jayvoa
Part of things
Posts: 229
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Dec 16, 2012 13:59:17 GMT
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Over the next year I'm planning on fitting bike carbs but I'm not sure what happens with the vacuum advance from the dizzy, and whether having an Accuspark unit fitted makes any difference. Anybody got any advice? I've found a bit of info about having a vac advance with bike carbs, but nothing that mentions if the Accuspark makes any difference. I'm not the most mechanically minded, so any help is appreciated!
Cheers!
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Dec 16, 2012 14:18:41 GMT
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Accuspark makes no difference - it just replaces the points as the switch in the dizzy. The centrifugal and vacuum advance mechanisms still control the timing. Keep the vac unit - it will help fuel consumption and part-throttle torque.  |
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danh73
Part of things
Posts: 15
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Dec 16, 2012 17:37:03 GMT
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i had the exact same question a few months ago. the advice i was given by someone who had been running bike carbs for ages was keep the vac advance. when you have the manifold made up have a boss fitted to one runner to supply vac for the servo then t that line to supply the dizzy with vac. i havent tied this yet myself, but the people i spoke too know there stuff.
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Rusty Hookers Dub Club
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jayvoa
Part of things
Posts: 229
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Dec 16, 2012 18:52:02 GMT
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Nice one, cheers for the advice guys! For some reason I thought that the Accuspark might have made a difference to the vac advance... not sure why.
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Copey
Posted a lot
Posts: 2,845
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Dec 17, 2012 14:15:22 GMT
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yeah, you need to keep the vac advance, but, time up the carbs without the vac hooked up
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1990 Ford Sierra Sapphire GLSi with 2.0 Zetec
1985 Ford Capri 3.0 (was a 2.0 Laser originally)
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jayvoa
Part of things
Posts: 229
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Ah, cheers Copey. I actually forgot you had a bike carb'd pinto before. Just had a quick look at how you did your setup in your Capri Power thread. It's safe to say my shopping list of parts is growing!
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Copey
Posted a lot
Posts: 2,845
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Dec 19, 2012 17:05:27 GMT
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haha, yeah, always need more bits haha, gimme a shout if you need any help buddy
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1990 Ford Sierra Sapphire GLSi with 2.0 Zetec
1985 Ford Capri 3.0 (was a 2.0 Laser originally)
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Dec 20, 2012 15:50:05 GMT
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Isn't it going to be a bit sh1p for even vac if you have no plenum? Or is a plenum planned rather than trumpets or individual filters etc..
IMO if going to all the trouble of these extensive modifications then why not fit mappable ignition? It does not have to be expensive and it unlocks so much power, torque and drivability compared with sh1ppy vac advance
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Dec 20, 2012 16:19:59 GMT
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Plenum will only affect the vacuum if it's after[/]i the throttles - not before, as would be the case with ITBs/bike carbs.
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Dec 20, 2012 18:25:50 GMT
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Really more about the issue was my point. If you have no common chamber which all cylinders draw from then you'll only have VAC when the cylinder you are connected to draws breath.
I suppose if you had a capillary tube connected between the carbs you could take a common vac feed from that.
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RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
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Dec 20, 2012 18:35:54 GMT
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Even if they're joined by a common plenum then the vacuum in the runners post throttle will be identical, it doesn't matter what you do before the throttle plates because it'll always be atmospheric pressure. The vacuum's caused by the throttle plates, so it only exists after them, meaning that on a bike-carb or ITB setup you need to take the vacuum from the manifold runners.
Like you say you can put a capillary between them to even things out, and people sometimes put them through an expansion chamber to help smooth it out even more.
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Last Edit: Dec 20, 2012 18:37:48 GMT by RobinJI
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