Twin Weber 40's

[bullstreetboy]

Guys

 

I thought an update is order after such a long time.

 

I found the problem to a an air leak somewhere on the rear carb. I replaced both mounts with Misabs and ditched the Thackerary washers. Problem solved. It's now running almost perfectly. Just a slight occasional spit back on very light throttle. (mixture too weak?)

 

Anyway for those that my be interested:-

 

40 DCOE's with 30mm choke.

45 Aux chokes

130 mains

F11 emulsion tubes

175 air correction.

 

It pulls really well with a noticeable power band.

 

The Kangaroo effect with the SU's on light throttle is just a distant memory now thankfully.

 

I'm going to try F15 tubes and see it that fixes the spit back.

[Ashley James]

It's important to be aware that you're only guessing unless you use a rolling road, not on with Webers, but with the original carbs to original settings, albeit to a lesser extent. Modern fuels sometime mean a change of needles is needed.

 

For anyone with a reasonable distance of Stroud Glos there is Spamspeed. Spam is a genius and completely unrated by any engine, although he started by tuning A Series. It costs £185 to have an engine properly tuned and to know exactly how much power yours is producing. A friend's E Type arrived there with 90bhp and left with 190! Turned out it had fast road cams, but a diff coil and incorrect needles had hidden them well.

[Dick]

Had a Peerless once with 42 DCOEs.. it went well but fitted 45s to my 2.2l 3a and lost the will to live with them....back to good old SUs.

 

I was once told that SUs were right for any but the extremes of road car and when set up properly...with everything else right ..will deliver well over 130hp......and be economical with it.

 

DCOEs do look good though.

[bullstreetboy]

Guys

 

After many months of trawling the Net and reading many articles I got there in the end:-

 

Car now running fine. I think I have a standard 83mm liner engine.

 

I'm now running to twin 40 DCOE's

 

I could not find any info on the net for 40's but plenty for 42's that are like rocking horse **** so I stared from scratch.

 

Main Jets 120's

Air Correction 170's

Idler jets 55F9's

 

From my experience:-

 

If fitted CLOSE the air bleed screws under the white caps.

 

Run the richest idler jets that will give you 1 - 1/1.5 turns from seated. Anything more and you will have to turn the throttle stop screw too far - and in so doing expose the air bleed's behind the butterflys. More than the suggested screw settings you will go lean when going for idler to main jets and get the dreaded spit back.

 

Adjust the ignition timing(no vac advance) by "sound" and then back it off 4 degrees(half a turn). My pulley does not have any timing marks!

 

It has however been a very interesting learning curve.

 

With a stainless exhaust it sound superb.

 

Anyone after Weber jets give me a call!

[M. Pied Lourd]

Good Timing!

 

I just picked up a set of DCOE 42's last weekend for my 60 TR3A project. I hope to get these installed after I complete my painting in the next few weeks.

 

bullstreetboy, would you be able to post a picture of your throttle linkage/Set up...I think that I have it figured out but I have a couple of more pieces left in the box....

 

Cheers

Tush

[bullstreetboy]

I had an expert look at the car just after I fitted the 40's and his comment was "what a weird linkage"

 

So, it may be weird but it does work so give me couple of days and I'll post.

 

I think I should re-iterate my limited experience:-

 

The idle speed screw does seem to be critical. If the butterflys are too far off closed to get the idles speed that you want, when you go from 800 to about 1500 RPM you will do lean and get spit back when they go too lean. This was my biggest learning issue. If your idler screw are over 1.5/2 turns out from seated go to bigger one - this will bring the tick over speed screw down and so close the air bleeds behind the butterflys. It seems to me that the white capped air bleeds fitted to some DCOE's are for the purist trying to EXACTLY match both throats - Mine are all fully closed.

 

Overall was it worth it - yes I think it was. The learning curve was enthralling for me, but then I have a lot of time to spare.

 

Performance - who knows and I don't really care. It does sound wonderful to me.

Edited July 31, 2015 by bullstreetboy

[vivdownunder]

I have a pair of 40 DCOE's used in 1955 on the major race winning TR2 that put TRs on the map here. All these years later that same TR2 is now the London based 2008 and 2010 Classic LeMans category winner belonging to a forum member.

 

Funny enough info from the era matched data in post 26 including trying F15 tubes if spitting. Also that 40s were prone to minor fuel leaks. Post 29 will help with rolling road tuning when I get around to fitting these Webers to the 3A.

 

Viv

[TriumphV8]

Interesting to read through the post during the years!

Agree that WEBER DCOE always can be made a good add to any engine

because they have so many parts to change to fit to any circumstances.

 

But as so many parts can be changed the problem on the other hand is

that they must be changed correct to let the engine run properly.

 

The fun starts with a proper fitting of manifold and carbs.

As setup is judged as a summary how engine responds and there

are 4 individual runners it is essential that they all do the same.

 

So all jets should be checked as the chokes, too for same size.

Throttle plates and progression holes should be inspected also.

 

Than referring to the fuel level the setup of the bowls to a size of 8.5mm (often)

or 11mm (seldom) can only be a coarse starting point.

Weber made several fuel bowls and the heavier the bowl is the higher the fuel level will be.

Also a lot of different fuel valves are availiable. The bigger the hole (1.5 to 3mm) the

more the fuel can press the valve down and rise the fuel level.

 

The only correct way is to measure the fuel level inside the carbs after sudden cut off from driving.

Unfortunately this essential way got lost through the years but was common and recommended in the 70s.

Screw out the main fuel system and measure from the carb body down to the fuel level with a gauge.

Anything else is nothing perfect and leaves a lot room for mistakes.

If all the setup is done around a wrong fuel level height its all done for the bin!!!!!!

Mismatch in the fuel height between two or more carbs never lets the engine perform perfect.

It takes more fuel than needed and has less performance!

 

Dripping of Webers is horrible and can not be accepted. If they let fuel out there is something wrong.

Besides the fuel level there are parts below the fuel level that have to be tightened. Any fuel loss will

sooner or later create a nice fire and if started it is impressive how quick it finds the fuel in the carbs

and how much is in the fuel piping. Fuel fire is extremly difficult to extinguish and should be avoided.

 

Weber made over 100 different 40 DCOE types. Beware of copying others setups!

In the bodies are the progression holes hidden that changed significantly over the years!

From 2 holes they changed to max. 5! Cars with different holes react different on idle jets.

Spitting at low throttle opening is always a problem of idle jet, progression holes and throttle plates.

Yes, there are also different throttle plates in use that make life more complicated.

The main system with the mentioned emulsion tube F15 is not engaged at that point.

 

One last remark: It is often said that 1.5 turns of mixture screw is an indication that idle jet is correct.

Be aware that also different screws with different tips with other cones are in use.

Also the position of the throttle plate to the progression hole makes things different.

Still I would recommend to rely on the 1.5 turns but if the setuo becomes difficult and progress

is poor it is worth to keep in mind that many carbs need different turns up to 3.5.

 

Ignition must not be changed due to Weber although I would try a modern electronic system

with adjustable part throttle advance to save fuel in the range of 0.5l/100 km

and get crispy response to throttle movement. 123tune is such a system and actually pretty cheap

due to the exchange rate.

 

Setup with a wideband AFR controller makes life much easier!

[Lebro]

Think I'll stick with SU's then

[M. Pied Lourd]

I had an expert look at the car just after I fitted the 40's and his comment was "what a weird linkage"

 

So, it may be weird but it does work so give me couple of days and I'll post.

 

I think I should re-iterate my limited experience:-

 

The idle speed screw does seem to be critical. If the butterflys are too far off closed to get the idles speed that you want, when you go from 800 to about 1500 RPM you will do lean and get spit back when they go too lean. This was my biggest learning issue. If your idler screw are over 1.5/2 turns out from seated go to bigger one - this will bring the tick over speed screw down and so close the air bleeds behind the butterflys. It seems to me that the white capped air bleeds fitted to some DCOE's are for the purist trying to EXACTLY match both throats - Mine are all fully closed.

 

Overall was it worth it - yes I think it was. The learning curve was enthralling for me, but then I have a lot of time to spare.

 

Performance - who knows and I don't really care. It does sound wonderful to me.

Thank You,

That would be great.

 

Cheers

Tush