Gt125 Comet will not start

[Wayne]

Hi, I’ve owned a GT125 Comet (2008) from new. It has always been a bad starter but i thought that was normal. The bike has been stood for a number of years now (Only done 6000km) and i am in the process of getting it going again. I was trying to get it started, engine cranks but won’t fire. I removed the spark plug to test for a spark and noticed something, as the engine is cranking there is no spark but just as i release the ignition button the spark plug sparks (maybe 2 sparks at most), is this normal? If not, then what could be the issue. I seem to remember the bike always started after i released the starter button. Thanks in advance.

Removed old fuel, Cleaned the carbs and fully charged the battery, and used booster battery for starting.

I do have a fuel leak at the vacuum valve under the fuel tank. Needs replacing.

[Simon]

Check the interlocks side stand switch, clutch switch first.

[Wayne]

Thank you, i will do that.

Just for peace of mind though should the spark plug be (sparking) all the time the starter motor is turning the engine over?

Ordered a new petrol Vacuum valve to fix the fuel leak, won’t be doing anything on the bike until that arrives. Will update as i progress through the repairs.

Bike needs a lot of things looking at but i’d like to know that it will start before i throw a load of money at it.

[♠️ M77]

Go with what simon says ,
Side stand switch = follow its wires and cut them. Ditch the switch. Join wires at the loom side. Please protect that area by waterproofing with good tape! I mean be ocd about this.

Clutch handle bar = follow its wires , the switch will say 0 ohm on the meter when you squeeze on and off on the lever, that means it’s dead.  But luckily , i sell the clutch switches, should you need one!

Your fuel tap was posted today , so you should have it soon,  we are in yorkshire too just as you are 🙂

When cranking the bike, the plugs will be sparking bright.  This means its ready to fire.  Dull yellow usually means bad coil,  stator (it is also part of sparking due to its pickup sensor inside it), bad HT cap, or plug has broken down.

[Wayne]

Thank you.

As the bike stands now, the plugs only spark brightly as i release the start button.

While the starter motor is turning the engine, there is no spark at all, until i release.

Daft question now, is there a separate starting ignition system to a running ignition system?

[♠️ M77]

This is the process of the bike to get sparks and start it.

Key On

Press Start Button

CDI checks rider has held in the clutch lever  = Make sure switch is OK or replace it.

CDI checks the neutral light is on = Make sure rear wheel is actually freely moving, since fake neutrals are rare but do happen some odd cases.

CDI checks side side stand switch  = bypass this unit, remember what was said in previous comments above from myself and Simon

Now the Solenoid  (Starter Relay) clicks to initiate the power to the starter motor to spin it & crank engine.
A bad solenoid or a bad starter motor will make the sparks weak.
Why? They are straining the battery in excess

As the engine starts spinning (cranking)

The “STATOR UNIT”  tell the cdi how many revs it’s doing
(Hint, the rpm gauge will be bouncing 600 rpm as bike turns over)

Now the “STATOR UNIT” will also tell the cdi how much to spark

The CDI unit, then tells the coils to charge up & fire up 10,000 volts down the HT caps to fire the plugs
You will not see sparks or they will be very dull, if
– Coils are shot
– HT Caps are shot
– Battery is too old  (volts dropping)
– Battery is too weak  (AMPS aka Cold Cranking Amps isn’t sufficient to crank and power up the bike, electrics etc while engine is cold cranking)
– Plugs have given up  (Replace them)

Once the plugs are sparking , the engine comes to life thanks to the pistons drawing fuel out of the carbs and creating vacuum for the tank taps & fuel pump to keep the fuel supply going.

If the clutch lever switch acts weird while bike is running, then it will cut the sparks off almost instantly or when dropping to 1st gear.

If any parts above ^ that were involved in starting the bike act funny while its running, the cdi cuts its sparks off.

If compression is WEAK,  it will be hard to start.
If valve clearances are “too tight” or “too lose”, it will be hard to start.

But let’s cross this bridge if all electrics are sorted out first and its still not starting but i do pray the engine itself is OK.

Also, try this when it is safe to do so please.

Make the bike ready and connect everything and make sure battery is fully charged. Find a private road. Sit on the bike , and have someone push you till you get 10mph on the dash  (jogging speed-ish) , then  drop to 1st gear ,  have choke on.  and be ready to twist the throttle to scream it to life.

If it starts by “pushing” the bike , then let us know.   Don’t jump start a bike with jump leads with a live running van or car as they will 100% burn the electrics of the bikes.

[Wayne]

Thank you for the information, it is very helpful.

New part arrived today so i will be tackling the bike again this weekend, I think the brakes are seized too….

I’ve never had to hold the clutch in to start the bike in the past and the manual says that if it is in neutral the engine will start regardless of clutch and side stand position, but i will still be checking them. I found the maintenance manual online and it has all the info on electrics.

Thanks again for your patience.

I will update at the weekend regardless of outcome…lol.

[Wayne]

Update

She lives!!!

Starts ok, ticks over nicely.

New problem, dies as soon as I knock it in to gear. Is that the clutch switch by any chance?

Still lots of work to do so not street ready yet.

[Wayne]

Scrap that last bit, had a dumb moment….the side stand was down.

All good engine wise, now to sort the brakes.

[Wayne]

Doing quite well so far, brakes are ok too. Got a leaking front fork now, can’t find the part in the shop though, any ideas where to get oil seal from?

[Simon]

Pyramid parts make them, you can pick them up easy on ebay.

 

[Wayne]

Thank you

Ordered a pair on ebay, now to find a video on YouTube on how to replace them.

 

[Author]

Posts

[Wayne]

Hi, I’ve owned a GT125 Comet (2008) from new. It has always been a bad starter but i thought that was normal. The bike has been stood for a number of years now (Only done 6000km) and i am in the process of getting it going again. I was trying to get it started, engine cranks but won’t fire. I removed the spark plug to test for a spark and noticed something, as the engine is cranking there is no spark but just as i release the ignition button the spark plug sparks (maybe 2 sparks at most), is this normal? If not, then what could be the issue. I seem to remember the bike always started after i released the starter button. Thanks in advance.

Removed old fuel, Cleaned the carbs and fully charged the battery, and used booster battery for starting.

I do have a fuel leak at the vacuum valve under the fuel tank. Needs replacing.

[Simon]

Check the interlocks side stand switch, clutch switch first.

[Wayne]

Thank you, i will do that.

Just for peace of mind though should the spark plug be (sparking) all the time the starter motor is turning the engine over?

Ordered a new petrol Vacuum valve to fix the fuel leak, won’t be doing anything on the bike until that arrives. Will update as i progress through the repairs.

Bike needs a lot of things looking at but i’d like to know that it will start before i throw a load of money at it.

[♠️ M77]

Go with what simon says ,
Side stand switch = follow its wires and cut them. Ditch the switch. Join wires at the loom side. Please protect that area by waterproofing with good tape! I mean be ocd about this.

Clutch handle bar = follow its wires , the switch will say 0 ohm on the meter when you squeeze on and off on the lever, that means it’s dead.  But luckily , i sell the clutch switches, should you need one!

Your fuel tap was posted today , so you should have it soon,  we are in yorkshire too just as you are 🙂

When cranking the bike, the plugs will be sparking bright.  This means its ready to fire.  Dull yellow usually means bad coil,  stator (it is also part of sparking due to its pickup sensor inside it), bad HT cap, or plug has broken down.

[Wayne]

Thank you.

As the bike stands now, the plugs only spark brightly as i release the start button.

While the starter motor is turning the engine, there is no spark at all, until i release.

Daft question now, is there a separate starting ignition system to a running ignition system?

[♠️ M77]

This is the process of the bike to get sparks and start it.

Key On

Press Start Button

CDI checks rider has held in the clutch lever  = Make sure switch is OK or replace it.

CDI checks the neutral light is on = Make sure rear wheel is actually freely moving, since fake neutrals are rare but do happen some odd cases.

CDI checks side side stand switch  = bypass this unit, remember what was said in previous comments above from myself and Simon

Now the Solenoid  (Starter Relay) clicks to initiate the power to the starter motor to spin it & crank engine.
A bad solenoid or a bad starter motor will make the sparks weak.
Why? They are straining the battery in excess

As the engine starts spinning (cranking)

The “STATOR UNIT”  tell the cdi how many revs it’s doing
(Hint, the rpm gauge will be bouncing 600 rpm as bike turns over)

Now the “STATOR UNIT” will also tell the cdi how much to spark

The CDI unit, then tells the coils to charge up & fire up 10,000 volts down the HT caps to fire the plugs
You will not see sparks or they will be very dull, if
– Coils are shot
– HT Caps are shot
– Battery is too old  (volts dropping)
– Battery is too weak  (AMPS aka Cold Cranking Amps isn’t sufficient to crank and power up the bike, electrics etc while engine is cold cranking)
– Plugs have given up  (Replace them)

Once the plugs are sparking , the engine comes to life thanks to the pistons drawing fuel out of the carbs and creating vacuum for the tank taps & fuel pump to keep the fuel supply going.

If the clutch lever switch acts weird while bike is running, then it will cut the sparks off almost instantly or when dropping to 1st gear.

If any parts above ^ that were involved in starting the bike act funny while its running, the cdi cuts its sparks off.

If compression is WEAK,  it will be hard to start.
If valve clearances are “too tight” or “too lose”, it will be hard to start.

But let’s cross this bridge if all electrics are sorted out first and its still not starting but i do pray the engine itself is OK.

Also, try this when it is safe to do so please.

Make the bike ready and connect everything and make sure battery is fully charged. Find a private road. Sit on the bike , and have someone push you till you get 10mph on the dash  (jogging speed-ish) , then  drop to 1st gear ,  have choke on.  and be ready to twist the throttle to scream it to life.

If it starts by “pushing” the bike , then let us know.   Don’t jump start a bike with jump leads with a live running van or car as they will 100% burn the electrics of the bikes.

[Wayne]

Thank you for the information, it is very helpful.

New part arrived today so i will be tackling the bike again this weekend, I think the brakes are seized too….

I’ve never had to hold the clutch in to start the bike in the past and the manual says that if it is in neutral the engine will start regardless of clutch and side stand position, but i will still be checking them. I found the maintenance manual online and it has all the info on electrics.

Thanks again for your patience.

I will update at the weekend regardless of outcome…lol.

[Wayne]

Update

She lives!!!

Starts ok, ticks over nicely.

New problem, dies as soon as I knock it in to gear. Is that the clutch switch by any chance?

Still lots of work to do so not street ready yet.

[Wayne]

Scrap that last bit, had a dumb moment….the side stand was down.

All good engine wise, now to sort the brakes.

[Wayne]

Doing quite well so far, brakes are ok too. Got a leaking front fork now, can’t find the part in the shop though, any ideas where to get oil seal from?

[Simon]

Pyramid parts make them, you can pick them up easy on ebay.

 

[Wayne]

Thank you

Ordered a pair on ebay, now to find a video on YouTube on how to replace them.

 

[Author]

Posts