Newbie question

[allantheboss]

Alright, I feel like a nob asking this, even though I'm new to biking, but I thought I'd be better off asking than not knowing for longer.

What are the differences incurred by a bike being fuel injected rather than not? And what are the differences between a pointy and curvy otherwise? The paper specs seems pretty darn similar.

Don't say "looks" or "pointys are cooler". But you can say "curvys are cooler"!

[merlin427]

A carb' measures the quantity of air passing through it and mixes fuel with it based on sizes of jets which act at different air flows and throttle positions the size of which has been determined for a standard engine setup with standard exhaust/airbox. It also has devices such as an accelerator pump to assist with changing throttle openings the type of carb used on the SV (and most road bikes), a constant velocity, restricts the throttle opeining with a piston/diaphragm which movers as airflow increases to stop the engine 'bogging' if the rider opens the throttle too much. With fuel injection the sensors on the electronic system monitor the contritions and 'turn on' the fuel injector to inject the correct quantity of fuel this. As the fuel is injected much closer to the inlet valves than the carb' allows this improves combustion due to fuel not 'dropping out' of the flowing air onto the inlet tract walls which causes rich or weak running (for short times).

Any changes made to a carb'ed engine need modifications to jets and needles this can be very difficult as modifying a jet to effect one area (part throttle for instance) tends to effect others (such as idle). With FI this can be done by altering the pulses sent to the injector (by plugging in a laptop and possibly using a power commander) and specific areas can be targeted without effecting others.
I prefer FI so my explanation probably favours this system.

[Alpinestarhero]

Ok, fair question, i think you will spark a good debate and discussion about this
So older bikes are more likley to sport carbs - certainly for the SV, they had carbs from 1999 to 2002. Carbs are great because they are easy to understand and work with when they have a problem; its a mechanical object, not electrical so you can pull it apart and twiddle and clean and replace until it works again. Carbs have ben aorund for ages and ages, and therefore can be made to work really really well - it has been noted that carbs generally provide smoother throttle operation than fuel injection. Cheapr fuel injection systems can be snatchy from a closed throttle to just open, but more sophistiacted systems are every bit, if not better, than carbs.

One problem with carbs is the slightly more involved cold-starting, because you need to use the choke. Leaking an engine on choke for too long is bad (the extra petrol washes oil off the bores, causing wear to the engine). A good FI system will sort cold starting out for you itself, hopefully keeping the choke cycle to a minimum to reduce potential wear on the cold start.

One great thing about carbs being mechanical is that if your battery goes completly flat, you can still bump start the motorcycle into life. On an FI bike, if you cant get the fuel rail to prime (indicated by the whirring noise when you flick the ignition to on), then you cant bump start the bike!

Carbs can make an engine a real pig to start in the very cold; the SV has carb heaters, but these need some time to warm the carbs up properly. Until then, you can suffer from a poor running engine, as fuel flow is restricted by the ice forming on the needles / jets (whatever, someone correct me!). FI dosnt have this problem!

I'll let someone else carry on, but hopefully that gives you some food for thought

[allantheboss]

That is pretty darn confusing! But thanks to Merlin!

[Sid Squid]

What are the differences incurred by a bike being fuel injected rather than not? In practical terms not much. FI bikes don't suffer from carb icing, and the choke plungers can't stick - 'cos they're aren't any. Carbed bikes still run ever-so-slightly nicer, but not so much you'd be well advised to choose one over the other.
And what are the differences between a pointy and curvy otherwise?
In practical terms not much. Dimensionally they're pretty much identical, early FI bikes have a slightly higher seat, Curvy rear brake is maybe a bit better than Pointy - but that's only when everything is working properly. Front suspension is as near identical as makes no difference, rear is a different unit but no improvement. Ownership of either is a notably similar experience.

The paper specs seems pretty darn similar. Yes. That's 'cos they are.

If you were minded to buy an SV650, I'd advise to buy the best bike you could find for the money you have, and not fuss over which model that was.

[allantheboss]

At no offence to Merlin, Mr. 'starhero's explanation made much more sense to me! And helps with thoughts I've had about my bike not cold-starting. Is it just a simple case of re-oiling the bores if they've been all washed off? My chokes' been on quite a fair amount when trying to get the bike started. And what are the symptoms of a "poor running engine" because of carb-icing?

[Alpinestarhero]

With carb icing, you'll find the engine wont idle at the correct speed, generally it'll idle very low or just cut out all together. When on the move, you may find the engine dosnt accelerate so easily.

With the whole oil-washed-off-the-bores thing, when the bike is off the choke, then the air-fuel mixture returns to normal, and so the petrol is all burnt off and dosnt "thin out" the oil and hence wash it off :) so its ok, and as long as you correctly use the choke (keep it on for the minimum amount of time and dont have it on full all the time its on) then it really isnt much of a problem at all :)

[allantheboss]

So,
Curvy - Slightly smoother on throttle, and can be started on a dead battery
Pointy - Better at cold starting

[allantheboss]

With carb icing, you'll find the engine wont idle at the correct speed, generally it'll idle very low or just cut out all together. When on the move, you may find the engine dosnt accelerate so easily.

With the whole oil-washed-off-the-bores thing, when the bike is off the choke, then the air-fuel mixture returns to normal, and so the petrol is all burnt off and dosnt "thin out" the oil and hence wash it off :) so its ok, and as long as you correctly use the choke (keep it on for the minimum amount of time and dont have it on full all the time its on) then it really isnt much of a problem at all :)

Cool! That makes me less worried. And my engine has cut out many times as soon as I've gotten the engine going, with the revs just lowering until it cuts out, even when I have the choke on. From what you described, this seems like the effects of icing?
I normally can't start the bike again after this. Know why?

[Alpinestarhero]

You might not be able to start the engine right away because of the ice covering the needles / jets (whatever) and not pulling fuel through. You can use a petrol additive called Silkolene Pro FST to help combat carb icing (150-200ml per tankfull of petrol). I use shell V-power fuel instead of standard unleaded which seems to make cold starting less fraught with carb icing. If you can get some, use isopropanol instead of the silkolene pro fst - Pro FST essentialy is isopropanol, but isopropanol is cheaper (or at least it should be!).

HTH :)

[allantheboss]

Yeah, as soon as these festivities were over, I was going to wait for a dry day and take Optimus (my bike) out to get some Silkolene. You know where I can get some isopropanol? And I live a SV's push away from a Shell station (I have learnt this the hard way); I use V-Power too most of the time

[Alpinestarhero]

Hmm, if your having problems then with carb icing while using v-power, try using silkolene pro fst. You might want to see if you can the the carb balancing checked and amended aswell :)

[fizzwheel]

So,
Curvy - Slightly smoother on throttle, and can be started on a dead battery
Pointy - Better at cold starting

I never had any trouble starting my curvey in the cold....

Now I might have my science wrong, but I was under the impression that carb icing was caused by the venturi effect of cold damp air being accelerated as it passed through the carb jets, which I would imagine means you may not suffer from it when you are trying to start the bike.

I rode in some serous sub zero temperatures on my curvey I only used to get carb icing once I got into the ride. Never when I started it and I'm talking -7 and colder temperatures.

You can always jump start a pointy off of another power source if the battery is to flat to prime the fuel rail, but you'd have to have a seriously flat battery to not be able to do so.

Sid Squid is right, by the best example bike you can find for the budget you have. In real terms there f*ck all difference between them IMHO.

[allantheboss]

I own one already! But thanks. Either way, I have trouble starting in the cold. Ill get some Silkolene. I will probably only have my curvy for another winter, until my restriction comes off, I'm 21, insurance isn't a byatch, and student loans will buy me a new bike!

Fizzwheel, what do you think all the problems people have with cold-starting is then?

[sunshine]

they forget to use the choke is the main problem i think, my curvy starts first time everytime

[MattCollins]

Now I might have my science wrong, but I was under the impression that carb icing was caused by the venturi effect of cold damp air being accelerated as it passed through the carb jets, which I would imagine means you may not suffer from it when you are trying to start the bike.

Sorta... The acceleration of air around any disturbance in a carb lowers pressure causing vapour to condense. Fuel absorbs energy (heat) during phase change which lowers the charge temperature by as much as 20C and causes further condensation (double whammy) and freezing of water vapour.

....

Carb icing is not just a winter phenomenon. It also occurs at temperatures around 20C and high relative humidity.

[fizzwheel]

Fizzwheel, what do you think all the problems people have with cold-starting is then?

I dont think the cold starting issues are as bad as are being made out to be.

As long as you keep your bike well maintained and looked after you should never have any trouble with it, cold starting or otherwise, if you let things slide and dont keep on top of the maintenance then as sure as eggs are eggs at some point something may well go wrong. Of course theres always the unexpected sudden failure that you cant plan or account for.

If you are having cold starting problems its more than likely down to :

1. A battery near the end of its servicable life
2. A charging circuit that isnt charging which means your battery isnt fully charged.
3. A stuck or seized choke plungers.

I dont think its correct to label curvies as "bikes that suffer from cold starting problems" because in my experience its simply not true.

[yorkie_chris]

Now I might have my science wrong, but I was under the impression that carb icing was caused by the venturi effect of cold damp air being accelerated as it passed through the carb jets, which I would imagine means you may not suffer from it when you are trying to start the bike.

I rode in some serous sub zero temperatures on my curvey I only used to get carb icing once I got into the ride. Never when I started it and I'm talking -7 and colder temperatures.

Curvy frame is better bit of kit IMO. They only changed to pointy frame because it is cheap.

Either you buy around same price will have knackered running gear, shock that never worked from new and forks with less damping than a biro.

I prefer carbs, I think EFI is too complicated for good of maintenance. Carbed bikes start fine if they are healthy. And carb ice can be cured with a little isopropanol in the fuel.

[zsv650]

[QUOTE=yorkie_chris;2134322]Curvy frame is better bit of kit IMO. They only changed to pointy frame because it is cheap.

QUOTE]
no doubt but it's also way stiffer and lighter i think so depends :thumleft:

[yorkie_chris]

Lighter? Says who.

Stiffness, what will be stiffer, U shape or round tube?

[zsv650]

twas what suzuki say.

[yorkie_chris]

In advert, sure :smt005

[zsv650]

In advert, sure :smt005
well if you know better than suzuki then good for you :smt056

[yorkie_chris]

No but I remember someone weighing both frames and getting close enough same number. I think it was TWF on svrider but I could be wrong.

As for stiffness, I've never heard of anyone with a rig to test it. Only other bet is putting entire frame dimensions into an FEA package, which I could do but I don't have the computer power or measuring devices for. And it would still be an approximation. Otherwise you might as well rely on people saying something feels stiffer and that's about as reliable as predicting weather next tuesday by spitting on your boot.

I hear some people say 2gen is stiffer when they mean the rear suspension, the linkage is different so maybe 2gen has different progression giving that effect. But I can't see how you'd put numbers on it.

And of course suzuki are 100% guaranteed to go "woohoo new lighter and stiffer frame!" rather than "we saved £50 on new frame!"

[zsv650]

at the end of the day does it really matter you havnt got a pointy so why you worrying about it.

[yorkie_chris]

I'm not worried, guy asked pros and cons of EFI model or carby. For first bike I doubt he would care about couple % difference in stiffness but you did say it is stiffer and lighter.
Only reason it matters to me is if I thought pointy frame was better I would build bike around it instead of curvy frame.

[zsv650]

let's be honest if you were building a bike from scratch there's better frames out there to do it with.

[embee]

The curvey frame is a thing of beauty (apart from the swingy bit)
http://i258.photobucket.com/albums/hh268/Hi-vis/sv650frame.jpg

The pointy one.....isn't (IMO)