Dual Weber 40 Setup

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THOM
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Re: Dual Weber 40 Setup

#16

Post by THOM »

Hummmm, I actually have 6 dual 40 Webers ( I use to to be an ALFA guy) I hadn't yet considered fitting them to my GL1100. I'll be watching to see how the linkage is made. I've never tried to do any modifications yet.
:idea:
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desertrefugee
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Re: Dual Weber 40 Setup

#17

Post by desertrefugee »

Doing some research, now I'm not so sure the higher RPM issue I'm having is a progression issue. The mains are coming in much lower - like starting at 1500! So, I'm starting to think it's more likely to be accelerator pump related. For sure, I'll need to scientifically sych them. For now, I did the "idle drop" thing with mixture screws and that helped quite a bit. Still...I think a bit more riding is in order to more fully understand and characterize the behavior.

(I'm having fun with this beast).
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Re: Dual Weber 40 Setup

#18

Post by desertrefugee »

Went up a size on the idle jets. Motor really liked it. Idles better, still a little ragged (chain rattle). Sychrometer due Saturday. Getting closer. Still have a bit of a bog in the midrange. Might respond to an even fatter idle jet to feed the progression circuit - or dinking with the accelerator pump...

Still tuning, but very streetable now. Loves the throttle - and I'm not afraid to apply it! Fun setup to play with.

...and one thing I've heard mentioned is certainly true. It draws attention.
Just another tuning assessment run...
Just another tuning assessment run...
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gregforesi
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Re: Dual Weber 40 Setup

#19

Post by gregforesi »

Well it's been a while since I changed anything on the carbs. It's running really well. Here's a couple of thoughts...

Lean-best-idle should be with the adjustment screws between 3/4 and 1 turn off the seats. If you try to make up for wrong jet sizes by increasing the idle with the butterfly adjustor, some of the progression holes will uncover. It'll work at idle, but there will be problems in transition from idle to mains. I'm running 50 idles and they dialed right in.

When backing down from high rpm, if the exhaust is popping, the idle adjustment needs to be richer by maybe 1/8 turn.

If the bike is falling on it's nose as it winds up under full throttle, it's probably the accelerator pump adjustment. More threads showing on the adjuster means more fuel and the squirt will last longer allowing the engine to wind up and get fully on the mains.

I had mine on a dyno, and with 175 air correctors it was running out of fuel at the top end. I'm running 135's and it's much better. Don't be afraid to pour the fuel in, better to start rich and then lean it out.

If you are going to run velocity stacks or something else that doesn't cover the carb top, you need to address junk getting into the holes in the carb top. The idle air holes are small (yellow circles in the picture), but junk can still get in. Some pieces of air filter foam can be cut to fit on the underside of the carb top to at least keep boulders from getting in them.
There are two oval shaped vent holes on either side of the center screw hole that were meant for the idle enrichment system. They can be permanently closed off with JB weld.
The float chamber vent is big and oval and right in the middle between the jet holders. The second photo is my fix for that one. It's a cross-drilled aluminum block with a feature on the bottom that fits into the float vent hole and then it's just JB welded in place. The second photo also kinda shows the direction of the cross-drilling. One hole goes up at a 45 degree angle to make it hard for rocks to climb up. The second hole comes up from the bottom to intersect the angled hole.

And now for the important part...What do you think of the carb sound???
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2006 GL1800 (Brutus Maximus)
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Re: Dual Weber 40 Setup

#20

Post by desertrefugee »

Thank you for weighing in, Greg. (Sorry for the delayed response. I've been asleep at the wheel). I have a large directory of info/resources on this conversion. To be honest, I actually have the majority of your commentary over the years neatly organized by discussion in that directory. It has been very helpful - including the bit about the vulnerable holes on top of the carbs. The naked stacks are not going to be permanent. I'll eventually come up with a method to employ a proper air cleaner.

...and about that sound. It is certainly distinctive. With the stacks, it probably makes nearly as much noise as the exhaust! I like it - it fits my mentality.
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5speed
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Re: Dual Weber 40 Setup

#21

Post by 5speed »

Have you considered something like this for your air filter issue?
https://www.ebay.com/itm/DATSUN-Weber-V ... hF&vxp=mtr
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Re: Dual Weber 40 Setup

#22

Post by sunnbobb »

Really nice pile of stuff you got!
I found the end of the internet

---- Bradshaw Bikes custom polishing for your wing. Visit us on facebook!

1978 Learning Experience
1980 County Road Hauler "Brain Damage"
1978 Cafe Custom Gl1000 "Vyper"
1977 Bulldog Inspired "Vaincre"
1981 Street Fighter GL1100 "No Quarter"
1983 Supercharged Street Drag "Anubis" (in worx)
1983 gl1100 mint restoration "Kristen"
1985 Aspencade..pondering.
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Re: Dual Weber 40 Setup

#23

Post by sunnbobb »

We use panty hose at Bonneville for air filtration..
I found the end of the internet

---- Bradshaw Bikes custom polishing for your wing. Visit us on facebook!

1978 Learning Experience
1980 County Road Hauler "Brain Damage"
1978 Cafe Custom Gl1000 "Vyper"
1977 Bulldog Inspired "Vaincre"
1981 Street Fighter GL1100 "No Quarter"
1983 Supercharged Street Drag "Anubis" (in worx)
1983 gl1100 mint restoration "Kristen"
1985 Aspencade..pondering.
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