Over the years, I've heard a lot of questions. Maybe you'll see yours here...
Everybody tells me Weber carburetors are impossible to keep in tune. Is that True?
My first response to everybody who asks this question is "Did somebody tell you this who has owned Webers?" Usually it's someone who heard it from somebody. The truth is that these carburetors, if set up properly in the beginning, will give you years of trouble-free service. They are no more likely to go out of adjustment than a Holley. The linkage is of high quality and holds adjustment without any problem.
What about cold starting? I notice there are no chokes.
Webers literally squirt fuel into the intake ports, typically just outside the combustion chambers. Fuel doesn't have to remain in suspension and arrives with full force. When the engine first starts, they will sneeze for a minute or so, but drivability is the same cold as hot. The engine will settle down and idle right away without nursing it, unlike an engine running a conventional carburetor with no choke. By the way, on a Weber, the word "choke" refers to the venturi, which is a removable cylinder inside, so don't be confused.
How do I start my engine without the use of a choke?
Hit the pedal about 3 times and crank the starter. Weber engines like the shot of raw fuel and always come to life instantly. Chokes are for sissies.
Are the Webers sensitive to high altitude?
No more than any other carburetor. If they get rich at high altitude, it's easy enough to lean them with a smaller main jet and idle jet, or a larger air corrector. They are much easier to rejet than conventional carburetors because Weber jets are accessible from outside.
What kind of a cam should I run?
Any cam is fine as long as you pay attention to the lobe separation angle (LSA). A 112-114 degree lobe separation is ideal for Webers. I generally discourage the use of anything tighter, like 108, or 106. A 110 LSA is marginal. The problem with a lot of overlap is that it causes "reversion"...which are pulses from the exhaust stroke while the intake valve is still open, that have nowhere to go but up into the carburetor. This disturbs high rpm airflow and causes the engine to think it's too lean at high rpm’s. Without a plenum, the flow is pulsed backward up into the carburetors because there is noplace else for the reversion pulse to go. To find your cam's lobe separation angle, check your cam card. Just add the intake centerline and exhaust centerline and divide by 2.
If you have no clue what I'm talking about, that's okay. Here's a diagram of what it looks like, courtesy of Popular Hot Rodding. This should clarify it for you. It's okay if you don't know about this stuff...if that's the case, this is part of your education. Click the link below:
Lobe separation angle explained
What kind of performance gain can I expect?
The difference with Webers will not be so much on the top end as throughout the midrange, where you will be using the engine most. Webers will bring the torque on very quickly, and the engine will rev a lot faster because it will be in its torque range anytime you are running on the main circuit. A four barrel intake has to move a large mass of air. The manifold air speed (velocity) is what produces torque, which is why 4-barrel engines typically make their real power on the high end...those manifolds require rpm's to get the air moving fast into the combustion chambers. That is not the case with Webers (or Hilborn-style fuel injection). With Weber carburetion you're moving eight small individual columns of air. Each column is independent of the others, so when you crack the throttle, those 8 columns all move fast, each one by itself.
So, while you may make more ultimate hp at the high end with a 4-barrel, the 4-barrel engine is not as flexible or "torquey" as the Weber engine everywhere else in the rpm range. Floor either one at 3500 rpm and the Weber engine is off like a rocket because the manifold velocity is already there. The Weber carbureted engines rev very fast and are peaky all the time. This is why they are still the carburetion of choice for any kind of sports, vintage, and SCCA road racing where power is desired throughout the entire rpm range, not just at the high end, like in drag racing. Webers are really well-suited for for road racing and hot street cars.
Are you available to tune my car?
Yes, but I ship every setup as a fully assembled unit, ready to install. I also supply you with all the tech help you need when you install it, plus you will also have my installation and tuning manual, which comes with every system I build. This provides a "walk through" in simple terms, of how to tune an engine with my Weber carburetion system installed. I doubt you'll need me, but I will tune and road test customer's cars. For hands-on tuning, I charge $85 per hour. I am two miles off I-95.
How long will it take for me to receive a carburetion system after I order it?
I am usually comfortable quoting 6 weeks delivery. The carburetion systems requiring the most custom work may take more than 6 weeks, all depending on how fast the chrome plater or polisher is. Plain carburetion systems go out very fast, often within 2 weeks. Any units with turkey pans take several weeks. I order these pans from my fabricator "as needed" because they're too expensive to stock on the shelf.
How do I place an order?
Just call and provide me with all the information on your engine and car. I would like the displacement, compression ratio, type of heads, type of headers, and what transmission and rear end are in the car. My terms are half up front and the second half when I ship, with UPS Ground shipping, handling, and insurance added to the second half payment. Final payment is made by credit card.
Will you come to my location to tune my car?
I am sorry, but I no longer travel to tune cars. The hassle of air travel has taken all the enjoyment out of it.
I bought my Webers from someone else, and they don't run very well. Can you rejet them for me?
Yes, but if only if you watch my video first as your punishment. If you missed the video link on the home page, please go back to the home page and watch it ...I want you to feel as guilty as possible. I can correct anybody's mess, but before I send you any jets, it's important to establish the basic parameters. Your float setting is critical beyond words. We need to confirm that they are all set to factory specs. If that remains an unknown, rejetting won't correct float-related problems. Any problems you have can be corrected.
With Webers, your ignition timing is critcal, and if set wrong, can create serious heat in the block, cause percolation of the fuel, and make a correctly-jetted engine completely undriveable. Also, the fuel pressure and the type of regulator you have are extremely important.
Before calling about rejetting, please go to the Exploded Views page of this site and identify all the jets and calibrated pieces, then pull them out of one carburetor so you can tell me what the sizes are. I am interested in the sizes on items #11, #19, and #45 through #50 on that Exploded Views page.
All the main metering pieces are accessed right under the jet cover screen (or cap on the DCOE) on top, and you can see the choke size by looking down the carburetor with a flashlight. Item #11 is the only one you may not find...on an IDA, it's under the float in the bottom of the float bowl, so you have to remove the screws that hold the carburetor top, remove it, then unscrew the float fulcrum pin (which may or may not be safety wired), and take the float out to get at it. If you are not inclined to do that, then for now, you can leave it and we'll see what the rest of the pieces look like. On the DCOE, the float comes out when you lift the tiop off the carburetor. The valve (item #11) in in the bottom of the bowl. Another choice is to just send me the carburetors, then go back in the house and have a cup of coffee. I will send them back ready to install back on your engine.
What "they" say about Weber carburetors... (and who is "they", anyway)?
This is an email I received from a great guy in Virginia named Corey Zimmerman. Corey was struggling with a badly jetted carburetion system on his 427 Cobra, even after receiving quite a lot of advice and conflicting technical input from others. After I rejetted Corey's carburetion system, he sent me this. I am reprinting it here with Corey's permission because it says volumes about those mysterious unknown people we refer to as "they" or "them", who apparently know more than anyone about anything.
Email from Corey:
"Well, I learned that even though I know better, I still sometimes listen to "them" and get confused. Who are "them"? Them are the ones that we constantly reference when we think or say " they say such and such or they said that..... ". What am I talking about? I'll explain.
My last email to you was concerning the readouts from my LM-1 A/F ratio meter system. If you remember, I was concerned because the setup that we had done on my Cobra was reading out with A/F ratios in the 11's. I was concerned because "they" had all said that it should be around high 12s to 13 to get the max HP output and performance. (See...the first part of this message is beginning to make sense). "They" say that 11s are too rich and it should be in the 13s and then drop to 12.7 when accelerating.
As has happened in the past, I succumbed to believing all that They say. I recently was looking at Pat Braden's book again and came across the chart where he is discussing A/F ratio and performance. It was interesting because he shows that the curve of Percent Normal HP is basically flat at almost 100% from 14:1 to 11:1. So as long as the car drives well and is in this range of A/F ratios, then I am getting the best HP out of the car. Not surprisingly, your setup is doing just that! (but you knew that.) I'm going to try the 180 air correctors just to see if it will lean things out a bit without a negative impact to see if it will improve the gas mileage a bit ($3.00 a gallon and unemployment don't mix well ). Otherwise, I am going to stick with your setup and continue to drive happily into the sunset.
Thanks for patiently putting up with my moments of doubt."
**The moral of this story is don't listen to anything "They" say unless "They" have hands-on experience. You will find there is no shortage of people who feel qualified to provide advice, much of which leads to total confusion. If you ask me a technical question, I offer over 30 years experience as my "well of knowledge". I have been tuning and building Weber systems for Cobras since the days long before there were replicas (and it's a good thing they came along, or I'd be a useless old dinosaur by now).
--Jim
Newest questions...
This is an email I received, where the prospective customer asked some good questions, so I'm sharing his questions along with my answers...
Q:
I read both sides of the coin, 481DA Webers are difficult to tune, and also that they are not. My SU's on the MG are not bad at all, and I can't imagine that Weber's can be running always out of sync or rich if they are adjusted now and again.... your thoughts?
A:
Webers are easy to tune and simple to work with, but in some cases, you may have to put in some extra road-testing time to find the right idle jet and idle air bleed combo to see what your engine likes. Two similar engines can require a different jetting package. But I work closely with my customers to get them dialed-in. In many cases, they are fine right out of the box.
As far as going “out of tune”, this can happen because the linkages are not assembled correctly and have too much play, with the levers rotating on the carburetor shafts ever-so-slightly. If that’s the case, this will translate into a synchronization problem at idle, and they will constantly change. Or, the linkage just may not be designed well in the first place. With a correctly-assembled unit, there is no reason to keep synchronizing your carburetors; they don’t go out of synchronization for nothing, or run good one day and bad the next. I never touch the ones on my cars after they’re synchronized, other than checking them in the beginning of the season when they come out of mothballs in spring. It’s usually not even necessary.
Weber carburetors don’t just “go rich” on you. Here’s where that reputation comes from: in the old days, nobody ever knew they had to run a fuel pressure regulator, and they fed the carburetors right from the fuel pump. Even the Cobra factory race cars never ran regulators. A standard mechanical fuel pump typically puts out 9-12 psi. Webers cannot tolerate anything over 3.5 psi...the needle valves are lifted right off their seats, so with that much fuel pressure, the carburetors will not only drip at idle, but will also flood the engine after shut-off. Naturally, the #%$@&# carburetors got blamed for this, so they got an undeserved reputation for being quirky and a lot of trouble (which they were, of course...but that was because the fuel pressure was wrong) and it stayed with them. But there was never a problem with the carburetors. The problem was with the installation.
Q:
Is it my imagination somewhat, or does the engine sound different with Webers on a V8?
A:
It’s not your imagination; they do make a sound all their own. At wide open throttle (WOT) it’s a “howl”, and it’s louder than a big four barrel without an air cleaner. On a Cobra, you might not hear it as much as on a muffled car, because the side pipes can be so loud. The exhaust may sound deeper, or louder, as well. As an engine’s horsepower increases, it naturally gets louder. Also, Weber-carbureted engines rev pretty fast, and that adds to the different sound of the exhaust. So, between the “howl” from the engine bay, a little louder exhaust note, and faster revs...yes, your car will sound different to you.
Q:
I had looked at a couple of crate-engine companies before, but with my plans shifting to the 481DA's, I am wondering what you think might be my best option(s) so make sure I have a 351 w/ components that will net me 500hp with your intake system? Ford-direct crate engines seem logical, or do you work with a supplier who would have things ready for for a 481DA system?
A:
The Ford engines are excellent. I’ve built Webers for virtually ALL of them, and the strokers are particularly nasty little engines; you get a good bang for your buck. Having an engine custom-built in an engine shop can get pretty expensive. Just be sure you don’t have too much overlap in the cam; independent runner engines don’t like that, and they become inefficient with a lot of valve overlap. Keep the lobe separation angle at 110 degrees or wider and you’ll be fine.