shin2chin
Part of things
Making curse word cars slightly better
Posts: 820 
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Just a quick question,
I'm just building a manifold for a bike carb conversion.
I know most people take a vacuum feed off each runner for dizzy advance and brake servo but is there any reason why I couldn't take it from the redundant injector holes in the head?
I thought it would be quite a tidy solution?
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1977 PORSCHE 2.0na 924
1974 VW Beetle 1600
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Kieran
Posted a lot
Posts: 1,092
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Brake servo will run fine off only one runner.
The dizzy advance doesn't want to come from the runners. On a normal car carb, it comes from just above the Venturi butterfly. If you pipe it directly from the runners, the amount of advance vacuum will be too high pretty much all the time except full throttle.
Unless you are piping them into a MAP sensor, in which case carry on!
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The Ashby Jackson fleet:-
1979 Mini Clubman 1.8 K series
1978 Skoda 110r Project 130RS K-oupe
1978 Austin Allegro 1500 SDL Estate
1984 BMW K100 Sidecar outfit
1999 Yamaha FZS 1000 Fazer
1991 Kawasaki ZXR400 race bike
2002 Kawasaki ZX9r race bike
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shin2chin
Part of things
Making curse word cars slightly better
Posts: 820
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My plan was to join the 4 pipes into a small vacuum reservoir to stabilize any pulsing and then feed the dizzy and servo from there which I hear will be fine.
I just wanted to know if it would make any difference taking the vacuum from the injector holes rather than tapping the manifold runners.
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1977 PORSCHE 2.0na 924
1974 VW Beetle 1600
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shin2chin
Part of things
Making curse word cars slightly better
Posts: 820
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Jan 11, 2015 15:09:38 GMT
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Any more opinions on this? Yay or nay?
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1977 PORSCHE 2.0na 924
1974 VW Beetle 1600
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Bike carb questionslater
@slater
Club Retro Rides Member 78
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Jan 11, 2015 20:53:42 GMT
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Sorry i wasn't thinking about the dizzy when i replied eariler. It wont work for traditional dizzy vac advance. You need the vac signal from just before the butterflys or else you will get vaccuum when the throttle is closed and you don't want it advanced with throttle shut! Id just ditch the vac advance and save up for megajolt.
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madmog
Club Retro Rides Member
Posts: 1,155
Club RR Member Number: 46
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Bike carb questionmadmog
@madmog
Club Retro Rides Member 46
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Megajolt can be MAP sensor or TPS. I went with MAP but no idea whether TPS would have been better.
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