BlownCorona Posted May 12, 2013 Share Posted May 12, 2013 So im now at the all exciting stage in my bike carb conversion of fabricating the manifold. local OSer PhiberOptik CADed me up some manifold flanges and ill be getting some pipe for the runners this week and making a start on the whole thing. 2 questions though, For the brake booster, how do i go about this, take vacuum from one runner (will this screw up this cylinders running when i brake) or take vacuum from all 4 runners (will this cause issue with running/tuning in general) or am i missing something totally obvious? second question is how much of a difference does the length of the runners make? and what sort of difference? though i may be quite limited to the area the carbs can sit, being a sideflow engine, id still like to make it optimal. lastly, Any other important details i should consider, PLEASE HIT ME WITH THEM. Cheers Quote Link to comment Share on other sites More sharing options...
Ned Posted May 12, 2013 Share Posted May 12, 2013 You can get these chamber things that connect to all the runners and have a brake booster thing and a smaller one for vacuum advance. I haven't actually seen one, but I've been told. Let me know when you find one Quote Link to comment Share on other sites More sharing options...
BlownCorona Posted May 12, 2013 Author Share Posted May 12, 2013 so you mean like a tube across all 4 runners with the 2 fittings for booster and advance (advance was the other thing i meant to ask about but i presume its gonna be the same solution as booster Quote Link to comment Share on other sites More sharing options...
durty Posted May 12, 2013 Share Posted May 12, 2013 Didn't mikuni build something like that for the chevette and it worked like balls? Quote Link to comment Share on other sites More sharing options...
Ned Posted May 12, 2013 Share Posted May 12, 2013 Pretty much. Not completely sure though as I haven't seen one, was just told about them and my googling came up with nothing.... Vacuum from 1 runner will probably not be quite enough (or so I've been told) and you could run it off 2 of them. Just don't pick 2 that fire in sequence, pick the 2 opposite ones so the vacuum is a bit more even. I disconnected vacuum on the brake and distributor when I ran my bike carbs, but that brake pedal felt mighty tough and was worried about how well in would be able to stop in an emergency. Worked OK for normal driving once you got used to it though Quote Link to comment Share on other sites More sharing options...
dirty_leppa Posted May 12, 2013 Share Posted May 12, 2013 for the vacuum side of things, you can use a vacuum manifold. basically each runner has a hose go to a sealed box/compartment to supply a decent amount of vacuum. from there you can have your brake booster/ everything else vacuum run of it. if that makes sense heres what i mean Quote Link to comment Share on other sites More sharing options...
Truenotch Posted May 12, 2013 Share Posted May 12, 2013 You can pretty much take the tubes from anywhere behind the throttle plate and jam them into a collector that feeds the booster. There's a limited amount of vacuum with bike carbs or quads too. Quote Link to comment Share on other sites More sharing options...
Benno Posted May 12, 2013 Share Posted May 12, 2013 Would using a similar setup to that above with non return valves work? That way each runner would contribute to the overall vacuum, would would not induce vacuum in other runners? I've never done anything with bike carbs so no idea if it would work or not, I'm just thinking in basic fluids concepts. Alternatively, you could perhaps replace your alternator with one from a diesel with a vacuum pump and connect the brake booster to that? The vacuum of a single runner might then be enough for the vacuum advance. Quote Link to comment Share on other sites More sharing options...
Valiant Posted May 12, 2013 Share Posted May 12, 2013 I don't think you need to worry. I ran my Escort booster with sidedraughts and one vaccum line off one runner for years. I had to make a restrictor for the PCV valve to stop jumping about at idle. If you do have problems make up a vacuum canister for the booster. Quote Link to comment Share on other sites More sharing options...
BlownCorona Posted May 12, 2013 Author Share Posted May 12, 2013 damn leppa that vacuum colector is ugy, but i get the idea now. ive just looked at heaps of bike carb manifolds and not seen a trend in design really. if i were to link all the runners, would i get away with hosing them up in the same style that multiple carbs are hosed up for fuel? nice and tidy IE or does the chamber do something important? Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 12, 2013 Share Posted May 12, 2013 pretty sire the chamber acts as an damper and smoothes out the vacuum signal 2 Quote Link to comment Share on other sites More sharing options...
Rookie Posted May 12, 2013 Share Posted May 12, 2013 Those collectors are for getting a good map signal for an ecu and they don't work very well anyway. For bike carbs, don't worry, just hook it up to one runner, you will only get vacuum when the throttle is completely closed anyway, and it shouldn't mess with the running of it. For the same reason don't worry about the vacuum advance on the dizzy, as you will only get advance at idle, hence pretty much pointless. Quote Link to comment Share on other sites More sharing options...
peteretep Posted May 12, 2013 Share Posted May 12, 2013 i get vac advance pulse at idle from my runners, even though all 4 are hooked up Quote Link to comment Share on other sites More sharing options...
Rookie Posted May 12, 2013 Share Posted May 12, 2013 Oh true? haha, fuck that is useless. Get a proper dizzy Pete. Quote Link to comment Share on other sites More sharing options...
peteretep Posted May 12, 2013 Share Posted May 12, 2013 I just hooked it up for motorway speeds, i assume it works as I get relatively good economy on long trips Quote Link to comment Share on other sites More sharing options...
Spencer Posted May 12, 2013 Share Posted May 12, 2013 Yea vacuum advance should still work sweet at highway speeds, not so much if you have a Randy Jackson spec cam, I'm all for running it if you can. You won't have a ported vacuum spot to shut it off at idle on bike carbs but having it all in at idle is acceptable, some factory setups run this way. Quote Link to comment Share on other sites More sharing options...
Rookie Posted May 12, 2013 Share Posted May 12, 2013 I guess it depends on your motor, but in my experience motors with webers/bike carbs etc don't make enough vacuum to make efficient use of it at cruise throttle openings, but yea of course if it works use it. Quote Link to comment Share on other sites More sharing options...
Spencer Posted May 12, 2013 Share Posted May 12, 2013 Yea it is very motor/setup specific, some still pull heaps of vacuum at cruise Quote Link to comment Share on other sites More sharing options...
BlownCorona Posted May 13, 2013 Author Share Posted May 13, 2013 so I take it that I should set vac advance up, and if it works, great, if not, look at other options? Quote Link to comment Share on other sites More sharing options...
Rookie Posted May 13, 2013 Share Posted May 13, 2013 Other options being, don't worry about it. Quote Link to comment Share on other sites More sharing options...
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