kj
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| posted on 24/8/09 at 09:54 AM |
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bike carbs + vac advance
I know that if you run bike carbs on say a pinto you have to leave the vac advance disconected or change the dizzy.
I know that some people use a small copper tube with 4 from the carbs into 1 then accross to the dizzy, so would this work as they are cheap, its from
micro bore plumbing £3.00.
Think about it, think about it again and then do it.
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r1_pete
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| posted on 24/8/09 at 10:14 AM |
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This is how I've done it for magajolt, the large tube provides smoothing for the vac pulses.
Not sure you need that for the distributor, so those connectors should work ok.
 
Rescued attachment DSCN0858.JPG
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mookaloid
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| posted on 24/8/09 at 10:23 AM |
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Pretty sure that it doesn't work for vacuum advance.
you need a proper vacuumless dizzy or megajolt, or just run it without the vacuum connected and advance the timing to suit.
"That thing you're thinking - it wont be that."
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whitestu
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| posted on 24/8/09 at 11:00 AM |
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I'd go with a Megajolt - I had no choice as I run a Zetec, but it is an excellent piece of kit. Being able to connect the laptop and adjust
ignition settings accurately on the go is great.
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will121
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| posted on 24/8/09 at 11:42 AM |
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im running zx6 carbs on a 1600cvh using the standard vacume advance dizzy connected with 4 hoses from the manifold with no problems
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mookaloid
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| posted on 24/8/09 at 11:51 AM |
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quote:
Originally posted by will121
im running zx6 carbs on a 1600cvh using the standard vacume advance dizzy connected with 4 hoses from the manifold with no problems
How do you know you have no problems? just connecting it all up will not reveal that the vac advance is not working. if you disconnect it from the vac
advance and plug the pipe does it make any difference? if not then it wasn't doing anything in the first place.
"That thing you're thinking - it wont be that."
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MikeRJ
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| posted on 24/8/09 at 12:22 PM |
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quote:
Originally posted by mookaloid
How do you know you have no problems? just connecting it all up will not reveal that the vac advance is not working. if you disconnect it from the vac
advance and plug the pipe does it make any difference? if not then it wasn't doing anything in the first place.
Why would it not work?
Tapping downstream of the butterfly is going to provide a vacuum signal of sorts, since people have used this for MAP sensing with throttle bodies.
The real question is not IF this works, but how well this works, since the vacuum signal will be different to the original carb setup.
Maintaining some form of engine load sensing for ignition is greatly beneficial for road use. You can't simply advance the timing to compensate
for removing it, since you will also increase advance at high engine loads which vac advance doesn't do.
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mookaloid
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| posted on 24/8/09 at 03:02 PM |
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It won't work because there's nothing to maintain the vacuum between pulses on each of the cylinders.
ie when one cylinder is sucking, it won't pull the vac advance because there is an open to air inlet somewhere else and it's easier for
air to flow in from one of the other inlets than to pull the vac advance forward. in other words as vacuum is created by one cylinder it is lost by
one of the others.
But don't take my word for it, try it with a vacuum gauge and see for yourself.
I'm not saying there won't be any vacuum at all because the 'inertia' of the air will provide a little - enough I believe to
read with a MAP sensor for MS but not enough to activate a vacuum advance properly.
I understand that Bogg brothers don't think it works either perhaps a call to them would clear things up?
Cheers
Mark
"That thing you're thinking - it wont be that."
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jacko
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| posted on 24/8/09 at 03:36 PM |
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Im with Mookiy on this one i had all my vacuum tubes connected together and to the dizzy
Bogg brothers removed them when setting my carbs Mr Bogg set my dizzy to 34% at 3500 rpm till i could get a modified dizzy
Jacko
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britishtrident
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| posted on 24/8/09 at 03:57 PM |
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Vac advance is just a part throttle ecomomy device, to enable the engine to run with a weak mixture.
If your carbs aren't designed to work with it don't use it.
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