How to add 50 CFM to a lowly two barrel carb 

The people who don't watch David's videos don't know what they are missing out on!

My gal sat down and was listening to you while I was watching this vid today and said “I could listen to him for hours”! I told her…”I do”! 😉

This build, Mission Impossible, is really opening doors that we would never ordinarily go through. It is illuminating areas and ideas that every Hot Rodder should be well acquainted with. Bravo gentlemen! Well done!

I think a fitting term to replace Amateur would be Enthusiast. It fits well as a counterpart to Professional where those of us not doing this for a profession are doing it for our own enjoyment.

When we do these carburators... We increase the size of the pull over enrichment circuit... Just increase the size of the exit for the fuel..This makes that circuit act like a second accelerator pump.. It will make it come on sooner.. CrazyHorse Speed Shop N.J.

I think the very concept of mission impossible was one of the best ideas uncle tony has ever come up with on his youtube channel. Then to basically hand it over to you for completion is icing on the cake. Really digging all the info and tech coming from these videos.

Back in the 60's these ideas were almost a standard for any carb rebuild for performance. Even the ordinary daily driver could benefit from a good cleaning, deburring, and fitting the gaskets to the castings. Emory cloth was a must to smooth out the 'barrel' and the boosters. THANK YOU for bringing up these simple yet forgotten basics. "The only thing common about 'common sense' is that it is uncommon!"

Some of these tricks are familiar to me; I figured some things out myself when I was rebuilding carburetors back in the day. Another thing I did to smooth the bores, after some judicious grinding, was to put steel wool on a taped dowel (chucked into a drill) and run it through until the ground surfaces looked really smooth. I didn't have a flow bench, but it seemed logical to remove flash and casting irregularities for smoother flow. The new thing I learned from this video is the remodeling of the throttle plates and shaft. Thank you for the great information!

I was a carburetion mechanic back in the '70s and I always wondered if there were ways to increase CFM in all carbs.

This "Mission impossible" is a great series! Not a typical "just thow money at it and buy this or that", but rather useful knowledge gained from experience being passed down; things that can be applied to any engine. I'm grateful to all involved: Uncle Tony, David, Andy, Charles plus all the people doing all the filming and editing, etc. The work is slow and tedious, but it shows what can be gained from a lot of effort but little expense! I'm excited for the results, I think it will be a success even if it doesn't hit the 1hp per cu.in. mark!

Just re-watched; as this is a great reference video. Realised you're getting +105m/s through the 30.1mmØ venturi's. That's an awesome effort and what I'd consider: 'pretty much all there is to get.' Since you'll very rarely see air speeds in 'conventional' systems exceed 110m/s. (For those that are wondering, this speed represents the point at which airflow transitions from 'incompressible' to 'compressible.' Basically you kind of run into a brick wall around this air speed in these sorts of systems. Additionally beyond these velocities in a carb, meeting fuel accurately becomes increasingly difficult as the mass flow of air, no longer follows a linear relationship with air velocity) So again; awesome effort.

You missed one.... those boosters are massive. Start stacking booster gaskets, one by one, until you start to lose booster signal. Subtract 1 gasket, and mill (shorten) the boosters by same amount of added gaskets. You will be lifting the booster, up out of the venturi and increasing air flow. Because the flow goes up, so will the booster signal, until you run into diminishing returns. Of coarse, you will want to taper off the OUTSIDE of the booster after milling.

The screwdriver with paint on it makes me feel better about my "shade tree" knowledge. Wish my one barrel luck. 🇺🇲🍺

Geat video! 2 intakes and one head almost done on my end! Thanks

Love this series DV- thank you!

This is an exciting series ! Thanks for your work on this .

Really interesting to see the baseline pulls, ideas form for improvements, the mods done, and the results. Very cool! I'm excited to see the complete engine come together with this same philosophy. Great work!

Great work DV and Andy! 🏆🏁

That was some great info and to be honest pretty eye opening for me. Thanks as usual for the vid D.V. and Andy!!

I have a set of jewelers files I use to deburr the throttle bores and boosters..Did this to 800cfm Quadrajets years ago to feed big inch Pontiacs..I also discovered that the Ram Air floats were smaller than regular Quad floats....more fuel in the bowl. Easy swap..grind the throttleplate screws smooth...it's just a pressure differential device...smooth the airflow and give the boosters a good signal

Thank you David and Andy.

Thank you, Sir, these are eye-opening simple mods everyone should be a ble to accomplish. So glad I've subscribed.

Without a doubt some of the best info ever on RU-vid!!! Thank you D.V. and company!!!!!

Impressive detail work

That’s crazy how much you got out of that. Do all that to 3 more and you will have a killer motor. This is a really cool deal and get your mind thinking out of the box. Nice job guys and can’t wait to see this soon on the motor working.

Your content is getting better with each episode guys and to make money for such a good cause is remarkable.

Fascinating stuff. It’s great to be able to see David here after years of reading his work years ago.

Great episode! Thanks!

This is a good way to make almost free power.Thank you D.V.!

completely fabulous, what an education, Tham You DV!!!

DV tank you very much. I really apreciate you knoledge and your time. Very good video.

If you plug and smooth the hole where the choke plate shaft went through there should be some gain there. If it's allowed I would round the entrance of the air horn like a velocity stack.

Great upload with priceless knowledge to share to us mere mortals, as usual. I tell ya, if Mr. Visard was my close relative I'd be waiting at the shop every morning at daylight. Eager to soak up as much of his knowledge as humanly possible.

I'm enjoying this immensely!

Thanks David, brilliant stuff as always

Fantastic! David - please consider adding link to Andy's work in the description to make it easy for others to find.

Awesome, loved every second. So interesting and a BIG cheers for sharing your hard earned knowledge, much appreciated.

Thks David , I was waiting for this !! I did mods on a Carter 1V carb for a 300 I6 on the air and choke plate removal. Now I know I'm on the right track!!! 👍👍

In the past I have milled the bottom off the booster venturi up to the discharge tube then tapered what's left to an edge and found no detriment to transition to main circuit, this of course on increases VE motors as like you stated the signal has improved as has air flow and speed from engine upgrades and higher compression also improves signal, long before it was fashionable we were cutting the front two bbl off 4bbl holley to make big 2bbl, even did it with a Dominator when budgets allowed to build to 2bbl rule

we did up the throttle shafts and butterflys on our race kart carbs thanks DV

Awesome ! Id love to see some crazy mods done to this type carb, great information,

I think polishing the air horn, base plate openings, throttle blades, and shaft would make a difference as well.

Yes, with modern vehicles it's a bit harder to get incremental gains than with the old iron, but there is still room for "free" improvements if one is prepared to spend the time. Many years back, I used a combination of Mr Vizard's "A" series, and Mr Yunick's tuning tricks to get an esimated 30-40*% gain in mid-to-upper mid torque/power to modify the OEM parts (student budget, but access to machining)) and fabricated exhaust (OEM manifold, reworked). *from ~100kph to ~130kph on the same hill, both figures were consistent, so real-world gains.

An air cleaner base with a radiused entry would probably help quite a bit as well…..one could easily be stamped from sheet metal because the carburetors entry is round…..or if you don’t want to use a filter, then it could become a longer velocity stack profile.

Excellent content and testing to back up the changes! When we raced restricted to stock 2 barrel a lot of little things added up. With the air cleaner off our carburetor was nicknamed ‘coffee can’ and boy did it let the engine breathe:)

Thank you David appreciate you taking the time to share your knowledge, these are things wouldn't even have thought about , it would probably work pretty good on a little webber 2 barrel carb on a vw 1835 I'm going to have to try some mods now 😁👍

David, this is eye opening stuff.

great for many carbs ! thanks A & DV

Another great video! 20 years ago a very experienced race mechanic down in Daytona by the name of Crandall taught me about knife edging carburetor butterflies. He quoted some ridiculous HP gain (20?) but that's on a fully built Cup engine. The guy was one of the great ones.

Thats quite fascinating! Good stuff.

Very informative. Andy to make a slide throttle plate for the win!

great info love it ! 300cfm plus

I did some of these mods to my Carter BBD some time back, and it was worth the effort, although I did have to fight a bit to stop the lean out. Mostly it was a fight because I didn't know anything about carbs before this project.

thats was a amazing secrets you have shared,i dont think most guys would ever think it possible ..the carb is a mystery for a lot of us and wouldnt touch it until now thanks DV .. andy keep up with your homework lol

As always well done David and Andy. The best part of this series is that the incremental changes were backed up by quantitative data. Personally the one test which I felt you should have peruse was the entry loses into the carb inlet itself. Given that the test of throttle plate in isolation represented the ideal maximum (372cfm), it also included the use of putty to create a radiused entry. To an apples for apples comparison the final test (all modifications undertaken) should also have included the same putty treatment at the carb inlet. This would definitely show improvements in cfm viz. bell mouth entry, which some air cleaners of the era tried to emulate.

Good stuff once again!! 👍

Hi David and Andy, I love this build series. A good mate has an idea that I think you will like. His idea is to "siamese the intake ports", like an A series Mini engine and the manifold. He has done this to a 318 head. I have pics if you are keen!

Love these videos, thank you for posting these. Invaluable information! One suggestion: a darker background 22:00 would make David and his magnificent mane pop better. :)

Awsome, thank you guys!

You sure have made me a believer in your channel when you mentioned Saint Jud

Love seeing these carb mods. in the process of doing something very similar to a 34ADM weber. Can't wait to see this project hit the dyno

Another great video.

This is the kind of stuff i really enjoy. Anyone can buy the most expensive parts but the fun is boing with only time and effort.

Outstanding! Thank you!

Fascinating!

Been waiting for this

This does work. I have done it years ago to a Holley 4 barrel and went up one jet size from looking at the plugs. Seat of the pants feeling it worked.

Thanks for this . Cool stuff

Just awsome stuff guys!!!!

You're a wealth of knowledge. Cheers

truly impressive

Thanks David

I think it was Braswell that used to spot weld the throttle plates to the shaft, eliminating the screws altogether.

Thank you sir. Great vid. 👍👍🌄

You are a genius good sir!!!

The word amateur comes from the Italian word adore to do something for the love of it!

I Have Been Waiting For This for Decades. This is the Real Deal on A Good Sleeper which I Live. I had a friend and brotbyears ago who won thousands of dollars with cheap sleepers. When I finally made friends with them omg I learned a lot. I never knew who taught them. I think it was their grandfather from the fifties racing scene. They dominated southeast Texas and south west Louisiana back in the eighties. They told me back then their best month they won 10,000 dollars and then had to lay low for eight mo. People are poor losers. They had a different car every three weeks. That’s how they pulled it off heads cam gear. Three ingredients before nitrious

great stuff.

I did many of these things to a motorcraft 2 barrel back in the early 90s including chopping off the choke horn epoxy a few areas and smooth up everything essentially smoothing all the radius areas. had a loose 351w with an automatic in a mercury capri, nary a 5.0 could touch it. Must have been embarrassing to follow someone back into town spouting how they gotta have nitrous when I popped the hood and took the air cleaner off and said “show me the nitrous dude” 😊

Very interesting guys 🧐

Right on! Have done that to other carbs and Carter 2 bbl running on stock eliminator automatic, there are other approved replacement carbs for 318 listed for that engine that van flow more with mods. Ps, try with a 4" stack on dyno, fuel stand-off with the open plenum single plane manifold, attn: Andy.

Brilliant

I would presume these mods would work with basically any carburetor, holley, edelbrock, or quadrajet. Very nice work

Thanks for taking the time to share your knowledge in these videos David. I'm curious to know what the weight reduction was on the 318 rods. I went back to see what I guessed. The first video (small end) I guessed 96 gr and the second (beam) video I guessed 32.5 gr for a total of 128.5 grams per rod reduction.

Hey Dave/Andy not sure if anyone has said it in your previous videos but ignore is spelled with an "E" love your builds and books!

Nice!

THIS IS AWESOME!!!

Due to cam profile the idle may need raised whitch gets you off the transition slots so you may need to drill the plates to give it the air it need to get it back to closed plates so the idle screws come in to play.

after this man showed the flow capabilities a of stock BBD carb,now imagine installing three of these on a 318 with these mods,all stock stuff,hopped up

Very nice! I am curious to see how Andy jets/rods this. That is one of the reasons I turned away from the BBD/BBD2 - no aftermarket tuning kits for them

Saw a video on the way Nissan used a large box(?)..plenum...to store volume on a restrictor plated race motor...I think Australian racing series...very nice...

to compare the modified carter to a holley 2bbl, it needs to be flowed at 3" of vacuum. holley 4 bbls are flowed @ 1.5" of vacuum. a holley 500 cfm carb flows around 354 cfm when compared to a holley 4 bbl.

I can't wait. I got a 1000cc BMW with 32mm carbs. Maybe I can get some cfm.

Great job… excellent info,thank u both .. Tony blows

A little bit goes a good ways!

David Vizard the carburetor Wizard!!!

There was a guy in Shelton that embarrassed all the four barrel cars at the Bremerton raceway .name was joe Lambert,hes on the calendar that year for any doubters .

I've been working on my own carbs = carter 1 barrel & carter 2 barrel for my slant6 's and doing same mods . I sent Andy an email about it and I have videos on my channel - Moparman1978 on my butterfly plates and choke plate I took the flate edges and gave them a knife edge. I'm also planning on cutting Dow and smoothing out the opening on the throat of the carb and cut down and smooth out those tabs aka ears that hold the air clear housing rod up. I also thinned the boosters as well

A new gasket will not overhang the throttle bore like that. Your gasket is old & has shrunk. Staying tuned, this is getting interesting. Once upon a time, long, long ago there was a guy campaigning a Dodge station wagon (B body) with a 2 bbl 273. I can't remember what his times were but for a 2 bbl 273 they were respectable. Wonder what he did to the carb? I think MoPar Action magazine did an article on it.

Subscribed! 😁