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> Weber 44 idf flat spot
tornik550
post Jul 4 2013, 11:59 AM
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So I recently purchased new weber 44 idf's. They didn't work out well so I went back to an old set of weber 44 idf's that I had. I thoroughly cleaned the carbs, sprayed carb cleaner through all jets, tubes, etc. I have also balanced the linkage. Set the floats, etc.

The car starts well. Idle's well. When I drive the car I get a major flat spot between 1500 and 3000 rpm's. Below and above the car accelerates normally.

What changes should I make?

My current setup for my 2258 (dual webers, big cam)
-idle 55
-main 160
-et F11
-ac 200
-vents 36

Are there other issues that can cause this type of problem (timing,etc?)
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ThePaintedMan
post Jul 4 2013, 01:36 PM
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QUOTE(tornik550 @ Jul 4 2013, 01:59 PM) *

So I recently purchased new weber 44 idf's. They didn't work out well so I went back to an old set of weber 44 idf's that I had. I thoroughly cleaned the carbs, sprayed carb cleaner through all jets, tubes, etc. I have also balanced the linkage. Set the floats, etc.

The car starts well. Idle's well. When I drive the car I get a major flat spot between 1500 and 3000 rpm's. Below and above the car accelerates normally.

What changes should I make?

My current setup for my 2258 (dual webers, big cam)
-idle 55
-main 160
-et F11
-ac 200
-vents 36

Are there other issues that can cause this type of problem (timing,etc?)


36 vents. Too big for just about any kind of Type IV you can think of, at least until the higher RPMs.
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Elliot Cannon
post Jul 4 2013, 01:36 PM
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QUOTE(tornik550 @ Jul 4 2013, 10:59 AM) *

So I recently purchased new weber 44 idf's. They didn't work out well so I went back to an old set of weber 44 idf's that I had. I thoroughly cleaned the carbs, sprayed carb cleaner through all jets, tubes, etc. I have also balanced the linkage. Set the floats, etc.

The car starts well. Idle's well. When I drive the car I get a major flat spot between 1500 and 3000 rpm's. Below and above the car accelerates normally.

What changes should I make?

My current setup for my 2258 (dual webers, big cam)
-idle 55
-main 160
-et F11
-ac 200
-vents 36

Are there other issues that can cause this type of problem (timing,etc?)

My problem with 44idf's was a stumble coming off idle. I did some experimenting with different size idle jets and had great improvement. Try a different size idle jet. They are fairly inexpensive and easy to change. You may also have idle jets that are clogged. My engine has 96 pistons and a 76 crank which I think is just a tad short of 2.2. F11 emulsion tubes, 130 mains, 175 air jets. I think I have 51 idle jets. I have no real expertise with Webers. The engine was set up by FAT Performance and any adjustments I made with the carbs. was trial and error. (IMG:style_emoticons/default/biggrin.gif)
Cheers, Elliot
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r_towle
post Jul 4 2013, 02:02 PM
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f7 or turbo emulsion tubes help with flat spots, as well as smaller venturis, possibly 32mm

rich
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brant
post Jul 4 2013, 02:24 PM
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28 vents. Perhaps 40 mm carbs
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Starlack
post Jul 4 2013, 02:41 PM
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Hello
This is the transition area from idle jet to Main Jet.Das same problem I once had. Reduced to 150 main jet
The acceleration pump 2 turns further rotated in ...
My engine 2366ccm type 4 Weber 44 IDF
Main Jet 150
Idle nozzle 55
Venturie 36mm
Air correction 200
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tornik550
post Jul 4 2013, 02:57 PM
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The interesting thing is that my car ran great in the past with the same carbs. I had the same jets and venturis installed then.

The crazy thing is that I found that the secondary venturis were installed up side down by the local guy who rebuilt my carbs. Now that they are installed correctly, my engine runs like crap


I have that flat spot but also the engine stumbles when I stomp on the gas.
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tornik550
post Jul 4 2013, 03:12 PM
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Thinking about this situation, I think the suggestion about the Venturi size is probably accurate. I think that the air is not flowing fast enough to suck in the fuel there by causing a lean condition. I ordered new vents. We will see.
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McMark
post Jul 4 2013, 03:16 PM
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The carbs weren't really flowing fuel when the secondaries were flipped. Now they are. I think your main jet is way too big. I also agree that the venturies are too large. You're probably getting a flat spot because the 36 vents don't create enough vacuum to engage the main jets until 3000 rpm.
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tornik550
post Jul 4 2013, 03:45 PM
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Ok, I am getting a bit pissed off at weber now. The way that I realized that my secondary vents were in up side down was because when I purchased my new webers I saw that the new secondary vents were installed opposite to mine. I assumed that the carbs from the weber factory were correct. I just looked at a diagram and I think that my carbs were correct and the carbs from weber were up side down, wtf!

So for the record- does the longer side of the secondary vent point towards or away from the butterfly? Does the angle where the fuel comes out point towards or away from the butterflies?
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sean_v8_914
post Jul 4 2013, 04:05 PM
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good advice above
smaller vents
smaller main jets
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sean_v8_914
post Jul 4 2013, 04:06 PM
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long side of taper down. spray hole down


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sean_v8_914
post Jul 4 2013, 04:07 PM
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http://www.carburetion.com/diags/40IDFDiaginfo.asp
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sean_v8_914
post Jul 4 2013, 04:09 PM
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a wide band O2 would be nice for selecting the true correct jet size. guessing jets will add up quickly $$$
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tornik550
post Jul 4 2013, 04:17 PM
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QUOTE(sean_v8_914 @ Jul 4 2013, 06:09 PM) *

a wide band O2 would be nice for selecting the true correct jet size. guessing jets will add up quickly $$$


I do have a o2. It goes super lean during the flat spot.

The diagram is for 40idf. My 44 idf secondary cents look different. Right now I think mine are in correct. On mine, the long part is down and the taper is pointing up.
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Mblizzard
post Jul 4 2013, 04:25 PM
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On my weber 44s, 28 vents made all the difference. 36s are too big.
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Woody
post Jul 4 2013, 08:53 PM
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I run 36 vents and the car runs great. I have a set of 32s and it's a dog.
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McMark
post Jul 4 2013, 11:54 PM
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If you take the vent out you'll see one side is actually a fuel flow passage. That needs to line up with the hole in the side of the bore (towards the middle). It'll only work one way.
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ChrisFoley
post Jul 5 2013, 06:55 AM
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QUOTE(tornik550 @ Jul 4 2013, 04:45 PM) *

So for the record- does the longer side of the secondary vent point towards or away from the butterfly? Does the angle where the fuel comes out point towards or away from the butterflies?

The longer end is the inlet, facing upward.
The fuel inlet is angled down.
Otherwise air rushing thru the tube will push fuel back into the float bowl instead of acting as a venturi.
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tornik550
post Jul 12 2013, 08:15 AM
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I have worked out my flat spot. I found that the accelerator pumps on one carb were partially plugged.

I have ordered several sets of venturis in different sizes. Although my engine is running very well right now, would there be any reason for me to change to a different size venturi? I have weber 44 idf's with 36mm vents. I get decent low end torque and excellent high end power. I ordered 34 and 32 vents.
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