Carb Sync with bypassed Vboost

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VS Bullet

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This is a 1988 model that I purchased used a month or so ago, but just now getting arounnd to working on it. The bike has not been maintained, and about everything on it is original except the tires. I suspected that the Vboost had been bypassed or not working on this bike, but didn't think about it messing with my carb sync. It has been running rough, I also suspect a vacuum leake, noticed some cracked boots and the engine is slow to return to idle when revved. But I wanted to try the carb sync first, just for practice and to get my first look at these carbs.

The idle is rough, but the engine runs mostly good at speed.

The 2 carbs on both sides are showing the same pressure, and the sync screws have little affect so obviously the Vboost has been bypassed. How do I sync now. Is it possible to turn the Vboost on to sync, or do I just do the best I can and balance the sides?
 

sdt354

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This is a 1988 model that I purchased used a month or so ago, but just now getting arounnd to working on it. The bike has not been maintained, and about everything on it is original except the tires. I suspected that the Vboost had been bypassed or not working on this bike, but didn't think about it messing with my carb sync. It has been running rough, I also suspect a vacuum leake, noticed some cracked boots and the engine is slow to return to idle when revved. But I wanted to try the carb sync first, just for practice and to get my first look at these carbs.

The idle is rough, but the engine runs mostly good at speed.

The 2 carbs on both sides are showing the same pressure, and the sync screws have little affect so obviously the Vboost has been bypassed. How do I sync now. Is it possible to turn the Vboost on to sync, or do I just do the best I can and balance the sides?
I'd make sure the vboost was CLOSED to sync. or it'll be near impossible. Any intake leak should be fixed before sync, too.If you here the vboost cycle when the key is turned on, kill switch on too, there's a good chance it's in the closed position running at idle. If you here nothing,your vboost could be just unplugged to stay on all the time.Hope this helps get you started.
Steve-o
 

VS Bullet

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The two banks of carbs have different readings, but the 2 carbs on the same bank(both sides) have the same reading, so I am assuming the VBoost is not working. When I turn the power on, all I hear is the fuel pump.
I wasn't sure what is involved with bypassing the VBoost, if parts are removed or whatever. Maybe its just unplugged. So I will start by troubleshooting the VBoost.
 

veebooster

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Could be unplugged or butterflys completley removed. (Some stage 7 installs put in bypass tubes so it's on all the time.) I don't know how they sync them with that set up.

Dale #2592
 

tugla

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well make sure you have the vboost valves in there first off, and or you are sure its the fuel pump you hear clicking when you turn the key? the vboost will make two distinct whining sounds with a third little whine and after turning the key a few times the fuel pump wont make the clicking sound once the bowls are full on the carbs.

so if you dont have vboost and need to sync can get left and right close to each other or can get a weber carb sync, it goes over the top of each carb and can set sync like that.
 

SpecOps13

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Special gauges that go on the top of the carbs to measure actual flow for each carb......:bang head:
 

VS Bullet

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I was able to see the VBoost manifolds and linkages, so hopefully someone just unplugged it. Didn't have time to go further, and forgot to search for a bypass switch. Most of my time was spent on the starter because of the hot start problem, that should be fixed now.
If I can't get the VBoost operational, I'm going to try and operate it mechanically just to get the carbs balanced.

Thanks for the help, I will keep you guys posted.
 

Rusty McNeil

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I removed my servo motor and controller box, but left the butterfly manifolds in place. Left the linkage cable to the butterflys to where I could get to it. Used a "thottle stop" set screw thingie like on lawnmowers etc available at any parts store on that cable to be able to pull the butterflys open and tighten the screw keeping them open. You can then release the set screw and let the butterflys close for synching.

If you have vaccum leaks synching is pointless other than as you say for practice, and it's impossible to synch them with a vacuum guage with the butterflys open which is why I did not install the stage 7 manifolds....there is a flow device that measure air flow on top of the carbs that will do it...never actually seen one tho'.

Good luck and welcome to the forum!
 

tugla

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I removed my servo motor and controller box, but left the butterfly manifolds in place. Left the linkage cable to the butterflys to where I could get to it. Used a "thottle stop" set screw thingie like on lawnmowers etc available at any parts store on that cable to be able to pull the butterflys open and tighten the screw keeping them open. You can then release the set screw and let the butterflys close for synching.

If you have vaccum leaks synching is pointless other than as you say for practice, and it's impossible to synch them with a vacuum guage with the butterflys open which is why I did not install the stage 7 manifolds....there is a flow device that measure air flow on top of the carbs that will do it...never actually seen one tho'.

Good luck and welcome to the forum!
do you still have the servo and or wanting to sell it?

the carb tool that goes on the top to check flow is called Weber, got one works great and super accurate.
 

Rusty McNeil

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do you still have the servo and or wanting to sell it?

the carb tool that goes on the top to check flow is called Weber, got one works great and super accurate.
I gave away the controller, I still have the servo I believe, can check when I get back in town but am 99% sure it's in my parts pile........

Let me check and see what it's generally worth, PM me to remind me if your interested. I won't rape you I promise.
 

VMike

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Tugla or anyone else that uses the Weber...What is the model number of the one you use? I just got my Carb Tune today and went to sync my carbs only to find out V Boost eliminators have been installed and after reading this I guess the Carb Tune won't work.:bang head: Anyway I looked at some different Weber air flow sync meters but the sizes seemed too big for the carb bore.I believe mine are 35mm. Any help would be appreciated.
Mike
 

tugla

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i'll send you info/pic when i get home this evening, just cant remember which of the two webers i got.
 

VS Bullet

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Crap! I finally got around to working on the bike some more, and discovered that the V Boost has been removed from my bike also. Everything on this bike is oem, and I mostly assumed that everything was still on except for the air filters. Now I have discovered that it is been modified with Stage 7 and V Boost removed.

Let me verify this. The two carbs on each side are only connected by a metal tube. There is no linkages or other mechanism between the two carbs just the rubber joints and a metal tube or straight manifold. So the V Boost has been removed?
 

MaxMidnight

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Let me verify this. The two carbs on each side are only connected by a metal tube. There is no linkages or other mechanism between the two carbs just the rubber joints and a metal tube or straight manifold. So the V Boost has been removed?
Your deductions are correct.
 

KJShover

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gamorg02

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the two port ones on ebay are only like $20 too.
 

VMike

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I also have the the V Boost eliminator tubes and just ordered one of the Weber SK air flow meters yesterday.Can't wait to try it out. I had just bought a Morgan Carb Tune only to find out my bike has the eliminator tubes.:bang head:I tried it out just for grins and it seems you probably could balance the left and right banks but not the individual carbs with it. Sold my Morgan the next day to my firend with a ZX 12R and he loves it. I really don't know why anyone would take those butterflies out. Just having them wide open really can't be that restrictive and having them to close for syncing the carbs would be great IMO.
Mike
 

gamorg02

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I also have the the V Boost eliminator tubes and just ordered one of the Weber SK air flow meters yesterday.Can't wait to try it out. I had just bought a Morgan Carb Tune only to find out my bike has the eliminator tubes.:bang head:I tried it out just for grins and it seems you probably could balance the left and right banks but not the individual carbs with it. Sold my Morgan the next day to my firend with a ZX 12R and he loves it. I really don't know why anyone would take those butterflies out. Just having them wide open really can't be that restrictive and having them to close for syncing the carbs would be great IMO.
Mike
i completely agree!
 
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