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TVR 2500M Triple Weber 40 DCOEs

MatthewsTVR

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I have a question for the TVR/Triumph guys out there. I own a 1974 TVR 2500m and it has three weber 40 DCOE carburetors on it. These carbs look great, but the problem is that there is a stumble in the acceleration of the car. I have to take off very slow until the RPMs are higher in range. It is sort of manageable if I toggle the choke while driving...It definatly feels like a lean out situation (not enough gas or too much air). The problem never really goes away though.

I have made sure that all of the jets in the carbs are clean and I recently put a fuel regulator on the car which helped a little.

Has anyone else experienced this problem? I need help with this aggrevating problem, I can't find the solution!

Any help or suggestions would be great!

Thank You in Advance,

Matthew
 

ralph_s

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Can't answer your question, but am envious of the triple webers!!
Two years ago, attended Jonh Twist's MGengineering 3 day seminar and spent some time w/ Carl Heideman @ Eclectic Motor works. They've done several triple carb convesions and I'm sure they can help w/ your problem. I'd recommend you email Eclectic Motor Works. They are really good people.
 

DrEntropy

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They'll ask what comes after the "40 DCOE" first, then you will learn about "progression ports" under the brass caps just outboard of the idle screws.
 

Rocky_LC

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I know this is an old thread, but…..

I just rev up the engine and slip the clutch a little more! It makes for a more exciting drive!
 

DrEntropy

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Since the thread has been risen from the BCF dust, another "stumble" on acceleration may be due to the choke tubes being too large an I.D. Drop those down to the next smaller size and see what happens. Pierce Manifold or Summit should be of help supplying the smaller chokes.
 

Rocky_LC

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I read about that as a possible option…. That might be something that I experiment with. It’s likely that my problem with my minor acceleration stumble is much less serious than the original poster’s was.

My issue is just a minor inconvenience, but I would like to get a little more experience working with these carburetors.

Thanks -

Rocky
 

DrEntropy

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Rocky, if your stumble is from the off, not somewhere after 1,500 ~ 2.5K RPM, check to insure ALL the accelerator jets are squirting properly. With the carbs off the engine, gas in the float bowls, with a full throttle application you should be able to put someone's eyes out at ten feet or so... ;)
 
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Rocky_LC

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Thanks for the advice…. I’m not at my car for a while, but I’ll give it a try when I get home!

I have a Weber manual that will also help with figure these carbs out!

Generally, my car runs pretty good, so I’m a little afraid to touch the carbs! They look pretty complicated!

I have had the whole manifold & carbs off for cleaning…..

F047D519-49C7-46FE-90B9-5A63A54C9BC9.jpeg
 

DrEntropy

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Those are the Spanish version, produced after emissions standards were enacted. Bit more fiddly but the principles are the same.

The cover on the #3 accelerator jet looks a bit crusty! Is its O-ring perhaps leaking?

...and I don't see the choke cable on that carb.
 

Grantura_MKI

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Wow. Those need a good cleaning IMHO. Would move the petrol hose for easier access to the tubes.
may not need the choke, just a pump and hit the key?
 

DrEntropy

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Wow. Those need a good cleaning IMHO. Would move the petrol hose for easier access to the tubes.
may not need the choke, just a pump and hit the key?
Been my experience as well. In all but really cold weather there should be no need for the choke, just pump once and start it up.
 

Rocky_LC

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I agree on the choke comments…. I live in Arizona, and the car starts easily with no choke after just one throttle pump…

Since it’s a TVR Vixen 2500 that had two SUs originally, only the back two (of three) Webers have the choke hooked up, but that has never been a requirement to get the car started..

My picture isn’t the best, and may be before I cleaned up the carbs, but I only cleaned the outside of them…. I’m too scared to take them apart - the car runs well as it is…

Better pictures to follow!

Rocky
 

Tybalt

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Since the thread has been risen from the BCF dust, another "stumble" on acceleration may be due to the choke tubes being too large an I.D. Drop those down to the next smaller size and see what happens. Pierce Manifold or Summit should be of help supplying the smaller chokes.
I'm with the good Dr on this. The later 40 DCOE units (40 DCOE 18 IIRC) fitted to the TR6 conversion kits have a 30mm venturi as opposed to the 28mm venturi fitted to the earlier kits that used the 40 DCOE 2 (IIRC). When I was going through the set up calculations I kept coming up with the primary veturis being 27mm or 28mm depending on exactly what RPM I used for the maximum horsepower point. It was relatively easy to find 28mm venturis, difficult to find 27mm but, hey were made so there are some out there somewhere. Odds are unless you are running the early TR6 US spec camshaft, the 28mm is probably the better choice. The venturi size would be the the first place I would look if those are anything other than the 40 DCOE 2.

TRF used to offer the John Passini book on Webers, I don't know if it is still available from them or not. Brooklands out of the UK did a reissue of the Passini book about a dozen years ago, but again don't know about availability. Plus there is the Haynes Weber book and a Pat Braden book on Webers that go through the various circuits in these carburettors as well as graphs and general calculation information for the various jets as a function of venturi size.
 

DrEntropy

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There was a lot of the "just bolt 'em on and go" with 40 & 45 DCOE so-called "kits" in the past. We've had to go thru some and re-jet from the supposed "right setup" out of the box more than once...
Brooklands out of the UK did a reissue of the Passini book about a dozen years ago, but again don't know about availability.

The Passini book is about the best, IMHO. And there was a "Part 2" as I recall. I can't seem to put my hands on them at the moment though.

The Haynes one would be my last choice.

Rocky: The sizes are in raised numbers on the inside lip of the tube, not difficult to pull out from the front of the carbs while still on the engine if you want to check the size. The venturi and choke tubes are "indexed" in a slot in the carb body, so you can't get them back in the wrong position. It's worth a look! (y)
 
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Rocky_LC

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Thanks for all your suggestions. I had heard about the 30 mm, and 28 mm Chokes (actually Venturi), But hadn’t gotten to the point where I was ready to start messing around with them. It would be definitely good idea to know what exactly is inside my carburetors.

The system was installed by the previous owner. I have a receipt that shows he spent about 40 hours on a dyno tuning it.
 

Tybalt

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The Passini book is about the best, IMHO. And there was a "Part 2" as I recall. I can't seem to put my hands on them at the moment though.
The Passini book from TRF was Part 1 and Part 2 combined into one book. The Passini book I have was purchased from TRF and is effectively the combined reissue of Weber Carburettors 1: Theory and Weber Carburettors 2: Tuning and Maintenance from Motor Racing Publications Limited with a 1992 copyright date. It looks like the Passini books are on Amazon, 1 & 2 in paperback at reasonable prices but the hardcover Passini book that I have was shockingly high with used prices ranging from just shy of $300 to $550. On another used book site I saw one for over $750, yikes!

Amazon also has the Brooklands Weber book in paperback at a much more reasonable price range for both new and used ones. It does not list Passini on the cover but if look at the preview, it is identified as the Passini combined book.

The Pat Braden book looks to be readily available. One I forgot about earlier is the Veloce Publishing SpeedPro series book from Des Hamill on Weber DCOE and Dellorto DHLA. Des Hamill had done a bunch of stuff regarding BMC and Triumph engines as well but I don't think any of the Triumph stuff is readily available anymore.

I concur that the Haynes book is the weakest of the bunch but if that is all you can get your hands on, it's better than having nothing.
 

DrEntropy

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Rocky: Any progress on this?
 

billspohn

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I like Webers when they are set right - do a great job and never go out of tune (if you leave them alone) but getting them perfectly tuned can be a real bear.

I hate seeing TR6s with those horrid downdraft Webers, so at least the OP opted for the right Weber model.

Not sure why I haven't seen more set ups like this (on my MGC, but triple 1 1/2" or 1 3/4" would work well on the TR6 engine).

mgc2.jpg
 
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