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Bike carb conversion- wiring in fuel pump
Eviljohn - 10/8/17 at 06:54 AM

Hi all. Hope you and your rides are well. As subject says, doing bike carb conversion on a 1983, 1043cc polo. Engine is pretty much stock. Had a facet fuel pump and pressure regulator to start with but that was too much for bike carbs. Just overfuelled like crazy. Did some homework, switched to bike fuel pump
Mounted it where i had the facet to start with, worked but not very well. Did some more homework, going to fit it down and further back, next to fuel tank.
Question is: do i run extra wire from the bay to power it or can i tap into say, wiring from the rear washer bottle to power it? Currently have it wired straight to the coil.
Thanks for stopping by and any guidance is much appreciated.

craigdiver - 10/8/17 at 07:05 AM

Car manufacturers are quite good at sizing wiring to suit the circuit (wire for washer bottle will be marginally sized to be able to carry the amps needed taking into account wire resistances / voltage drop etc.). This is done to save weight & money. The fuel pump is relatively hungry for Amps so if it were me I would run seperate wires for it with an inline fuse from the main switched supply circuit. If you use existing wiring at best you will have an unacceptable voltage drop (pump wont run as it should) or you may burn the wiring out.

gremlin1234 - 10/8/17 at 09:14 AM

as cragdiver says, a new wire is best, you may want an explicit earth wire too

craigdiver - 10/8/17 at 09:25 AM

quote:
Originally posted by gremlin1234
as cragdiver says, a new wire is best, you may want an explicit earth wire too


I'll second that, probably not needed but neg earth connections on older cars are a pain in the ass, run a pair of cables to the pump for an easy life!

SJ - 10/8/17 at 10:24 AM

If you check the wiring diagram there may be suitable fused wires going to the back of the car already that aren't being used.

Stu

Eviljohn - 10/8/17 at 10:47 AM

Cool. Thanks guys. I already have a fuse and inertia switch wired before the pump, and earth wire coming from said pump.The fuse wire is quite meaty but the rest of the wire is not so much. I'm really not sure what the value is of the rest of the wire i have so i imagine getting more would be a good shout.
Out of curiosity, if the wire isn't rated to carry the correct load that the pump requires, would that cause the pump to intermitently cut out? Had this issue when first fitted the bike pump. Thought it was either crap pump or blockage.

craigdiver - 10/8/17 at 11:27 AM

quote:
Originally posted by Eviljohn
Cool. Thanks guys. I already have a fuse and inertia switch wired before the pump, and earth wire coming from said pump.The fuse wire is quite meaty but the rest of the wire is not so much. I'm really not sure what the value is of the rest of the wire i have so i imagine getting more would be a good shout.
Out of curiosity, if the wire isn't rated to carry the correct load that the pump requires, would that cause the pump to intermitently cut out? Had this issue when first fitted the bike pump. Thought it was either crap pump or blockage.


Depends whether there are any electronic controls in the pump or just a motor. If the wire was too small the resistance would increase rusulting in a voltage drop. If the drop in voltage due to too small a wire is significantly then yes, it could cause the pump to cut out.

SJ - 10/8/17 at 11:39 AM

Whee you say cut out what do you mean? Bike carb pumps don't run constantly. Once the float bowls fill the pump switches of due to the pressure.

As the bowls empty and pressure drops they cut back in again.

Eviljohn - 10/8/17 at 02:20 PM

Switched from facet and fpr to bike pump. When i first switched, had bike pump mounted on inside wing/suspension tower. Ran smoother than with facet but kept cutting out. Would start pumping again if tapped. Originally thought that was alternator issue or position of pump. Or the fact it was a cheap, generic ebay pump.
I think, and feel free to correct me if you know better, the carbs i have, (cbr400, nc29 apparently,) have two inlets for fuel in, between the pairs of carbs, and a fuel return. I've downloaded the haynes pdf for cbr400 and can't find anything in there to confirm.

David Jenkins - 10/8/17 at 02:56 PM

I have CBR600 carbs, and they have the 2 petrol inlets, one between each pair of carbs. There's no return outlet though - the float valve shuts off the flow, and the fuel pump senses the restricted flow and cuts off. Note that I'm guessing that the CBR400 carbs are similar!

Coming back to the original question - I would run a separate new wire to the pump, with its own fuse (that's what I did, anyway). Makes subsequent fault-finding so much easier, if the pump decides not to work.

Eviljohn - 10/8/17 at 03:14 PM

I have same inlets. Reason for concluding two inlets and fuel return was by blowing into either inlet, (using new, clean hose,) air came out of return line. Will not come out of inlets if you blow into what i think is the fuel return. Assuming some kind of one way valve goin on. Also have an egr inlet too. Would post pics but haven't figured that out yet.
I will get some more cable and use that. Thank you.