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toplessFC3Sman 10-14-2009 11:43 AM

Project '73 CL350... fuel injection and electronic spark control?
Well, some friends and I picked up what the seller advertised as a '71 CL350, but after a bit of research appears to be a '73 (k5).

Anyhow, this is my first bike, and I'm working on getting back into good shape over the winter, which will involve the usual battery of de-rusting, painting, polishing, new rubber, cables and whatnot.

However, I'm very tired of dealing with the carbs over the past summer (as well as tank gunk), and the broken choke plate on the left cylinder. Instead of getting a new set of carbs and continue to mess with the adjustments... fuel injection may be an interesting project with potential gains in drivability, cold-start behavior and fuel economy... plus I don't think its been done before.

The plan is to go with a MegaSquirt open-source engine controller since not only are they cheap ($200!), but I've used them on project cars and through FSAE before, so i'm familiar with the hardware and software sides.

Then, i'd get some throttle bodies with injectors and fuel rails from a fuel injected bike (i'm thinking a CBR600 F4i since they come in banks of two, can be found very cheaply including injectors and everything), and have an integrated throttle position sensor. I'd need an in-line fuel pump, filter, and to add a return to the tank (probably just as a T in the tube that connects the two sides), but all of this is pretty minor.

On the signaling side, the contacts can be replaced with a toothed wheel and VR sensor or hall-effect sensor pretty easily to track engine position and speed (I have a spare sensor/wheel from my project car), and then use the megasquirt to control spark to the individual cylinders (it does have an odd-fire mode which should work)

The last hurdle would be tuning, but with a narrow-band O2 sensor and just tuning to stoich (or close anyway, to keep temps down), it shouldnt be hard, just a longer process since I dont really want to be riding with the laptop open on the gas tank... disaster much?

In addition, this would allow me to add a tach that actually seems to respond to the engine (the old one seems like its trying to move through peanutbutter...), as well as an idle valve, no need to ever re-jet, and if i wanted to go all-out, launch control, shift lights and some other neat little functions.

$200 for MS, $50 for throttle bodies/injectors etc, $70 for fuel pump, $30 for O2 sensor, $50 for misc. wiring supplies and electronics...tempting...

sjc56 10-14-2009 04:02 PM

Great project. Keep us posted.

SimpleSimon 10-16-2009 10:52 PM

Fantastic! Take a bunch of pics to share with the rest of us gearhead types.

toplessFC3Sman 10-18-2009 12:08 PM

Well, just got a set of 4 throttle bodies, injectors, fuel rail, throttle position sensor and whatnot off of ebay from an '04 CBR600 F4i. The injectors should be fine size-wise, since the cyl size for the CBR is slightly smaller, but it rev's a bit higher.

One of the castings is a little bit broken, but overall they're in great shape, especially for $43 w/shipping.

Project's off to a start!:clap

LoneStrom 10-18-2009 04:44 PM

Great project, I'm all ears. I've got a CB360 I'd like to do the same with.

toplessFC3Sman 10-18-2009 09:37 PM

Does anyone know of a way to increase alternator output on these old hondas? I imagine having to run the fuel pump and injectors (the MS itself is a fairly negligible draw) may begin to overwhelm the stock alternator, especially if the bike's lights are on.

I'd probably convert at least some of the lights to LEDs to save a little bit of power, and possibly hook up an HID projector from a wrecked car's headlight (they're pretty ubiquitous now, even in junkyards) for the headlight, giving not only a much better light pattern, but lower current draw and a new and interesting headlight form factor.

Stagehand 10-19-2009 06:36 AM

have to get the stator re-wound at least to bump output. Consider just a larger amp-hour battery?

LoneStrom 10-19-2009 01:47 PM


Not as cheap as rewinding yourself, but would help to address the daytime/night charging setup on the old regulator.

Mr. Vintage 10-19-2009 02:06 PM

Cool project. Seems to me the stock alternator is good for 55 watts at full tilt, so LED's and a big battery might not be enough. It wouldn't surprise me if you need a real regulator too if you are going to operate anything electronic...

toplessFC3Sman 10-19-2009 05:55 PM

Well, i've already replaced the rectifier with a new, solid-state unit since the old one was bad, and havent had any problems with keeping her charged since then.

Is the upgraded stator in the ricks motorsports kit basically just a re-wound stock stator with more windings?

I dont see anything in the manuals/wiring diagrams that would keep the alternator from charging if the battery voltage dropped below the regulated value. What do you mean by a "real regulator"?

Mr. Vintage 10-19-2009 09:32 PM

I'll look for the link, but one of the bike electronics vendors sells a "proper" regulator, at least one that is more sophisticated than the stock Honda item. I have a voltmeter on my SL and with LED instrument lights and taillight it runs around 15 volts - I think the lack of demand confuses the stock regulator. Depending on battery condition I have had it vary between 8 and 15 volts (the light is really dim at 8, BTW :D ). Just something you might want to investigate...

I really like the idea - I have studied the megasquirt on a few occasions, eyeing the system for my Guzzi. The stock EFI doesn't have a feedback loop (just operates off RPM, throttle, manifold pressure, air and oil temp) and it seems a system with the O2 sensor feedback loop would improve milage and rideability - it can be finicky at times. But that project is down the list a ways...

LoneStrom 10-20-2009 07:50 AM


Originally Posted by toplessFC3Sman
Is the upgraded stator in the ricks motorsports kit basically just a re-wound stock stator with more windings?

Yes I believe so. The regulator should be different but like you I haven't found any wiring diagrams to show how the stock regulator actually works.

Having said that, the OEM regulator design is nearing 40 years old now so it might be worth your time to swap in a new one, especially given the new load the EFI will require. I've heard of the same deal with voltage related charging/discharging issues.

toplessFC3Sman 10-20-2009 07:56 AM

Thanks, I appreciate that! The fuel pump is going to be the biggest draw (smallest practical pump will prob be about 2-3 amps), and with only about 4.5 amps to play with from 55W, thats not going to leave much for lighting or injectors. I dont think a re-wind is going to cut it.

Maybe there's a stator from another bike with more poles/thicker windings that I can fit onto it with some creative machining and a new housing... I may need to pull the permanent magnets off of a newer bike too, and see what I can do to retro-fit them on the CL350. I have access to a machine shop so I can do the machining myself for adapter plates, spacers, and new housings. At the same time, I may as well get the voltage regulator from the same bike, and basically just update the whole charging system.

Does anyone know what size chain the CL 350 uses? the one on the bike right now is in rather poor shape, and I'd like to replace it with one of the low-maintenance o-ringed chains if possible. There's probably only another week or so of weather to enjoy the bike before its time to go into storage and the tear-down can begin.

Stagehand 10-20-2009 08:36 AM

All the parts supplies I can see are calling it (the chain) a RK50KS-102L. Runs about a hundred bucks.

They used it on a bunch of bikes.

Mr. Vintage 10-20-2009 08:53 AM

Found it, here's what I was thinking of:


$225 seems pretty cheap for what it does!

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