Honda SK50M not running, occasional spark

Hi everyone, I'm new here.

So the story is I bought my first scooter, a 1997 SK50M, not running. It had been sitting for at least 2 years. I got it home, drained the fuel tank, cleaned the carb, hooked it up to a car battery and tried to get it going. It would almost start, smoke would come out the exhaust but it wouldn't fire and run. Kind of like almost firing, as if out of fuel. The plug would come out wet. I tired this again for a couple of days, then the next day it randomly started right up first try and ran like a clock. No problems at all. I was very happy.

I actually left it idling for an hour and it started right up again as if it never quit.

Then, it wouldn't start a day later. Tested for spark, and it would maybe spark one time and then not again. It has a very weak and very intermittent spark. When I let go of the start button and then try testing for spark again a few minutes later, it would maybe spark a very small amount for a fraction of a second and then stop sparking.

I have unplugged and cleaned all the electrical connectors with contact cleaner. I have the Honda service manual but since I don't own a multimeter (and I don't know how to use it, but an electronics tech friend of mine does, might ask him to take a look but I wanted to see if someone had some good advice here first)

I cut back a bit of the ignition coil lead in case it was corroded. Tried a new spark plug too.

Unsure what else to try.

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Active Member
Welcome hessam.

Sounds like you did everything right to revive the engine.
There are a few things that could couse this error....
There could be a faulty ground whire but i suspect your coil is on its end.
To test this hold the sparkplug to the negative cable of the coil and see if it gives a good spark then.
If yes you have a faulty ground whire to engine, if no i suspect its the coil itself.
Let us know the outcome !
Thank you. I tried that, I removed the coil from where it bolts onto the plastic, does the coil itself need to be grounded (can't be tested by hanging by the wiring? I tried putting the spark plug tip on both the coil terminals, there was no spark. I will have to ask my friend to test the coil for me.
It sounds like the CDI unit (ignition coil) is broken. I had the same problem. Some times the spark plug sparked, some times it sparked very weak and some times not. I replaced the CDI unit for a new one and a new spark plug and the scooter worked perfectly. However I have a Piaggio 2 stroke and they have the ignition coil and CDI in 1 unit, so I don't know if the ignition coil and CDI unit is apart from each other but I think the problem is somewhere between the stator and the spark plug. Make sure you got the right main jet(?).
Thanks for that. I will check that when I have a multimeter. I also discovered that when I removed the starter relay, used a jumper wire to bridge two of the four terminals so that the starter continuously runs, I have spark. However once I install the spark plug I cannot get the engine to start. It almost does, and smoke starts coming out the exhaust, then when I fit the starter relay back in that's when I lose spark again. The spark seems to only work when the jumper wire is on the starter relay plug, as if the problem lies in the starter switch. But if this was the case why does the engine still crank using the starter switch? Thanks, Hessam


Active Member
Its very hard to say for sure what is happening with out measuring.

Are you sure you have the starter relais wired correctly ?
For example f the positive comes in contact with the negative at the relais it will drain all the positive leaving not enough for the coil to get a solid spark.

Make sure its wired correctly or remove the relais completely and try starting with the kickstart.

If that fails to then measuring whats going on is your only option.
Ok. I have a strong spark when kickstarting, but not when electric starting. However I cannot get the engine to fire! I have spark and fuel, and plenty of air.



Active Member
I think you have multiple issues going on at once.
With strong spark, fuel ,air and compression she should be running.
So what is not correct ?
Does the scoot start with starter fluid sprayed in the intake ?
I haven't tried starting fluid yet but I definitely will. So I have spark when kicking, and when bypassing the starter relay (jumper wire between 2 terminals of the starter relay plug to engage starter) During cranking, the engine tries to start, smoke emits from the exhaust pipe, but no run. Will not spark when relay is replaced and starter button is pressed.
Compression test: 140psi. Manual says spec is 142. I think the problem is electrical, perhaps the spark is not strong enough under compression and blows out. Maybe the stator is faulty and or the cdi or coil. Time to get the multimeter out and start testing.
Here's what I have found. By the way I bought a new coil, that did not help.

With every kick of the kickstarter, the spark plug only sparks ONCE. But the engine is turning over five or six times. Same with the electric starter, the plug is only sparking a few times a second, when the engine is turning over quite quickly. What should look like a constant spark (not on/off) is more like spark on, then spark off. Which is why the engine is trying to start with the plug installed, smoke comes out of the pipe and it sounds like it is firing but not running.

So what could this mean? I have not changed the stator but I have tested it and can confirm it is in spec.


Staff member
Well you should have at least 1 spark per revolution. And you are sure your air/fuel mixture is right? Have you tried the suggestion from @Kurmit with starter fluid sprayed in the intake?
Yes, the engine was running previously before all this began with the original CDI and coil. And then refused to spark/start again. The fuel pump is working, fuel is getting to the carburettor and the spark plug. The spark is sometimes there and sometimes not. I have tried the starting fluid. No change


Active Member
i think you have to sort out the spark issue first.

Check the clearance between the pickup coil and the notch on your flywheel.

Max clearance is the thickness of a creditcard.

Look at the following youtube film about testing the stator and buy a cheap multimeter.

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