Thoughts on EFI to carbs (no, it's not a 'which is better' discussion)

[grumple]

Hey all,

Maybe it's the fumes, but I've had a crazy idea whilst working in my garage recently. I have an EFI bike, and I've pretty much taken all of the parts on it off, so it's basically just a frame and engine, and I got to wondering what would it take to turn an EFI bike into a carb'd bike. Not necessarily saying I want to, or that one is better than the other (trying to avoid all the arguments which go along with that particular discussion), just wondering on what people's thoughts are on this, and if anyone has ever done it. I know there's a few guys who have done the reverse, so even hearing from them would be interesting too.

Just looking at the stripped down bike, it looks like it could be a carb'd bike. The EFI thruxtons even have fake 'carbs' to house the EFI stuff and fuel rails, so I can even see what it would look like. I know I'd have to change the fuel tank (with interal fuel pump) to one with a petcock, add some fuel hoses and carbs of course, and add an igniter somewhere, but the rest is just wiring, right?

Pat

 

[bobjohnson]

Its actually pretty simple. Figure out whether you want to go gravity fed or keep the pump, find some carbs thatll flow the proper amount of fuel and bolt em on. Youll probably either need to find or make a new intake manifold as well, but that shouldnt be too difficult. The wiring for the EFI, you can just throw that away. I know theres a way to work around the timing issue since im pretty sure your bike with the EFI would have the timing controlled partly or fully through the computer, not entire sure since ill be honest, never owned an EFI bike... Probably just need to swap ignition systems but i cant remember off the top of my head if theres a universal way to do it... You can search around for some of the drag car guys, a bunch of them have taken to putting weber carbs on their previously fuel injected cars, theres lots of good write ups. The hardest part for the car guys is getting the intake manifolds, since no one really makes them. The rest is a relative walk in the park as far as i remember.

 

[grumple]

Thanks Bob. I know the Kiehin FCR carbs are pretty popular for the thruxton, so I'll check out if I can get some intake manifolds to fit. I have wiring diagrams for the EFI and carb models, so that'll help with identifying the differences. And thanks for the tip re. the drag car guys, that should help.

So it sounds like it might be possible. I like EFI, but for how I'm wanting to build my bike, I like the simplicity of carbs (by that I just mean less wiring, more, I don't know, raw and authentic-ness, than a computer on a bike). This might be a fun project to think about doing one day.

 

[crazypj]

You may find ECU doesn't like it and will default to a 'limp home' mode (fixed timing, etc)
Probably have lots of flashing lights as well

PJ

 

[boingk]

I'm quite sure you could do it, but not quite sure as to why you would want to. I know carbies might seem more 'authentic', but they aren't anywhere near as efficient at delivering fuel. The beginnings of EFI started with mechanical fuel injection, used to good effect on German BF109 fighters in WWII. Electronic control came later, used in Formula One cars as a way of helping them meet fuel restriction targets (as far as I am aware). It really is a very good system. Perhaps it would be easier to simply buy a bike with carbies?

If you are set on doing it, you could probably just buy a new wiring harness and use that instead. You certainly wouldn't have to worry about sensors pinging the system then.

I'm assuming you have a Thruxton, right? Awesome bikes, wouldn't mind having one myself. Theres some trick aftermarket stuff for them as well, notably some exhaust systems that give a fair bit more power and torque.

Cheers - boingk

 

[Saki]

Hey all,

Maybe it's the fumes, but I've had a crazy idea whilst working in my garage recently. I have an EFI bike, and I've pretty much taken all of the parts on it off, so it's basically just a frame and engine, and I got to wondering what would it take to turn an EFI bike into a carb'd bike. Not necessarily saying I want to, or that one is better than the other (trying to avoid all the arguments which go along with that particular discussion), just wondering on what people's thoughts are on this, and if anyone has ever done it. I know there's a few guys who have done the reverse, so even hearing from them would be interesting too.

Just looking at the stripped down bike, it looks like it could be a carb'd bike. The EFI thruxtons even have fake 'carbs' to house the EFI stuff and fuel rails, so I can even see what it would look like. I know I'd have to change the fuel tank (with interal fuel pump) to one with a petcock, add some fuel hoses and carbs of course, and add an igniter somewhere, but the rest is just wiring, right?

Pat

If I was going from EFI to carbed on a new bike I'd get rid of the stock system all together and go with something like microsquirt to control just the ignition system so you dont have to worry about dealing with the stock computer freaking out at things. Myself I'm planning to convert my bike to fuel injection someday, but for now I have to hold off on such plans.