Idle Revs

[Draper]

So out this evening on a little ride to get battery topped up for a big journey tomorrow (damn alarm)

and i notice that when idling, the revs would vary between 1000-1500 randomly shifting. When I got back home, the bike sounded as if it almost cut out as the revs dropped :confused:

Also gear3 seemed to be abit odd, and when changing down to neutral to coast to a set of lights, i slightly over touched down into neutral and then a lot of gear crunching as it almost went into first (clutch in)

Is this a good sign?

After my alarm woes i hope that nothing else is on the blink

Draper

[toonyank]

Well not sure about the revs. I think spanner man could advise on this.

I wouldn't coast in neutral at all (not best practice). If you must coast just pull in the clutch.

[Draper]

yeah i was slowing down and thought i'd stick in it neutral before i was at the lights, normally just slow down using the engine breaking

Ive experience that crunching once before when going into first

[andyb]

I left my choke on once and the idle was hunting around the same as yours. maybe the choke is stuck (or like me your left it on?)

[yorkie_chris]

Hunting, IME, can also be caused by air leaks or lean running.
Try put the choke on slightly, if it steadies out at that point then you know somethings leaking or lean.

[toonyank]

Good point!

[yorkie_chris]

Also, Idle revs should be 1300rpm +/-100rpm according to haynes.

[Draper]

cheers lads. yeah the choke was fully in because i checked, if it happens tomorrow i will try giving it a little choke to see if it steadies it out

Dont quote me, but i have a feeling that haynes said anywhere in between 1100-1500... unless that wasnt haynes but someone else, or i just made it up

[yorkie_chris]

The idle adjustment doesn't change the mixture anyway, so shouldnt be making it hunt around like that

[Spanner Man]

Well not sure about the revs. I think spanner man could advise on this.

I wouldn't coast in neutral at all (not best practice). If you must coast just pull in the clutch.

BOING!!! like Zebedee here I am!:D

Your idle problem could be caused by one of the chokes sticking slightly even if the lever is fully home, as they're prone to this. If it occurs next time you're out on it I would investigate further, starting with as Yorkie suggests the possibility of an air leak, & moving on to the chokes.
As to the gearbox issue Toonyank is dead right about coasting, it really isn't good practise. Motorcycle gearboxes work best when both shafts are revolving at higher speeds, with 'load' on both shafts. Hence many gearboxes feel notchy at low speeds & engine RPM, especially when coming down through the gears. It's always better to release the clutch lever between changes, as this usually ensures that the selected gear is fully engaged.

Also make sure the clutch is adjusted correctly & that the gearlever linkage is moving freely, & returning to it's centre position upon release. A minor problem with either of these will exacerbate (big word for a Friday morning) the aforementioned issues with motorcycle gearboxes at low speed.

The Suzuki manual states idle speed as being 1300 +/-100 RPM. I prefer 1200 or even slightly under if possible.

Cheers.

[yorkie_chris]

exacerbate (big word for a Friday morning) the aforementioned issues with motorcycle gearboxes at low speed.

The Suzuki manual states idle speed as being 1300 +/-100 RPM. I prefer 1200 or even slightly under if possible.

Cheers.

it is indeed a big word.

Why do you prefer a lower idle?
when mine was set too low, at around 1000, there was a bloody big clunk on revving the engine, any idea what this is? (this is unrelated and went away when the revs were set right just above 1200)

[Draper]

cheers mr.spanner. Been on a cardiff to wolverhampton ride just now, did feel a little odd with a straight line motorway speed, gear 6, randomly seemed to find a false neutral, revs just went through the roof, turned them down, clutch in, flicked up into 6. I could have tapped the shift, but i dont see me having my foot suspended above the shift in order to knock it down in a false neutral :s the idle seemed to be hunting abit aswell

I'll be back to cardiff in a couple of days, i'll see how she fairs then, could have been one of those one offs

[Spanner Man]

Morning all.

Keep an eye on it, & if the problems persist then get it checked.

Yorkie old fella !000 RPM is a touch too low, & indeed they clonk if you blip the throttle, it almost sounds like cylinder knock, which is usually caused by incorrect ignition timing. I doubt that it actually is that, it's probably just a characteristic of the SV engine.
I have found that an SV will idle happily at 1100-1150 RPM providing it's in tune & you can move the mixture screws to eliminate any slight 'hunting' on either cylinder. It's not always possible as the screws are very prone to seizing up.
The slightly lower idle makes the bike a touch more pleasant to ride at very low speed, & slightly reduces the clonk when 1st gear is selected.

Cheers.

[yorkie_chris]

Mine hunts quite a bit at idle, hangs up when blipped too.
How do you identify which cylinder is running off? I was just going to set the mixture screws to about a 1/4 turn more than what they are at, as I dont have the advantage of a colortune to set them up perfectly.

[Spanner Man]

Morning all.

The best way of determining which cylinder is hunting is to adjust the mixture screws with the engine idling, you need a special 'gadget' to do this.
An old rule of thumb is to adjust the mixture screws on both cylinders until you have the fastest & smoothest idle. It takes a bit of practise, & sometimes you can find that to achieve a smooth idle, the screws may be out quite a bit further than the standard setting. This is particularly common on bikes fitted with race cans.

Yamaha often don't give a standard setting for mixture screws, 'preset' is the term in their manuals. I have seen 4 cylinder Yamahas with the screws on each carb varying between 1 turn out & 3 turns out. Which may have been ok when the bike was new, but after every component in the carburettors & the engine has worn at a different rate the can idle like a pig.

If you have a tool that can access the screws while the engine is running you don't have that long to get it right, for the internal temperature of the cylinder will quickly rise above the norm, even when the coolant & oil temperature is relatively normal.

Cheers.

[yorkie_chris]

My front mixture screw is siezed solid :mad:

Given the back one a slight tweak and its not hunting aroud at idle any more, still hanging slightly, the flatspot doesn't feel as pronounced but will let you know on the score when I've been to uni and back

Chris

[Spanner Man]

Morning all.

If one screw is seized it's always the front one! GRRRRR!

It may be that that's causing the lag you're experiencing, unless you can free it off which is doubtful, you're 'stuck' with it! (pun intentional):D.

Cheers.

[yorkie_chris]

I think I'll just leave it be, I'm somewhat nervous of taking an impact driver to a carb.
I may see if dizzyblonde will sell me a front carb as she has spares :-P

Otherwise could you drill the needle and replace it? Or is it likely to be stuck on the metering part rather than the threads resulting in a totally f##ked carb?

[Spanner Man]

Morning all.

You're right about an impact driver, they're a big no-no when it comes to carburettors!
With the carbs removed & inverted, fill the recess where the screw is with a penetrant of some sort, and leave for several hours topping it up frequently.
Sometimes with a bit of back & forth movement you can persuade the screw to come loose.
If not, they can be drilled & collapsed, as it's usually the thread that actually seizes. Do be careful if using this option. I find that a tiny milling tool & a Dremel is better than a drill.

Cheers.

[yorkie_chris]

Do be careful

More than careful!

Now I can't decide wether the flat spot is annoying enough to take the risk of drilling...
Not to mention the cost of a new needle, presuming its a stealers only part and I haven't called them yet to check the price

Chris