GN 125 not getting above 30

Simba76 · Renault 5 Driver Joined: 18 Dec 2014 Karma :

Hi, My first post so go easy.
Looks like there is a huge amount of knowledge on here so hopefully somebody will put me right.

I have a 2002 Suzuki GN 125 with 25,000 on it.

What sort of revs should the choke be adjusted to?
It starts out idling at about 2500 but after a few minutes, when I'm stopped at lights its up to 4000 or higher!
I am just learning the manual choke so it might be this.
The bike does not seem to get above 30 when I'm riding it, even with the taps fully open. Cold?

How long should it need warming up before riding?

Thank you in advance!

yen_powell · World Chat Champion Joined: 22 Jun 2008 Karma :

Start it, ride off straight away, turn the choke off when you're moving, if you've got your hand on the throttle you can keep it going with no choke until it's warm enough to tick over on its own.

Re the 30mph, that's not right. You are using the gears aren't you?
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Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

If you have the choke on still, then it probably wont go over 30.
The choke, is a flap that covers the inlet to the carb to 'choke' the flow of air in to it, and richen the mixture for cold start.
The 'Throttle' is a 'gate' in the carb that restricts the flow of 'charge' (Air+Petrol) into the engine... so if you have the choke on, you can open the throttle as much as you like... it's like opening your front door and running into the closed porch door and wondering why you cant get out.
As for the revs? Choke doesn't 'set' idle revs. As said, it chokes air to the carb to richen mixture for cold starting when the fuel is less 'volatile' and harder to catch on fire.
Depends how cold it is how hard the engine is to start, and how 'low' it will idle on choke when it catches; then having started, as burning fuel starts to get metal warm, 'less' choke will be needed to keep it running, and the idle is likely to 'race' over normal tick-over as it gets warm enough to run without choke.

My bike, idles at about 1000 revs 'normally'.. no choke, a warm engine.

On a summers day, will tend to need a bit of choke to 'start' first thing fro cold. Soon as its caught, though, choke can go straight off, and I can ride off. Rest of the day, shouldn't need any choke to re-start.

On a cool spring morning; needs full choke to get it to catch; and I have to leave the choke on and the engine idling, about as log as it takes me to stick my hat and gloves on,open the gates, wheel it through, and shut the gates; by that time the idle, that was a bit 'lumpy' and low when I got it started, will have lifted and it'll be ticking over a little over higher than normal tick-over... but can knock the choke back to half and it comes down, and, ride at 'part throttle' half choke letting enough air to get the bike moving to the end of y street, where I can knock the choke off, the engine 'warmed'.

Were I to go out now and try start the bike? Well, its not VERY cold, but its getting there.. it's three layers of trousers whether..... would take full choke to get t to catch, and probably a few prods before it did; probably 'conk' on me while I was doing the gates and wheeling it out, and need a re-start to carry on warming while shut them behind me.. if not, tick-over would be rather low and lumpy.. then, gates done, might have to sit on the drive for a couple of minutes to let it get warm enough to knock the choke back a bit, before I could think of pulling off up the road, putting the motor 'on-load'

Which is all a bit more 'exaggerated' than you should expect with your bike, being a small singe; mines a four cylinder air-cooled 750, so there's a fair bit more metal to get heat into; but gives you an idea of the principle.

If the revs are leaping up that much 'on choke', then you are probably leaving to too long; and as said, if you try riding off with it full on, its like having a rag stuffed up the carb, its not going to be able to suck the air it needs to make power to go very quick.

So, use choke to get t started, knock it back as the revs start to ride to hold a comfy idle; give the thing a chance to get a bit of heat into it on choke before you start riding it; choke 'off' before you try giving it more than 1/4 throttle, all should be good.
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Simba76 · Renault 5 Driver Joined: 18 Dec 2014 Karma :

Cheers gents.

Explained very clearly for a novice. Very grateful indeed.

Take care. Have good Chrimbo!!

Simba76 · Renault 5 Driver Joined: 18 Dec 2014 Karma :

Just been out for my first proper run. 35 minutes through the countryside. Got it up above 50 no probs. had a moment when I couldn't get 1st on a busy but slow round a bout. But that could have been just me!
Still sounds a little rough and spluttery.
What would adjusting the mixture screw do? I will check the carb collar for holes as well.
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Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

Simba76 · Renault 5 Driver Joined: 18 Dec 2014 Karma :

More wise words. Cheers

I have a mate of mine who used to repair bikes giving it the once over tonight.
He has already remarked it will need the tappetts adjusting which he will do.
As well as the fact the revs are not dropping as soon as you release the throttle. He thinks there could be an air leak in the carb seals which he will also check out.
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talkToTheHat · World Chat Champion Joined: 21 Feb 2012 Karma :

i know the GZ's choke was a fast idle device rather than a real choke, does the GN have the same carb?

Engine/gearbox are related but not quite identical. Both of my GZ's were reluctant to find first gear, fresh oil significantly better than old sludge. Try to engage 1st before coming to a stop, or let the clutch out a bit in 2nd and inch the bike forward, pull it in and try again. Mine were awkward, and had the unnerving habit of displaying the neutral light when in gear and clutch in. Check your chain tension, gearbox is irritatingly sensitive, and if the GN is anything like the GZ keep an eye on the cush rubbers as the bike will eat them.
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