Nsr 125 coil earth and misfire!

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

I have had a slight misfire on the bike at high revs for a while, it's noticeable but still rideable.

So I've tried the usual things, new plug, drained changed fuel, cleaned carb, changed needle positions (pin is now at the very top) but none have corrected the issue, piston changed less than 500 miles ago.

Plug seems to get blacked up and needs to be changed often, wouldn't start the other day due to plug!!

ALSO

Some one has put a direct wire from battery negative straight the coil, there is no earth in the green coil connection and I've tried tracing with multi metre but can't find the earth so must have a break in it somewhere.

Any ideas??

Mentacycle · Borekit Bruiser Joined: 09 May 2017 Karma :

Id grab a multimeter, set it to 200 range, and get testing the resistances...

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

Where from? What on? Cheers

Mentacycle · Borekit Bruiser Joined: 09 May 2017 Karma :

Hi,

Id test your pulse coil, charge and charging coils resistances, battery voltage, kill switch, ignition switch, stand switches for a break or a short.

If possible try another CDI and see if the problem persists.

Wise advice can be found here: https://www.dansmc.com/troubleshooting2.htm

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

Cheers will do,

With relation to the earth on the coil!!

The actual green earth lead just runs up to a plug witch goes to the ignition switch! There are two earths on this plug one is grounded the other isn't I'm guessing that this may be a faulty ignition switch?? Possibly when the key is switched on both earth are grounded making the coil grounded??

Mentacycle · Borekit Bruiser Joined: 09 May 2017 Karma :

There could be moisture in the kill switch, might do it good to open it up and clean it up...

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

Kill switch works absolutely fine! I bypassed it and still the same outcome!

Mentacycle · Borekit Bruiser Joined: 09 May 2017 Karma :

Great, so that can be ruled out!

When you say 'at high revs' , how high do you mean?
Used in anger high revs?

What is your current plug gap?

iooi · Super Spammer Joined: 14 Jan 2007 Karma :

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

It's speradik to be honest but mainly 9000 and above no specific rpm every time!!! Sometimes I can be mid bend and get back on the power tho and there is nothing, nothing, nothing, then just as I think I'm about to go into the hedge I get power!! Scary stuff at speed.

There is no mixture to adjust on the NSR125 and the carb has upgraded jets (delorto upgrade) due to exhaust, barrel, reed, upgrades and settings are as recommended air screw 2.5 turns out and tickover 1500rpm when warm, needle set at second from top (4settings) tried at the top but will not Rev freely at all!!

I have taken the carb off again and am having it vapour blasted and ultrasonic to make sure it is clean ordered new jets again and new iridium plug!!

iooi · Super Spammer Joined: 14 Jan 2007 Karma :

alains · World Chat Champion Joined: 08 Jul 2004 Karma :

most of the time it's a faulty choke
1rst check the cable for any sharp bend
2nd undo the screw on top and take out the piston
underneath it's a convex rubber which is very often worn
eventually change piston & spring
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/vhb-vhbz-vhbt-parts/choke-piston/
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/vhb-vhbz-vhbt-parts/spring-6/
afterwards adjust the mixture with the small screw (the one inserted) at 2 1/2 turns out , then set idle at 1400 rpm +or- 100 rpm using the big screw (the one with the spring)
clean the black/yellow connector on the coil (oxyde is your enemy)
____________________
the worst day fishing is better than the best day working

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

Alains

Thanks for your response

The plunger looks brand new but I will change the small Oring as that was brittle and broke when I took it off.

Any idea regarding the coil wire? I have traced the green wire from the coil to the ignition switch plug! This should be earthed, however it isn't?

alains · World Chat Champion Joined: 08 Jul 2004 Karma :

you may make an other earth (it wont be bad) but i would be more suspicious with the black/yellow wire at both ends (coil & CDI)
____________________
the worst day fishing is better than the best day working

Farmingstock · Spanner Monkey Joined: 17 Jun 2016 Karma :

Right

I've had the carb vapour blasted and ultrasonic cleaned. The jets are brand new delorto upgrade, air and tickover set, new br9iex fitted, new air filter foam fitted, power valve set bang on the line, oil pump was a little over so adjusted back a little.

Bikes still in bits (no fairings etc) so not been on a long run only up and down a private road and it's raining so the tarmac is slippery. But was spinning the back wheel in first and second when it hit the powervalve and sounds a little more ricey now!

I'll give it a decent run when it's dry and everything is tightened up!!