I have a 4 cyl motorcycle, 4 carbs, each has a stub to connect to a vacuum balancer, three stubs are blanked off and one is connected to the fuel tap which is vacuum opperated. If the stubs were linked and in effect all were connected to the fuel tap would the vacuuum applied at the tap increase? I think not, the vacuum from all 4 carbs will be the same so will be absolute, rather like pressure and volume being independant.
Any thoughts ?
Thanks
|
|
The vacuum would be the same. However if there were any flow of gas (as when the tap diaphragm is pulled down) the flow would be fourfold. Its a bit like connecting four batteries, of identical voltage, in parallel - the voltage (vacuum) stays the same but the current (flow of air) would be four times greater.
|
Don't often disagree with what Aprilia says but the electrical analogy is wrong. 4 batteries in parallel give the same voltage as one, so current stays the same, assuming the resistance they flow through is unchanged - it's just that the amp-hour capacity increases four-fold. Now, four batteries in series give four times the voltage and hence current increases by a factor of four, again assuming the same resistance.
It's true that the vacuum in this case will be unchanged no matter how many stubs are conected though, so like the batteries, the flow induced by the vacuum would be unchanged. However, I can't see what flow is being referred to - presumably this tap actuator relies on vacuum alone, and doesn't have any flow - otherwise it would upset the mixture. So, I can't see why flow would be fourfold - or am I missing something?
JS
|
Don't often disagree with what Aprilia says but the electrical analogy is wrong. 4 batteries in parallel give the same voltage as one so current stays the same assuming the resistance they flow through is unchanged - it's just that the amp-hour capacity increases four-fold.
That is what Aprilia means, that as with the four vacuum stubs the four batteries in parallel will provide the same current (vacuum) though have the ability to generate four times the capacity (flow).
It's true that the vacuum in this case will be unchanged no matter how many stubs are conected though so like the batteries the flow induced by the vacuum would be unchanged. However I can't see what flow is being referred to - presumably this tap actuator relies on vacuum alone and doesn't have any flow
Yes, this is no flow as such, only a few CCs of air will be displaced when the tap is actuated.
The background to this is that I have removed what Kawasaki call the Kleen Air system which injects air into the exhaust ports at idle/low revs (using vacuum from two carbs which are therefore linked) to burn off unburnt fuel on the exhaust to aid emissions, it comprises all sorts of tubes anv valves across the top of the engine and the bike runs more smoothly with out it. Of the other two carbs, one has a cap on the stub and the other has a vacuum feed to the fuel tap. I think I will try linking all four carbs via the stubs (which assists balancing) and connect the link to the fuel tap.
|
Cheedar
Er, no. Trust me, my electrical analogy is correct. Vacuum (ie voltage) is pressure so it remains unchanged. Current is flow.
Sounds like you don't need more than one connection to the vacuum operated valve, and as it takes no flow it's unlikely to affect running. Balance pipes are not uncommon on inlet manifolds and can be useful. If the connections you've removed provided a balance effect between the inlets, then it may be useful to reconect them.
JS
|
|
Come on guys we all know what Aprilia meant, ok perhaps capacity would have been a better term but hey. The point here is that the probable reason for two carbs being link to smooth out the vaguum to stop the exhaust bleed valve from chattering at tick over. Regards Peter
|
If you want an electrical analogy then think of the frequency quadrupling if you used all four cylinders rather than just one.
There's more thank enough 'suck' from one to hold the fuel tap open and there is usually a small bore restricter to smooth out pulses.
|
You will probably see a slight rise in effective vacuum (negative pressure)
What you start off with is like a single cylinder evacuator producing a pressure pulse like a sine wave (well not much like but it is a wave). Adding cylinders gives you more waves and hence longer suck during the cycle. Consider putting single phase AC through a simple diode then three phase through 3 diodes with the outputs connected.
|
|
|
|
The point here is that the probable reason for two carbs being link to smooth out the vaguum to stop the exhaust bleed valve from chattering at tick over. Regards Peter
Yes, however the reeds valves are now isolated though I think there is still a benefit to be had from linking the carb stubs in balance terms.
|
|
|
|
Cheedar Er no. Trust me my electrical analogy is correct. Vacuum (ie voltage) is pressure so it remains unchanged. Current is flow.
But that is what Aprilia said and is surely what I said in my clarification!
Sounds like you don't need more than one connection to the vacuum operated valve and as it takes no flow it's unlikely to affect running.
>>
That is the case.
>>Balance pipes are not uncommon on inlet manifolds and can be useful. If the connections you've removed provided a balance effect between the inlets then it may be useful to reconect them. >>#
The removed conection did not provide a balancing effect for all four carbs however my plan is to use the redundant connections to create such an effect thus the question re the vacuum opperated tap etc.
|
Reading this again, I think John S did make a different point re current being flow.
Anyway, I have linked the stubs on three carbs though currently left the fourth connected to the vacuum tap on its own.
|
Reading this again I think John S did make a different point re current being flow.
I started the electrical analogy to try to make it simpler to visualise. Probably a bad idea because it got taken too far. John S launched off into trying to compare against Ohm's Law in an electrical circuit.
|
|
Agreed Aprilia, the analogy was taken too literally nevertheless is served to illustrate a point.
|
|
|
|
|
![2023 Skoda Kodiaq 2.0 TSI 190 Sport Line 4x4 5dr DSG [7 Seat]](http://images.honestjohn.co.uk/imagecache/url/crop/90x60/https/cdn.uk.prod.group-mobility-trader.com/images/cas/c7f8c343ee529b7868de5b82629c374b/0c72f57f88825115e0fb666b8b727800.jpg)
