Carbs out..Fuel Injection IN

[bugjuice]

don't think paint would, but begs the question; why'd you ask.....??

[flying_zzr250]

hehe
got the tank painted and did a bit of procastinatin in cleanin properly from inside

[Artifice]

some paints will break down in petrol if not properly laquered.
the guy who had my nc b4 me got the tank painted white. then spilt petol all over it at the garage. he hadnt had it clear coated yet and a huge amount of damage done to the paint. that i guess could build up inside your fine jets and stuff.

[Devil]

hehe
got the tank painted and did a bit of procastinatin in cleanin properly from inside

Make sure theres a filter on your fuel tap. The 250's are really prone to choking on shitty fuel. Take the tank off when its just about empty some day, unscrew the fuel tap, there should be little filtery things for the main and reserve pipes.

[TwoSeven]

some aussy enginnering student i think have FI a CBR250rr with alright success but their site, which i lost seem to show them as rather smart cookies

Yes, some of the chaps on the JDM forums did it to a CBR250RR - but its not true injection (as per moddern bike) - more just spraying some fuel into a hole and hoping it works - which is what many of the kits do.


One of the differences between the early (1992+) FI bikes and the later (2000+) FI bikes is that the early machines focused on trying to deliver precise fuel/air at high RPMs. Once the mechanics of that was worked out, they then started to change it at different RPMs (throttle settings).

Now since the mechanical side is pretty much sorted, they are focusing on changing the bore x stroke x compression and other engine parameters to get the same level of performance with less fuel requireing even more precision.

The problem with adapting an old bike is that it hasnt had all of those engine changes made to it so it cant cope with that extra level of precision required.

Stock carbs that came on the bikes are pretty cheap and rubbishy block things with only a few settings. If you adapt individual race carbs and spend time and effort analyzing your average winter and summer settings - you can tune the carbs in pretty close to what a modern FI system can deliver. The only drawback for carbs is that changing the settings is a manual process which can only be done before you ride the machine and invovles dismantling the bike. A modern system adapts itself while you are riding simply by analysing the throttle and surrounding settings (although production versions of this are still pretty cheap and nasty).

Personally I still like carbs on road bikes because I like the feel of it. I've noticed with some FI bikes their attempt at building that feel back in is a bit feeble at best.

[FlyingDutchMan]

I'm planning on FI my bike + build a new ignition unit for it, but that all has to wait until after I've handed in my damn thesis (5 weeks). I recon it'll give much better performance that what it does now.

[Timetogo]

Bike carbs are bloody near as good as FI anyway, you have one per cylinder, just like you do with FI, they have close to tuned inlet lengths etc. Bikes have only really gone to FI to improve emissions and then only in the last few years. Admittedly there is some performance gain but not a lot. Cars went to FI for fuel economy not performance; they typically had one carb for all cylinders and much messier inlets so the performance gain was greater. Sounds like your carbs just need properly sorted, I doubt you'd get much of an improvement with FI and it'd COST.
Whats your thesis on ??

[vifferman]

Stock carbs that came on the bikes are pretty cheap and rubbishy block things with only a few settings.

Depends on the bike.

Personally I still like carbs on road bikes because I like the feel of it. I've noticed with some FI bikes their attempt at building that feel back in is a bit feeble at best.

The good thing about EFI is if it adjusts for variables like changes to airfilter, altitude, different zorsts, etc., or if it can be easily adjusted to do so.
However, as has been mentioned, EFI systems are often used for emissions control, so they are (like engines in general) set up to pass emissions testing, with a big lean spot somewhere. Also, I read that at high revs, the time an injector is open is almost 100% of the time, so there's no advantage to be had of it supplying extra fuel (except, of course, that injectors are pressurised, whereas carb jets rely on suction).

Interesting that the Yamaha M1 is carbed, due to the 'improved feel' available, but has a partially electronically-controlled throttle to control engine braking.

The VFR (injected) has a slightly jerky response off idle, and cuts the injection if you back off the throttle at low revs (dumb emissions compliance!). This is its one real drawback, but I didn't really notice after riding the VTR1000, as the (carbed) VTR was a bit like this too, being a biggish v-twin. If anything, I found the throttle response of the VFR smoother.

[Motu]

The reason FI bikes have such crapy low speed performance is that they don't have idle control like a car.The IAC (idle air control) is a stepper motor controled pintle valve and it works constantly controling fuel mixtures.Drive a car hooked up to a scanner and you will see the duty cycle constantly changing.

[Cliff Jefferies]

You should not confuse idle control with low speed running. They are unrelated.

Idle control is used on cars because of the varying loads on the engine, air conditioning mainly, and for cold running.

There is no reason a FI should perform badly down low except for incorrect setup or bad implementation.

[Motu]

In a perfect world - dream on! The biggest problem with carbs is getting them to run right when things get a wee bit worn,the ideal is out the window and you haven't got a shit show of getting it right.There are FI systems out there without idle control and they are the same as carbs with age...a pandora's box to attempt a tune up on.By the time I see any vehicle it is well beyond it's design life and manufacturers lifetime warranty is over and out.Idle control on a 10 yr old vehicle is an absolute necessity.

[Cliff Jefferies]

The reason FI bikes have such crapy low speed performance is that they don't have idle control like a car.

Perhaps you should have qualified this statement to say 10yo FI bikes with components that have become out of spec.

It is not uncommon for newish FI bikes that have this problem and it is usually for the reasons I mentioned. Once sorted there are no low speed performance issues.