GEN III Twin Weber 40 Consumption Manifold Set (Specs)


As put in and examined on RC003

The final word carb conversion for GL1000/GL1100. Twin Weber 40IDFs…the world’s most tunable efficiency carbs!

Particular due to Don Luther. Don has had his twin Weber-equipped GL1000 on the highway for a few years. His bike – “Wang Thang” was the inspiration for this venture. Don offered a lot early steering on this venture. Thanks additionally to “NiteMare” Pete and “Frenchy” for help. Additionally, Greg Foresi offered invaluable help in figuring out the relatively advanced math for optimizing the throttle linkage angles for the contra-rotating throttle shafts. These are primarily a “Scotch Yoke” mechanism that translate a sinusoidal movement to a linear movement.

You have to to supply your individual Weber carbs elsewhere (they’re straightforward to search out) together with all the opposite bits wanted to finish the conversion.



Proven painted with high-temp engine enamel (gaskets and {hardware} not included)


Proven with customer-sourced chrome plating (not included). Because of James Jeffrey – Paris, France for picture.


Proven with customer-sourced semi-gloss black powder coat end (not included). Because of Attila Baraczka – Toronto, Canada for picture.



Air Filter Choices


Particulars on sourcing two totally different air filter meeting choices are offered:


Filter on left can be utilized with out modification… Filter on proper requires slight modification (filter assemblies should not included)


“Rain Hats” enhance climate safety (plans to supply and mount these are offered)


Efficiency Knowledge


Prime gear 60-80 roll-on occasions have been decreased by 0.4 seconds common. This can be a good measure of general energy and tune …a lot safer and gentler than 1/4 mile runs from standing begin. Primarily based on my on-the-road testing and the roll-on numbers, I predicted that I’d discover 5-8 further max horsepower on the deliberate dyno exams. I additionally didn’t discover any low velocity lack of torque even thought the straight consumption runners are relatively quick.



Dyno Outcomes


On October 12-13, 2006 dyno runs have been performed at Ray Value Harley-Davidson in Raleigh, NC. Ray Value has one of many high dyno rooms within the nation. No shock, since Ray Value himself is without doubt one of the greatest Prime Gasoline drag racers within the nation.

Jason Clement and Bruce Downs of Ray Value Harley performed these exams.

Listed here are the dyno outcomes for the Twin Weber set-up:

Max Horsepower: +8.25 horsepower gained! (+13.8%)

Max Torque: +3.04 foot-pounds of torque gained! (+6.2%)

All these outcomes are relative to the very glorious set of inventory GL1000 carbs in razor sharp tune beforehand on the take a look at bike (RC003). The OEM Honda carbs have been primarily inventory. We’d beforehand applied the “off idle” repair and in addition balanced the CV slides to inside 0.1 gram every on the inventory carbs. They have been completely synchronized.

As predicted, there was no lower in torque at any level throughout the rpm vary with the Webers.

Remember the fact that dynos are notoriously variable from one to the following. Absolute values should not very significant…solely comparative runs on the identical dyno will let you know a lot. Honda was shy about publishing horsepower outcomes for the GL1000, however most magazines on the time pegged it at about 80 hp on the crank. Hold it thoughts that on a shaft drive bike, parasitic losses within the drive practice lead to 20-25% lack of horsepower from the crank to the again wheel.

In the event you have a look at the charts, each set-ups present torque curves which might be VERY FLAT and horsepower curve which might be VERY LINEAR. This explains the nice highway manners for a well-tuned GL1000 with excellent-performing OEM carbs. I’m very impressed with the outcomes that the Honda engineers got here up with on this engine / carb mixture!

Air/ Gasoline mixtures for each setups have been very constant and near-optimal throughout all the rpm vary as effectively.

The Weber setup confirmed dramatic enchancment throughout all the rpm vary in each torque and horsepower. Curiously, there’s an particularly important constructive enchancment in torque on the Weber setup from 3,000 – 4,000…the spot have been most cruising is completed. This “candy spot” explains a part of the very satisfying seat-of-the-pants increase you possibly can really feel with this setup.

Evidently, we’re thrilled with these outcomes.


  • That is the final word efficiency carburetion setup for the GL1000/GL1100. The one different paths to extra energy could be the expense, complication, weight and warmth era concerned with superchargers, turbochargers or inside engine modifications.
  • This setup is roughly 7 kilos lighter than the OEM carb setup!
  • Very quick, remoted consumption runner design ensures that every cylinder is tuned the identical.
  • Carb icing won’t be a difficulty!
  • Low gasoline mass to maneuver upon throttle demand for excellent throttle response.
  • Most tuning flexibility. Webers are the final word carb for exact tuning! All jets will be swapped in seconds with out carb elimination or disassembly.
  • Ease of upkeep. These are quite simple and straightforward to keep up carbs. Floats will be adjusted with out carb elimination. Elements are available worldwide. Orifices are a lot bigger on the idle circuits in comparison with the OEM carbs, so there’s much less likelihood of blocked idle circuits.
  • Superior float design for glorious gasoline management.
  • Higher engineered low velocity circuits allow very exact idle regulation and a barely decrease curb idle velocity.
  • Superior development circuit design offers prompt off-idle response.
  • Accelerator pumps present glorious transition beneath exhausting acceleration.
  • No choke mechanism required. Accelerator pumps make glorious chilly begin priming machine.
  • Removing of inventory carbs and airbox frees up appreciable “actual property” beneath the glove field. Hmmm…we expect a nitrous oxide bottle may match there.




  • Not really helpful for many GL1000 / GL1100 homeowners. Most homeowners could be well-advised to retain their OEM carbs to maximise future resale worth. That is very true you probably have a excessive worth collector high quality machine. Most future collectors won’t be overly impressed with this setup. OEM carbs are stellar performers unsurpassed by different carburetion set-ups…aside from this twin Weber configuration.
  • These manifolds are supposed for off-road or competitors use solely. They aren’t authorized for on-road use in lots of jurisdictions. Suitability and compliance to native legal guidelines is your duty.
  • This isn’t a “plug and play equipment.” Solely a pair of manifolds, set up suggestions, materials lists, provider contacts and baseline jetting suggestions included. Although we’ve performed the toughest half for you, you’ll nonetheless want appreciable mechanical means to pick, overhaul, re-jet and set up the carbs that you just supply. You have to to have the ability to fabricate an correct, dependable and secure throttle linkage -without slop! Poor throttle linkage will doom your venture!
  • Baseline jetting suggestions offers you a terrific place to begin, however it’s possible you’ll must refine primarily based upon different variables corresponding to air cleaner and exhaust specifics in addition to altitude. You have to some tuning experience.
  • Baseline jetting suggestions are calibrated for GL1000 fashions. GL1100 jetting needs to be very shut, however you will want to find out your individual calibrations ranging from our baseline solutions.
  • The air consumption roar from this setup is a bit loud! It sounds completely great…paying homage to a Ferrari Dino! Your neighbors will in all probability not agree.
  • This can be a fair-weather setup. It’s not supposed for prolonged use in heavy rain. Not included: particulars on putting in rain hats to enhance climate safety (proven above). Rain hats additionally muffle the consumption roar considerably to extra socially acceptable ranges.
  • Match on later “non-naked” bikes with manufacturing unit fairings has not been verified. Some interference with the fairing could be anticipated.
  • Spark plug upkeep is a ache for those who retain the OEM plug wires/caps. I strongly suggest you improve to aftermarket coils, wires and caps. Use straight plug caps. Accel and Dyna make glorious excessive efficiency coils and wire units for early wings. Be sure to get coils suitable together with your ignition system.
  • Prime shelter covers can’t be pivoted down per regular apply because the carbs placement interferes. Answer: take away the highest shelter cowl decrease pivot pins. Then the highest shelter covers will be secured with simply the big black knobs. The covers will be lifted out vertically for straightforward upkeep. Make sure you safe the highest shelter hinge bushings with RTV adhesive or they are going to be misplaced. They nonetheless should be in place in order that the highest shelter covers are positively situated.
  • These should not fixed velocity (CV) carbs just like the OEM models. CV carbs have ingenious mechanical logic constructed into them that meters air/gasoline combination considerably in response to precise engine load no matter ham-fisted throttle inputs from the rider. These non-CV Weber carbs take a little bit of delicate throttle hand retraining for greatest outcomes. When you get accustomed to the moment throttle response, you’ll prefer it so much.
  • Riders taller than about 6′ 2″ tall could have clearance points with their left knee. I’m 5′ 11″ and haven’t any clearance points.
  • Manifolds have been bead blasted and coated with rust preventative oil after fabrication. Since they’re product of metal, you will want to color, chrome or powder coat them to keep away from corrosion. Minor floor rusting could happen throughout storage and transit.
  • A wholesome clutch is necessary to deal with the facility output.

Recommendation on Deciding on Carburetors


  • Weber 40IDF is the really helpful carb. Mannequin quantity is stamped on the decrease carb flange.
  • Weber 40IDF Mannequin 70 is the popular mannequin. This mannequin is broadly used on VWs and Porsche 356/912s. It ought to have jetting from the manufacturing unit near what you want.
  • Weber 40IDF carbs with adjustable accelerator pumps are strongly really helpful for this software.
  • Bear in mind that earlier proprietor of your carbs in all probability made jetting adjustments, so confirm your precise present jets, and so forth. earlier than ordering further jets or different calibrated components.
  • Weber 36IDFs will work, however these carbs should not broadly out there within the US. 36IDFs are effective as long as the venturis are 28mm. Relying on the mannequin automobile they have been initially destined for, there could also be some non-adjustable idle air bleed jets which aren’t appropriately sized for this software. If yours are improper, they are often soldered shut and redrilled to the proper dimension. Be certain the passages behind the left /proper steadiness adjustment are clear. They’re “sealed” and exhausting to entry on some 36IDFs (in contrast to 40IDFs) Ray Proebstl of Munich, Bavaria, Germany not too long ago went by means of this set up with Weber 36IDFs and he was ready overcome these quirks.
  • Weber 44IDFs or 48IDFs needs to be averted – they won’t be near the calibration you want and can most probably have essential venturis which might be too giant.
  • Confirm that the carbs have 28mm essential venturis earlier than your buy. These will be modified if mandatory, however it’s an pointless trouble and expense. Venturi dimension is stamped and visual on the highest, inside floor of the venturi close to the outlet for the accelerator pump nozzle.
  • Dellorto downdraft carbs are suitable with these manifolds however haven’t been examined. Downdraft Dellorto 36 is mostly equal to Weber IDF40.

I received’t be publishing the jetting specs. That analysis and testing was very time consuming and costly and is a part of the “worth add.” You’d faint for those who noticed the invoice for the primary prototype and creation of all the mandatory tooling to provide these!

Keep in mind: Carbs, linkage, air cleaners, and so forth. should not included.

My value consists of solely the pair of manifolds plus a complete set up information (45+ pages) which incorporates step-by-step directions, dimensional drawings, close-up photographs, materials lists, provider contacts and jetting specs. I additionally embrace a set of Viton O-rings to mount the manifolds to the cylinder heads.

Appreciable talent is required to put in these manifolds appropriately. Since I can’t management this essential variable, there isn’t a guarantee on these. Relaxation assured that they’re of the best high quality supplies and workmanship.

You have to appreciable mechanical means to pick, overhaul, re-jet and set up the carbs that you just supply. You have to to have the ability to fabricate an correct, dependable and secure throttle linkage – with out slop! Poor throttle linkage will doom your venture!

Notice: Within the curiosity of making a little bit of turbulence to assist even gasoline mixtures, the transitions inside these intakes haven’t been overly completed or polished. This intentional “roughness” is useful and shouldn’t be polished out.

Notice: DO NOT BUY THESE MANIFOLDS IF YOU EXPECT PERFECT TRANSITIONS TO THE INTAKE PORTS “OUT OF THE BOX.” Be ready to do your individual “porting” work for those who require excellent transitions.

Notice: The welding on these manifolds will probably be practical, however could not method the creative high quality as proven on the samples above. High quality of the welding is determined by the person talent of the welder chosen by my fabricator for every batch.

Notice: These Weber manifolds should not marketed for GL1200s despite the fact that they bolt up effective. The issue is GL1200 heads have a lot smaller ports, in order that creates a “step” that adversely impacts move. Some clients have overcome this by putting in machined “transition” spacers between these manifolds and the GL1200 cylinder heads. A greater path is to place GL1000 heads (’75-’77 most popular) onto the GL1200 engine. That offers you hotter cams, higher respiration mixed with the bigger displacement engine and leads to a really highly effective mixture. It often means changing to a GL1000-style ignition pushed off the left cam within the standard GL1000 trend.

Dyno Chart

GEN II enhancements embrace OEM-sized O-ring grooves the place the intakes mate to the cylinder heads. A set of Viton consumption o-rings now included with every order.

Notice: The provided Directions (45+ pages) are proprietary mental property and are protected by copyright legal guidelines. The pictures, textual content, baseline jetting specs and different content material might not be copied, reproduced, distributed, saved, or manipulated in any method.

To learn extra opinions on this and different merchandise go to our Evaluation Website,