Holley/Weber 32/36 Jetting Tips

[jamyers]

I'm collecting jetting info, and something struck me as odd with these carbs...

The secondary side is larger by 4mm, should flow more air, and need more fuel as well. But:

Virtually everybody's jetting setup/recommendations have the secondary side with smaller (leaner) idle jets, and smaller main jets (less total flow) with air bleeds that will give a richer mixture, but less overall, which looks like with the additional air, would give a total mix that's either leaner or the same as the primary side.

What's up? I'd think the secondary side would be slightly richer than the primary, and have more fuel capacity. Am I missing something?

 

[xctasy]

On most carbs, the secondary jet size is 1/16 to 1/23 rd the size of the venturi.

Throttle size is irrelevent, the only thing that influences jetting is venturi size.

In metrics, 26 and 27 mm is a lot different to 32 and 36 mms. The scale of the jet size is similar to the venturi diameter divided by 16 to 23. Vitually every carb follows that scale factor, except triple booster Holley 4360 4-bbl, Rochester Qjet 4-bbl and Varajet 2-bbl.

The secondary auguments (adds to) the primary, its not a second carburettor in its own right. Its part air operated, part mechanical secondary.

It's really like a second barrel for wide open throttle and acceleration only.


The carb jetting is the same all over the world, from the first 1969 Capri 2000 to the last 1985 ish 2300 Mustang that used these kind of carbs. It's actually very rich at wide open throttle.

 

[jamyers]

OK, I'll buy that they're rich at wot, but I don't understand why...and my pitiful math is making me think they'd be lean. I don't think I'm grasping your comments about jets and venturi size...help!

I've collected the 7 sets of 6-cylinder Weber 32/36 jetting info I could find on this site, and put it in a spreadsheet so I could try and find some common settings and maybe educate myself about these carbs. (If I can figure out how to post a table, I'll show the numbers.)

Here are my observations:
1. Most secondary side Main and Air Jets will give a richer mixture than their primary sides - as a % of each other.
2. All secondary side Main Jets are the same or smaller than their primary side Main Jets.
3. The larger secondary side ventury should dictate a larger Main Jet.

I'm fine with #1, but #2 and #3 seem to be at odds with each other, which makes me wonder...why doesn't anybody have larger Main Jets on their secondary side (bigger venturi - more fuel), and use the Air Jets to get the richer mixture?

Here's why:

If the jets are scaled to the venturis, then 1/16th and 1/23rd of 26 and 27 mm venturis is:
Primary (26mm) 1.13 to 1.63mm jet size
Secondary (27mm) 1.17 to 1.69mm jet size
(quick question - are Weber jet sizes related to mm or inches?)

So the secondary side would still have a jet sized larger than the primary side, wouldn't it? But from all the Weber carb jetting info I can find people on this site using, the secondary side main jet is either the same size or smaller, sometimes much smaller (like 170/140 in one case).

When looking at everybody's Air Corrector jets, nearly all of them will make the secondary side richer than the primary when taken as a percentage of their Main Jets.

But I'm still hung up on the secondary main jet being "too small"...

 

[jamyers]

Here's my attempt at posting a table...arrrrgh! heck with it...I can post it as a jpeg image...

(I'd only found 6 people's jetting, not 7.)

Weber jetting combinations, with Main Jets to Air Jet percentages, as well as Primary to Secondary side percentages.

My Weber came from Tom at Stovebolt, and is apparently jetted for a 4-cyl...no biggie, I've got an assortment of jets on the way... For the record, my current idle jet is too small (duh!), but the primary side drives ok, the plugs look a bit lean...and the secondary side is WAY too lean, it stumbles, bogs, and pings like crazy.

 

[Redfalken]

I'm hoping to get my 32/36 on soon and ordered an assortment of jets to tune it. I was searching on Google and came across a thread on another forum that mentioned a good place to get Weber jets on eBay. The seller is alfa1750 and they are $1.95 each and $4.50 shipping for up to 24 jets. He's based in Italy so it takes a couple of weeks but nice price!

I should get them next week so I can't say firsthand if they're high quality but he got good reviews on the forum.

 

[jamyers]

That's the same guy I just ordered mine from - by far the best deal I found anywhere. (and when I saw 'Redfalken' as a previous buyer I figured I was in good company!)

 

[Anonymous]

Hey everybody - I just found this site, and Ford sixes, recently. I've installed the DGV series of carbs on quite a few different engines, from 1.2 liter Datsuns to 4.2 liter Jeeps, and one general pattern holds true: If you look back to stang200's and the others' posts, you may notice that even though the main jets get bigger for a bigger engine (more fuel at low RPM,) the air correctors get bigger too (more air in the emulsion tube or main fuel circuit=less fuel at high RPM.) Since the DGV series is progressive, the secondary barrel starts to open right about the time the primary fuel circuit has worked its way through the "meat" of the main jet's range and is starting to be seriously affected by the primary air corrector. If the secondary main were jetted too rich, you'd have two things making the mixture rich at once - bad news: Big time bog. Thus the smaller secondary main jet to avoid bog when the secondary opens, and a suitably sized secondary air corrector to set all-out max RPM mixture strength.

Jamyers, your secondary jetting looks lean to me. (Which is odd, since smaller engines like the 4-banger you said this carb came from give less vacuum to the carb and so need bigger jets usually.) I know, you don't know me from Adam, but compare your numbers to the other stuff you've seen. Another possibility - slim as it might be with a new carb - is that the brass fuel delivery tube inside the auxiliary venturi for the secondary barrel may have rotated. Shine a light down into the throat; you shouldn't be able to see any "features" on this bit of brass in the middle of the throat, because its slot (about 1.5mm by 4mm) faces downwards when everything is hunky-dory. If you can see the slot, or a portion of it, you need to take the auxiliary venturi out, remove, re-install, stake, and superglue that tube. It's mainly a buzzy-engine, old-carb problem, but it could happen. If it does, the affected barrel goes totally lean. If you have to do surgery, be sure to get the o-ring (not shown in the schematic, btw) that seals the aux venturi to the carb body back in its spot.

AFTER you get your secondary main/air jetting set, then look at your secondary idle/slow jet. It's more of a band-aid, and if the carb is set up correctly otherwise, it's not much of a concern, unless your drivetrain setup has you cruising right at the onset of secondary barrel opening.

 

[powerband]

I posted previously that I obtained a brand new - old stock 5200 spec'ed for use by a 170CID (Capri 2.8 V6). I opened it up to see what what size jets it has.

http://photobucket.com/albums/v296/Powe ... 170%20CID/

Primary / Secondary
Idle Jets - 65 / 50

Air Bleeds - 190 / 180

Mains - 171 / 477 (Yes that's right 477) I guaged the 477 to @ .071" .

The '477' jet appears to be the on the largest end of the scale available and physically is much larger than any I've seen. There is some confusion (on my part) because there was a change from 'flow rate' to diameter in mm. and can be mixed.

The NOS carb is actually disappointing because although 'brand new', is in poor shape from shelf storage and has significant Aluminum corrosion. It will need complete disassembly and carb kit before use.

Powerband

 

[addo]

Thanks to Five10man for a terrific first post!

 

[jamyers]

Thanks to Five10man for a terrific first post!

I'll second that - Thanks, it's starting to make sense now!

Five10Man, you're absolutely right, my secondary side is WAY too lean...but I'm getting around just fine without using it until the jets arrive, my "new" 200 is plenty peppy on the primary (which is also lean, but the plugs aren't showing lean enough for me to worry about burning something up.).

Powerband, I'd missed that jetting info - but I'll add it to the spreadsheet!

One odd thing I've noticed in looking for information on tuning these carbs (which, btw, I've loved ever since I had one on a '71 MGB) is that nearly every site claiming to tell how to tune them only tells about setting the primary idle jet via the idle mix and speed screws...only ONE site I've found has a decent explanation of what's going on with the main and air corrector jets: http://www.datsun2000.com/tech/weber_tu ... dology.htm

So how do I tell when my secondary jetting is right? My Ranchero is geared pretty low (3.20 with small tires), so it's not in 1st or 2nd very long at all at wot...


I need to get the Weber book, but nobody local has it, so I'll get it ordered online I guess...

 

[cfmustang]

Welcom Five10man!

It is always good to add another Weber expert to the forums (I am clearly not one of them, although all my troubles with my old 32/36 last Summer sure taught me alot!). It just seems like info on the Weber is so hard to come by. Its a shame, they really are nice carbs. I love my new 38!

 

[Anonymous]

Thanks for the welcome, guys. Someone at my shop has a Falcon, and he just about exploded when we dug up this site/forum and the info about Ozzie heads. He's already taken a bandsaw to the log on his 250 head, and we're kicking around ideas for installing fool rejection and making a rat rod out of his baby.

The Weber book by HPBooks is good, if you're the type who can gain from reading a tech manual. It seems like half advertising for Weber and Redline, but they do a decent job covering tuning.

The reason most sites/books focus on the primary idle jet/screw is that it is where people feel it the most: in their wallets. The first 15-25% of throttle opening is where most street cars spend their time. During this time, the throttle plate is uncovering the progression slot (or holes, depending,) and this gets its fuel from the idle jet. [All of this advice assumes you have no vacuum leaks!] Your low-throttle-opening driveability and economy are all dependent upon this jet. The screw doesn't feed the progression circuit, so it affects ONLY the idle mixture. It may help to think of the screw as a "percentage" of the idle jet: if it takes two turns out to make a smooth idle with a #50 idle jet, it may only take 1-3/4 with a #60 idle jet installed. Either way, the screw affects only idle mixture, not off-idle or low-speed cruise. A side benefit of tuning the idle jet lean is that the engine is less likely to backfire on closed-throttle decel - even with exhaust leaks at the header/manifold.

When rolling on the throttle, it's hard to tell sometimes where the idle jet stops playing its role and the primary main steps in, but the nice thing is you don't have to worry about the air corrector until the carb throat in question is sucking at about 50% or more of its airflow capacity. In other words, if you are at high speed cruise, the main jet is working, with the air corrector doing little if any modification to the mixture. The more a carb throat is drawing, the more the air corrector aerates the fuel within the main circuit of the carb (like those annoying sink aerators) and so the less fuel gets delivered. This is a necessary thing, due to the way the carb is set up internally (ask if interested about emulsion tubes.)

FWIW, I set up my carbs to give chalk-white plug readings at all speeds/loads with the secondary barrel disabled. I make the engine just rich enough not to surge. Then I reconnect the linkage to the secondary and tune the secondary barrel for power, so I can have the best of both worlds. Since I'm not romping on the pedal with only the primary barrel open, I don't have to worry about cylinder pressures and temperatures spiking and eating pistons for me. Also, with WOT being noticeably richer and more powerful, I can feel on the butt-dyno when the secondary opens (in addition to hearing it) so if I'm driving for economy that day, it's a reminder and I can back out of the throttle. It might not be for everyone, but it serves me and the customers who want a better than bolt-on tune.

BTW, if your float is set too low, your engine will surge at part throttle cruise, usually at freeway speeds. If set too high, you will have a rich bog/stumble as you make a hard turn - for some reason, no matter the carb orientation, it seems to be right turns that bring out this phenomenon most often. Maybe it's the more violent sloshing; I don't know. Anyway, the correct float level is a valuable thing. I (here in AZ) coat my carb gaskets in Vaseline or Chapstick so they don't stick to the castings. Either one works well, but the cherry smell is worth the $1.29 the next time you open up your carb with a friend standing by, just so you can see the look on his face as he sniffs the wind...

 

[jamyers]

Woot! Thanks for the info!!! Now these carbs are making a lot more sense to me...

I like the way you're talking about tuning the primary side lean and the secondary side richer, that's the same way I've got my Quadrajet set up on my Buick, and it's not too bad economy-wise, but a real blast when you stick your foot in it.

OK, so my current idle jet is a #65, and the idle mix screw is turned out just over 3 turns, so it's too lean and I need to go to an idle jet big enough to get the smoothest idle with the idle mix screw at 1.5 turns out and the idle speed screw .5 to 1 turn in.

Now, driving around town with a #143 primary main jet and a #180 air corrector, the engine doesn't surge on light/moderate acceleration or cruise, and if I hold it at high rpm in a lower gear, doesn't surge or buck at all. Plugs are white, with a little bit of red deposits on one side of the insulator, but nice annealing around the base of the center electrode. I figured it was telling me it was lean, but not enough to do damage. Am I right about that, and/or should I worry about richening up the primary side? #143 seems awful small compared to everybody elses...? If I do need to richen it up, I'm assuming I should go to a bigger main jet and leave the air corrector alone.

Apart from an obvious surge/bucking or bog, how do you know when the secondary side is right? Seems that the throttle opens so quickly that it would go right through and past the secondary idle circuit in a heartbeat, so how do you know which idle jet?

Are there any "rules of thumb" for selecting secondary main and air jets?

Questions, questions, questions....

 

[Anonymous]

You can't judge the correctness of your idle jet by the number of turns on your idle mixture screw. If the screw's range of adjustment is lost - all of the adjustment is in half a turn, or all of it is at the ends of a 4-turn range - that's an indication of an unusual situation, like a too-small or too-big idle jet. However, the main purpose of the idle jet is to provide fuel for the progression slot. Since we have only rough changes (whole jet sizes) that we can make with the jet, and fine tuning we can make with the screw, AND the jet changes the screw, the place to concentrate our attention (as far as this circuit goes) seems self-evident.

A plug reading is as good as the skill of the reader. You need a clean kill, and then the history of the engine's mixture is shown to you from the most recent - closest to the tip - to the oldest/strongest impression made. It sounds like your plugs tell a good story.

Getting the secondary side jetted right is a matter for plug reading and/or instrumented testing. Since you're tuning for power, a G-Tech or the like can serve, although a buddy with a stopwatch can be had for beer money. More reliable power gains are had if the friend is paid afterwards.

Many DGV-series carbs don't even have a replaceable secondary idle jet - that's how much it matters! I don't have a number for you, but if you do the very-lean-primary/very-rich-secondary thing and the throttle feels too "digital" at the switchover point, you might try changing the secondary idle jet to some other number you have laying around. Unlike the primary, it's more a matter of guessing, IMO.

Tuning guides (I'm not one, I just play one on TV!) have rules of thumb for jets if you want numbers. I do it step-by step, tuning the mix from low load/low RPM to high load/high RPM, moving from jet to jet as they become the controlling factor. I start with the primary idle and end with the secondary air corrector. That way, I spend max time with good economy, and minimum time exposing the engine to less than ideal mixture when under a load.

 

[xctasy]

Welcome five10man.

Sorry to get techie on your first vist!

One guy here had problems tuning his to run on his 250 engine. It failed to produce the performance of even the stock 1100 1-bbl. I told him the veturi size would limit its abilites.

Since you've placed it on a 258 Jeep, perhaps you could help him out. Does an I6 engine over 130 hp NEED bigger venturis?



Some back ground info.

The 32/36 was available on two six cylinders engines in 5200 Holley Weber form on the 2600 and 2800 German Ford V6.

The air correctors do the rest of the tuning. From Pat Ghanrl's V6 Performance way back in 1982!

With an adaptor, it goes anywhere!

Only limit is the venturi size. Past 200 cubic inches or 130 hp, it starts to become very restrictive. (It starts to run under more than 2" Hg of vacuum wide open throttle. On a 250 or 258 reving to 4500 rpm, it is over 3" Hg.


In the past, based on the evidence, the only recorse for a real hot engine with this carb is to get a special NASCAR type cam which increases vacuum (used on NZ six cylinder oval track 250 Falcons). Running puny 390 cfm carbs on 650 hp NASCAR's sort of proves little carbs on big sixes work okay.



Other option on an engine above 130 hp net at the flywheel was to flycut the venturis up from the stock 26 and 27 mm to 30 and 32 mm (used on 2.0 and 2.3 Pinto and Lima Ford OHC's). Very easy to do.

There is just enough zinc oxide in the die casting to do that, and if it does break through, then you can add JB Weld to build it back up.

The DGV Weber isn't rare, its around overseas in millions in junkyards the world over.

CFM depends on air flow. Vizard quotes 227 cfm at 1.84"Hg , Holley quote 230 cfm at 2" Hg for one version of the early 5200, then at 280 cfm at 3 "Hg for the later 5200. Various Vega 5210 and Chrylser 6500's flow differing amounts but have the same basic venturi sizes, so there are gazillions out there in Omins, K-cars, and Vegas, Bobcats, Pintos, Mustangs and Fox body Fairmonts.

Vizard found another 17% more air flow when the venturis were enlarged, and that takes it within 14 cfm of a 350 CFM Holley. That means the 175 to 180 hp claimed by using it on a 250 Falcon six looks very plauseable.

The 5200 is a handed 32/36 DGV

 

[jamyers]

OK, now I'm gonna have to print this thread out and do some reading / re-reading / studying...

I love it! 8)

 

[Anonymous]

Considering only all-out horsepower, the DGES 38/38 is a better match than an unmodified DGV, performance-wise, for the bigger engines (250 cid / 4 liters and up,) especially with modified engines. On some big-inch high-revvers, a stock DGV won't do, with its lower CFM. Depending upon whom you believe, the DGV flows 255 to 325 CFM, and the 38/38 flows 390-400. FWIW, there are kits to install two DGVs on a 145 cid six-banger - I came across two of my DGVs that way, by dismantling a Datsun 240Z. They rev a bit higher than most pushrod engines, but food for thought...

An 85% efficient 250 engine pulling 5K RPM needs about 305 CFM, which is at or near the top of the DGV's range. A 200 at the same engine speed needs about 245, or right in the sweet spot for a DGV. Maybe someone here knows what the 38 DGAS' venturi size is? Perhaps, since the choke point (no pun intended) is the venturi, a DGV could flow as well as a DGAS/DGES if one took a mill or brake hone to it, and progressive action with good flow could both be had. The only time I've installed the DGAS was when a customer was paying for it, so there was no motivation to modify - he just bought the bigger carb, and it served well. Bigger hammers can be useful, but when you're saddled with trying to hang pictures with that 5 lb maul, you start to appreciate flexibility a bit more.

The air correctors do the rest of the tuning. From Pat Ghanrl's V6 Performance way back in 1982!

This is especially true as you approach the breathing limits of the carb (or carb throat, if you've disabled the secondary and are just tuning the primary.) As you approach those limits, the engine is applying more vacuum to the same jets, so they flow more - thus the smaller main jet on the secondary barrel. This effect gets stronger as airflow increases, so the bigger your engine and/or higher it revs, the more the air corrector becomes your best friend.

Here's another friend to help you with that last jet: Although most driving conditions are too transient and too rich or lean to make one useful, a narrow-band oxygen sensor (the common and cheap kind) does a good job of telling you about constant-load conditions, especially high load and high RPM. It's really valuable for doing the air corrector tuning, especially if you can find a long hill to climb to maintain a load. Any muffler shop will weld in the bung for cheap - $20 or so - and a cheap sensor (also $20 or so) is an easy install. It can be read with a cheap gauge - check any ricer website - or a digital voltmeter can give you the same info (0-1 volts, .45 volts=14.7:1, lower is leaner.) Leaded gas will foul the sensor, but the same place that sold you the bung can also sell you a threaded plug to install in place of the sensor after you've done your tuning. It's a whole 'nuther thread, I know, but it deserves mention while on the topic of getting mixture correct.

 

[robbinsj]

The choke sizes on the 38 DGAS are 28mm (99% sure anyway). I went from a 32/36 to a 38/38 on my 250. The 32/36 was a vast improvement over the stock carb. But with the larger valves in my reworked head, the larger cam, and headers, the 38 was needed...
-Joey

 

[jamyers]

Any chance we can get this thread made into a sticky?

 

[jamyers]

OK - I ended up with the 6-cylinder jetting indicated in the first post, and it's happy as a clam, except the idle jet is a bit too lean - just above idle it surges/bucks just a bit.

This is on a stock '68 200 with a DuraSpark/MSD ignition.