Jetting advice needed

[Tobi/DFL]

Hi everybody,

I just finished installing my new engine and I´m looking for an jetting advice to start with. The final jetting will be made with help of a lambda tool but I need something to start with and hope that some of you can help. So here is the technical data of my engine:

- 2789cc (86x101,6mm)
- CR 11,5:1 (Aral Ultimate 102 octane)
- custom cam, 266° @ 0,05", valve lift IN 14,42mm, valve lift EX 14,0mm, 106° lobe centers
- T.Pieper CNC heads with 48/39mm valves
- 50.5mm IDAs with 44mm JPM venturies, two progression holes
- CSP/JPM WASP 2 stepped header with WASP stage 2 muffler

Thanks in advance for your help!

Tobi

[Jim Ratto]

Hi everybody,

I just finished installing my new engine and I´m looking for an jetting advice to start with. The final jetting will be made with help of a lambda tool but I need something to start with and hope that some of you can help. So here is the technical data of my engine:

- 2789cc (86x101,6mm)
- CR 11,5:1 (Aral Ultimate 102 octane)
- custom cam, 266° @ 0,05", valve lift IN 14,42mm, valve lift EX 14,0mm, 106° lobe centers
- T.Pieper CNC heads with 48/39mm valves
- 50.5mm IDAs with 44mm JPM venturies, two progression holes
- CSP/JPM WASP 2 stepped header with WASP stage 2 muffler

Thanks in advance for your help!

Tobi

65 or 70 idles with 120 holders
180 main
F4 emulsion tube
215 air
3.0 needle valve

[Tobi/DFL]

Thanks, Jim!

Can you tell me which effect the F4 emulsion tube will have compared to a F2 emulsion tube for example?

Tobi

[Deadly1]

Perhaps these will help. Not sure if I have attached the images successfully?
Wayne
[ Attachment: You are not allowed to view attachments ] [ Attachment: You are not allowed to view attachments ] [ Attachment: You are not allowed to view attachments ]

[Tobi/DFL]

Hi Wayne,

your PDFs are very helpful as I did not know how the emulsion tubes work before reading the article. THANKS ALOT!

Tobi

[Jim Ratto]

Thanks, Jim!

Can you tell me which effect the F4 emulsion tube will have compared to a F2 emulsion tube for example?

Tobi

Tobi, the F4 will allow larger volume of "reserve" fuel

Here's info from VW Weber tuning book I am working on (not finished yet)



Emulsion Tube Selection
   Once venturi diameter has been established, the next step is to establish which emulsion tube to use. Unfortunately, selecting emulsion tubes is one of the least understood aspects of Weber tuning. Most of this is due to Weber’s numbering system of the emulsion tube. Remember this: the number assigned to an emulsion tube has NOTHING to do with number of holes, the outside or inside diameter of the emulsion tube or where holes are oriented. So do not assume an “F6” emulsion tube is one step richer or leaner or has any type of relationship whatsoever with an “F5” or “F7”. In many cases, despite adjacent numbers, two tubes will have nothing in common other than they are both emulsion tubes. In order to keep this discussion somewhat simple, we will discuss only four different emulsion tubes: F2, F4, F7 and F11.


   What is an emulsion tube and what does it do? Physically, the emulsion tube is a brass tube which, in the case of the 48 IDA and IDF series carburetors, carries both the main and air corrector jets. The main jet is inserted, as a press fit, into the bottom of the emulsion tube, which locates it against the seat at bottom of jet well in carburetor, below fuel level line(adjacent to float bowl). The air correct jet, again by press fit, inserts into the top of the emulsion tube, which locates it at top of jet well, above fuel level line, and exposed to atmospheric air pressure.
   Where the discussion tends to get complicated is to discuss what the emulsion tube actually does, in terms of fuel and air metering. In the simplest terms, the emulsion tube determines how and when the main and air corrector jet interact not only with each other, but also with idle and transition circuits. It also determines how and when liquid fuel mixes with air before it is emitted from the fuel duct. Some tubes are designed to “bring in” the main circuit strong and early. Other tubes are designed to delay or soften the influence of the main circuit. Other tubes may increase effect of air corrector, soften the air corrector effect, or delay it. Different outside diameters are another factor to consider. 
Here’s a few points to remember when deciding on which emulsion tube is right for your engine and carburetors:
•   A smaller outside diameter allows for a greater volume of fuel “on reserve” in jet well (beneficial to engines with high air/fuel demand, i.e. large cc, high rpm). This volume of fuel can be referred to as a “curtain” of fuel.
•   A larger outside diameter decreases the volume of fuel on reserve in jet well. A tube like this is helpful when engine size is small or moderate and in mild or moderate state of tune. It also may help with engines with strong vacuum pulses in an effort to stall main circuit.
•   An engine will not run on liquid fuel. Fuel needs to be mixed with air into a finely atomized “mist”.
•   Larger or more holes at top of tube help to mix more air with fuel at lower rpm.
•   Larger or more holes in “waist” or mid-section of tube allow more air to mix with fuel in middle rpm ranges.
•   Larger or more holes in lower portion of tube allow more air to mix with fuel at higher rpm ranges. They also allow a certain amount of fuel to enter inner area of emulsion tube, increasing fuel “curtain” reserve.
•   Smaller outer diameter tubes work with bigger cc engines, wild camshafts, large venturies and larger main jets.
•   Larger outer diameter tubes work with smaller cc engines, mild or moderate camshafts, smaller venturies and smaller main jets


Suitable Emulsion Tubes for Use in 48 IDA or IDF on VW Engine

•   F2  Outside diameter: 7.5mm; Inside diameter: 3.0mm; This tube has 2 x 1.0mm top row holes, 2 x 1.0mm holes in next row down, 8 x 1.0mm holes in next row down. At bottom of tube are 4 x 2.5mm fuel holes. The F2 has been popular as OEM tube when larger venturies are used. Works well in 48 IDA with 38-42mm venturi. May need air corrector larger than 200 in large engines to prevent over-rich condition at high rpm. Brings in main circuit later and weaker than F7.
•   F4  Outside diameter: 7.5mm; Inside diameter: 3.0mm; This tube has 2 x 1.0mm top row holes, 2 x 1.0mm holes in next row down, and 8 x 1.0mm holes below that. In mid to lower portion of tube there are 3 rows of 4 x 1.0mm holes. At bottom of tube are 4 x 2.5mm fuel holes. The F4 was originally used in racing applications, most often used with alcohol-based fuels. The Weber 40 DCM2 as used on Porsche 1600 Carrera used F4 as OEM tube. The F4 allows for large reserve of fuel at all rpm ranges and permits air to mix with fuel clear into higher ranges. May require air corrector jet smaller than 200 to prevent lean conditions in higher rpm range. Works well in large cc engines with 40mm or larger venturies, especially where fuel demand is high. Runs similar to F2 in low rpm ranges.
•   F7  Outside diameter: 7.5mm; Inside diameter: 3.0mm; This tube has no top row holes, and no second row holes. The third row is made up of 8 x 1.0mm holes, and these are in mid portion of tube.  Below this, in lower portion are 4 x 1.0mm holes. At bottom of tube are 4 x 2.5mm fuel holes. The F7 has been popular when using dual 48 IDA Webers on all sized VW engines. Its lack of top and upper holes will bring in main circuit very early and very strongly. Attention must be paid when using F7 that idle and main circuit are tuned as to not “overlap” and create an over-rich condition at lower and mid rpm ranges. Works well in 48 IDA with 36-40mm venturies, especially with extreme cam timing and/or low airspeed in intake ports.
•   F11  Outside diameter: 8.0mm; Inside diameter: 3.0mm; This tube has 2 x 1.0mm top row holes, 2 x 1.0mm holes in next row down, 8 x 1.0mm holes in next row down. Below this, in mid portion of tube is a row of 4 x 1.0mm holes. At bottom of tube are 4 x 2.5mm fuel holes. This tube has been used as OEM tube in smaller cc engines running venturies of 28-36mm. Larger O.D. of tube reduces fuel reserve in jet well and may create dangerous lean condition in large cc engine. Best used in 1600-1900cc and 28-36mm venturi, or engines with extremely strong vacuum pulses in intake. Main jet of 145 or under. May require air corrector over 200 to prevent over-rich condition at higher rpm. Better used in 40 or 44 IDF

[Jim Ratto]

Hope this helps

[Jimbo01]

Great info Jim. Looking forward to the book

Jim

[Tobi/DFL]

Thanks a lot,  Jim!!! l am really looking forward to that book.

Tobi

[Jim Ratto]

Thanks guys, I will get it done soon. Let me know how it runs, Tobi.

Jim

[TexasTom]

Definitely will be a must-have publication for just about any enthusiast ... Look forward to it, JIM!
TxT

[neil68]

Hi everybody,

I just finished installing my new engine and I´m looking for an jetting advice to start with. The final jetting will be made with help of a lambda tool but I need something to start with and hope that some of you can help. So here is the technical data of my engine:

- 2789cc (86x101,6mm)
- CR 11,5:1 (Aral Ultimate 102 octane)
- custom cam, 266° @ 0,05", valve lift IN 14,42mm, valve lift EX 14,0mm, 106° lobe centers
- T.Pieper CNC heads with 48/39mm valves
- 50.5mm IDAs with 44mm JPM venturies, two progression holes
- CSP/JPM WASP 2 stepped header with WASP stage 2 muffler

Thanks in advance for your help!

Tobi

My engine is a 2332 cc with 10.7:1 CR, 98 RON and this jetting:

F2
65 idle 120
185 main
220 air (elevation 927 m)
180 air (sea level...not tested enough)
44 Raptor venturi & stacks
48 IDA with 3rd hole
MS230 with 48 x 38 mm valves
Custom Raptor cam 274-degrees (at 1.27 mm) & 15.1 mm lift (1.4 Scat rockers)
CSP-JPM Wasp Stage 2

[Tobi/DFL]

Hi,

first of all thanks alot to everybody who gave  me jetting advices.

Some days ago I tried the following jetting:

70 idles (1.2mm idle holder)
F2 emulsion tubes
175 mains
180 air correction

The car drove much better than before but was a little lean from 3000 rpm upwards. After changing to 180 mains the carbs flooded badly so I had to stop testing for the time being.
In the meantime I ordered the F4 emulsion tubes that Jim Ratto recommemded. Besides a little bigger main jets (180) the jetting remained the same as before. The result was overwhelming. The car pulls like a train and seems to have lots of power. The jetting is still a little bit on the rich side but it will be no big problem to get the fine tuning sorted.
So thanks Jim for your very valuable recommendation!

Tobi

[Jim Ratto]

Good to hear. They tend to make a world of difference on big cc motors. Good luck getting it spot on.

Jim

[Pasi]

Hi, this is my first post to lounge.

First sorry about my bad english, hope you understand.

I just build engine, which is not driven than a few kilometers.

Engine specs:

- 2332cc 84x94
- Webcam 86c
- Cb super pro heads, 44x37 with w650 springs
- Cr about 10.6:1
- A1 low down header 1 3/4
- Rocker shaft cb 1.40
- Connecting rods aa 5.5
- Jaycee short manifolds
- Cb crank, with chevy journals
- Mahle pistons and barrels
- Spanish weber ida 48, with 2 progression holes and 37 vents

The problem is the idle circuit, i have tried diffrent combos but i have not succeeded yet.

I have tried 60,65 and 70 idle and 120,110 air holder, does not work well. Idle speed can be tuned well, but when you start driving the car,  engine stumble almost immediately. AFR show 15-17

60 idle jet and 80 air holder i have be able to run pretty well, but when you accelerate 1 and 2 gear there is a lean spot, AFR show 14.7 - 16.0 but it goes over it and runs good.
When you drive 4th gear about 50km/h the engine is really rich, AFR show 10.0-10.9

What should i do?  Smaller idle jet 55 and smaller air holder?

Main jets 150 emulsion tube F7 and air 190

Good advice for anyone?  I hope someone understood something about this

BR Pasi

[Jim Ratto]

Hi, this is my first post to lounge.

First sorry about my bad english, hope you understand.

I just build engine, which is not driven than a few kilometers.

Engine specs:

- 2332cc 84x94
- Webcam 86c
- Cb super pro heads, 44x37 with w650 springs
- Cr about 10.6:1
- A1 low down header 1 3/4
- Rocker shaft cb 1.40
- Connecting rods aa 5.5
- Jaycee short manifolds
- Cb crank, with chevy journals
- Mahle pistons and barrels
- Spanish weber ida 48, with 2 progression holes and 37 vents

The problem is the idle circuit, i have tried diffrent combos but i have not succeeded yet.

I have tried 60,65 and 70 idle and 120,110 air holder, does not work well. Idle speed can be tuned well, but when you start driving the car,  engine stumble almost immediately. AFR show 15-17

60 idle jet and 80 air holder i have be able to run pretty well, but when you accelerate 1 and 2 gear there is a lean spot, AFR show 14.7 - 16.0 but it goes over it and runs good.
When you drive 4th gear about 50km/h the engine is really rich, AFR show 10.0-10.9

What should i do?  Smaller idle jet 55 and smaller air holder?

Main jets 150 emulsion tube F7 and air 190

Good advice for anyone?  I hope someone understood something about this

BR Pasi

I bet your float settings are off. I would check and reset both the float height and needle-valve height before throwing different jets at the carburetors. Your lean AFR when you try to come off idle doesn't make sense with your jetting.
I would suspect your engine may run better all around with 40 mm venturi, at least after 3000rpm. But I wouldn't change anything until you confirm floats and needle valves are exact to Weber specification. If you don't have floats set precisely, it won't matter what jets or emulsion tube settings you try, nothing will work.

Once floats are set I would try:

40mm venturi
65 idle fuel with 115 air idle corrector or 60 idle fuel with 110 air idle corrector
closed acc pump exh jet
F2 emulsion tube with 165 main and 155-160-165 air corrector
or
F4 emulsion tube with 160 main and 190 air
2.50 needle valve unless you run into fuel starvation under WOT/high load. The latest 3.00 needle valves from Weber are tall, and when used with fiber gasket (which you have to sand down), sit low in float bowl, so you have to be careful.

I would also make sure those short manifolds don't have the carburetors interfering with cylinder head covers and/or fan shroud, which would cause a massive intake leak.

Good luck

Jim R.

[K-Roc]

Hi, this is my first post to lounge.

First sorry about my bad english, hope you understand.

I just build engine, which is not driven than a few kilometers.

Engine specs:

- 2332cc 84x94
- Webcam 86c
- Cb super pro heads, 44x37 with w650 springs
- Cr about 10.6:1
- A1 low down header 1 3/4
- Rocker shaft cb 1.40
- Connecting rods aa 5.5
- Jaycee short manifolds
- Cb crank, with chevy journals
- Mahle pistons and barrels
- Spanish weber ida 48, with 2 progression holes and 37 vents

The problem is the idle circuit, i have tried diffrent combos but i have not succeeded yet.

I have tried 60,65 and 70 idle and 120,110 air holder, does not work well. Idle speed can be tuned well, but when you start driving the car,  engine stumble almost immediately. AFR show 15-17

60 idle jet and 80 air holder i have be able to run pretty well, but when you accelerate 1 and 2 gear there is a lean spot, AFR show 14.7 - 16.0 but it goes over it and runs good.
When you drive 4th gear about 50km/h the engine is really rich, AFR show 10.0-10.9

What should i do?  Smaller idle jet 55 and smaller air holder?

Main jets 150 emulsion tube F7 and air 190

Good advice for anyone?  I hope someone understood something about this

BR Pasi

My motor is almost identical to this, same cam, .600' lift at valve,  even compression is the same. with the exception of the heads ( mine are 044 heads 44 x 37.5 ported by me ) but very similar to the Super pro in port volumes.

37 vents are way to small, I even had rich zones with 42 Vents.   just too much air speed ( pressure drop ) in the carb. I was going pig rich a light cruise speed on the highways too.

Go up to a 44mm Vent, or even a 45... double check those float settings and tune from there I bet it responds much better.

FYI I have 60/110 Idles, with 3rd progression,   165/210 over an F2 was was I ended up with in the end.  I had good success with the F4 but I like the seat of the pants feel better with the F2 than the F4. ( every combo will be different though )

[Pasi]

Thanks for the answers, i will check float levels and needle valve and potential intake leak.

I thought that the 37 venturi is too small for this engine. My friend will borrow 44 vents and i try again with F2 emulsion tube.

Idle 60-65
Idle jet holder 110-120
Main jet 160-165
Air 155-190

I hope it runs better with these adjustments

thanks

[Jim Ratto]

Any news on making your car run better?

[Pasi]

Hi

Not yet, stil waiting smaller idle jet holder, probably get them on monday. I checked float levels, it was ok.  The height of the needle was 25.6mm and 25.5mm i sand the gasket and now is 25.0mm both, how that has affected the idle circuit?

There is 200 needle valve, should i get 250?

I decided to put 42 vents and those f2 emulsion tubes. Idle timing was earlier 10 btdc and now i set it 12 btdc.

When i get those idle jet holders i start tuning/driving without main jets, emulsion tubes and air correctors so they do not mess up the idle circuit.

Jim,  you mentioned earlier that should put closed acc pump exh jet, how that effects?

BR Pasi

[Pasi]

Hi

We did some tunig and test run yesterday. Several combinations were tested:

idle jet / jet holder

70 /120 progression goes lean, low speed driving 2000-2300 rpm is very rich, afr 10.0
60/80 progression not good, lean. Low speed driving 2000-2300rpm, afr 10.0
65/110 not work at all
70/110 progression lean, low speed driving 2000-2300rpm, afr 10.0
70/80 this was best combo so far, progression ok, but low speed driving 2000-2300rpm, afr 10.0

Why that low speed driving is so rich?

I`m going to try with 75 idle jet and 90-100 holder,  and if it does not work i have to think about the third progression hole drilling.

Good advice anyone?


BR Pasi

[Martin S.]

My gauge only goes as rich as 10.0. Is your gauge working properly?

[Pasi]

My gauge only goes as rich as 10.0. Is your gauge working properly?

I think so, 20.0 is lean and 10.0 is rich. Gauge shows different readings when driving.

Just starting the car and notice that, 2 cylinder acceleration pump jet is dropping fuel when you hold steady rpm 1500-2000. This may be the reason why it goes so rich low speed driving.

How to fix that dropping?

-Pasi

[Martin S.]

That sounds like pure gas is flowing into the carb near idle, like a problem with the float valve. I'm sure someone on here can figure out that out. Your AFR gauge is telling you there is a problem!

[Jim Ratto]

My gauge only goes as rich as 10.0. Is your gauge working properly?

I think so, 20.0 is lean and 10.0 is rich. Gauge shows different readings when driving.

Just starting the car and notice that, 2 cylinder acceleration pump jet is dropping fuel when you hold steady rpm 1500-2000. This may be the reason why it goes so rich low speed driving.

How to fix that dropping?

-Pasi

the roller on the accelerator pump bell-crank might have a flat spot worn into it, which allows free-travel of accelerator pump. or the idle pulsation are causing butterflies to slightly move, which is just enough for nozzles to dribble. You may need to slow idle speed some. Or replace rollers or make a sleeve to slide over old ones (I have used small bronze tubing in the past). I was advised to use a non-closed accelerator pump exhaust jet (which returns some of the pumped fuel to float bowl) to cure this, which helped, but it also created a bad lean hesitation. Also make sure base gasket isn't interfering with idle fuel holes under base of carb, I've had them "swell up" and cause fuel to pool up there and not meter correctly.
Good luck,

Jim Ratto
Jim