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Posted by: SKL1 Nov 22 2015, 09:32 PM

2.0 with Webcam and Mallory distributor. Timing set and carbs synched, but really flat just off idle. Runs better when further up in the revs.

At 1800' in AZ.

Currently: 40 IDF, 200 air correction, F11 emulsion tube, 115 main, 58 idle, 55 float bowl, 28 venturis

TIA...

Posted by: r_towle Nov 22 2015, 10:22 PM

What linkage are you using?

Posted by: SKL1 Nov 23 2015, 12:21 AM

Tangerine Racing linkage

Posted by: Elliot Cannon Nov 23 2015, 01:33 AM

What size venturi? You might want to experiment with different venturi sizes. I also think those idle jets are too large.

Posted by: Ansbacher Nov 23 2015, 06:08 AM

In my experience with Webers and Dellortos, a flat stumble off idle is usually cured with smaller venturis (32s in your case) and a liberal dose of gas via the pump jets (crank 'em up). I think your idle jet size is fine- 60 is usually nominal for a 2.0L.

Ansbacher

Posted by: ThePaintedMan Nov 23 2015, 07:28 AM

Yeah, knowing the vent size would be the first step. 58 idles *might* be a okay, but is largely dependent on venturi size as well.

115 mains also sound way small. Typically you'd be more in the 135-145 area.

Posted by: rhodyguy Nov 23 2015, 07:51 AM

Where do you have the air-bypass screws set? With 40mm the throttle plates should be @ 28mm unless the carbs have been worked over. Confirm the size.

Posted by: bulitt Nov 23 2015, 08:31 AM

This technical talk makes me giggly. Been 45 yrs since I messed around with Webers.
Would simply solder the jets and redrill them until I go the size right then order the permanent ones. Broke ass college kid.

Posted by: rhodyguy Nov 23 2015, 11:17 AM

If you don't own one buy the CB weber book. Go thru the pre-install procedure again. Verify fuel pressure, timing and valve adj.

Posted by: 72hardtop Nov 23 2015, 05:00 PM

What vent size are you running? 40IDF's come with 50 idles.

58 idles is pretty big. Be sure your fuel pressure is no more than 3.5psi before anything. Also make sure the float height is 10-11.5mm with gasket in place and ball NOT depressed.

With 28 vents and your altitude...47.5-50 idles, 120 main jet, 200 air corrector, F11 tubes

Posted by: SKL1 Nov 24 2015, 12:14 AM

Gonna check my venturi size tomorrow if I find the time. Should have noted that!
I haven't heard good things about weber carb direct around here- what do people like around here for Weber parts source? CB? Other ideas?

Posted by: Darren C Nov 24 2015, 06:34 AM

Interesting feed back here;

I'm running 55 idles, 135 main jet, 200 air corrector, F11 tubes in my 40IDFs floats set 10mm & 42mm on my 2.0L stock cam & dizzy with vacuum pipe from both banks.

Just spent a good while setting up and balancing (+ guage set fuel pressure to 3psi) and I'm getting an odd post ignition "pop" of un-burn fuel in the exhaust on an over run (when I let off the throttle) and after siting at idle a long while when accelerating after.
This may mean my mains/idle are too large or is it just running a tiny bit rich? When I lean off the "popping" gets worse?
I'm at sea level so not sure how you make the altitude calc?
Ideas please guys?

Posted by: SKL1 Nov 24 2015, 03:40 PM

28 venturis- just checked... fuel pressure 3.5 assuming regulator works! Everything else cleaned before I put back together. New filter, etc.

Some trial and error in my future...

Posted by: ThePaintedMan Nov 24 2015, 04:07 PM

OP - you did you due diligence with the fuel pressure, good to know. As Kevin mentioned, go ahead and check/confirm your timing (around 34 degrees @ 3400 RPM) and make sure you have a good valve adjustment on it. As was mentioned, float height plays a role here too, but hopefully you got that right when rebuilding the carbs.

Those 28mm venturis are a good size for that engine and a good place to start. You might get a little more top end out of it later with 30mm chokes, but it's going to mean retuning the idles and mains and probably best done on a dyno. For the time being, I would go with the specs that 72Hardtop suggested. As you are at altitude, you're dealing with a less dense charge which will require less fuel. 58 idles does indeed sound big. 50 idles should do the trick, and go ahead and bump the mains up. Down here at sea level, 130s were right in the ballpark, so maybe you could split the difference at 125. Running a little rich won't be a bad thing. There is a guy on Ebay, Alfa1750 who sells quality Weber stuff from Italy. I've dealt with him before and he has been prompt and gotten my order right each time. You could also try buying used jets from somewhere like TheSamba, but keep in mind that a lot of people like to drill them and you may never know exactly what size you're getting without a jet guage.

Darren, have you checked the sync on the carbs? What you're suggesting sounds like a lean overrun, explained like this to me by Racer Chris himself: a lean condition means that ignition does not occur on one compression stroke, then the next time around the excess fuel ignites, causing the overrun (again, only as I understood it). While the 55 idles do sound a little big, you might have one bank, or even one cylinder leaned out too much. Check the sync on both carbs first, with all bypass screws closed. Verify that synch at both idle and at part-throttle. Then move to bringing up the "low" cylinders with the bypass screws. Finally, adjust mixture screws for lean best idle - some folks add an 1/8 turn to make sure they stay a tad bit rich as these engines tend to run best that way (again, just my understanding). If having any issues tuning out the mixture, or if you're more than 2 turns IN, than your idles are too big.

Posted by: Elliot Cannon Nov 24 2015, 04:35 PM

I know you're getting a lot of advice from different people. Remember that when you're setting up Webers, you have to take it step by step and it has to be in order. I have 44idf Webers with 76 crank and 96 cylinders which is about 2.2 liter so my setting might not be much help. I use 130 main jets, 175 air jets, F11 emulsion tubes and I'll have to pull one of my idle jets out cause I can't remember what they are. I can't remember what web site I used but it gave a step by step procedure that helped a whole lot. These guys can be helpful. You can see from their jetting chart that 58 idle jets might be a largish. http://www.cbperformance.com/SearchResults.asp?Cat=152

Posted by: Darren C Nov 25 2015, 03:02 AM

“Darren, have you checked the sync on the carbs? What you're suggesting sounds like a lean overrun, explained like this to me by Racer Chris himself: a lean condition means that ignition does not occur on one compression stroke, then the next time around the excess fuel ignites, causing the overrun (again, only as I understood it). While the 55 idles do sound a little big, you might have one bank, or even one cylinder leaned out too much. Check the sync on both carbs first, with all bypass screws closed. Verify that synch at both idle and at part-throttle. Then move to bringing up the "low" cylinders with the bypass screws. Finally, adjust mixture screws for lean best idle - some folks add an 1/8 turn to make sure they stay a tad bit rich as these engines tend to run best that way (again, just my understanding). If having any issues tuning out the mixture, or if you're more than 2 turns IN, than your idles are too big.”

Many thanks Paintedman, The carbs are balanced with a sync gauge (and to be fair these seem to be the best Webers I’ve ever balanced, they are perfectly matched on all 4 cylinders with the air bleeds shut, all I needed to do was balance them between each carb and the job was done)
I set rough the mixture screws before fitting the carbs by turning in fully closed gently on to the seats, then opening 1 ½ full turns; then ran the engine for the first time to balance up and set idle at about 950 rpm. Checking and rebalancing side to side until perfect. Reving and over run was fine then with no post ignition popping.
It was only when the engine was fully warmed up and I wound the idle screws in to set the mixture by listening to a cylinder drop out (then turning back ¼ turn) when I started to get the popping on over run. Your answer of “lean over run” seems the best explanation. Particularly as I know the mixture screws are more than 2 turns in. (by the way I’ve not heard the 2 turn rule v idle size before) I’ve got some 50 idles, so will swap them over and see how that works out.
Many thanks for the good advice.

Posted by: Eric_Shea Nov 25 2015, 07:32 PM

You need to know the displacement (which you have). The rpm at which the cam makes peak hp (which you don't have, at least in this post) and your altitude (which you have).

The most important missing piece of the puzzle is that cam information. Not only will that dictate jets and venturi's but, emulsion tubes as well.

If you can get me that info I can help dial in your carbs and save you quite a bit on multiple jet experiments.

Posted by: Eric_Shea Nov 25 2015, 07:51 PM

Also... based upon this:

*AC's seem a little high. You may want to try 190-195's. If you feel it die close to redline, decrease a little.

*F11 is probably the best. This is where the cam info would help.

*Mains are too small - I would suggest 145 for 1800ft.

*Idles are big - I would suggest 50 for 1800ft.

*(not sure what a float bowl jet is)

*Venturies are too small - I would suggest 32

Hope that helps. The proper peak hp from the cams may make these change some but, I used 5,000 RPM and it should be close.

Posted by: Eric_Shea Nov 25 2015, 08:11 PM

I'll use the same data from my spreadsheet that I just used above meaning, 2 liter with a cam that makes peak hp at 5000rpm. Tell me if you have anything different. Here's the sea level calculation:

Venturi's = 32
Mains = 150 (yours are too small - lean condition)
Air Correction = 165 (yours are way too big, this can cause that lean condition and limit your power at higher rpm's)
Idle jets = 55 - Yours are fine.

Popping can be a lean condition or, an exhaust leak (popping on decel). Type IV's are prone to exhaust leaks.

I'd dump the vacuum dizzy for a euro .009 or, try the new MSD setup (system) for VW's. You'd have to change some plug wires around but, that's a promising alternative from what I'm seeing.

Raise the fuel pressure to 3.5. Perhaps even 4 if the pump is in the front trunk.

There might be a better emulsion tube for that cam but... You really need a new cam to take advantage of everything the carbs have to offer. If I were you I would either look for a cam or look for the stock fuel injection to bolt back on that thing.

Posted by: SKL1 Nov 25 2015, 08:37 PM

Thanks for the suggestions Eric. I'll have to look up which Webcam it is- told them it was for a carbed 2.0 type IV. (can't remember where I got it from- been a while...)

You do more than brakes!!

Posted by: Eric_Shea Nov 26 2015, 01:00 PM

Happy to help. I went through so many carb woes, I developed a spreadsheet using all of the calculations from the Weber books etc.

With our new division, PMB Motorwerks, Gene and I have come up with some killer 2056 big valve motors, and a carbed 2270. Quite a few of these 2056's are carbed. At our altitude (4300) carbs and jetting can be a "stimulating" experience. The spreadsheet has been refined over time and has really proven itself.

You probably have one of the 86 grinds. You are leaving a "lot" on the table with your current jet and venturi combo. You'll love the way it drives once you get everything set up.

Posted by: Darren C Nov 26 2015, 02:09 PM

Many thanks Eric, much appreciated I'll give that combo a try.
SKL, apologies for hijacking your thread, but I thought it might be best to keep all the jetting questions in one thread rather than start yet another with the same request for help!

Posted by: CG-914 Nov 27 2015, 04:09 AM

Couldnt agree more with Eric!

Also if you have trouble getting of idle, you should check if you are too lean in that moment. Check your excelerator pump jets, if you make them bigger you still get the same amount of fuel from the pump but delivered quicker. Another method would be increasing the size of your idle jets and turning the mixture screw in further, but then they really become hard to tune in idle!

Use a O2 sensor and do some runs to get the perfect jet set up. For idle only a CO and HC tester would give you a perfect adjusting but they are hard to come by or very expensive!

Good luck! Carbs are fun once you get more into them.

Posted by: SKL1 Nov 27 2015, 10:12 AM

Oh no, another PMB division! Another place to spend more $$

Posted by: stugray Nov 27 2015, 10:57 AM

Here are my notes from my racing logbook this year:

Carb configuration:

40 IDF Webers (Italian)
Venturis 28mm
Idle Jets 60
Main Jets 115
Air correctors 200
Emulsion tubes F11
Accel Bypass valve .55
Float valve set to 14mm (closed) to 24mm (open)

I since changed the mains to 120, but I dont feel much of a difference, but my AFRs dropped a little lower than necessary.
When I collect all the AFR data from a race and average the WOT data only, I get ~12.5-13.5 AFR.
EGTs never get above 1200-1300

This is with a webcam 86b. stock heads, 2056, 5000 ft. alt., 91 pump gas.
Mallory unilite, MSD 6AL 34 degrees advance at 3500.

I am considering going to larger venturis, but I run almost exclusively at high altitude, and havent sprung for the $$ new 32s.

I would LOVE to have a peek at Eric's spreadsheet! :-)

Posted by: SKL1 Nov 28 2015, 04:14 PM

Seems like CB is the easiest place to source jets, etc for Webers... The kit on my '73 came from Redline, but I've had trouble getting them to respond to inquires on line or the phone. Replaced their linkage with Chris' from Tangerine...

Posted by: SKL1 Jan 13 2016, 09:31 PM

Gonna have to see if that spreadsheet from PMB Motorwerks is available. Still playing with jetting...

Does run a little better now that timing is correct at 34 @ 3500. Valve adjustment is fine. Still falls flat when accelerating at around 3500 rpm... the saga continues.

Weird thing is my '71 has a 050 Bosch distributor, Webers, same Webcam but runs a lot better through the rpm range. It's in IA at 800' whereas my '73 is in Scottsdale at 1800'.

Posted by: michael7810 Jan 14 2016, 06:26 AM

Dougs Bugs and Bunnies over in Mesa has a good selection of jets AND you only have to buy 1 set as they will swap for different sizes for free. They're a quick drive down the Beeline from you.

Posted by: jmill Jan 14 2016, 11:18 AM

I never understood why everyone stuck with the F11 ET. It was specifically designed to provide a lean mixture at lower velocities. Try the F7. It's the opposite of the F11 and provides mixture enrichment at lower velocities.

If you swap to the F7 you'll need to reduce the size of your idle jets.

Posted by: jmill Jan 14 2016, 03:29 PM

The reason you have that flat spot is due to the idle jets dropping out before the mains come in (lean transition). You're trying to fix that flat spot by increasing your jet size. It helps a bit but it's not going to eliminate it. You have to do 1 of two things and maybe even both to fix it.

#1 - Smaller venturis - increase vacuum signal to the mains to bring them in sooner

#2 - Emulsion Tube - get an emulsion tube that works on a lower vacuum signal and provides a richer transition like the F7

You'll then find your idle jets are too large and you'll have to drop down to 50-55. If you go with the F7 you may even need to drop down your main jet size and step up the AC jet to lean it up at the top.