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awaffa2003 08-10-2012 02:55 PM

Megasquirt :)
So I'm starting to get a list together of all the items I'll need to fuel inject my bike. I have a pair of throttle bodies from an RT an a pair of fuel injectors, I had an O2 sensor bung welded into my header crossover, and all i need now is the Megasquirt parts, board, and case. Now the questions, do I need the sensor that was attached to one of the throttle bodies? I imagine it was a throttle position sensor and if I need it for my application?

Airhead Wrangler 08-10-2012 03:06 PM

I know ZERO about fuel injecting airheads, and relatively little about fuel injection in general, but you'll also need some kind of mass flow sensor in the intake, won't you? (in addition to the TPS)

naginalf 08-10-2012 03:23 PM

Ah. Now here I can be of some help. I was thinking of doing this as well, but thought I'd leave well enough alone, however, it would be nice to have a redundant setup using the carbs as throttle bodies, but there doesn't seem to be enough room for the injector behind the throttle plate. Thought about using this little guy:

DIY autotune is a very good resource btw. I had done most of the research I needed for this mod when planning to fuel inject my old honda, people had very good success with it. But is there anyone who's already done this to these bikes? You might do some research on the megasquirt forums and find all your maps already made :D.

To answer your question, yes that was a throttle position sensor, you'll be needing that trust me (although, you can get away without it, the pressure sensor can cover most if not all instances, the TPS just tells the pooter when you've got it hammered and is a little more precise when throttle is further open). In fact, you can do some super simple but very effective fuel maps with just the throttle position. You actually don't need the o2 sensor once you have your maps made up, but it's good to have some wiggle room for the o2 to adjust. The problem is that unless you go with a lamda sensor, it's not a very accurate affair, it basically bounces around between rich and lean and doesn't do much else. Wrangler is correct tho, you may want some sort of air flow/pressure sensor. Most 'squirters just use an air pressure sensor, usually the barometric correction type, that along with your throttle sensor is more than enough throttle/air input. Oh and you need an intake air temp sensor and it's preferable to have an engine temp sensor. With air cooled motors, you don't want to use an oil temp sensor because it heats up too quickly, usually people find a way to mount a cylinder head temp sensor to the back of the head between fins.

However, for a super simple FI, all you really need is a throttle position sensor, an intake and cylinder temp sensor, and some sort of RPM trigger. The rest is icing for smoothness (air sensors), power (the full gamut of sensors), and economy (o2 sensor).

You're also gonna want to install a trigger wheel somewhere, probably on the timing chain crank sprocket. It's not necessary per se, you can use the stock ignition trigger, but then it is much harder to play around with spark advance and whatnot (actually, I think you are forced to use the stock ignition). Plus you can replace the stock ignition all together, while leaving it in place for a backup.

I wouldn't do a megasquirt tho, it's not sealed. Get a microsquirt, it's all sealed up waterproof, made for bikes, small, and has everything you need built in.

As for the O2 sensor, I was considering adding one simply for tuning the carbs, but I got to thinking about it this morning and was wondering where to put the sensor and wire up the heater, then I realized that there is the perfect bung already installed on the bike where the secondary air system went. I wonder if there's any o2 sensor that will fit there? Plus, then you don't need the heater (2 wire type as opposed to 3/4 wire type).

naginalf 08-10-2012 03:38 PM

Your next biggest problem is going to be installing the fuel pressure system. You CANNOT get away with simply using the petcocks for fuel delivery to the pump. It is a much more complicated system than you think, do some research on how the fuel pump and pressure regulator works, that is key.

Your best bet is to customize your tank to fit an all in one unit like the suzukis use. It has the pump, pressure regulator and filter all in one unit. Or you can install a vent tube for the regulator to vent into. With these bike however, you could use one petcock for fuel delivery and remove the other and install a vent tube in its place. You can't use the fuel cap's vent because you still need that to let air in when it uses gas of course.

Sorry for the long winded replies, I'm just so excited to see someone else considering this. Subscribed!:lurk

ignatz72 08-10-2012 03:40 PM

I was expecting porn links inside...

But I'm just as happy following the FI progress, neat project!

disston 08-10-2012 04:18 PM

Ha Ha Ha...But I do hope it works.

Yes you need a fuel pump. FI usually uses 100 psi or close to it. And a return line too, so the gas tank gets really hot.

The system using a Mass Air Flow (MAF) is usually considered the best but it can be done with out that. I forget what it's called but relies on more computer data and less real time data.

A manifold Air Pressure Sensor and a Barometric Air Pressure Sensor. Sometimes one sensor can do both of these.

What you really need is a kit isn't it? Or can you write the program for this yourself.

Please tell us more.

Airhead Wrangler 08-10-2012 07:25 PM


Originally Posted by disston (Post 19331346)
Yes you need a fuel pump. well as a charging system that can support a fuel pump.

naginalf 08-10-2012 09:43 PM


Originally Posted by Airhead Wrangler (Post 19332679) well as a charging system that can support a fuel pump.

+1 definitely, this was the biggest problem on the old hondas, unlike these bikes the hondas had no aftermarket electrical system upgrade, you had what you had, you could make it beefier but not more output. We were skimping on everything we could, especially lights. Did you know that even only a few incandescent gauge lights take as much as 35W? But the 400W alternator upgrade would be ESSENTIAL for this project without having to skimp on the lights and such. Although you can shave a whole lot of power by going LED on everything you can and using an HID on the headlight (HID uses 35W vs 55 for a halogen).

I love this idea, but I must say, the carbs on these bikes are so simple and easy to work on and get to. My honda was a PITA with 4 in a row literally stuffed behind the motor. Here you're replacing a simple, easy system with a complicated electronic system that takes a lot of custom programming, all for negligible gains. But if it's a project yer dedicated to, go for it. Make sure you're really dedicated because it's a lot of work to get it right and it could really hurt your bike (or yourself) when doing so.

RGregor 08-11-2012 02:02 AM


If you can read german search for "Ohne Vergaser"
User Euklid55 has successfully done the conversion using the ignitech injection module.
Good luck to your project.

Best regards, Rudi

wmax351 08-11-2012 08:21 PM

I'm planning to megasquirt my K75. Much less ambitious undertaking.

In regard to the fuel pump, you could use a low power fuel pump, like one for a scooter or small motorcycle.

You would only need maybe 4 gallons/ hr for an airhead. 100 hp requires about 7 gallons/hr. Pairing this with a fuel reservoir might work.

Prutser 08-12-2012 12:30 AM

Silent Hektik

Its not as much fun as making it your self but its an option.

disston 08-12-2012 05:59 AM

The fuel requirement is not only a matter of the volume or amount of fuel but the pressure feeding the injectors. They need a certain amount of fuel pressure to work. That smaller fuel pump may be suitable but I am puzzled by their omission of data relateingf to fuel pressure. You can have all the volume you want, just use a larger tube.

naginalf 08-12-2012 08:48 AM

DIYautotune has this walbro unit for $100:
But that's just a aftermarket car part replacement, they make fuel pump replacement parts for almost any car but they're made in china by the millions. Here's an MSD Ignition unit for the same price, I'd trust it a little more, at least you'd actually get service on the warranty (diy makes no mention of one, contacting walbro would prolly be a laugh). Plus, as you can see, it's more of a universal fit and mounting affair, with the attachment hardware and barbed ends included.

Beater 08-12-2012 08:55 AM

Very interesting project. 21st century technology attack on stone age technology. I like it.


US_Marshall 08-12-2012 09:12 AM

Your fuel pressure is dependent on the injectors your using. Some of the smaller side port injector (used in TBI) operate on 13 psi. A MAP sensor and IAC valve can be located in the air box with a cross over tube between cylinder.

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