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Old 10-27-2008, 05:42 PM   #1 (permalink)
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Scooter Fuel Injection?

I own a venerable '73 Yamaha U7e scooter. It's extremely similar to the Honda Cub/Passport models, and is still in production (2-stroke and all) in Asia. It's a single-cylinder, 78cc. And it's pretty worn. I call it the Twenty-First Century Sex Machine.

I've already switched to a near-smokeless synthetic oil. But I feel I can do more. Inspired by the claimed successes of Orbital Technologies and their co-project with Envirofit, converting Bangkok tuk-tuks to Direct Injection, I've decided I'd like to come up with a conversion for the 21CSM.

I'm slightly ahead of the game, in that the 21CSM has oil injection within the crankcase, so I don't need to worry about how to lube the engine once the fuel is no longer entering with the air.

The general plan.
I want a returnless system. Add-on components will probably include:

1) Engine control module (possibly Microsquirt or similar)
2) Fuel pump
3) Fuel line--probably hydraulic flex-type--and filter.
4) Crank position sensor, possibly a Hall effect type running off a magnet tapped into the crank on the generator end.
5) Throttle body, possibly machined using the original carburation intake as a template, with Mass Air Flow sensor.
6) Throttle position sensor
7)Injector

I'd like to avoid having to add air injection, and I think I can.

Now for some questions:
First, has anyone out here tried this before?

Secondly, could someone advise me: For cleanest burn, the injector will need to fire the fuel into the chamber just as the piston ports are closed, which means it'll be shooting into a pressurized chamber. How do I determine how much pressure I need from the injector to acheive decent distribution of fuel in the chamber?

Thirdly, the fuel will need to be finely atomized upon entry. Without injecting an air charge, does anyone know of a way to do that? I read that the Aprilla system uses injectors with twelve or sixteen holes in. Anyone know what'll work?

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Old 10-27-2008, 05:48 PM   #2 (permalink)
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I can't give you any advice, but I'm interested to see how you do this. I've also got a 50cc honda metropolitan engine for sale if you want it,
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Old 10-28-2008, 12:51 PM   #3 (permalink)
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Probably the easiest way to go would be to copy an existing GDI (Gasoline Direct Injection) setup. For instance, find out what pressures the Audi GDI injectors are run with, and use those--they should atomize the fuel nicely.

It's not the cheapest way to go, I'm sure, but those folks have already solved the problems. Much easier to use what they've done...

-soD
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Old 10-29-2008, 12:54 PM   #4 (permalink)
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@SVOboy:
Thanks for the 50cc offer, but I'm enjoying the challenge of thinking this through. I have looked around, and I think the Baja series of small ATV engines, which are four-cycle engines, would be a great improvement and look like a near-direct mounting fit. So if I give up on the GDi idea, I'll probably go with that.

@some_other_dave:
It's interesting. Theoretically this should be a load simpler. I've only got one cylinder, right? :-)

The problem is that GDi is relatively new in the auto market. In scooters I believe Aprilla's been at it awhile, as have some snow machines. If I could find either a snowmobile wrecker or an Aprilla scooter in my local yard, I might try scavenging some bits.

I'm also concerned about what would happen were I to transfer an injector from a much-bigger-volume cylinder, as I don't have any idea how to figure out the required fuel pressure. The only reference I've encountered said that one's injectors should run roughly 2 bar over cylinder pressure. In my scoot, which compression-tests at 100lbs, that's roughly 130lbs, which seems high.

The injector also has to survive the heat and pressure in the head, and not get clogged up with oil.
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Old 11-21-2008, 01:55 PM   #5 (permalink)
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Further Investigations #1

I've done a bit more research:
Aprilla uses the Orbital injection process, which involves setting up a compressor and air lines. While I doubt it's entirely beyond my capabilities, it's more than I want to tackle right now.

On the outboard motor front, there's the Etec or Eco-tec system by Evinrude. The main disadvantage is that it cools itself with fuel, so you have to have an extra fuel circuit running through the injector.

There's an injector called the Multec 10, manufactured by Delphi, that looks like a good bet. It runs 10-100 bar, which is roughly 2 bar (28 psi or so) more than I think I need, but it's the only in-head application injector I've found that I'm sure scales down that low and doesn't seem to need cooling.

Now I just need to find someone who'll sell me one! I'm still looking into other ideas, and keeping an eye out for wrecking yards with GDi vehicles, but I think the Delphi option is the way to go, thus far.

Hey--wouldn't that make a great summer reading title? "The Delphi Option".

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