Suzuki GN125 wont start if cold but starts when push started

[madmadi]

Hi guys,

I need your help.

Firstly my bike's details:

Suzuki GN125, 2004 year, Chinese version, 120,000 km done
Carburetor Mikuni: https://www.brooksbarn.co.uk/GN125-CARB-NOT-H-MODEL-SILVER-TOP-DIAPHRAGM-TYPE_ART61.aspx

Now the problem. Engine won't start from electric ignition when cold but it does start when pushed and it does start when engine is warm.
New battery, new spark plug, fuel is going to carburetor freely (checked fuel tap filter), there is a good spark (taken spark plug out and touched to engine and pushed the ignition, good spark)
So, there is a fuel going freely to carburetor and there is a spark.

I have cleaned the carb, but to be honest there was no rubbish in it.
There was some white stuff in the rubber hose which is going from air filter to carb, like soapy stuff.
Adjusted a fuel/air mixture as was told by friend that maybe there is too much fuel and not enough air- when cold and rainy outside (live in Scotland) maybe the air filter is getting wet and there is not enough air going to carb?

When trying to start the engine there is an explosion sometimes. Trying to start it with and without choke which is manual of course.

Another thing, the fact is that the engine starts sometimes even when cold, I just observed that there is a problem when is wet outside (keeping the bike outside)

The problem started recently, but as I said it sometimes starts, sometimes not. I use the bike everyday for going to work which is 8 miles one way. After 8 hours of work it starts most of the time, but after night it doesn't. Almost always it starts when pushed and from the 2nd gear.
By the way, I don't know if that's normal but when I start the engine on the choke and it starts the revs are around 4000rpm but sometimes after 30secs, sometimes after 2 minutes revs going down to 1000rpm-1500rpm - does it mean that engine adjusting the choke automatically when warm? Doesn't it suppose to have big revs when choke is fully open, even when engine is warm?
Now few possible reasons (in my opinion):

Wrong fuel/air mixture (even after adjusting it- half rotation on the mixture screw)
Bad compression
Wrong valve settings (gaps)
Ignition settings
Blocked fuel stream from carb to engine (?)
Choke problems

Any ideas???
Thanks in advance,
Martin

[blurredman]

Battery needs a good long charge I reckon.

I'm having the same problem with my CX.

Full choke + ignition button = nothing but the occasional backfire, the starter motor can turn for ages and ages making me believe that it's got the power to start the engine, but it simply doesn't. The occasional backfire being the sheer amount of fuel igniting when a sufficient spark ramdomly occurs (I believe).

A good long battery charge has solved this for me.
____________________
CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 39k, 1989 MZ ETZ251 - 50k.

[ricklincs45]

Hi Martin,

Ok, my first thought is that if engine won't start on electric start when cold, but will 'bump' start, it would suggest you aren't getting enough voltage/power to the starter motor. Will the engine turn over on the button, or is there nothing at all? If nothing at all, I'd expect you to also be having other electrical issues. The fact that it will start on button after being run, but not when left overnight suggests a power/voltage drain somewhere in your electrical system.

The white stuff in rubber hose might be emulsified oil (presuming there is a breather hose connected into the airbox from the engine - this is done to reduce emissions).

Regarding cold starts, your engine should definitely not be revving to 4000rpm when cold - this will eventually knacker your cylinder head and camshaft - I'd urge you to get this looked at as soon as possible. I'd expect it to rev to around 1800rpm on choke.

Summary; I suspect you've got two unrelated faults here from what you've posted - one being an electrical fault, the other being the choke (which could be anything from the engine needing a service, but most likely a bad carb' set-up or fault).

Just out of curiosity, you mentioned something about the air filter possibly getting wet; is the bike completely standard, or has it got an aftermarket air filter fitted?

Rick
____________________
Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[J.M.]

When were the valve clearances last checked?
____________________
2004 R1 & 2018 XSR900

[madmadi]

[madmadi]

[madmadi]

[madmadi]

[ricklincs45]

Just because the battery is brand-new doesn't mean you don't have an electrical fault elsewhere. As Blurredman posted, a weak battery (for whatever reason) will give the symptoms you're getting, and as an aside, you don't have to SHOUT when posting - unless you want to piss-off the people who are trying to help you.

If you have a standard air filter, it shouldn't be getting wet, so discount that.

If your manual says the bike should rev to 4000rpm on full choke, then ok, that's what it's meant to do, but don't expect the engine to last very long - a Japanese-made GN (or any other single-cylinder 125 will rev to about 1800rpm max on choke).

As for revs going down 'after a while', how long do you mean? Tbh, you can't expect any engine, whether it's a car or motorbike to run on full choke for very long at all. By applying full choke, you're starving the engine of air, this is why the revs will drop - leave it long enough and it'll simply choke itself and stall. Again, to compare to Japanese 125's (and I've owned/run perhaps 20 of them, so I know what I'm talking about) about 10 - 20 seconds is the maximum they'll run on full choke before needing it knocking onto the half-choke position. I very much doubt there's any form of temperature sensor in there that's knocking the choke off by itself.

Firstly, as Blurredman posted, I'd take the battery off and give it a good charge on a low-amp charger - be wary about using car chargers as they tend to be a bit too high-output for bike batteries.

Once battery is fully charged, see if you get any improvement. If not, ask one of your friends etc if they are handy with a multimeter and get them to check the voltage being given when the bike is off, running, running with lights on etc - you may find voltage is less than it should be.

Get valve clearances checked & re-set, sounds like they're about due.

Rubber valve in float: this is acutally the needle valve (metal) which has a very thin rubber coating on its tip - in 30-odd years of having bikes, I've never heard of one being 'too hard' to close properly (though it is possible for them to not close properly if they are worn or have dirt underneath). If it were my bike, I'd get on top of the electrics and valve clearances first, then look at the carb. Even if you find no fault in the electrics, at least you've removed one possible area of fault.
____________________
Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[madmadi]

[ricklincs45]

No problem Martin, we're here to try and help.

It is possible you have a bad earth - this would cause voltage to drain-off. Your bike being a 2004, it's definitely worth checking them. Usually there are one or two earths bolted to the frame (often one is somewhere near the battery). Undo the bolts and give the connectors a good clean with some fine-grade emery paper until they're shiny - then do the same for where they mount on the frame. Bolt them back up, then put a dab of Vaseline or petroleum jelly (same thing, just not a brand name) over the top.

Regarding checking the electrics, you'll probably need a workshop manual to check what voltages you're meant to be getting with bike not running/runnning/running with main lights on etc. If you don't have a manual, try giving a dealer a ring - ask nicely and they'll probably tell you what you should be looking for.

Good luck with the bike, hope you get it sorted. Any other help you need, just post back.

Rick
____________________
Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[madmadi]

[blurredman]

[madmadi]

[madmadi]

Gentleman,

I would like to thank you all for your help and time you have spent for replies to my post, really appreciate it.

My bike is working now, it seems that there was a problem with the spark and moisture. I have dried the electric module and the HT cable, charged battery over the night and it is fine now. Also changed the fuel/air mixture a little (half screw turn) so there is less fuel, more air.

Now, the only two things which changed comparing to before the fault is that now at high revs it doesn’t have the power (slightly only, above 9000rpm).
as I have bended a little the carb float part so it closes the fuel flow earlier than before, so I think I will bend it back to the original position.
My “neutral” revs should be 1800rpm and it is fine, the thing is that when I stop at lights and revs are going down they are going to 1500rpm for around 2-3 seconds and then going back to 1800- it wasn’t like that before- will it be carb float level or air/fuel mixture? I think the latter.

I tried to close the carb float and see if the fuel is leaking but no, it is fine.

So, so far so good, I am covering the bike for the night and outside work because it was all about the moisture.

Thanks again for all your help
Wishing you wide roads and rubber trees!
All best,
Martin

[ricklincs45]

Hi Martin, glad to hear she's nearly fully sorted

The dipping revs, from 1800 to 1500 may be due to the air screw adjustment. Bear in mind that air screw only adjusts the fuel up to 'roughly' one-third throttle openings. Beyond that, the jets take over.

This is how I used to set my Honda 100/125 singles; it always helped them tick-over smoothly. First, set the air screw to where the manual says it should be. Get the engine up to normal operating temperature, then set the tick-over speed using the tick-over screw. If your tick-over is meant to be 1800rpm, set it as close as you can.

Once you've done that, only then go to your air screw. Now adjust the air screw in or out, but only very slightly. Go one way first, and listen to the engine, at some point the revs will either speed up, or slow down. If it slows down, go the other way. What you want to find is the place where the air screw speeds the engine up so it's running smoothly. This is usually within half a turn of where the manual says the screw should be.

Once you've got that set, then go back to your tick-over screw and re-adjust to where you want the revs. Now your engine should tick-over smoothly.


____________________
Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[madmadi]

[madmadi]

Hello again guys,

Just an update, bike starts every time now

One more question. When I ride fast (if you can ride fast on 125 ) around 50 mph there bike is like braking, choking or something as if it would not get a fuel or spark. It happens only on 4th and 5th gear and on above 6000rpm. When, while riding, I open the choke it seems to help a little.

My theory is that maybe the engine/carb getting some extra air? The air/fuel mixture is set up as originally and apart from that I have only adjusted a little the float previously but put it back to original position.

So, three options here in my opinion:

Air/fuel mixture
Float level
Extra air from somewhere

What do you think?

[humanbeing]

Does the electric in good condition?
A uncommon fault in chinese made Suzuki

[madmadi]

[madmadi]

Hi guys,

Just an update and another question....
Bike starts every time now, there was a problem with electricity, wet cables etc. So now it is fine.

BUT

Now when I ride more than 40mph sometimes the bike is "choking" like the fuel would be cut off for a moment, like you would hit a brake. I noticed that the it is worse when is windy.

Is is possible that the carb takes some extra air (it would explain why is choking when is windy) or maybe there is some problem with electricity and when riding fast the spark is weaker? I check on two different spark plugs and two spark plug caps and there is still a problem.

The thing is that this choking started after I took out the carb. The only two things I have changed are fuel/air mixture and bended a little float so it closes earlier (thought before that the engine won't start because too high fuel level in the carb)

I have changed the air/fuel mixture few times, every time just a little but it doesn't help. Also, recovered float lever to original state.

Any idea guys?

Again, my theories are:

- carb takes some extra air when riding fast - but the question is, through where the air is coming to the carb?

- the spark is weaker and is breaking when riding fast (more resistance in the engine?)

- rings are weared and/or compression is wrong - but it is not really possible as the problem started after dissembling the carb

Thanks in advance,
All best
Martin

[Astandane]

Hi there,

I too have just come into the possession of a GN125, mine being a 2002 bike. I may not be able to offer much help in the way of solving the issues you are having but I will give you my experiences.

At first, my bike did rev high after ignition but only for a very short period of time before it settled, though that was with the choke on. Riding around town as I have been, I have had only a few hiccups.

A) One or two (at most) coughs in power delivery-I think this just may be the old fuel getting through the system.

B)Sudden or quick stopping sometimes feels like the bike wants to cut out, has done once or twice, but this isn't new to me (my previous Kymco had done this on rare occasions).

C) Revs do sometimes stick a little high, say, after slowing in traffic.

For me this doesn't bother me, my previous 125 was a total loss and I'm glad to have a bike that by all signs seems to be working fine.

One thing I would like to ask, as I have no manual...is there a steering lock? Forgive me if this sounds pathetic, but I really cannot fathom it out. The ring around the key slot says 'Off' followed by a dot which turns the bike on, and another dot which turns it off but (from what I can tell) nothing else. Any ideas?

[madmadi]

[Astandane]

[trevor saxe-coburg-gotha]