I'm at a complete loss for what to do next.

[Lord Percy]

Most of you probably saw all my other posts about my dodgy GN125, so here's an update.

New carburettor. That seems to have fixed the high idling. Although... when I rev it, how quickly should it go back down to normal? If, for example, I rev it up to 4000, it seems to crawl back down to normal at a slower rate than I would expect.

Total oil and filter change. There were a couple of fairly large chunks of metal in the oil.... any opinions on that?

And now, instead of just 'losing power' when it's going at top speed, it actually wants to stall during the higher levels of acceleration. The effect of the throttle complete goes to zero momentarily, normally when trying to accelerate at the higher end of the speed range.

So, with a new carb the power seems to have come back a touch, but it's now occasionally LOSING all power, and this has only been happening since I did the oil and filter change. So... what did I do to cause it?!?!

[GREENI3]

The bit's of metal in the oil sounds like potential engine damage.

I'd get that checked out asap.

[The Artist]

Is your air filter the standard one?
Is everything tight around the carb area?
Is the carb the right one?
Does it have the right size jet?
Fresh petrol?

Metal in the oil doesn't sound good. Do another change after a couple of hundred miles, will only cost a fiver for just the oil. Make sure there are no more "chunks" of metal. How big are these chunks?

[dungbug]

What state is the plug in? Might explain a lot about what's happening inside the engine (lean/rich mixture etc). Any photo's of said metal bits that came out with the oil? Doesn't sound good gent, any knocks or rattles when starting up/running?
____________________
CBT: Pass 25/06/2011 Theory Test: Pass12/06/2012 Mod 1: Fail 08/07/2012
Mod 1 Retest: Pass 15/0702012 Mod 2: Pass 03/08/2012
Suzuki GN125 (Sold) ~ Current bike: Yamaha YZF 600R Thundercat

[Lord Percy]

There were several small flakes of metal, like little harmless shards but probably two chunks. They were about 3 or 4mm in size.

I've played about with the air filter and air inlets and all that is fine as far as I can tell. If I totally block the air inlet it begins to stall, and if I totally remove the air filter and leave it as a great big gaping hole, there's no change in the running of the engine.

The carb rubbers are fine as far as I know. I've sprayed WD40 all over them to block any gaps while the engine was running to see if there was any change, and nothing happened, so yeah, I assume the rubbers are fine.

I'm guessing it's some kind of electrical HT coil spark plug sort of thingy because it literally just suddenly wants to die after only a short time of maintained engine work, and only when the bike is actually moving. I mean, if I have it up on its stand it never stalls or sounds weak when I rev it for a while. It's only when the bike is actually in motion.

Any ideas? It always seems to run quite happily at idle speeds, but it sometimes just chugs out in a stalling kind of way if I ask it to accelerate/maintain the higher ranges of the engine. And also it only seems to have started doing it since I did the full oil and filter change. I did dick around with the spark plug too though, so maybe I've messed that up?

The plug is a nice healthy tanned brown colour when I take it out, so I figured the fuel/air mix is ok now, which is what points me to it being a possible HT coil thing, but I don't know a thing about those things. I called the guy who sold me it, VINCAN E TWO MOTORCYCLES, and he reckoned it could be the HT coil, low engine pressure, or something to do with the exhaust.

If I can't sort it, he assures me I can ride it over to him on Wednesday so he'll check it out for me...

[dungbug]

Not a lot you can do wrong with a plug apart from gap it correctly, is the plug new? Plug cap replaced?
____________________
CBT: Pass 25/06/2011 Theory Test: Pass12/06/2012 Mod 1: Fail 08/07/2012
Mod 1 Retest: Pass 15/0702012 Mod 2: Pass 03/08/2012
Suzuki GN125 (Sold) ~ Current bike: Yamaha YZF 600R Thundercat

[Lord Percy]

I have a new plug and an old plug, the problem is the same regardless.

The plug cap hasn't been replaced.

One thing that bugs me is that the plug cap has threads so it can be screwed onto the spark plug, but it's 100% impossible to screw it on because the engine gets in the way?! I have to just push it on until I hear it click a bit onto the spark plug. Come to think of it, that sounds like the problem. Although this current problem has only been happening today, and I've had the spark plug and plug cap off before, a few days ago. The plug cap is a pretty good shout though.

...are there different shapes and sizes of plug cap to suit different shapes of engine and positions of spark plugs?

[Lord Percy]

This is the plug cap I have.

https://www.ebay.co.uk/itm/Reliable-Waterproof-SPARK-PLUG-CAP-SUZUKI-GN125-/160543042898

[Nick 50]

If you have chunks of metal (even flakes) something is seriously wrong! If you can, I would stop using the bike completely and identify where the metal has came from.

If some is breaking, using the bike further will degrade the breaking parts even further.
____________________
Current Bikes: ZX7r 97 (Black Beauty), VFR400 NC24 (The banana)
Previous Bikes: Aprilia Tuono 03 (The Beast), CBR600f (97)
First bike: A GZ125 Lemon.......

[The Artist]

Spark plugs have a threaded piece on the top and with your sort of cap, they need a little metal female threaded nodule that looks like this.

https://www.sparkplugssource.com/images/IZFR6K11.jpg

[dungbug]

[The Artist]

[Lord Percy]

Mine can screw on at both ends, but anyway it grabs enough for it to be sparking fine. I reckon it's still a fuel/air mix problem....

the metal bits may be gone now. It could be because the tacho drive had cracked and the broken bits were in the engine. I guess I'll do another oil change before I have to head down south next week, and if there's no more metal, the problem is done.

the main thing is that the bike really does run fine at low/idle speeds, in fact with this new carburettor it seems near enough perfect, but it just seems to want to totally die out when the engine is worked a bit.

Oh and also I've just had it on it's stand outside and here's another symptom that may or may not help...

If I rev it up to about 7000 and hold it for several seconds so it's nice and hot then let go, the revs then smoothly go straight back down to zero, and the engine stops. So it's definitely the higher revs that are killing it. And I'm 95% certain it's only an issue when the engine is really hot.

Fuel/air problem??

[_Iain_]

https://www.bikechatforums.com/viewtopic.php?p=3308437

Regarding my experiences of metal in oil

Check the inlet rubber for splits, cracks or anything. Makes all sorts of funny things happen...

If metals gone round the engine, its going to need a filter change too, aswell as the sump off and the bits scraped off the pickup. Dont run it, get a new engine and fob the other one off as "Got as a job lot of spares with my bike, engine turns over freely, However has not been fired up."

Might get half the money back for the engine that way
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[Nick 50]

[Lord Percy]

I did a full oil and filter change today, including taking out the gauze filter and cleaning that. That's when I found the metal bits.

I know it's a pretty bad thing that there is, or was, metal in there, but that aside, the whole thing runs absolutely 100% brilliantly until it gets hot and tries to maintain itself at the higher running range.

Maybe a new engine isn't such a bad idea. Although... I was actually thinking of trying to fit a 250 engine onto it (or even 400?!) after I get my full licence, so I didn't want to do any engine swapping quite yet.

[Lord Percy]

Can anyone put this into really simple terms for me? It's some advice from my uncle about the 'points'. It's probably really easy to understand if you know what you're talking about, but for me I'm a bit lost. Here are his words:

"[The points are little things on the end of the crankshaft that open and shut that tells yer coil when to let the spark plus,release a spark , inside the coil you have two windings one for when your goin slow and when you go faster another kicks in so you have two feeding the spark plug, some times the coil breaks down under constant demand so in tboery you won't get a spark so the bike will conk out as it has no spark to ignite fuel.]"

So that's what he said. With that in mind, which bits should I check, where abouts, and what am I looking for???

[The Artist]

[Lord Percy]

I do actually have a mate who's really keen on motorbikes and is a quarry truck mechanic by day, so he's a full on grease monkey. I've had a word with him and he's on the case. I just thought I'd get a few tips from here.

Fair point that it's quite hard to diagnose over the Internet though!

[Teflon-Mike]

Points & Ignition timing are not relevant to you.
Points are a mechanical 'switch' on the crank or cam-shaft that make & break the ignition circuit to fire the spark plug at the right time.

You don't have any.

Some bikes do... but rare these days.

What you have is a box of electronic tricks, that fires the spark-plug, which takes its 'signal' as to where the crank-shaft is and how fast its spinning from an induction sensor on the flywheel.

Points ignitions were user serviceable. mechanically operated, there was a shoe that ran on a cam that opened and closed the switch, and as it wore down, closed the points gap, changing the ignition timing. Also the points themselves 'wore-out' opening and closing. So it was a chore to keep adjusting them to keep the contact faces clean, and the contact gap and hence ignition timing correct.

Modern CDi ignitions have no moving parts. There is usually a notch or a nobble on the flywheel, and a coil of wire next to it on the engine. When the notch or knobble passes the coil, it disrupts the electromagnetic field and causes a very small 'pulse' of electricity.

Box of electrickery, senses that pulse, and via an amplifier circuit, triggers the coil to spark the spark-plug. Nothing to set, clean or adjust, its essentially maintenance free system.

OK.... so having explained that red herring.... where are we we weren't before?

You have done an oil change, good. Right grade, Level? All hunky dory there?

CHANGED CARBURETTOR....

From where you were at before, you were looking at teh carb, and tinkering with it and not getting anywhere, and I said, MAKE SURE its IS the carb before you swap it out....

Apart from oil change..... what else have you done?

Some-One suggested Tappets, which was good advice... have you adjusted them?

This is the gap between the top of the valve and the lever that opens it.

As engines get hot, bits of metal expand, and depending on what expands more and what expands less, those gaps can get bigger or smaller as you get to running temperature.

If the engine gets TOO hot, then gap can get monsterousely wide, in which case power drops off as cam-shaft is waggling lever in gap half the time and only opening valves a 'bit' rather than moving lever through 'bit' of gap and opening valve a lot.

Alternatively... gap goes small, and cam holds valves open, or stops them seating properly and sealing.....

Again, power fade, occurs... and I was pondering that compounding problem, tight tappets,particularly on the exhaust can see poor seated valve not seal, so engine goes 'lean' and over heats, making problem worse, AND with the exhaust valve not getting ground against its seat, deposits building up on the lip, so that when you DO adjust the tappets.. still don't seal, becouse of crud on the lip.... and if it starts to wear that off.... then the tappet gap goes to pot again, probably closing up, and you are back to square one!

However... question was, have you set the tappet adjustemt? And if not, again, do that before swapping carbs.

Eliminate variables, dont ADD them!

You now have a new carb.... 'factory set'... which could be as far out of tune as what you had to start with...

And the problem could STILL be 'anwhere' else in the engine.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Pete.]

[Lord Percy]

When you talk about tappets, do you mean the valve clearances? I did those yesterday, if that's what you were meaning. The engine sounds a little happier since I did it.

To re-cap on what I've done and what's happened - Since I changed the carburettor, the original problem of high idle revs has gone. It never does it now. I'm certain the new carburettor has been a good move.

I did a full oil and filter change, and even took out the gauze at the sump and gave that a clean. And I've switched the spark plug around twice. So one worry is that I may have bodged something up with the spark plug wiring.

The thing that's happening now is a whole new problem. At first, if you remember, the bike didn't like going at its top speeds. What I mean is, the engine felt kind of weak and lost power when it was worked hard and got hot, but it still always ran. Now, however, the engine feels a good deal 'stronger' (hence me thinking the new carb was a good choice), but it just wants to suddenly randomly splutter and die when its being worked hard. I physically feel the machine die for a moment. This is what points me to it being ignition/spark/wiring/HT thing (but I have no idea what). It really feels, for the moment it happens, that the combustion process has totally halted, and then it kicks in again.

What's happening now is totally different to what was happening before. Hmmmmmmm

[dungbug]

When you checked the clearances was the engine stone cold? & Tef is right, no points on the GN.

BTW did you strip the fuel tap & clean it? There was a fair bit of crud in the old Carb so the tap gauze & bowl might be choked as well.
____________________
CBT: Pass 25/06/2011 Theory Test: Pass12/06/2012 Mod 1: Fail 08/07/2012
Mod 1 Retest: Pass 15/0702012 Mod 2: Pass 03/08/2012
Suzuki GN125 (Sold) ~ Current bike: Yamaha YZF 600R Thundercat

[Lord Percy]

Engine was cold when I did the clearances.

I've not actually checked the fuel tap, but when I open the valve it absolutely gushes out, and I let most of my fuel out into a clear container and there were no little bits of rust or anything in it. So I'm guessing that can be ruled out.

It all runs totally fine when the engine is cold, and then when it's hot is when the problems begin I think. That's when it starts wanting to die out when I try to work it a bit more.

[dungbug]