Weak spark could it be the coils?

[jave101]

My gs400 has got a few issues, I've put pods and exhaust on it and I thought this could be why it's backfiring and running like crap above idle. The plugs are carbon fouled so I replaced the plugs with fresh ones to eliminate them as a problem. Now I'm not getting any spark.

I suspect the coils as they are after market ones and are not producing a strong spark. Left hand coil is getting 11 volts to it and resistance of 2.2 ohms. Right hand side is getting same voltage and is 3.8 ohms across the terminals.
Also my bike doesn't have condensers if this could be an issue.

Any help would be greatly appreciated. I'm getting to my wits end trying everything. Timing is good, set with a strobe. Carbs have been cleaned.

[barnbiketom]

It will not make a correct spark with no condensers

[tkent02]

Points ignition? Electronic?

[jave101]

Points, timing is set with a timing light too.
The manual shows the condensers mounted behind the coils. I'll try and source some off eBay.

[Agemax]

surprised you are getting any spark at all without any condensers fitted?

[jave101]

It's my understanding the condensers act sort of like an electronic buffer to stop arcing at the points and don't really affect the spark at the plug.

[Agemax]

without the condensers the voltage will arc across the points instead of going to the coils. i suppose you possibly still could get a very weak spark at the plugs.
have you looked to see if the points are arcing badly when running?

[jave101]

There is arcing across the right hand side defiantly, small blue sparks. Can't really see much arcing on left hand side. This is the stronger of the two and can run by itself, right hand the one with arcing at the points struggles to turn the engine over by itself

[Nessism]

Funny thread. No condensers.

The original coils in your bike had something like 4-5 ohms resistance. 2.2 ohms is too low and will result in burned points, or so I've read.

Hope you rejeted when installing pods.

Good luck

[posplayr]

I'll hazard a description of what the condenser is for.

It is correct that the ignition will fire without the condenser. The condenser is to protect the points from arching and keep the points contacts free of burning from arching sparks.

We should all know that the coils create a large voltage spike (on the secondary) when the coil primary is fully flowing current and the points are opened. There is also a rise in the voltage above 12V on the primary side. The voltage is high enough to jump the points gap just after the points open. Remember it is the opening of the points gap that causes the large voltage spike, but this also occurs when the point gap is the closest, so the points tend to arch and wear out/burn fast unless there is a fix.

The fix is a condenser or capacitor in parallel to the points. The condenser will not allow the voltage across the points to build up too quickly as it absorbs the current as the voltage tries to rise quickly across the points. So the capacitor keeps the voltage across the points from building quickly while the points contacts are separating which keeps them from arching and therefore dramatically increases the lifespan of the points.

As Ed said, there seems to be something wrong with the coils measuring only 2 ohms. It suggests shorted winding which will create more current flow and likely limit the output voltage due to the reduced number of turns.

[JayWB]

The magnitude of the spark / voltage developed in the coil’s secondary depends on the rate of voltage change in its primary. A very rapid change from 12 volts to zero volts in the primary will develop a substantial spark in the secondary, but if the primary voltage bleeds off slowly it will develop a weak spark, if any at all.

Having said that, the collapsing magnetic field in the coil tends to maintain the current flow in the primary even after the points open. It’s sort of electrical momentum, the current tries to flow even with the circuit broken. This results in arcing across the points, and consequently a slow bleed-off of primary voltage. This will, of course, result in a relatively weak spark.

The capacitor, or condenser, across the points fixes this. As the points open the condenser takes the current rather than arcing across the points. By the time the condenser is fully charged the points are open enough and the coil’s energy has dissipated enough that arcing across the points is no longer a problem. Even though the condenser has prolonged the voltage drop time it hasn’t prolonged it nearly as much as an extended point arc would, so the secondary voltage is much higher and the spark stronger. Since there was no point arc the point’s contacts are saved from excessive wear.

When the points close again the condenser is discharged and the cycle begins again.

[jave101]

Ok finally some good news!
Measured voltage to the coils and it was only 11v. Battery was 12v so I ran a wire from the positive on the battery to both the positives on the coils. Hey presto! Running strong and hard.

Condensers are on their way and ill be installing them as well.

Thanks for the help guys

[jave101]

Ok so I've been doing a bit of testing on the wires and cleaned the terminals.
What I have noticed is when the original wiring is hooked up the voltage to the primary coil was 10.8 volts but when the coils were unplugged the voltage when back up to 12v.
But using a wire from the positive on the battery to the coils the voltage only dropped to 11.8v.
So I'm guessing there is a bad wire somewhere along the way. Apart from pulling apart the whole harness and replacing the wires what can I do?
Run my own wiring in place of it?

[hjfisk]

Ok so I've been doing a bit of testing on the wires and cleaned the terminals.
What I have noticed is when the original wiring is hooked up the voltage to the primary coil was 10.8 volts but when the coils were unplugged the voltage when back up to 12v.
But using a wire from the positive on the battery to the coils the voltage only dropped to 11.8v.
So I'm guessing there is a bad wire somewhere along the way. Apart from pulling apart the whole harness and replacing the wires what can I do?
Run my own wiring in place of it?

Try going through the wiring harness plugs and cleaning up the terminals pull them apart and either use a chemical cleaner or polish up the contacts and apply some dielectric grease then check the voltage again. The ignition circuit will take in the wires at the coils, the ignition switch, the kill switch , fuse panel, the wires from the points plate, it is also suggested that you do this on ALL the wiring connections on the bike. It may save you from sitting beside the road some day. All this and much more is discribed in full detail in Basscliff's site Check it out.

[pete]

Pull apart your right hand control where the kill switch is and give it a real good cleaning with contact cleaner.

Do the same for the ignition switch.

Use the contact cleaner on all connections into the main harness for those as well.

I can't remember if you've swapped out the dodgy stock glass fuse and holder or not, but replace that with an inline blade holder and fuse.

Until I did all that, I lost about 2 volts from battery to coils, now I lose half a volt or so from memory, makes a huge difference!