American Wire Gauge (AWG) size is listed instead of the actual diameter.
Normally a seperate part number is provided for each change of orfice diameter.

I have not done the calculations but it may be feasable / desireable to switch over to another YF carburetor.
Such as the YF 2392S used on DJ's or the YF 4002-F that was used with emmission controled Hurricanes.
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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M606
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Ken,

I finally found the information I needed regarding low speed jet part no. 11-186S. Indeed, the orifice size for this jet is .029". I've got a Carter Specification Sheet for 636SA carburetor where is described a jet diameter modification for the later production. The jet .026" diameter was superseded by the jet part no. 11-186S which is .029" diameter.

The behavior of air/fuel flow in a carburetor is a fluid dynamic process which can be described by Bernoulli’s equation. By using a simplified model of Bernoulli’s equation for fuel flow in a single jet carburetor, it’s necessary to consider not only the fluid flow area, but also the density of the fluid that is flowing. Density influences fuel flow speed through the jet. As density increases, fuel speed decreases and, consequently, fuel flow decreases. Thus, regarding carburetor recalibration for the use of E22, we must consider the fact that E22 has a higher density than gasoline. The 1.122% fuel to air mix ratio increase from gasoline to E22 cannot be taken as the only element to be considered for the increasing of the orifice jet area.

See below how I did my calculations by using the simplified model of Bernoulli’s equation for fuel flow in a single jet carburetor:

Wa/Wf = (Aa x Ca)/(Af x Cf) x (Pa/Pf)1/2

Where:
Wa = weight of air flowing per second
Wf = weight of fuel flowing per second
Aa = throat area of the choke
Af = orifice area of the jet
Ca = coefficient of discharge of air
Cf = coefficient of discharge of fuel
Pa = density of air
Pf = density of fuel

Re-arranging the equation we have:
(Wa/Wf ) x (Af x Cf) x (Pf)1/2= (Aa x Ca) x (Pa)1/2

Where (Wa/Wf) is the Air/Fuel ratio, (Air/Fuel)

So, for gasoline we have:
(Air/Fuel)g x (Ag x Cg) x (Pg)1/2 = (Aa x Ca) x (Pa)1/2

So, for E22 we have:
(Air/Fuel)e22 x (Ae22 x Ce22) x (Pe22)1/2 = (Aa x Ca) x (Pa)1/2

After combining both equations we have:
(Air/Fuel)g x (Ag x Cg) x (Pg)1/2 = (Air/Fuel)e22 x (Ae22 x Ce22) x (Pe22)1/2

After considering:
(A/F)g = 14.7
(A/F)e22 = 13.1
Pg = 0.7410 kg/L
Pe22 = 0.7495 kg/L
Cg = Ce22 (they have almost the same value)

We have:
14.7 x Ag x (0.7410)1/2 = 13.1 x Ae22 x (0.7495)1/2
Ae22 = 1.1158 x Ag

The areas are:
Ag = (PI x (Dg)2)/4
Ae22 = (PI x (De22)2)/4

Considering:
Dg = present jet diameter for gasoline
De22 = new jet diameter for E22

So, here is the final gasoline to E22 jet convertion formula:
De22 = (1.1158 x (Dg)2)1/2

For a Dg = 0.0935”, then De22 = 0.0988”, which is 5,6% larger.

If you want some technical literature regarding this issue I can send to your e-mail.

Regards,
Felipe



Luiz Felipe Santos
1965 Kaiser M606
1951 Willys M38
Rio de Janeiro, RJ
Brazil
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oldtime
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Felipe,
That's excellent and it appears to be quite accurate.
I never even bothered to figure in the fuel density in my approximation.
It appears that you are well on your way to building a carburetor from scratch.

The truth is that unless one fully understands the function of each orfice restriction and every air bleed of the Carter YF it will be near impossible to set it up for a specific fuel.

Obviously the Main Jet and the Metering Rod are of primary concern.
The Low Speed Jet Tube is also very important.
Yet there remains several other air bleeds and restrictions that may also need a recalibration.
Even the Carter YF engineers obviously used a lot of trial and error in their attempts to perfect these carburetors.
That's exactly why many of the parts were superceded.
Experimentation (trial and error) proved that certain changes had merit.

That's why I suggest trying a YF that was set up for other other similar applications.
From what I can tell the YF 2392 S ( from DJ-3A) yeilds a slightly richer fuel mix than the YF 938 SD.

I have a fair amount of information concerning air bleed restrictions and orfice sizes if that is of interest to you.
From what I know any carburetor should be within 5% of proper specification to be considered effective.

Here are some numbers I found for the:

Low Speed Jet Tube
11-161S = superceded to 11-163S
11-163S = .028"
11-660S = .031"

Main Metering Jet
120-155 = .096"
120-160 = .091"
120-166 = .0935"
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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M606
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Ken,

I agree with your comments. Besides that, carburetion is not an exact science. During a long time, engineers had been trying to make carburetors as perfect as possible and, consequently, they became each time more sophisticated until the advent of the electronic fuel injection. The trial and error ruled them during all this time.

There are a lot of factors involved in the carburetion process, such as fuel properties variation, intake air density/temperature etc. which make impossible a perfect set up, even for a specific fuel such as gasoline or E22. Due to this fact, you are right when saying that any carburetor should be within 5% of proper specification to be considered effective.

Regarding you suggestion for trying the YF 2392 S, I think that the recalibration of my YF-938SD is the best cost-effective solution in order to get a suitable carburetor for E22 use. It requires the replacement of the jets for jets which have orifice diameter 5.6% larger. I have already bought such jets: the low speed jet (P/N 11-186S = .029") was found on eBay and the main jet (.098") was found at Mike's Carburetor Parts (www.carburetor-parts.com) who provides main jets of many different orifice sizes for YF carburetors, as well as other parts for YF carburetors. They will be arriving to me in the next 30 days.

Another issue to be considered is regarding ignition advance. As ethanol has a higher octane number than gasoline, it works as an octane-raising for gasoline with anti-knock properties. Therefore, the addition of ethanol at 22% by volume in gasoline turns E22 into a fuel with higher octane rating than gasoline. This higher octane number may be utilized by advancing the basic ignition timing. However, there is a limit to the amount of ignition advance the Hurricane engine will tolerate even if no combustion "knocking" is heard, and this limit I need to find degree by degree on a trial and error basis.
Luiz Felipe Santos
1965 Kaiser M606
1951 Willys M38
Rio de Janeiro, RJ
Brazil
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oldtime
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As you know...
The Willys 134 engines all have a very low compression ratio by modern standards because they were originally designed to run on uncracked gasoline.
Uncracked gasoline is roughly 69 octane.
Todays cracked gasoline blends have a much increased octane rating.
Thereby they are able to run efficiently at much higher compression ratios.
Raising the compression ratio significantly is the main thing that one should consider to improve the engines overall efficiency.
The proper Autolite distributors with vacuum advance should also be considered.

We are certainly interested in your efforts to re-calibrate the YF, so please keep us informed.
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

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