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Weber Conversion

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A

Azfire

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Hi !!

I need help and advice on this. I own a '72 Spitfire MkIV, and I'm considering to use a single Weber 40 DCOE instead of those SU's. I've searched around, and noticed that I'll have no place to connect the vacuum advance of the distributor. I read somewhere that it's ok for competition use, where the rev's are kept high, but what about for road (fast-road /ubbthreads/images/graemlins/cool.gif ) use?

Thanks! /ubbthreads/images/graemlins/smile.gif

Regards,

Filipe Guedes
 
Hello Filipe,
ther's no problem running without the vacuum advance, as it is only an economy device. Obviously you will need to get the Weber set up.
I would consider, though, whether there is any real gain, except, perhaps, in the looks. A single Weber is not going to give any significant, or indeed any power gains. A twin Weber set up gives only marginal top end gains over twin S.U.'s even with serious engine modifications and you will lose on flexibility. To me the S.U. is the best option for a road car.

Alec
 
I disagree piman. Twin Webers do give a fair amount of power, especially compared to Strombergs (don't know about SUs), but that's not the real point. Webers (DGV downdraft) don't have to be tinkered with and adjusted nearly as much as Strombergs or SUs, because they are not atmospheric dependent. And you don't have to wait for the floats to fill up for them to start the engine. It just fires up, like that. IMO, they are worth it. With all that said, I've never experienced SU carbs, only Strombergs. And regarding vacuum advance, it can be connected to DGV Webers, but not the side draft DCOEs.
 
[ QUOTE ]
...Webers (DGV downdraft) don't have to be tinkered with and adjusted nearly as much as Strombergs or SUs, because they are not atmospheric dependent...

[/ QUOTE ]

I've heard you say that a couple of times and don't understand it. It is my impression it is the CD (SU & ZS) that are not sensitive to atmospheric changes and the Webers that are. In this locale we sometimes have club drives that range from 2200' to 9000+' altitude and the cars with the Webers start gasping around 6000'. Maybe they aren't set-up right but the SUs and ZSs are totally indifferent to what the altitude is.

As for tinkering with the carbs -- I don't touch them for years at a time and certainly do not require the cranking you describe to fire up and go.
 
Hi all,
The Webers are tuned by replaceable venturi's where the SU's are constantlay adjusting air flow & fuel through the rising piston & tapered needle. To be honast the SU is easy to tune & requires very little adjustment after.
The big problem I have with the downdraft Weber set-up is the poorly designed intake manifold. The flow is not direct & detracts from the posible performance gain. If other modifications were not made to the motor to take advantage of the additional fuel/air very little will be gained & fuel milage may suffer. The Webers can be de-tuned to match the motors needs but it may not be worth it.
Kastner did some amazing things with the SU's & Strombergs.
 
Hi all. My 2 cents worth. I have found you can tune the SU and ZS's to run with a really good engine and even a bad engine to give the car it's max ability with the engine configuation. Sure it takes a little time to get the plugs gapped right and the plugs the right temperture in some of the older baggers, but if you can keep the guys at the service station with his screwdriver away from them, they will stay tuned until the engine changes in some way. Wayne
 
Those in the know will tell you that a Weber is a bad choice over a ZS or SU carb for a Triumph. I certainly do not count myself as one of those experts, but 30 years and four Triumphs later I must agree. The people that push Webers are the same ones that sell them.

Bill
 
I have run tripple webers for 8 years after adjusting the jetting one time. I have ran the car from the ocean to 8000ft elevation and autocross with no problems. what a difference from my zs that I had before---always having to rebuild, rebush, readjust and re-oil. I would rather run one weber before going back to the zs, (only purist and hardheads pretend like they are great, people who knock webers are usually the jealous type. Allan
 
[ QUOTE ]
[ QUOTE ]
...Webers (DGV downdraft) don't have to be tinkered with and adjusted nearly as much as Strombergs or SUs, because they are not atmospheric dependent...

[/ QUOTE ]

As for tinkering with the carbs -- I don't touch them for years at a time and certainly do not require the cranking you describe to fire up and go.

[/ QUOTE ]

Mine sure did. It generally took 5 seconds of cranking before it would start, which is a lot. 'Course that could be contributed somewhat to other factors, but I've talked to a few people from out local car club who've said the same thing.
 
WOW!!!!
Gotta love it, a lot of loyalty being exhibited here; and about Carbs?
Just wait till the PI junkies get started on this thread!
I'm just glad the darn thing starts and doesn't leak fuel all over the show.
 
WEBERS HAVE FLOATS THE FLOAT CHAMBER FILLS WITH FUEL THE SAME AS ANY OTHER CARB! This has nothing to do with the ease with which the engine starts. What a Weber does have that helps starting is an accelerator pump unlike SU's. Therefore if you hit the accelerator pedal they squirt gas into the cumbustion chamber, thus making starting easier. I have a set of Webers and manifolds sitting on a shelf in my garage. They were great for SOLO II but for all around driving I don't like them. Between tours of Michigan at 600' and tours to 11,000' on the way to Yellowstone the SU's work fine and no I do not fiddle with them all the time.
 
GeoHahn; no SU Carb that is set up at or near sea level is going to run at 9000' elevation with out being leaned out{Fiddled With} additionally the engine power will drop about 3%/1000' increase in altitude.---Keoke /ubbthreads/images/graemlins/yesnod.gif
 
Hello Webb,
does your fuel pump click a lot when you switch on the ignition. Often, particularly with HS S.U.'s and I guess with the ZS having the jet assembly sealed by O rings from the float, the fuel leaks away overnight and you have to fill the bowl before it will start. Take care of the seals and you will often find that cure for slow starting.

Alec
 
Hi Filipe,

I've had a pair of 40 DCOEs on my TR4 for over 25 years. There is little to wear out on them and they worked well for me on the street (the car is presently not on the street, it's being restored). It's engine is moderately modified with increased compression, oversize pistons and liners, oversize valves, header and sport exhaust, and it is getting a new performance cam soon. Without these mods, the Webers would give little improvement by themselves. The whole idea is to get the engine to breathe better, and it takes a package of modifications to really get the best performance with these carbs.

As others have said, the strength of Webers is high speed performance. They can be tuned for just about any situation, though. But, an SU in good tune is likely a more flexible, all-around street carb.

You cannot use a vacuum advance distributor with DCOEs (but you can with some downdraft Webers). You'll need to convert it to strictly centrifugal advance. This is possible with the stock distributor on the TR4, and my car ran fine with one for years. I'm currently installing a dual point Mallory system, to replace the worn orignal dizzy.

I'm not sure the correct setup on your car, but I would think that using just one carb, a 45 DCOE might be a better choice.

Installing a Weber, you really need to hook up with a local tuner who has a dyno and a pile of jets for the carb. There are many different jets, emulsion tubes and venturis that can be tweaked to get a car to perform. That's the most important part of the installation, setting up the carb to your specific car. Ideally, a tuner would just swap jets and then test the car, arrive at the right setup. Then you are ready to go. At leat until you change something else, such as adding or changing a header, then it's back to the dyno!

Trying to select jets, etc. by trial and error will make you crazy and buying the various sizes of each to do this sort of experimentation will empty your wallet!

A lot of folks have talked down SUs and talked up Webers over the years. Truth is, the SU is a good carb and has a lot of potential, if you want to play around with tuning it. There are larger SUs, too, if that makes sense with your car. Webers are good, too, but use a different approach to metering fuel and air into the engine. There are good books regarding both carb styles and a ton of information available, including recommended Weber configurations for specific engines. You'd do well to track down some of these books and read up before making a final decision.

Cheers!

Alan
 
Hello Webb,
It looks as if we have to agree to disagree, I maintain that even a twin DCOE gives only a marginal increase in top end power only, and unless you have an extensively modified engine then they are a waste of money. Agreed you can pump the throttle on a Weber to give a rich starting mixture (although I imagine it runs rough until it warms up some, unless you also use the choke), the other carburettors have an equally effective choke. You should not have to fill the fuel bowl, if you do the carburettor needs some attention.
A point also is that if you put a new Weber on to replace badly maintained original instruments then I would expect a better performance, in other words, get the originals right rather than replace them.

Alec
 
[ QUOTE ]
Hello Webb,
does your fuel pump click a lot when you switch on the ignition. Often, particularly with HS S.U.'s and I guess with the ZS having the jet assembly sealed by O rings from the float, the fuel leaks away overnight and you have to fill the bowl before it will start. Take care of the seals and you will often find that cure for slow starting.

Alec

[/ QUOTE ]

You're probably right Alan. My Strombergs were in bad shape, and like I said, it could have been attributed to other factors.
 
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