Weber 44 IDF jetting help

[bw65vw]

I finally got my multi-year project on the road this past weekend and put about 80 miles on it. I have a 2276 with dual Weber IDF 44 carbs. The things I noticed while driving it seemed to be happy and make good power around 2500-3500 RPM. It seems to stumble when I get on the gas kind of hard taking off. When I was on it a little hard then lifted to shift it backfired most of the time. It also would backfire right after I shut the engine off. I assumed this was unburnt fuel in the exhaust meaning it was rich, but reading the old Weber tuning manual it suggests this means it is lean. I am going to try to pull a plug tonight for inspection. Here are some of the engine and carb stats:
Dual Weber 44 IDF's 36mm Venturi
150 mains, 200 A/C, 50 idle jets
Tims Stage 2 Cylinder Heads 42X37 valves
AA 94 mm P&C
CB 82mm Super Race Crank VW journals
CB H-beam connecting rods
Dan Ruddock Beehive Springs and 1.5 ratio rockers
Dan Ruddock Push Rods done right
Webcam 86A+3
9.3:1 compression
1 5/8" exhaust

Thanks in advance for the help.

[RLFD213]

I went through this with my car,. 2276 44IDF’s. I ended up going to 60’s on the idles and fine tuning with the accelerator pumps. You can put 55 idles in and ream them till you get it or just put 60’s in and call it a day. Chances are they need 58’s so 60’s aren’t that rich and won’t hurt anything

[slayer61]

I have to ask.... before you installed the carbs, did you pull them down, clean and set the float level? Did you sync them after starting the motor? Synchronizing them made a world of difference on mine.
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[bw65vw]

[Rob Combs]

Just curious, what are you running for carb linkage?

Reason I ask is because synching with a snail gets the carbs lined up but synching the linkage is quite another matter. That’s important too. I learned this the hard way, going through three sets of linkage before i got it reasonably close.

Also, how’s your ignition timing management? What kind of timing management are you using? Is it backfiring though the carbs or out the exhaust? Ignition timing needs to be verified as well.

Verify all above, but stumble and popping back through intake usually indicates a lean condition in whatever RPM & throttle range it’s stumbling.

[VW_Jimbo]

Agree with the above. Sounds lean, but I am not there. Typically popping at idle or just off idle out the carb is a lean idle condition. Like the intake cannot support what is needed. Maybe in air or fuel or both.

Your venturies seem small for that 42mm intake valve. That is a shit ton of air being pumped and in this case restricted, I believe. The motor is fighting itself for air and fuel. What is the common denominator. Based off of my limited knowledge, and the size of that intake valve, I would think a 38 or a 40mm venturi would be in order. Then jet it from there.

Have you checked the float level?

My 2 cents.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Schepp]

How did you set the position of the throttle plates when you did the initial tune? John from ACN suggests hooking up a vacuum gage and setting the plates at zero for idle.

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https://www.thesamba.com/vw/forum/viewtopic.php?t=390844

[bw65vw]

I'm running the sync-link for linkage. I balanced the carbs with the snail gauge with the two.sides disconnected. Then reconnected and adjusted the cable until the butterflies on both sides seem to.open at the same time. I did set the float levels when I reassembled from.cleaning.

[bw65vw]

[SGKent]

use your hands to cup around the carb body top(s) more and more to see if they are rich or lean. If the engine speeds up as your hands approach it is lean. If it slows down then it is rich. You want it to remain neutral as long as possible to where you are almost on the carb with your hands. Basically you are using your hands to disrupt the air flowing in and draw more fuel as you approach. If more fuel slows the engine then you have too much already. If the engine speeds up then it wants more fuel.

General rules - 3 air correction jets equal one main size

General rules - make sure the throttle plates are closing and centering properly and that no transition holes are exposed at idle. If they are, then they are providing fuel at low speed and that will throw any jetting off by the amount of fuel they are providing.
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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[ZEKE65]

I would vote to go to the 60 idles. When I tuned my 2017cc with IDF44's, I did 20 different jetting changes with a wideband, and ended up using the 60 idles. Ended up with 145 mains, 200 airs, and 60 idles.
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1965 VW Sedan, 1968 C10 Step BB, 99 C5

[oprn]

It took 10 replies before someone mentions a wideband? What the heck?
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Our cars get old, we get old but driving an old VW never gets old!

[bw65vw]

[bw65vw]

Finally pulled a plug and took a pic. Looks lean to me...

[mikedjames]

Compared with the cost of all the engine parts that go into a build, a wideband is cheap.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[bw65vw]

[oprn]

[bw65vw]

[94touring]

I have a wideband on the shelf I use for tuning various cars that I got off Amazon for $120 or so. Nothing fancy about it. I keep one permanently installed in a couple other cars of mine I'm always tinkering with setups. You can start to really fine tune with one, I find myself going half size mains.

[oprn]

I have the Innovative LM-2. Some claim to have had the sensors fail but mine is still working fine.
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Our cars get old, we get old but driving an old VW never gets old!