EFI Kit - Fuel help

[arancara]

Right, I have started creating mounts etc for the EFI kit, its all working etc... but I'm stumped on the fuel line plumbing. The manual does not go into this. I managed to get the seller to send me a digital manual which google doc translated again. No mention of fuel line plumbing.

Basically you have the tank, the tank goes to a filter, then into the injector. The injectors has a return, where does this go?
a) T-connection before/after filter?
b) back into tank (drill new hole and weld a return pipe?
c) whatever you guys suggest ;)

I really am stuck on this as there's no fuel pump either, so I'm guessing its gravity fed like the carb, but looking at some pictures from other build threads I really can't see where the injector return goes too! So please help me out and thanks in advance.

[Lao Jia Hou]

Interesting dilemma in an interesting EFI system.

Off the cuff, I've always assumed that pressurized EFI systems use a fuel regulator and a return line to keep line pressure rather constant (since the fuel pump is usually "always on"), and also to help overcome vapor lock (which is more likely with pressurized fuel). The return line always goes back into the tank, so the heated fuel (causing the vapor lock) is mixed back in with the cooler tank fuel. It seems to me that splicing the return after the filter would actually increase the rate at which vapor lock would occur. Splicing the return before the filter would be a little less, but still resulting in an increased likelihood of vapor lock. I understand that most factory EFI systems purposefully mount the fuel pump inside the fuel tank to keep it cool, and also minimize any effort the pump needs to bring fuel into it.

But your "no fuel pump" EFI system is where I get quite confused. I can't quite understand how fuel can be vaporized/injected at the throttle body using only gravity-feed, unless the system is somehow also using engine vacuum at the throttle body to suck fuel, rather than a high pressure pump pushing the fuel into the injector. Given atmospheric pressure (sea level) of about 14 lbs, and typical EFI pressurization of at least 40 lbs (3 times the amount), gravity feed seems to be woefully inadequate at the injectors. Do you think the system is using vacuum at the injectors? If it is, it logically seems that vapor lock would indeed be a concern - because the throttle body is pulling the fuel on one end, but on the other side of the injector, the fuel is probably sitting at 14 lbs.

You said "it is all working" ... have you actually got the bike running? If so, is it just an occasional dribble coming out of the return line? Or is it a constant drip/stream?

Maybe with a little engine, this is all moot. Trial and error might be necessary - splice before the filter and see if it works, and give the bike a hard run on a warm day. If you get sputtering and stalls, and the bike is difficult to start until it cools (vapor lock), then maybe make the effort and change the return to the tank.

[arancara]

Here's the kit:

http://a.m.taobao.com/dp18473830220....b6977&picNum=1

no pump included I am beyond confused! Here's a useful link in the manual but sadly it's not helping:

http://www.motosd.com/vip/dispbbs.as...&page=1&star=1

and

http://motosd.w1.hongsite.com/vip/di...&page=1&star=1

maybe you can make more sense of it all I can see is T-pieces but bounded where return goes?

[998S]

I have never done any conversion, but have experience with EFI bikes in general.
Lao Jia Hao is correct on layout and the return, as well as the need for a pump.
I can't think how it can work without pressure.

I quickly went through your links, and below picture is basically what you normally have under the tank, holding the pump / filter / hoses assembly on top, and with the connector on the bottom (why it has one connector only is a questionmark to me):

201142419173385470.jpg

Below you see the same assembly for a Ducati 999:

WP_000451.jpg WP_000456.jpg
As you can see, it got 2 connectors, one for pressure, one for return.

You might want to have a look at an other low displacment bike's layout, they might simplify things on those compared to big, multi cylinder bikes.

Good luck,

E.

[Symon260z]

Hi,

I have been involved in EFI conversions on classic cars and on one motorbike project a few years ago, i have also been involved in tuning Jap car fuel system, combined with extra boost can make impressive power gains.T

he basics are the same just more complex on cars and more cylinders and fuel flow is needed. I can't add anything to Lao Jia Hao's comments except it seems that you are missing a few bits that the seller has not included in his kit.

Good Luck !

[arancara]

This advice is very good. I was always under the assumption you had a return and pump so this kit threw me off and the manual isn't very helpful even when translated.

What I'll do is buy a universal pump, any particular specifications as some of the cheaper ones only make 6psi the more expensive ones say 1.2-4bar. I'll well a return into the return as well.

What else is missing apart from a pump, fuel regulator? Never done a kit yet from scratch so this is keeping me interested.

[Symon260z]

As far as I know to convert from Carbs to EFi you need.

Fuel pump, pressure regulator valve, injector + throttle body + suitable air filter, ECU. and if you are looking for decent performance an O2 sensor to be fitted in the exhaust system, close enough to get very hot and far enough down stream so that the exhaust gases are well mixed. Best O2 sensors are the 5 wire types that are preheated.

Piping from tank to fuel pump, then on to pressure regulator valve then the return to the tank. Also from pressure regulator valve to injector. This piping has to be good quality as the pressure is high, so best use metal pipe as much as possible

Wiring for injector, throttle body, ECU and O2 sensor.

Next thought is that you need some battery power to run all of this so I hope that your bike can produce enough current to keep your battery charged.

[998S]

Your minimum required fuel pressure depends on the injector.
And I am not sure if a pressure regulator is used on smaller EFI engines, but they are surely part of big bike systems.
You might want to see if there is anything mentioned on this before you buy a pump.

[arancara]

looks like I have everything except pump and regulator. don't think a regulator is used but only question left is how much pressure the pump needs to produce?

Alternatively I could do the maths of how many L/min I need to produce 15bhp and select a pump adequate for that, does that sound like a reasonable assumption?

There's really not much information and so far I can only find electric pumps for 250-400cc Chinese bikes as everything below seems to be carb.

[998S]

Is there nothing marked on the injector or injector housing?
Perhaps they indicate the required pressure.

If you are going to use a pressure regulator, then the pump should deliver a higher presure.
That pressure is the limited by the pressure regulator.
So your pressure regulator and injector should match.