Weber vs Dellorto

[ronskydivepops]

Just wondering if Weber 40 side drafts, or Dellorto 40 side drafts are the best options for my engine build. I've read so much in the posts and threads that I'm getting dizzy. I'm building my 1.9 GT engine into a 2.0 with the block and head resized accordingly. Just looking for some honest opinions ( without too much detail ) on what some of you think from your own experience!! Thanks Ron

[jordan]

Weber carburetors will have the best tech support and easier jetting options. An upgrade of the weber dcoe 40 is the dcom 40 which has some features that ease in tuning and reliability. eBay Motors: WEBER 40 DCOM SIDE DRAFT CARBURETORS (item 260044257807 end time Dec-20-06 19:33:20 PST)

[GTJIM]

Fuel Injection is probably the 'best' for street motors!
The DOCM Weber is pretty good (it has the same improved accelerator pump as the Dell'Orto) and a vacuum port for the distributor can. Next, the Dell'Orto is good too - followed by the DOCE Weber which is really a 'racing' carb. Not much in it but the DOCM Weber is the most modern design made for street motors.

[baz]

weber's for ease of service bits and posts in side draft carbs forum to ask in the right place

as far as the 2 go i would say they perform much the same , have much the same design but i can go to a tune up shop 5 miles away and they will have every part i would need there and then for a weber but would have to order just about everything for a dellorto which is why i changed to them when i ran a lotus 907 in my gt

[ronskydivepops]

Looks like the opinions lean towards the Weber, as I thought they would. Guess the last opinion I'd ask about would be , whether to use 40 or 45 side draft Webers? Then I'll start my search for the short intake manifolds, Sprint exhaust manifold, and get them ported to match the carbs. Then the fun of putting it all together. ( Soon, I Hope )

[jordan]

For a 2.0l I would definatly not use 45mm carbs. 40's would be your best bet, depending on cam choice and valves they may even need to be choked down some. Also the manifolds should not need to be port matched for 40mm carbs if you get irmschers or the replicas.

[kent]

You might want to read this they seem to think either will work but 45s would be optimal.

[jordan]

I was under the impression that a 1.9 would commonly want 40's choked down to 36mm-38mm and a 2.0 should be happy right at 40mm, a 2.2 could do 45mm and a 2.4 could do 45mm if not even the 48's.

[kent]

Thats what I had thought also, what they are saying is that the optimal body size is 1.25x the choke( this was figured based on displacement and peak rpm) so if your using 36 x 1.25 you get 45? Maybe someone with more experience could weigh in?

[ronskydivepops]

Oh Oh!! More experience = more for me to learn doing this engine build. And to think all I did 30 years ago was put gas in my first GT and beat the hell out of it. Oil leaks and all.. Gotta love it.

[soybean]

Sort of off topic but pertaining to the Webers, don't know if the Dellortos need or use them, but what about the soft mount kit for the carbs. Are they absolutely necessary in our applcations? Thanks, Jarrell

[tekenaar]

Originally Posted by jordan Weber carburetors will have the best tech support and easier jetting options. An upgrade of the weber dcoe 40 is the dcom 40 which has some features that ease in tuning and reliability. eBay Motors: WEBER 40 DCOM SIDE DRAFT CARBURETORS (item 260044257807 end time Dec-20-06 19:33:20 PST)

. . . and in a complete turnaround, adapted (copied) from Dell'Orto.

A bit of sidedraft history perhaps. Weber originates sidedraft dual throat carbs with the DCOE. Dell'Orto improves Weber's bacic design with their DHLAs. Weber adapts Dell'Orto design improvements in their DCOM series. All the others, Solex, Mikuni, etc., are basically copies of the latest series. Now you know all . . .

[RallyBob]

Weber 40 DCOE's that are sized for a stock 1.9 are commonly fitted with 28 mm venturis. For a typical warmed-over street 1.9/2.0 then you can start thinking about 32 mm, maybe 34 mm. If you are looking at going to 36 mm for better high rpm power, then step up to a 45 DCOE so the throttle plate/venturi ratio is better.

But in general the short-stroke 1.9/2.0 engines need the smaller venturis to keep some semblance of velocity in the induction system, otherwise torque and driveability goes to hell in a handbasket.

Bob

[tekenaar]

Originally Posted by soybean Sort of off topic but pertaining to the Webers, don't know if the Dellortos need or use them, but what about the soft mount kit for the carbs. Are they absolutely necessary in our applcations? Thanks, Jarrell

YES!!

[GTJIM]

Getting carried away with carb/venturi size with twins on a street motor is one of the things that makes it less enjoyable. Tune for best torque on a street motor ... not maximum horsepower

30 or 32mm venturii ("chokes") in a 40mm carbs give better mid range and low end drivability than 34 or 36mm ones in 45mm carbs - if you must tune for top end power then use the bigger carbs with the same venturi size. The difference between venturi and throttle plate size is important to produce the best signal response for fuel mixing. A 36mm venturi in a set of 40's gives top end power at expense of low speed smoothness compared to 36mm venturii in 45mm bodies. If you need 38mm venturii then move up to 48mm carb bodies.

The 'soft' mounts isolate the carbs from both heat and vibration. Vibration can 'buzz' the fuel in the bowls so much that it allows air to enter the fuel metering circuits ... and lean out the mix. Hot fuel is less dense and alters fuel mix also. The basic problem is that even with Irmscher "shortie" manifolds overall length is at a premium and the bit of extra length pushes the carbs into the heater box on a GT. There are two types of soft mount generally available - a plastic individual one with 'O'-rings both sides (longer) and a double one made from sheet metal with two "O"-rings moulded on to it (slightly shorter). Fit the soft mounts if you can - the carbs are designed to work with them.

[tekenaar]

Originally Posted by RallyBob Weber 40 DCOE's that are sized for a stock 1.9 are commonly fitted with 28 mm venturis. For a typical warmed-over street 1.9/2.0 then you can start thinking about 32 mm, maybe 34 mm. If you are looking at going to 36 mm for better high rpm power, then step up to a 45 DCOE so the throttle plate/venturi ratio is better. But in general the short-stroke 1.9/2.0 engines need the smaller venturis to keep some semblance of velocity in the induction system, otherwise torque and driveability goes to hell in a handbasket. Bob

. . . of course Bob is talking about twin duals here, EVERYTHING changes for SSD . . .

[tekenaar]

Originally Posted by GTJIM Getting carried away . . . Tune for best torque on a street motor ... 30 or 32mm venturii ("chokes") in a 40mm carbs give better mid range and low end drivability . . . The 'soft' mounts isolate the carbs from both heat and vibration. . . . There are two types of soft mount generally available - a plastic individual one with 'O'-rings both sides (longer) and a double one made from sheet metal with two "O"-rings moulded on to it (slightly shorter). Fit the soft mounts if you can - the carbs are designed to work with them.

. . . and, because the CIH engine uses a non-crossflow head, intake and exhaust on the same side, use the Misab softseal mounts and always fabricate some sort of heat shield hanging off the two lower carb mounting bolts to isolate carb fuel bowls from the exhaust heat! . . . you'd be amazed at how much this little piece of metal reduces heat at the carb bowl!!!

[namba209]

Originally Posted by RallyBob But in general the short-stroke 1.9/2.0 engines need the smaller venturis to keep some semblance of velocity in the induction system, otherwise torque and driveability goes to hell in a handbasket. Bob

Just to amplify what Bob Said, way back,in the mid 60s when I was racing bikes, I had a pair of 36 mm Keihin carbs on my Honda 250cc twin. It wouldn't idle below 2000 RPM and was gutless below 6000 RPM. But when it got there, you'd best be hanging on, and lean well forward, all the way to 14000. I should say it was not a stock motor, ported and highly polished from carb to exhaust, with an experimental Yoshimura cam. 1/4 mile time was 12.38 and top speed was 140 MPH.

[GTJIM]

Been some nice alloy or stainless steel shields on eBay from time to time - bolt to bottoms of carbs and deflect hot air up around the carbs.
Stainless steel may be harder to work with but has a far lower heat transfer rate.

[tekenaar]

Originally Posted by GTJIM Been some nice alloy or stainless steel shields on eBay from time to time - bolt to bottoms of carbs and deflect hot air up around the carbs. Stainless steel may be harder to work with but has a far lower heat transfer rate.

Very nice pic . . .

Carbs shown are DCOEs and those particular heat shields shown will ONLY work on DCOEs, NOT on DCOMs!! Reason? . . . screws used to mount shields to the bottom of carbs as shown are where the DCOM accelerator pump is located . . . one of Dell'Orto DHLA's original DCOE design improvements that Weber later copied from them in turn, BTW.

. . . better just to hang heatshields off lower two carb-to-manifold mounting bolts, IMO.

[ConreroGT]

Those stainless steel heatshields are nicely made. I have a set. The carbs are difficult to get on if you mount the shields BEFORE installing the carb to the manifold but do-able if the carb is already on. Just need a good short, fat screwdriver to clear the old heater platform if you have duals. Real awkward angle to work at.

And I SECOND the MISAB soft gaskets. The other plastic gaskets that have the 2 o-rings on each side are a P.I.T.A!!!!!!!!!!! The rings would sometimes get "slimy" from fuel and pop out like a cheap falsie.

[soybean]

Ok time for stupid question. Where do you get the MISAB soft gaskets? I wrote 5 places trying to find some and explaining what they were going on.

One of the places had the heat shields that Kyle and Jim were talking about in both Stainless and Aluminum. I just can't remember which one. I'll hunt it up tonight and post the link.
Jarrell

[GT Tim]

I tried to find those gaskets as well with no luck.I have 40 Dellorto's for my GT.I have not run them yet though.I am also going to be trying to use a Dbilas box for my carbs for the heat.Thanks Tim

[tekenaar]

Originally Posted by soybean Ok time for stupid question. Where do you get the MISAB soft gaskets? I wrote 5 places trying to find some and explaining what they were going on. One of the places had the heat shields that Kyle and Jim were talking about in both Stainless and Aluminum. I just can't remember which one. I'll hunt it up tonight and post the link. Jarrell Originally Posted by GT Tim I tried to find those gaskets as well with no luck.I have 40 Dellorto's for my GT.I have not run them yet though.I am also going to be trying to use a Dbilas box for my carbs for the heat.Thanks Tim

Have you tried Gabriele (ALFA1750) in Italy?

[GT Tim]

Thanks Otto, I'll shoot him a message.