Weber Carbs

Bigger ain't always better.  My bet is the 40s are good w the 2110.  That might be a good match for around town driving and the mandatory pedal to the metal now and then.  If carb too big, air speed in venturi to low, atomization not optimal, etc. etc.  and driveability may suffer. And the jetting.  Need that right as well.  If you plan to race, and engine will be huffing near the redline mostly, then maybe.  Others here will have various opinions, based on experience, about what would work best.  They will want to know things like cam grind, rocker ratio, head style, valve sizes, and like that.

I have a 2,110 and a pair of 40mm Dellortos.  I did a lot of flow calculations before I bought any carbs and for the valve size (40mm), cam used (Engle 120) and exhaust characteristics (a Berg extractor with 1-1/2” tubes) a pair of 40mm carbs worked out to be perfect.  And they have been for the past 18 years.

... like I said . . .

CRM posted:

I have a new 2110cc engine in my speedster with dual Weber 40 IDF's.  Can anyone tell me if I will see any appreciable gains in all around driving if I upgrade to 44 IDF's?  

 

Thanks

What heads, cam/rocker combo and exhaust does it have now?

Edit- Unless you're looking to make power in the 6500- 7,000 rpm range and are willing to sacrifice the snappy throttle response at lower rpm's that I'm sure an engine that big gives you, stick with what you have. Do you know what size venturis are in the carbs? How high does the engine rev to with power when you push it in 3rd gear? Although it will rev higher, you'll feel it flatten out when it goes past peak power. I know I'm asking a lot of questions about the particulars of your engine, but it's quite possible that the combo is optimized now and bigger carbs could be a mistake.

Great information, clears the question.  Thank you for the input.

With the help of Pat Downs and Jim Ansite, I finally got my Weber 44's working correctly. I think the 40's would've been much easier to dial-in.

Waiting for an engine build sheet which would be invaluable in making changes/mods or just plain knowing what exactly I have.  My fault for not specifying in advance.

Will Hesch posted:

With the help of Pat Downs and Jim Ansite, I finally got my Weber 44's working correctly. I think the 40's would've been much easier to dial-in.

I'm sure they would've been.

I ran 40s for one summer on a 2332 that made 200 hp with 48s  (after the 48s nearly burned the car down). I tuned those 48s with a wideband and O2 sensor, and they were fantastic at WOT. The engine was built to flow them (1-3/4" header, 44 mm intakes, etc.), and they were instruments of shock and awe when the hammer fell.

But I had a carb fire (the result of a backfire gone wrong, which is not uncommon with carbs tuned to deliver 10/10ths) which melted the aux vents on one of the (NLA) carbs. In disgust and a desire not to waste a summer looking for parts that were last made in the Reagan administration, I threw on a set of 40s I had laying around.

I probably gave up 20 hp with the switch. The car absolutely came alive. It was hands down more fun to drive than it ever was making 20 hp more.

I learned a lesson from that. Most guys overcarb everything in search of power they will use maybe 5 times a year, and give up all the golden goodness that comes from enough airspeed for the transition circuit to work well.

40s are perfect on a nicely built 2110. If it's the lump some builders put back there (stock heads, 110 cam), a set of NLA 36 Dellortos would be better yet.

Forewarned is forearmed.

Huh... Now Im left to wonder why my 2054 came with 44s!

TRP posted:

Huh... Now Im left to wonder why my 2054 came with 44s!

Stan Galat posted:

Most guys overcarb everything in search of power they will use maybe 5 times a year, and give up all the golden goodness that comes from enough airspeed for the transition circuit to work well.

Drag racing is to blame.

Every engine builder in this hobby thinks every customer wants to take his car down to the strip every Friday. If not, they'll suggest a nice 1776 with stock heads.

What's more to your liking: A Dodge Demon, or a GT4?

If I have to pick a Dodge,  I take my old 1964 Coronet 440. 426 2x4's with glass packs and Hooker headers. (non numbers matching)

Called it 'the lub machine'. 

It would smoke the tires for a country mile. With dual 4 barrel carbs... I bet it was also over carb'd.

TRP posted:

Huh... Now Im left to wonder why my 2054 came with 44s!

Depending on the exact model of 40 IDF (some will accept 34mm venturis and some will only take 32's) some > 2 liter engines may find them just a tad on the small side, Ted. I believe the 40 IDF's in most VW dual carb kits are the latter, hence whoever built the 2054 equipping it with the 44's. 

@Stan Galat said- "I threw on a set of 40s I had laying around. I probably gave up 20 hp with the switch. The car absolutely came alive. It was hands down more fun to drive than it ever was making 20 hp more."

Do you remember how much short of redline it quit making power? You're right though, throttle response and power in the lower rpm's would have been fantastic! And if the engine was making any where near 200 hp then you gave up a lot more than 20. Just sayin'...

My 1914 came with 44s from Raby. 121 hp @ 5500 and like 124 ft-lbs at 4000, flat from 3500-5500 supposedly (I have the dyno sheet from a sister engine). Looks pretty good, but Jake's dyno sheet starts at 3500 rpm—gives no values below that or above 6000. I wonder what the 3000 rpm and lower numbers look like, and how they would change with a set of well-matched 40s.

If someone wants to lend me a set maybe I'll test them and report back. 

I've wondered that myself as my CB 1915 also has 44s.

Al's correct, 34's are the number we settled on and wow, what a difference the smaller venturi's make in the 44's!

How do you determine venturi size?  Is it a casting number than can be easily seen?

Lane, on the sets I purchased from CB, they aren't marked so I use a sharpie-marker on the O.D. I have a set of 32's that didn't work on Whitecloud though Pat gets many cars to run great with them, Whitecloud liked the 34's. My carbs came with 36's. Weber venturis may be marked, I gave mine to my tuner so don't have them handy to look.

Speaking of carbs, my Dells are, as I noted above, a really good fit for my engine.  In warmer months they operate well, but have always had a small hesitation when accelerating, just as if the accelerator pumps aren't squirting quite enough.  I also see the A/F gauge swing over towards lean and then come back (takes about 2+ seconds to swing and return).

Now, drop the ambient temperature down below 40 and the colder it gets the better they run - no hesitation, nothing, just go whenever the throttle is opened and the A/F gauge doesn't move.

Anybody better than me know what's going on?

I believe it’s because the charge is more dense in the colder ambient. 

Stan Galat posted:

I believe it’s because the charge is more dense in the colder ambient. 

I think you're right, Stan. Small carbureted aircraft engines will produce more power in cold air than warm because the air is denser as I understand it and more fuel / air mix gets in on every intake stroke. Gordon's carbs won't have cockpit adjustable mixture control like in a plane, but they're likely fixed close to optimum and finally hit the sweet spot when the temps are just right. 

Every carburated vehicle I've ever had-- minibikes, beaters, work-vans, 'murican V8 muscle-cars, dirt bikes, UJM street bikes, speedster-- all have always run better on a crisp morning or late at night than on a hot, humid afternoon.

I was taught that's all about charge density. I have no reason to doubt it.

I never knew how they called it but it is a phenomenon that I am familiar with my old IM ran sweeter in the fall cool air, and a friend who is a flight instructor confirmed that same phenomenon in his winter flying machines.  

Even old Chuck Berry knew that cool air made your car go faster:

The Cadillac pulled up ahead of the Ford,
The Ford got hot and wouldn't do no more.
It then got cloudy and it started to rain,
I tooted my horn for a passin' lead
The rain water blowin' all under my hood,
I knew that was doin' my motor good.

Maybelline may not be true, but cool air is...

Think " cold air intake" modification (moving the air intake to outside the engine compartment) on a lot of newer cars. With fuel injection it's a dream come true, with it's automatic a/f adjusting. If we could move more ambient air through the engine compartment it would carry away more radiated heat from the sheetmetal, alternator and engine case itself (and not pre-heat the air entering the carburetors and fan), it would overheat less and run in that sweet spot where it makes it's best power more of the time.