Carb Problems

[dungbug]

I've had some issues with my bike, which is a 1999 Suzuki GN125. She starts ok, rev's are little hesitant every now and then. She'll get up to 45+ without any trouble but will then lose power, almost feels like a bit of a misfire. I've replaced the spark plug with the correct model (NGK brand), replaced the cap (NGK) and replaced the HT lead. The plug suggests that the mixture is lean as the plug colouring is white(ish), however the spark itself is orangey in colour & I'd expected a blue spark. There's plenty of sparking going on but the colour seems wrong to what it should be.
I'm suspecting the coil is on it's way out but I'm looking for any other suggestions people may have/have seen the same before. I checked all the electrical connections a couple of weekends ago, they were all clean and firm as they should be.
I'm building a new carb for this bike as the carb that's currently fitted has a buggered mixture screw so no adjustments can be made with the mixture. I think the mixture is part of the problem but I can't ignore this orangey spark, it doesn't seem right......Or am I worrying about nothing? The engine itself feels strong and sounds healthy, no smoke, knocks or rattles and doesn't use/lose oil.

Any advice would be great, thank you.

[cb1rocket]

yes as you thought the spark should be a nice blue, so give the coil a go, seeing as you have replaced the other bits.

Is this a CDI ignition or contact breaker? I assume its the first anyway.

[dungbug]

CDI ignition on this, I hadn't thought that it might be the CDI.

[cb1rocket]

well you def know its something until its blue.

Also did you fit the right cap? Some have resistors in em!

Try your old plug as well to check its not a duff new plug

[dungbug]

I did try the old plug, same result with the orangey spark. The cap was ordered from Wemoto who I've always found to be spot on in sending the right bits. The old cap literally fell apart and it had (what I thought at the time) a resistor inside, would this have been right? Thanks for your help by the way.

[chris-red]

More likely the coil than the CDI no?
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[dungbug]

[steven_191]

Doesn't the CDI tell it when to spark and the coil supplies the strength of the spark?

Possibly coil not supplying enough umph anymore.

[dungbug]

[Pete.]

If it starts well from cold then stop worrying about the colour of the spark.

If you suspect a lean condition have you checked that you have an air filter fitted? If so you might want to give the carb a quick service and check the float height.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[dungbug]

[pepperami]

Have you thought about the battery?

An old battery and a cold snap = battery not performing as it should.
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[dungbug]

[Robby]

If the mixture adjustment screw is chewed up, then you know that someone has been at it in the past. Someone that didn't know what they were doing, who managed to mangle a screw.

Get the spare carb cleaned up and set to factory settings, it sounds like your problem is going to be in there.

[cb1rocket]

[dungbug]

[Pete.]

That round brass thing in the middle is the emultion tube. Push it out upwards and make sure the cross-drillings are not blocked. You might need to screw a small bolt into it to tap against.

Where the mixture screw is mangled it looks like there is some remnants of copaslip around the hole. Using copaslip on brass screws in an alloy housing can cause galvanic corrosion and seize the screws solid within a week. Never use copper grease on brass carb parts.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Robby]

When a mixture screw has been mangled like that on a 125 it's often down to an owner thinking that it will alter the mixture across the whole range of operation. This is incorrect, the mixture screw only affects the mix at idle.

Generally the sort of people who do this also think that more fuel = faster, so cock up the rest of the settings - the needle height may be wrong, or the main jet may be the wrong size. They also may have tried to clean the carb by poking steel wire or a pin through the jets. This is a bad idea, the brass is easily scratched and a small scratch can make a big difference in the fuelling.

The new carb looks pretty good, the shit in the float bowl will clean up. Be sure to fully remove the mixture screw and squirt carb cleaner or compressed air (I prefer carb cleaner for this job) into the recess. Use the plastic straw and poke it well into the hole, then keep your eyes well out of the way. It terminates in a very small hole that is easily blocked, and will lead to a weak idle and popping on the overrun.

Fit an inline fuel filter when you reassemble it, preferably a paper element type. They capture any debris from the tank, but more importantly they get stained by said debris. Provides a good indication of how dirty it is inside the tank.

Don't chase electrical phantoms until you have eliminated the carb being a problem. If it starts ok, and runs ok up to a point, an electrical problem is less likely, particularly inside a sealed component. A corroded earth is more likely if you start chasing electrical problems.

As for thoughts about the coil being dodgy, knackered coils, which are fairly uncommon - I have plenty of 30 year old ones doing fine - tend to break down due to heat, not load. The test would be to start the bike up, right straight off, and try to get up to speed. If the problem occurs, the coil is unlikely. If the performance gradually drops off as you ride and the coil gets hotter, then the coil could be suspicious. Always clean the earth points, paying particular attention to the coil mounting points, before replacing the part.

Tl;dr electric components are tough and rarely give trouble. Corrosion or a previous owner's bodges are far more likely causes for electrical trouble.

[dungbug]

[dungbug]

[dungbug]

[Pete.]

A quick search online suggests the GS125 (same engine) should be 24.5mm.
Turn the carb upside down with the float and needle properly installed and measure the distance from the gasket sealing face to the 'highest' part of the float.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[dungbug]

[Robby]

I don't think you mentioned the diaphragm change before.

2 things are likely:

1. The new diagphragm isn't any good. Hold it up to the light and look for holes, the tiniest pinhole will stop it from working.

2. It was fitted properly and wasn't sealing all the way around. It may have a tiny tab somewhere that locates into a little slot, make sure this lines up.

I despise carbs with diaphragms.

[dungbug]