VMAX Downdraft Carb conversion

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ericheath
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Re: VMAX Downdraft Carb conversion

#16

Post by ericheath »

Both look really cool. Thanks for the info, pics and detail.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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BLIGHT
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Re: VMAX Downdraft Carb conversion

#17

Post by BLIGHT »

Here's a couple of pics of the downdrafts with the velocity stacks... wasn't running all that well with 'em but she looked cool with the stacks!!

Photos taken at my garage at the end of Laguna Seca MotoGP weekend in July this year 2013:

Image

Image

Some larger mains would likely handle the extra air comin' in!!! Mebbe someday....

BLIGHT
'76 GL1000
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Re: VMAX Downdraft Carb conversion

#18

Post by sunnbobb »

Good work!
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Scottinaz
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Re: VMAX Downdraft Carb conversion

#19

Post by Scottinaz »

Cool looking setup. How does it perform compared to stock? Looks a lot like the webers in so many ways. Is there a possibility of some closeups of the linkage mods you had to do. I can see one extender for either choke or throttle, but other than that, not much. Also can you elaborate on the mounting, is it a stock venture or vmax part that you used that fits so well. Also, you mentioned tuning differences between vmx and venture, which set did you start with?
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Re: VMAX Downdraft Carb conversion

#20

Post by BLIGHT »

Scottinaz wrote:Cool looking setup. How does it perform compared to stock? Looks a lot like the webers in so many ways. Is there a possibility of some closeups of the linkage mods you had to do. I can see one extender for either choke or throttle, but other than that, not much. Also can you elaborate on the mounting, is it a stock venture or vmax part that you used that fits so well. Also, you mentioned tuning differences between vmx and venture, which set did you start with?
I don't know how it compares to stock, because I could not get it to run after I rebuilt the OEM carbs. It does run pretty fast though... surprisingly so!
Rideability, easy starts, and rock steady idle are definite bonuses. I had hoped for better than 30-35 mpg but, I guess I need to stop grabbing the throttle so much. I purchased Venture carbs, but I fit the nicer looking V-Max smooth diaphragm covers. Working, complete V-Max carb racks go for about $400 USD on ebay pretty regularly. I'd still buy the rebuild kits anyway. The Venture jets are tiny and the GL did not run well on the stock jets. Might be more 'turnkey' with V-Max carbs and less jetting & needle adjustment.

I don't have any detailed pics of the linkage, bracing, and so forth, as I never intended to publish a 'how-to' guide. I'll remove an air-cleaner tomorrow and take a couple of close-up shots for you. Basically you need to widen the spacing between the carbs where they mount to the engine to around 5" center to center. That means a longer choke rod and an extension 'finger' between the throttle butterfly actuators. Also an adjustable cross tie-rod to synchronize the carb pairs. It's not the best setup, but it works, and I'm just so tired of working on carbs... so it stays for now. You'll see how I did it in the photos.

The carb 'boots' are stock Mikuni rubber flanged adapters. The GL intake ports have the bolts offset a couple of mm, but when you position the Mikuni flanged adapters over the ports, there is enough 'slop' in the screw holes to move the adapter over to line up perfectly with the engine port... then tighten the bolts. Simple ss clamps secure the carbs in the flanged adapters.

So.. if you decide to do it, I can offer a few pointers but you'll need to do the lion's share of the work and figuring things out on your own, OK?
BLIGHT
'76 GL1000
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Scottinaz
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Re: VMAX Downdraft Carb conversion

#21

Post by Scottinaz »

BLIGHT wrote:
Scottinaz wrote:Cool looking setup. How does it perform compared to stock? Looks a lot like the webers in so many ways. Is there a possibility of some closeups of the linkage mods you had to do. I can see one extender for either choke or throttle, but other than that, not much. Also can you elaborate on the mounting, is it a stock venture or vmax part that you used that fits so well. Also, you mentioned tuning differences between vmx and venture, which set did you start with?
I don't know how it compares to stock, because I could not get it to run after I rebuilt the OEM carbs. It does run pretty fast though... surprisingly so!
Rideability, easy starts, and rock steady idle are definite bonuses. I had hoped for better than 30-35 mpg but, I guess I need to stop grabbing the throttle so much. I purchased Venture carbs, but I fit the nicer looking V-Max smooth diaphragm covers. Working, complete V-Max carb racks go for about $400 USD on ebay pretty regularly. I'd still buy the rebuild kits anyway. The Venture jets are tiny and the GL did not run well on the stock jets. Might be more 'turnkey' with V-Max carbs and less jetting & needle adjustment.

I don't have any detailed pics of the linkage, bracing, and so forth, as I never intended to publish a 'how-to' guide. I'll remove an air-cleaner tomorrow and take a couple of close-up shots for you. Basically you need to widen the spacing between the carbs where they mount to the engine to around 5" center to center. That means a longer choke rod and an extension 'finger' between the throttle butterfly actuators. Also an adjustable cross tie-rod to synchronize the carb pairs. It's not the best setup, but it works, and I'm just so tired of working on carbs... so it stays for now. You'll see how I did it in the photos.

The carb 'boots' are stock Mikuni rubber flanged adapters. The GL intake ports have the bolts offset a couple of mm, but when you position the Mikuni flanged adapters over the ports, there is enough 'slop' in the screw holes to move the adapter over to line up perfectly with the engine port... then tighten the bolts. Simple ss clamps secure the carbs in the flanged adapters.

So.. if you decide to do it, I can offer a few pointers but you'll need to do the lion's share of the work and figuring things out on your own, OK?
BLIGHT

Sounds good, I would enjoy seeing up close and personal how you did the linkages. Not trying to be daft, but the mikuni adapters you used were stock for the venture? I see plenty of them on Ebay that "say" they will work, but would prefer that it be confirmed by someone who did it before. I have done the Weber conversion successfully, but had to sell the setup due to financial concerns. This appears to be another workable setup that would work out cheaper than the Webers, and if the right carbs are sourced, cheaper than stockers.
'76 GL1000
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Re: VMAX Downdraft Carb conversion

#22

Post by BLIGHT »

Scottinaz wrote:
BLIGHT wrote:
Scottinaz wrote:Cool looking setup. How does it perform compared to stock? Looks a lot like the webers in so many ways. Is there a possibility of some closeups of the linkage mods you had to do. I can see one extender for either choke or throttle, but other than that, not much. Also can you elaborate on the mounting, is it a stock venture or vmax part that you used that fits so well. Also, you mentioned tuning differences between vmx and venture, which set did you start with?
I don't know how it compares to stock, because I could not get it to run after I rebuilt the OEM carbs. It does run pretty fast though... surprisingly so!
Rideability, easy starts, and rock steady idle are definite bonuses. I had hoped for better than 30-35 mpg but, I guess I need to stop grabbing the throttle so much. I purchased Venture carbs, but I fit the nicer looking V-Max smooth diaphragm covers. Working, complete V-Max carb racks go for about $400 USD on ebay pretty regularly. I'd still buy the rebuild kits anyway. The Venture jets are tiny and the GL did not run well on the stock jets. Might be more 'turnkey' with V-Max carbs and less jetting & needle adjustment.

I don't have any detailed pics of the linkage, bracing, and so forth, as I never intended to publish a 'how-to' guide. I'll remove an air-cleaner tomorrow and take a couple of close-up shots for you. Basically you need to widen the spacing between the carbs where they mount to the engine to around 5" center to center. That means a longer choke rod and an extension 'finger' between the throttle butterfly actuators. Also an adjustable cross tie-rod to synchronize the carb pairs. It's not the best setup, but it works, and I'm just so tired of working on carbs... so it stays for now. You'll see how I did it in the photos.

The carb 'boots' are stock Mikuni rubber flanged adapters. The GL intake ports have the bolts offset a couple of mm, but when you position the Mikuni flanged adapters over the ports, there is enough 'slop' in the screw holes to move the adapter over to line up perfectly with the engine port... then tighten the bolts. Simple ss clamps secure the carbs in the flanged adapters.

So.. if you decide to do it, I can offer a few pointers but you'll need to do the lion's share of the work and figuring things out on your own, OK?
BLIGHT

Sounds good, I would enjoy seeing up close and personal how you did the linkages. Not trying to be daft, but the mikuni adapters you used were stock for the venture? I see plenty of them on Ebay that "say" they will work, but would prefer that it be confirmed by someone who did it before. I have done the Weber conversion successfully, but had to sell the setup due to financial concerns. This appears to be another workable setup that would work out cheaper than the Webers, and if the right carbs are sourced, cheaper than stockers.

OK... here are some close-up pics:
This one shows a mount tab to hold the carbs square and on the right spacing. Made from 1/8" steel strap and drilled. Also shows the flex-coupler for the choke shaft. I got it to where I can pull the OEM GL choke knob and it lifts all 4 enricheners on the Mikunis... easy starts.
Image

This one shows the clear vent tubes going up under the shelter for still air space (important) Also shows the enrichener shaft and linkage.
Image

Pretty clear shot of the Mikuni rubber flanged adapter (carb boot) Vmax or Venture ones won't work! Also shows the vent tubes.
Image

This one's kinda ugly, but shows what's under the tank tray... electric fuel pump (2 psi MAX!) and some of the throttle cross bar (linkage)
Image

Over on the rider's left there are the two cable connections, one throttle (pull only) and the choke/enrichener cable (OEM GL1000) tight fit with the oval air filter, and an bit easier with pod filters
Image

This shows the carb pair cross brace (aluminum channel) bolted to the carb spacer plate. Another stiffener under the carbs by the spark plugs holds everything 'square' in the other plane. BTW, you will need the shorty NGK spark plug caps... OEM's are way too long and cause interference.
Image

Here's how I did the connection-extension of the throttle actuator and snyc-screws. Needs to be done on both pairs to widen carb spacing out to ~5" O.C., the little offset tabs are ~1" long, I made it out of steel strip so there is no flex. A lot of tedious cutting, grinding, bending, drilling and screwing it into place. PITA!!! If you get it right after a lot of trial and mostly error, it's pretty easy to sync carbs first as a pair on the left side, then do the right side, then adjust the crossbar linkage to sync the pairs. Sounds hard, but it isn't really if you know much about engines and individual carbs.
Image

Another shot from a different angle showing the synchronizer tab 'extensions' and how they relate to the spring-loaded screws that come on these carb racks. Also shows the short spark plug caps needed for this conversion. Easily found on ebay.
Image

Well... that's it! You're on your own now if you decide to do this... I kinda liked being the only GL1000 on the planet with VMAX/Venture downdraft carbs, so... if you decide to take the plunge and do it to your bike, please don't tell me about it! Good Luck!! ;)
BLIGHT
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Re: VMAX Downdraft Carb conversion

#23

Post by Scottinaz »

Very cool and very informative. thanks again. I guess I shouldn't mention that I was able to pick a set of the Venture 1200 carbs up for $35 bucks then......
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Re: VMAX Downdraft Carb conversion

#24

Post by BLIGHT »

Scottinaz wrote:Very cool and very informative. thanks again. I guess I shouldn't mention that I was able to pick a set of the Venture 1200 carbs up for $35 bucks then......
Don't mention it....
'76 GL1000
67rschev
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Re: VMAX Downdraft Carb conversion

#25

Post by 67rschev »

What an awesome machine you have put together , probably my favorite chopped up GL on this forum . Nice thinking out of the box on the downdraft set up , hope it runs as smooth as it looks .

On a side note , I was wondering where Freddie Spencer's endurance racer wound up , now I know ... those were the days . Just a beautiful 1000R :orange
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Re: VMAX Downdraft Carb conversion

#26

Post by BLIGHT »

67rschev wrote:What an awesome machine you have put together , probably my favorite chopped up GL on this forum . Nice thinking out of the box on the downdraft set up , hope it runs as smooth as it looks .

On a side note , I was wondering where Freddie Spencer's endurance racer wound up , now I know ... those were the days . Just a beautiful 1000R :orange
Thanks, that's a nice compliment!
'76 GL1000
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ericheath
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Re: VMAX Downdraft Carb conversion

#27

Post by ericheath »

Blight, you stil around? How did this conversion work?
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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BLIGHT
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Re: VMAX Downdraft Carb conversion

#28

Post by BLIGHT »

ericheath wrote:Blight, you stil around? How did this conversion work?
I'm alive.... the carb conversion works great. Better than my Mikuni flat-slide attempt!
My clutch has weird issues of grabbing and making odd sounds on engagement.

I have not ridden it for a while due to this.... I got some new Barnett plates 'cuz someone thought the old ones may be warped.
No time to put 'em in right now, swamped with work 7 days a week. Maybe when things slow a bit!
It's a fun bike to ride, and pretty powerful for it's size. Handles well too, as long as you remember it's lean-angle limitations.
BLIGHT
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Re: VMAX Downdraft Carb conversion

#29

Post by ericheath »

When are you going to connect the two intakes like a VMax?? I always wondered if that would gain anything, but the more I've read, most feel that was a hokey gimmick on a bike that made awesome power either way.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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BLIGHT
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Re: VMAX Downdraft Carb conversion

#30

Post by BLIGHT »

ericheath wrote:When are you going to connect the two intakes like a VMax?? I always wondered if that would gain anything, but the more I've read, most feel that was a hokey gimmick on a bike that made awesome power either way.
Hi, I'm just kinda done tinkering with the old girl... it's fast enough for me with the bike's chassis limitations.

My new love is a 2010 VFR1200..... 170 hp V4 and 95 ft-lbs of torque makes the scenery move verrry quickly!

Image[/url][/img][IMG]

BLIGHT
'76 GL1000
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