How I can check the ignition coils if they are working properly ?

You should be able to pull the plugs, earth them out and jump on the kick start. You should see them sparking. That's the quick test.
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Cheers,
Dave.

Then there is the method whereby you replace a suspect coil with another (known to be good) coil and see if it runs better. I used a Honda XR600 coil for this once.

Couple of things to check regarding coils:

1. Overall condition - cracks in the body, perished rubber boots, corrosion on the terminals etc.

2. Electrical resistance.

Carry out checks for (1) with the Mk.1 eyeball.

Carry out checks for (2) with a multimeter.

There are two parts to a coil, the low tension side (LT) and the high tension side (HT). The LT side connects the 12v coming from the ignition unit to the primary coil (the black and green terminals) and the HT side connects the secondary coil to the spark plug (HT lead and plug cap).



Still awake?

The coil is simply a multiplier, turning the 12v into 20-30,000 volts needed to jump the gap on the plug and create a spark. It does this through a transformer, where the primary and secondary coils act as the multiplying circuit - the secondary coil has a lot more windings than the primary.

This drawing is taken from the MC18 wiring diagram over on the main site, with lables added for clarity:



It works like this:

1. When a voltage is passed through the primary windings a magnetic field (flux) is generated around the windings.

2. If the voltage is interrupted (switched off by the PGM) the magnetic field collapses, which generates a voltage in the secondary windings causing the spark.

Simple!

To electrically test the coil, all you have to do is check that the resistance of the primary and secondary coils are correct.

Using a multimeter set to Ohms, check that the resistance across the two termials is less than an ohm:



Primary showing 0.3 Ohms here.

Now put one probe of the multimeter in the end of the HT lead. Put the other in the negative terminal and you should have about 20K Ohms (20,000 ohms). You may need to change the range on your multimeter to get a good reading.



Secondary showing 18.9 K Ohms (Scale is set to 20K, so multiply reading by 10)
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Excellent explanation, thanks!

Dave you are the man thank you again! when i opened the topic I was hopping to get an answer like yours!
I check them I have again problem with coils so I will buy 2 nsr 125 new coils and 2 ngk new caps !
And then rolling road to see what I did ! I modified the airbox (4 holes X 20mm) I change main jet and ems just knock my door with tyga reeds so next week dyno day


PS. When i modified the air box with Andy way I saw really difference in the road (Thank you Andy)

Great stuff! Make sure you post up any graphs you get from the dyno day.

Dave Ett wrote:Great stuff! Make sure you post up any graphs you get from the dyno day.

If it is from 55hp and up hehe
Just joking I will post it in garage section and in new thread !!!

Great pics and write up Dave.

Even I understand it.

I went to go for a ride this morning. Bike started third kick, which is very good for a Honda. Ran fine for the first minute or so, and then started to develop a miss. Another minute elapsed and it cut out on the lower cylinder and backfired (small popping) when rev'd.

I replaced the spark plug and started it again. No difference; this miss was still there. So I replaced the NSR250 coil with a Honda XR coil and started it again. The miss disappeared and I was able to take it for a good 60 km run without any problems.

Now that I'm home, I've gotten the multimeter out and tested them.

The LT on both coils reads 0.3 ohms. The HT side on the NSR coil reads 3,000 ohms while the XR coil reads around the 4,000 ohms (without the plug cap). Maybe this is a intermittent problem that only happens after the coil has warmed up a bit? I'm not sure, any thoughts?

Anybody know where I might find a new coil for the top cylinder (long lead due to 300 conversion)?
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MC21 Honda NSR250. TYGA 300 conversion.

Check the connection where the spade end from the harness slips onto the coil. I bet you see some scorch marks. Give the connector a bit of a squeeze and try again.....

Had this problem so many times on old NSR's. Drove me crazy the first time.

Yeah, no surprise, Matt is right. Your connection is likely a touch loose. I had the exact symptoms you describe, and that's what it was. Blades showed charring and some pitting. Drove me crazy for months. Only took taking some needle nose pliers and squeezing gently to make the connection firm. Haven't had an issue since.
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-Jim
'93 MC21

Had a look today, and sure enough there were scorch marks. I'll see if I can get a better contact and try again. Thanks for the great info.

This is what a good forum is all about.

Should have Noodle up and running soon, and testing the coils is one of the tasks that I will be doing soon.

Mike
p.s. I won't complain about '3rd kick', 50% better than it was
Why is it though that the Honda has this reputation for por starting. My YPVS starts 1st or 2nd kick...Always!
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I don't mind dying...I just don't want to be there when it happens!

Hobbit210 wrote:This is what a good forum is all about.

Should have Noodle up and running soon, and testing the coils is one of the tasks that I will be doing soon.

Mike
p.s. I won't complain about '3rd kick', 50% better than it was
Why is it though that the Honda has this reputation for por starting. My YPVS starts 1st or 2nd kick...Always!

My nsr always start 1 kick and sometimes when I have it about a month in garage 1-2 kick :S
With air choke open when it is cold!