View Full Version : Converting from Stromberg to Weber Carbs?

08-31-2004, 08:13 AM
How hard is it to convert from Stromberg carbs to Weber carbs on a TR4? My Strombergs just don't perform like I would like them to so I found a Weber conversion kit that includes carbs, intakes, linkage and filters but I'm curious whether this is a difficult job. Is it hard to set and tune the Webers too.

Simon TR4a
08-31-2004, 10:51 AM
Hi TR4!
I don't want to dampen your enthusiasm but this is an expensive change and unless you have a pretty specific goal in mind I wouldn't bother personally.
I am not very familiar with the webers, though I have one on my Spitfire, but I feel you will get little benefit from them compared with a properly tuned set of Strombergs unless your engine has other mods.
The webers require almost no tuning or adjustment once they are properly set up, they are tunable by changing internal parts, jets, chokes, air correction jets etc.
Keep things simple is my advice!

08-31-2004, 02:13 PM
Well, I had the Strombergs completely rebuilt and a very good professional tune them and the car ran fine for 1 day. I spent way too much for that so I don't want to spend more money on the Strombergs only to have them go bad again. I found a Weber conversion kit for a very good price but was hoping someone who made the conversion could tell me how difficult is is to do.

ron wilson
08-31-2004, 02:43 PM
Bot a 59 TR3 one year ago which already had duel Webers and it did not run welll at all. Stalled at stop lites/loped along/ could not get it to quit running rich(fouling plugs etc). fianlly had a local mechanic change the jets and put in hotter plugs and I think the most important thing is he installe a fuel regulator as the stock fuel pump was putting out about 5.5 PSI and a Weber manual I have mentions that they do not perform will at anything over 3.5. Since this was done the car runs fine. Just returned from a 250 Mi trip with no problems. It still is not hotrod and I don't know what difference in performance there is from Stromberg to Weber as I never had the strombergs in the first place. Do not know if the expense is worth it but I have a hunch it is not.

09-03-2004, 09:10 PM
m installing dellorto carbs, just like the webbers, and its been really fun until now, the installation you can do your self, its really simple as long as you have the correct linkage and your carbs are well tunned. the truth is that i have not started my engine, its been an almost 8 yrs project and im only two or one week away from hearing the original engine to my car for the first time in my life. the ironic part is that the car has been in my family for the past 37 yrs now. i cant wait. anyway, the instalation i did myself and i wont take you more then 4 hours as long as you have everything you need, meaning tools and spare parts. let me know how you do. by the way, i invested around $800 ... bought them used on ebay from a guy in italy. how about you?

09-03-2004, 10:51 PM
I found a brand new set of Webers with all the works for $775 which isn't much more than a new set of SU's. The SU's would require new linkage too so that's why I'm considering the conversion. I'll go through those Strombergs one final time to see if I can keep the car original. It's no fun looking at the car in the garage. Nice weather will soon pass.

Super 7
09-03-2004, 11:19 PM
Its not that hard to set them up. Webers are easier because they have more information, but I think the Dellorto is a better carb. I like the accelerator pump better, and the 5 as opposed to 3 progression holes. There is a pretty widely available book on tuning Webers that gives jetting for a number of cars. That gets you right in the ball park. I bought used Dellortos and a manifold and put them on the Cortina. Since it was a 1600, and I was expecting about 125 to 130 hp from the engine with the cam and porting and carb changes, I copied the jet and emulsion tube numbers from a Lotus Elan Sprint, as well as the venturi size which I hoped would get me in the ball park. Once again, it worked great.

The fuel pressure regulator thing is a good call, although none of my 3 cars running webers or Dellortos have them.

Lotus shops have jets for both Weber and Dellorto, if you cant find them, and maybe some ball park set up info that might get you close.

Once they are working good, they do not need to be messed with hardly at all, although I just had to change a float setting for some reason. Anyway, even if you don't get a lot more power they sure look great.

Webb Sledge
09-04-2004, 10:06 PM
I too am considering a swap to twin downdraft webers from my strombergs. Webers do not have to be tuned but ~once a year, and will run well in all different kinds of atmospheric pressures, unlike Strombergs. With 2 downdraft Webers, a header, and ANSA exhaust, another 25 horsepower can be extracted from the TR6 engine, but I don't know about the 4 bangers.

09-07-2004, 10:22 AM
Webers ... will run well in all different kinds of atmospheric pressures, unlike Strombergs.

[/ QUOTE ]


I think you've got that backwards. Fixed jet carbs such as Webbers have to be re-jetted for different altitudes (atmospheric pressures) unlike constant depression carbs such as the Zenith-Stromberg and SU. The CD carbs are really pretty simple and when set-up and maintained well will perform very nicely. /ubbthreads/images/graemlins/driving.gif

09-07-2004, 07:55 PM
/ubbthreads/images/graemlins/iagree.gif Once properly set up, SU's shouldn't need any adjustments for altitude changes. I've run them from near sea level to 11,000 feet without any tweaking at all.

09-07-2004, 08:54 PM
If the Strombergs were professionally rebuilt and only worked for one day,...I'd take them back to the "Professional" and chew him a new butt, and get him to make them right!

09-08-2004, 10:12 PM
There are many options you can go with. Stromberg cabs can be highly effective if built correctly. Check out this set up https://www.goodparts.com/parts_strom.html

The other opton for a TR 4 is SU's.

09-13-2004, 10:55 AM
Well, I made one last attempt to make my Stromberg carbs work. A TR3 buddy found an article that described my problem to a T which pointed to the distributor and not the carbs at all. The bush lead terminal had a problem and the article said the motor will even show signs of fuel starvation if this is not up to snuff along with the points. I changed them both and sure enough, the car runs GREAT. I can now support the statement that 98% of all carburetor problems are "ELECTRICAL" Thanks to all for showing interest.


Mickey Richaud
09-13-2004, 11:00 AM
Don't you love a happy ending?

Thanks, Phil, for following up with us. It's amazing how many times the solution to a problem is found in the least likely places. Info like yours helps all of us track down problems.


09-13-2004, 02:54 PM
Regarding the effectiveness of the Strombergs, remember that Kas Kastner got 186 HP out of his GT6 with stock Stromberg 150s.

Properly rebuilt and maintained, the Stroms are great carbs. Other carbs are better, but the Stroms should suffice for any street driving application. For racing, I'd go with PRI Keihns, Dellortos or Webers, in that order.

I got this info from Kastner's '03 book, BTW.

11-08-2004, 05:15 AM
Did any of you complete the conversion to the twin Webers?
I'm starting mine now and am wondering what to do with all the emission/vacuum lines.

11-08-2004, 06:59 AM
Hi, I've had a set of DCOEs on my TR4 for 20+ years. They are great carbs and replaced the original SU set that were giving me fits. The first concern is that there are a great many different Weber models. The side draft or DCOE are primarily a high performance carb and work best with other modifications, such as an exhaust header, increased compression and various head work to get the motor to breathe better. Side drafts really should be used with a mechanical advance distributor, which means either modifying your original or replacing it with a Mallory or similar.

Certain downdraft models might work better for daily driver usage with minimal engine mods, but you can also just set up a DCOE with modest jetting that doesn't take full advantage of the carb and engine potential.

Even within the DCOE design, there are a number of different models. Originally, DCOE 42s were often used on TR4s and 4As. It was a good size for the car, plus this model was widely available and relatively cheap in the mid to late 60 and early 70s. Now, though, the 42s haven't been made in some years and are getting hard to find parts for. However, if you pick up that Weber tuning book, you may find the 42s are still specified for your car.

Alternatives most often used on TR2 thru TR4A are DCOE 40 or DCOE 45. The smaller 40s need some of the larger available choke tubes installed to work properly most instances. The 45s typically use smaller choke tubes, unless the engine is highly modified. And, even within these two models, there are a lot of variants. For example, my Webers are DCOE 40/18s, which don't use the same ram pipes as many other 40s, seem to have been designed for use without ram pipes.

Using the smaller 40s, with the proper jetting and a mildly modified motor, my car ran great for ten years until engine and suspension wear and tear sent it to storage awaiting a proper rebuild. I'm now restoring the car and will be putting the same Webers back on. Rejetting will be necessary since I moved from high alititude to near sea level, and the motor is getting a few more modifications.

So, since you have the carbs, first I hope they are one of the models recommended for the TR4. The next thing is to pick up the Haynes book on Webers (some editions include SUs and Stroms). It will help you understand how the carbs work and provide a lot of info, such as the basic jets to start out with.

There are a number of little things that are important. The fuel system needs to be regulated to around 3-3.5 psi with most Webers. If you are installing DCOEs, you might want to take a look at www.cruzers.com/~twakeman/TR/WeberDCOEinfo.htm (https://www.cruzers.com/~twakeman/TR/WeberDCOEinfo.htm)

Also, with DCOEs in particular, mounting is important. Special rubber bushings are used to isolate the carbs from vibration. Equally important is to rig a brace to support the heavy carbs and manifolds.

One of the best sources for Weber related parts is www.piercemanifolds.com (https://www.piercemanifolds.com)

In general, setting up will take a little time and can be expensive... everything from ram pipes to air filters to swapping jets to get your car to run just right. And, every car is different, depending upon modifications, altitude, engine condition, etc. But, once a set of Webers is dialed in, you can pretty much rule out carb problems!

Rick O.
11-08-2004, 11:45 AM
The CD carbs are really pretty simple and when set-up and maintained well will perform very nicely. /ubbthreads/images/graemlins/driving.gif

[/ QUOTE ]
Absolutely. The CD design is as simple as it gets. If only they were made with throttle shaft bearings instead of bushings as that is it's weak point. Most folks get upset with their ZS's because of vacuum leaks along the shaft bushings that create idle/acceleration instability issues. When those leaks are gone, the carbs are excellent performers with minimal maintenance.

11-08-2004, 12:06 PM
Hello Alan,
since the S.U. is such a straightforward carburettor and also being constant depression is far better suited for a road car. Weber DCOE are an excellent carburettor for a performance engine but do not give the same flexibility for road use.
They are also expensive to buy, especially just to remedy a fault with the S.U.'s which, as I said, are straightforward to correct, should there be a problem with them. I also do not understand why you suggest a modified or replacement distributor as the original Lucas unit has mechanical advance?


11-09-2004, 12:45 AM
hey newbie, just to let you know that my dellorto 40 DLHA worked perfectly, i had some trouble with the original fuel pump, but i overran it and installed an electric one that supposedly pumps from 5 to 7 pound of pressure and they are now working just fine. they are simple and easy to tune, as long as you have a flow metter and a guide book. the guy that sold them to me is in italy and he also sold me the sealing and jets package for $18.00 each.

ive only ran my car for about 5 miles, cause as you can see on my other topics i had some brake trouble, but so far the carbs have worked fine, they were almost cheap and easy to repair.

let us know what you decide on the carbs and if you ever need help theres many people on this website who is more than willing to help.

paul /ubbthreads/images/graemlins/cool.gif

11-09-2004, 02:13 AM
Too funny...I was reading the thread all the way through, and I was just about to write: "Check your distributor and timing" when TR4 said he found the problem in his distributor.

It's so funny how a rebuilt set of carbs often prove that we have a small distributor issue!

11-09-2004, 05:44 AM
Hi Alec,

Overall, I agree with you. There is nothing wrong with the SUs at all, they are also a good carb. Side draft Webers are more of a performance carb and will cost quite a bit to install properly. To be honest, back when I installed the Webers on my car, I knew virtually nothing about SUs and not a great deal about Webers. In those pre-Internet days, in Colorado, parts and information for either were pretty hard to come by. It took my local supplier a full year just to find a manifold to fit the Webers and get it shipped in from Australia!

Now, I'd be tempted to work with the SUs (still have em, just in case) or maybe swap to H8 or HS8s, just to see what those would do for the car. My car already had some engine modifications done when I bought it, with somewhat of a racing history, and Porsche orange paint 8-( The Weber install, once I got all the parts, was pretty straightforward because nearly all the recommended mods had already been done.

With Weber DCOE you should not use a vacuum advance distributor. The TR dizzy is both vacuum *and* mechanical. One method to keep the original is to eliminate the vacuum, bolt the plates together and set up a mechanical only curve. Another method is to swap out for a mechanical-only dizzy, like the Mallory dual point model. By the way, I did run my car with with Webers and a vacuum advance dizzy for awhile with no major ill effects. It runs better without vacuum advance, though.



11-09-2004, 03:51 PM
Hello Alan,
yes, the vacuum device is designed to allow the car to be set up weaker, so as to aid fuel economy. So if you do a lot of cruising there is some point, but driving a sports car enthusiastically, it becomes redundant.


11-09-2004, 08:50 PM
It seems to me it's a toss up, why didn''t we vote. I go for SU's and Stromberg's. When the rest of the engine is right it takes 20 or so minutes to tune the carbs. Always loved the Strombergs on the 4A's as they could be tuned to work on a not so perfect engine, (got a set and thinking about putting them on the TR6). I have put SU HS6's on a couple of 6's, but a pain to get the float chamers right, but they ran fine. I don't remember which needle I used, been a looooonnnggg time, (30 years). Anybody know which needle to use in the old Stromberg off a 4 to go on the 6??? My guess is to use the ones on the car now and do a little work to get them to fit. There were some shops around that did what we called blueprinting the distributor, is this not done anymore?? Wayne