Weber jetting, what I've used that works

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bubbajohnson
Posts: 38
Joined: Mon Jun 24, 2013 12:13 am

Weber jetting, what I've used that works

Post by bubbajohnson » Wed Jun 26, 2013 1:43 pm

So I thought I would write up something to help those who are having trouble with their weber carbs and getting them dialed in. One of my biggest gripes through the last few years has been that although all the directions you will find say to look at and write down what jets are in your carbs, NO ONE seems to do this, or share the results. So here is what I’ve had in multiple Weber carbs, on multiple cars, with often vastly different engine set ups. These are all working setups, which were used on street driven cars, all adjustment screws were at or very near weber base settings. These are good functioning settings, which may not work perfectly for you, but can serve as a baseline. YOU still have to do the tuning and checking to make sure your car is in good running order, drive it, read the spark plugs, etc and decide if your carb tune is correct.

#1 32/36 DGEV on internally stock 3TC with approx 230-255k. Stock mechanical fuel pump/lines. Using a Offenhauser dual-port intake, pacesetter 4-1 header and 2.5 inch exhaust with high flow cat.
Primary Fuel Jet: 130
Primary Air Corrector: 165
Primary Idle Jet: 45
Secondary Fuel Jet: 125
Secondary Air Corrector: 150
Secondary Idle Jet: 50
Pump Jet: 50
Emulsion Tubes: F-50
Venturi: 3.5

#2 32/36 DGEV on completely stock 3TC with approx 160-185k miles. Stock mechanical fuel pump and lines.
Primary Fuel Jet: 130
Primary Air Corrector: 165
Primary Idle Jet: 45
Secondary Fuel Jet: 125
Secondary Air Corrector: 150
Secondary Idle Jet: 50
Pump Jet: 50
Emulsion Tubes: F-50
Venturi: 3.5

#3 32/36 DGEV on rebuilt/fresh 2.0L 3TC with fairly large cam, oversized valves, mild port and polished head and high comp 89mm pistons, 4-1 Header with 2.5” exhaust. 3/8 fuel supply and return lines with carter fuel pump and pressure regulator. This engine was dyno tested at 115hp and 112 ft/lbs of torque with a slightly different tune, that showed as being a little lean, so it was re-tuned richer, but not re-dyno’d.
Primary Fuel Jet: 150
Primary Air Corrector: 160
Primary Idle Jet: 70
Secondary Fuel Jet: 145
Secondary Air Corrector: 155
Secondary Idle Jet: 55
Pump Jet: 50
Emulsion Tubes: F-50
Venturi: 3.5

#4 32/36 DGV on 3TC with stock bottom end, oversized valves, an aggressive cam and 4-1 header with 2.5” crush bent exhaust. Stock mechanical fuel pump and lines.
Primary Fuel Jet: 140
Primary Air Corrector: 150
Primary Idle Jet: 55
Secondary Fuel Jet: 150
Secondary Air Corrector: 155
Secondary Idle Jet: 50
Pump Jet: 50
Emulsion Tubes: F-50
Venturi: 3.5

#5 32/36 Weber on very healthy stock 2TC with only 120k miles. Stock Mechanical fuel pump and lines. Factory 4-2-1 header and downpipe with 2” crush bent exhaust.
Primary Fuel Jet: 125
Primary Air Corrector: 145
Primary Idle Jet: 50
Secondary Fuel Jet: 130
Secondary Air Corrector: 150
Secondary Idle Jet: 45
Pump Jet: 50
Emulsion Tubes: F-50
Venturi: 3.5

#6 Single 40mm Weber DCOE 151, on very healthy stock 2TC with 125k miles. Stock mechanical fuel pump and lines. Factory 4-2-1 header and downpipe with 2” crush bent exhaust.
Main Jet: Unknown, they are unstamped, but visually they appear larger then 150 jets, which is the largest I had on hand to compare them to. EDIT 6-21-20: Recently because I was trying to tune my new engine, using a set of machining drill bits i did determine these to be 160 jets.
Air Corrector: 170
Idle Jet: 50F9
Emulsion Tubes: F11
Choke Tubes: 30mm
Venturis: 4.5

#7 Dual 40mm Weber DCOE 151, on rebuilt/fresh 2.0L 3TC with fairly large cam, oversized valves, mildly port and polished head and high comp 89mm pistons, 4-1 Header with 2.5” exhaust. 3/8 fuel supply and return lines with carter fuel pump and pressure regulator.
Main Jets: 145
Air Correctors: 190
Idle Jets: 55 F9
Emulsion Tubes: F2
Choke Tubes: 36mm
Venturis: 4.5

This is an update to entry #7 on my list.
Thanks to a wideband O2 sensor, discovering my fuel pump was not putting out consistent volume, a float adjustment and a whole lot of drive time, fiddling and tuning I think I have the dual 40's tuned as well as I can with what I know about tuning DCOE's.
Its now running:
Main Jets: 140
Air Correctors: 200
Idle Jets: 60F9
Emulsion Tubes: F2
Choke Tubes: 36mm
Venturis: 4.5
This set up runs GREAT!! Most of the problem with the old "tune" was my fuel issues both with the pump not holding steady because of a slightly loose wire, and I discovered one of my carbs float level was different from the other and they both were set way to high, causing an intermittent bogging issue. Now that both those issues are sorted out and I've logged a good 700+ miles just watching the air/fuel meter and observing then adjusting jets, I'm very happy! The car feels more powerful and responsive then it has at any point with these carbs, I have no random bogging and can drive like as much of a jackass as I want to :cheers:. Just last weekend me and 3 friends loaded up the car with ourselves and maybe 200lbs of gear and took a 240mile trip to the mountains and back. I had no problem holding 70+ up any grade, only shifting to 4th gear every now and again and we got over 20mpg on the trip!! My air/fuel mixture reads about 14-14.5 at idle, so maybe a touch lean, but not bad. 13-13.5:1 at 60-70mph in 5th gear while cruising (Not uphill!). 12-12.5:1 with mild load and on most up hill grades in 4th or 5th gears and 11.5-12:1 under heavy throttle/5000+ rpms right up until it hits my rev limiter at 7000rpm.
Last edited by bubbajohnson on Sun Jun 21, 2020 2:19 pm, edited 1 time in total.

bubbajohnson
Posts: 38
Joined: Mon Jun 24, 2013 12:13 am

Re: Weber jetting, what I've used that works

Post by bubbajohnson » Wed Jun 26, 2013 1:44 pm

Hi all, glad there's a 3tc forum again! Here's my weber jetting info from the old boards, hope it helps some folks :D.

pufito18
Posts: 375
Joined: Wed Jun 19, 2013 8:35 pm
Location: florida. usa

Re: Weber jetting, what I've used that works

Post by pufito18 » Thu Jun 27, 2013 3:43 am

good info i like it

User avatar
Grumpy3TC
Posts: 141
Joined: Sat Jun 22, 2013 12:48 pm
Location: Massachusetts

Re: Weber jetting, what I've used that works

Post by Grumpy3TC » Wed Jul 16, 2014 8:09 pm

Very Good, :ugeek:
MY 3tc is so Grumpy! I feel like eating one or two Rotaries for breakfast today!

bubbajohnson
Posts: 38
Joined: Mon Jun 24, 2013 12:13 am

Re: Weber jetting, what I've used that works

Post by bubbajohnson » Sun Jun 07, 2020 11:42 pm

Well it's been many years but it's time for an update to this thread and list. I've built a new engine for my 80 Liftback. Specs are:
- 3TC block, bored out to use 87mm 10.5:1 Wiesco pistons. (1.9-ish Liters). Stock crank and connecting rods. 0.10 oversize bearings
- 3TC head, gasket matched, lightly ported, bowl blended and EGR humps smoothed out. Stock size valves
- 278 Duration, .420 lift regrind cam from a local shop. Advertised specs. I measured the actual lift at .405, don't have tooling to check duration.
- ARP everything (head studs, rod bolts, flywheel bolts, clutch plate bolts, etc
- Ebay Stage 2 clutch. It's stiffer than a stock or Centerforce 1, not as stiff and grabby as my brothers six-puck clutch.
- Rebuilt early T50.
- Stock manifold with the long 2-1 downpipe. 2" diameter, with an Dynomax cat and super turbo muffler. Same exhaust system from the old single 40MM tunes. But I'll be going to a 2.25" soon as this system is old and starting to rust away.

I'm running the same 40mm DCOE from the earlier tunes, but the cannon manifold has gone away in favor of an LYNX crossover manifold. This manifold gives way better throttle response and seems like the engine breathes better with it. This engine build overall is nice and strong, well mannered on the street and sounds great when you set on it!

- Air adjustment screws are about .25-.5 turns out to even out flow.
- Fuel bypass screws are 2 turns out.
- Venturi: 4.5
- Chokes: 32mm
- Idle Jet: 60F9
- Main jet: 160
- Air corrector: 170
- Emulsion Tubes: Are Keith Franck "Non-frothing" Firecracker tubes. If you don't know this guy look him up! These are custom made and a total game changer. I don't think I've used a DCOE emulsion tube that gave such a smooth idle to main jet progression. They ROCK!
https://www.webstore.com/item/NonFrothi ... s/96119411
https://vintagetechnologygarage.groups.io/g/sidedraft
That said. This setup worked ok but not perfectly with both F2 and F11 Weber emulsion tubes. It required 65F9 idles to mostly keep the off idle stumble at bay. But it ran pig rich overall and was trying to foul my plugs, not ideal!

I need to do a little more driving but I think this is my baseline for this build. It works, runs strong and smooth. I am tempted to try a 55F9 idle and to up the main to a 165, only to try and save a little fuel and slightly lean out my 70+MPH freeway AFR, currently about 10.5-11.5:1.
When the main jets kick in and at WOT I get a consistent 12.5-13.5:1 AFR and it pulls very hard right up to 6500RPM. There is no bog or backfiring when you let off. Idle AFR is 13.5:1, a little rich, but when I turn the idle adjust screws in to lean it out more my idle gets rough, so I'm happy to leave it here for now.

It’s worth noting I would also like to try this setup with 34 or 36mm chokes as I think it would gain top end power. Which would certainly require an increase in main jet, and possibly air corrector size. Idle could probably stay the same. But I don’t have any chokes that size in my bin.

Will update if/when anything major changes. I want to tinker with this setup for another few days/a month-ish. I just scored a pair of 40phh Mikuni sidedrafts to throw on here to make even more power.

Cheers everybody!

- Rich

RRRichards
Posts: 1
Joined: Sun May 31, 2020 5:01 pm

Re: Weber jetting, what I've used that works

Post by RRRichards » Tue Jun 30, 2020 7:27 pm

Bubba,

As usual with your selfless sharing of information. We are in the 2TC facebook group and we discussed the twin carb setup.

I enjoy reading your stuff, i havent installed the twin carbs yet but i am thinking about a mild cam upgrade to match the added air/fuel intake and headers. Any particular parts that comes to mind you would recommend i consider?

I ordered the book you recommend that should cover tuning the twins when they get here, is there any engine building performance book that you like and recommend?

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