After warm up, idle unstable GN 125

Korshakov

Hey guys,

i have been trying to solve this issue for quite a long time, replaced carb, new HT coil, new rectifier, valve clearance checked regularly. The Engine works just fine but after an hour of driving idle rpms becomes unstable and motorbike is "lazy" to go up in rpms. Also the motorbike dies immediately when i set rpms to 5 000 and unplug battery. As far as i know the engine should be running without battery no? Resistance of each wires on alternator is 1.6 ohm. Regulated voltage at 5 000 rpm is 14.00V. Spark plug cap resistance 9.99Kohm (i think this is too high and by simple ohm's law this high resistance is reducing voltage on spark plug) i ordered new NGK cap with 5K ohm resistance. The reason iam asking for help is that the bike just ruined not even year old battery. Any ideas please what it could be?

spiggotpaddy

You could have a leak in the head gasket, when the engine is hot. Check the compression. A newish battery dying is the usually a reg/rec problem.

Korshakov

spiggotpaddy wrote: »

You could have a leak in the head gasket, when the engine is hot. Check the compression. A newish battery dying is the usually a reg/rec problem.

Thanks spiggotpaddy will try to check to compression tomorrow and will have a closer look into rectifier by measuring resistances.

spiggotpaddy

Check the carb intake rubber, could be perished expanding when hot, sucking in air.

Korshakov

spiggotpaddy wrote: »

Check the carb intake rubber, could be perished expanding when hot, sucking in air.

Compression is good i checked today, rectifier works perfectly all diods passed diod test. I think i found an issue today finally. I didn't check last time pulsar coil. It is suppose to be between 90 - 120 ohm. Mine was 180 ohms. Also secondary wiring on HT igniton coil was down to 10K ohm, should be between 15 - 25K ohm.

If the voltage signal from pulsar coil to CDI is lower it probably explains why my sparks are all the time orange/yellow. I suppose when the engine heats up the compression kills time to time spark on spark plug. And that would explain unstable idle rmp. What do you think about this theory?

spiggotpaddy

Yeah thing is with electrical faults is they're often intermittent. Can your meter readings be completely reliable, if the reg/rec is getting too hot it will send current everywhere and usually boil the battery and burn wires. Or could work fine at cooler temperatures. If the stator and pick up coil are reading right, I would try a new reg/rec . Happy hunting.

Korshakov

spiggotpaddy wrote: »

Yeah thing is with electrical faults is they're often intermittent. Can your meter readings be completely reliable, if the reg/rec is getting too hot it will send current everywhere and usually boil the battery and burn wires. Or could work fine at cooler temperatures. If the stator and pick up coil are reading right, I would try a new reg/rec . Happy hunting.

Thank you mate, will let you know here if i got it sorted or not. If yes i will try to explain as much as i can to help someone else in future trouble.

TeaBagMania

Simple compression test might not tell the whole story, perform a leak down test as well

two wheels good

My first thoughts were along the lines of others posts - air leak, head gasket, choke on, air filter\carb problem but these are unlikely to need an hour of riding to appear.

When the problem appears what's the voltage reading at the battery? Is that 14V reading you mentioned taken when everything is fine?

It does sounds like the battery could be almost flat due to a charging problem. Maybe the charging is okay but you have a draw on the battery.
If charging is suspect you could clean up the connectors on the rec\reg. Also check output from alternator.

The engine cutting out when the battery is removed might be correct. It's happened me on a 250 single before - when I was expecting the engine to keep running.

Korshakov

two wheels good wrote: »

My first thoughts were along the lines of others posts - air leak, head gasket, choke on, air filter\carb problem but these are unlikely to need an hour of riding to appear.

When the problem appears what's the voltage reading at the battery? Is that 14V reading you mentioned taken when everything is fine?

It does sounds like the battery could be almost flat due to a charging problem. Maybe the charging is okay but you have a draw on the battery.
If charging is suspect you could clean up the connectors on the rec\reg. Also check output from alternator.

The engine cutting out when the battery is removed might be correct. It's happened me on a 250 single before - when I was expecting the engine to keep running.

I was hunting those air leaks for quite a long time before it actually ruined battery and i could not find anything.

When the bike is hot the voltage reading on idle is 13.56V and at 5 000 rpm the voltage reading 14.02 V. All the connectors are cleaned and tight. Output voltage while cold (no load) 80 to 81 V on all 3 variations. Same for when its hot. Same apply to coil resistances 1.6 ohm on all of them while hot/cold.

The only 2 things which doesn't make me sleep well are: Pulsar coil resistance while cold 120 ohm, while hot 220 ohm. The reason why it doesn't make me sleep is that in Hayes repair book says: GN 125 V,W,X,Y and K1 model resistance between 100 to 300 ohm. My motorbike is Chinese import and i cannot for the lord sake find out properly what model my bike is. VIN decoder does not say anything about my model. All i can say for sure is that bike is from 2003. I know that Suzuki discontinued production at 2001 and China started again after, but what model they started from i cannot find out. If the bike is R model than the pulsar coil is ruined as the resistance is suppose to be between 90 to 120 ohm.

The second issue which does not make me sleep is: it doesn't matter how hard i try to set the air screw position to 1 and 7/8 turns out the engine does not react to it at all. I should set the turns as i wrote and then heat engine up and test 1/4 turns each way to find the highest rpms, it does not react to those 1/4 turns. Spark plug is gorgeous and no sign of bad burns or incorrect air mixture or even overheating spark plug (i only found out this issue yesterday, when i was hunting for everything possible related to unstable idle). Carb is not even year old. It is driving me mad because i had to buy new battery and i know something is probably ruining it again. If i don't find solution in a week I am just going to drop it to garage, because iam afraid i will ruin another battery.

The very last thing i tried and it failed test was CDI test when i was setting multi-meter to ohm scale x1 and inserting cables to CDI input from pulsar coil way i should have see spark on spark plug, but nothing even when i switched polarity. I am not sure if i am actually doing this correct, because if the CDI would be faulty then I would not get any sparks at all. But this is my own theory and I am not sure about this.

It really frustrates me because the bike great and very cheap to run and i never ever had such an issue with it before. The bike doesn't even have 10 000 km on the clock.

Korshakov

two wheels good wrote: »

My first thoughts were along the lines of others posts - air leak, head gasket, choke on, air filter\carb problem but these are unlikely to need an hour of riding to appear.

When the problem appears what's the voltage reading at the battery? Is that 14V reading you mentioned taken when everything is fine?

It does sounds like the battery could be almost flat due to a charging problem. Maybe the charging is okay but you have a draw on the battery.
If charging is suspect you could clean up the connectors on the rec\reg. Also check output from alternator.

The engine cutting out when the battery is removed might be correct. It's happened me on a 250 single before - when I was expecting the engine to keep running.

I was hunting those air leaks for quite a long time before it actually ruined battery and i could not find anything.

When the bike is hot the voltage reading on idle is 13.56V and at 5 000 rpm the voltage reading 14.02 V. All the connectors are cleaned and tight. Output voltage while cold (no load) 80 to 81 V on all 3 variations. Same for when its hot. Same apply to coil resistances 1.6 ohm on all of them while hot/cold.

The only 2 things which doesn't make me sleep well are: Pulsar coil resistance while cold 120 ohm, while hot 220 ohm. The reason why it doesn't make me sleep is that in Hayes repair book says: GN 125 V,W,X,Y and K1 model resistance between 100 to 300 ohm. My motorbike is Chinese import and i cannot for the lord sake find out properly what model my bike is. VIN decoder does not say anything about my model. All i can say for sure is that bike is from 2003. I know that Suzuki discontinued production at 2001 and China started again after, but what model they started from i cannot find out. If the bike is R model than the pulsar coil is ruined as the resistance is suppose to be between 90 to 120 ohm.

The second issue which does not make me sleep is: it doesn't matter how hard i try to set the air screw position to 1 and 7/8 turns out the engine does not react to it at all. I should set the turns as i wrote and then heat engine up and test 1/4 turns each way to find the highest rpms, it does not react to those 1/4 turns. Spark plug is gorgeous and no sign of bad burns or incorrect air mixture or even overheating spark plug (i only found out this issue yesterday, when i was hunting for everything possible related to unstable idle). Carb is not even year old. It is driving me mad because i had to buy new battery and i know something is probably ruining it again. If i don't find solution in a week I am just going to drop it to garage, because iam afraid i will ruin another battery.

The very last thing i tried and it failed test was CDI test when i was setting multi-meter to ohm scale x1 and inserting cables to CDI input from pulsar coil way i should have see spark on spark plug, but nothing even when i switched polarity. I am not sure if i am actually doing this correct, because if the CDI would be faulty then I would not get any sparks at all. But this is my own theory and I am not sure about this.

It really frustrates me because the bike great and very cheap to run and i never ever had such an issue with it before. The bike doesn't even have 10 000 km on the clock.

I will check on that draw as soon as i get chance.

Korshakov

TeaBagMania wrote: »

Simple compression test might not tell the whole story, perform a leak down test as well

Is there any way i can do this "home tools"? I don't have leak down tester.

TeaBagMania

Korshakov wrote: »

Is there any way i can do this "home tools"? I don't have leak down tester.

Its a special tool, if you google it you'll find pics

two wheels good

On the carb: If the mixture is already rich the pilot adjustment won't be noticeable.
Check the float level and the height of the main jet. Clean the pilot channel. Not with a wire; but you probably know that!
If the spark plug looks okay I wouldn't be too concerned. Pilot screw functions at small throttle openings and I don't think will be a factor in the problem.
Is the fuel supply okay; and the tank cap venting?.

Korshakov

Korshakov wrote: »

Hey guys,

i have been trying to solve this issue for quite a long time, replaced carb, new HT coil, new rectifier, valve clearance checked regularly. The Engine works just fine but after an hour of driving idle rpms becomes unstable and motorbike is "lazy" to go up in rpms. Also the motorbike dies immediately when i set rpms to 5 000 and unplug battery. As far as i know the engine should be running without battery no? Resistance of each wires on alternator is 1.6 ohm. Regulated voltage at 5 000 rpm is 14.00V. Spark plug cap resistance 9.99Kohm (i think this is too high and by simple ohm's law this high resistance is reducing voltage on spark plug) i ordered new NGK cap with 5K ohm resistance. The reason iam asking for help is that the bike just ruined not even year old battery. Any ideas please what it could be?

You say the bike dies after an hour, so I would be looking at head gasket and or coolant issue. Why is it good until it gets very warm. Are the plugs
gaped correctly? Do you charge your battery? you didn't charge it backwards?

Korshakov

two wheels good wrote: »

On the carb: If the mixture is already rich the pilot adjustment won't be noticeable.
Check the float level and the height of the main jet. Clean the pilot channel. Not with a wire; but you probably know that!
If the spark plug looks okay I wouldn't be too concerned. Pilot screw functions at small throttle openings and I don't think will be a factor in the problem.
Is the fuel supply okay; and the tank cap venting?.

The earliest i can have a look into this is Thursday. Will let you know how it went.