Turkey or more turkey ^ ^

There is only so much you can do with a factory EFI system.

They are really hard to beat for running nice and fuel mileage/emissions but if you are building a hot rod then you will not be able to make the changes that really need to be made.

Yes, you can re-flash and/or cheat the fueling tables and maybe even flow the throttle bodies but that will only go so far.

So carbs are the easy way out.

A high performance aftermarket fuel injection system could definitely out perform carbs but the setup is beyond most users. It's a whole different world.
Most people are shocked to see the many pages of settings it take to configure a port fuel injection system from scratch -things you never even thought of when your used to setting up carbs.

Things like-how do you know how much air is trapped in the cylinder on one particular intake event, so you can add the correct amount of fuel.
To know that you need to know the cylinder volume, the air charge temperature and you need to know the pressure in the cylinder at the instant the intake valve closes. To get that you take a pressure measurement for a couple milliseconds near the backside of the valve, at the correct time. To know when to take the measurement you have to know how long it takes the pressure signal to travel to the pickup port in the intake tract and then how long it takes that signal to travel up the hose to the sensor. Once you find the right crankshaft position to take the reading, then it will only be correct for that particular engine speed, so then you have to create a curve so that the pressure is read at the right instant throughout the rpm range.
And how much fuel condenses on the port walls when the throttle is suddenly opened and the pressure rises. You have to add time to the injection period to make up for the temporarily stuck fuel. And then remove injection time when the pressure drops and that fuel goes back into the airstream. Of course the condensation/evaporation rate varies with air and port temperatures and RPM so you need to create a couple more curves.
And the list goes on and on.
And then you make a couple little changes to the engine and your back to modifying a hundred little settings to make it work right again. Jim

The last paragraph is not just an EFI problem. Short of Direct Injection, it will happen with any method of getting fuel into the combustion chambers. Fuel drop out is one of the things that makes doing the set up so tricky - especially without an amount of measuring equipment.

Getting carbs to work decently is taking on more than most owners will be prepared to suffer. If your bike provider supplies you with insufficient space to adjust the air-fuel/ign tables then there are systems out in the after market with lots more adapability, and now sufficient workshops who can get them to work well. Probably for less than Keihin FC's + set up.

My car which naturally is fuel injected, had a new set of tables loaded (quite literally a computer to ECU upload), no parts changed. Claimed is about 25/30% improvement. In reality the max power is irrelevant to me. I don't need any more top speed, but the increased smoothness, much improved midrange and throttle response is. A bonus is the steady state fuel consumption improvement.
None of which is that unusual, but it is on one of VW's supposedly un-modifiable ECU's

Fast Eddie said:

Oh dear!

Bet he wishes he'd just bought a new 1200!

Click to expand...

The 1200s came out just after he went thru the t100 hotrod torture.
We are meeting up soon for a bike swap ride, his idea, could be expensive for him. :mrgreen:

Speaking of rejigging EFI, I had that done yesterday. The bike idled better than my carburetted bikes already, but every now and then it would bump up 50 rpm then back down. Also, some owners reported stalling and difficulty keeping things smooth at very low speeds ( wimps!)
Anyway, the bike seemed perfectly smooth to me but I thought what the hell, a free new better fueling map, go for it.
I have to say it is now ridiculously smooth at low speed, Nigel might even say too smooth. As smooth as the Latte I had while waiting for the new tune to be loaded.
My God that was a Yuppie experience. The scary thing is that I enjoyed it! What is happening to me?

I guess some bright young engineer in England has been pouring over all of the fueling variables Jim detailed above.

Glen

Although EFI is black art to me, some semi-amateurs are marketing their own ECU reflashes that appear quite successful. The factory settings are always compromised due to emission regulations, but they don't appear difficult to defeat. Not only fuel curves but ignition curves also are being fiddled with. The only reason I could see someone going back to carbs are that they are a known quantity. If electronic enhancements are insufficient, EFI throttle bodies can be bored and injectors swapped out making EFI tuning as flexible as carb tuning and more precise as well. Sometimes ya gotta dance with the girl that brung ya.