Bike stalls when pulling away

[zedhead]

Hi

Weird one here. My sons 125cc ebnduro bike will stall when you try to pull away.

If the bike is standing still you can rev the nuts of it so i am thinking the carb is getting enough fuel,but drop it into first and release the clutch blurrgh no power and it stalls.

This started after replacing the sprockets [same amount of teeth as old sprockets] and cush drive.

I have stripped and cleaned the carb twice but that made no difference.

If i had hair it would be out now.

zedhead

[eastanglianbiker]

changing the chain and sprockets would not cause this problem to arise,when you have been cleaning the carb out have you moved the mixture screw on the side of the carb at all or damaged the reed valve if it has one? and are you sure it hasnt run out of petrol?

[Tango]

If it'll rev off load but stalls under load I'd be looking at the spark and the plug.....just a thought....

[zedhead]

I didnt think the sprockets had anything to do with it but it helps to list the things youve done prior to the problem arising.

The only screw i have moved when cleaning the carbs was the pilot screw,and i put it back in the same number of turns that came out.Also i only cleaned the carbs after this problem arose.

Petrol tank full fuel petcock working fine and carb bowl always has petrol.

Checked spark plug-fine

Both front and rear wheels turning freely neither brake binding.

Bike revs throughout the range smoothly and flawlesly.

Sit on the bike release clutch and advance throttle bl**@y thing stalls.

[Guest Hodgy]

Have you checked the compression? just a thought

[Tango]

Have you got a nice strong spark?......if it's weak the bike will bog down and stall when you put it under load. Do you have a spare plug you could swap it with just in case? What colour is the plug? Clogged air filter? Seems a bit strange that this happened when you changed the chain and sprockets....but weird things happen sometimes.....

[Colin the Bear]

Have you trapped something changing sprockets.

How does it stall, does it just cut out or splutter and die, sidestand switch? , clutch switch?

[Tango]

Good Call Colin......sidestand switch may have taken a knock when changing the chain and sprockets.....

[Colin the Bear]

I just post sidestand switch to all questions and am right about 25%

[zedhead]

Ok finally got back to the bike. I checked the plug again getting good spark,checked fuel tank breather pipe,checked everything i could ,associated with things i had changed ie:sprockets to the functioning of the choke and throttle cables after removing and cleaning the carbs...phew!!.

Started bike ,runs perfectly throught rev range on idle,pulled away and it ran smooth with only a couple of dips which quickly disappeared. Bike now runs smooth as ever!!!!!! and i have no idea how it got fixed .

Will test run it more over the weekend and fingers crossed it's sorted.

Thanks to everyone who suggested ideas much appreciated.

zedhead

[Colin the Bear]

You must have found the right position for your mouth. This is critical for quick starts

That and the petrol fairy

[zedhead]

Ok first off apologies for the sporadic nature of these posts,other commitments mean i cant always get to the bike .

Took it out for a test worked fine did about three miles got bike nice and warmed up.

That's when it started again!!!. Bike revs freely throught the range in neutral ,but pop it into gear and it struggles to pull away. All you can do is pull clutch in and try againand again with the same result, no power to pull away. I have done an internet search for this problem and most of the answers lie in one of two camps..Carbs or Sparkplug. I have cleaned the former twice and the latter is in good condition [only done 10-20 miles on it since new] and gives a decent spark.On the subject of spark the battery does seem to lose charge easily if the bike is not used much. Not being used to a 125 for a long time could the battery condition affect the performance of a small cc bike?. I may be clutching at straws but ...

zedhead

[Joeman]

What bike is it?

if it revs freely in Neutral, how does it rev in gear with the back wheel off the ground?

[eastanglianbiker]

yes battery condition could affect the way the bike runs also the problem could be with spark plug i have just had similar problem with my bike started fine when cold ran fine but wouldnt restart when hot and was pig to keep running new plugs solved the issue.how old is the battery on your bike and have you checked charging rate

[Colin the Bear]

All electricals are routed through battery. You wouldn't believe the problems a duff battery can generate. If you suspect the battery, and considering the price for a 125, I'd replace it.

Did these problems start after fitting a new plug? New ones can be duff. Try another, if it's not that you have a spare

[TC]

Have you checked the compression? just a thought

 

I'm with Hodgy here, sounds like you are losing compression when the engine is under load,

[Voodoo]

Change the spark plug, they don't cost much and it will eliminate that as the problem.

[Colin the Bear]

Have you checked the compression? just a thought

 

I'm with Hodgy here, sounds like you are losing compression when the engine is under load,

 

I can't see how a loss of compression would give an intermittent fault

[Guest Hodgy]

Have you checked the compression? just a thought

 

I'm with Hodgy here, sounds like you are losing compression when the engine is under load,

 

I can't see how a loss of compression would give an intermittent fault

 

Maybe I miss-read the op, I didn't spot it was intermittent, I thought it was whenever he was setting off? You are right though, low compression can't be intermittant

[OhJay]

Not likely to be the clutch is it? Something snagging/clogging/dirty in there?

[Joeman]

Not likely to be the clutch is it? Something snagging/clogging/dirty in there?

 

That's why the OP should try lifting the back wheel, kicking it into gear, and seeing if it stalls then.

Might be low on G-box oil and seizing when it gets warm

[pointblank0]

From what I have heard, I would say that the cluth cable is either worn or too loose, just a thought. It seems that the engine runs fine in neutral, but when taking off, it stalls. I reckon it's worth checking, if those friction disks are compressing straight away, the bike will stall like you describe.

Does the bike creep forward when in gear and cluth lever pulled right in?

[Danny-B-]

I smell a faulty side stand switch by a mile ... if the top of the side stand switch is covered in gunk (oil from chain etc) then its shorting out the sidestand switch and causing the engine to cut out ... my old CBR did this when i was in gear and revving about 5000 ...

to eliminate the sidestand, take the switch off and short the two wires out ... (could have three, in which case, one is for the dash light)

[zedhead]

Hi again thanks for all the comments on this ongoing problem.

As i have been trying to sort this a few things have come to light.

1/ The bike from cold pulls away and runs fine.After a couple of minutes riding [maybe 5-10 min at times]. The bike will lose power.When i originally found the problem the bike had already been running, hence the title.

2/ The power loss can happen when pulling away or when riding at speed 30mph etc.

3/ I have jacked the bike up and ran the bike through the gears up to speed for 5 minutes and no loss of power.! It only appears when the bike is ridden.

4/ Spark is good, nice and healthy,there is plenty of petrol. The gearchange is smooth and the cable works fine. Battery is charging and holding charge.There is required amount of oil in the sump.

5/ After running the bike and the problem appears i leave it to cool for an hour. When i try again the bike works fine for a few minutes and then the problem is back.

6/ The side stand switch suggestion made me think, as this bike has wiring leading from the clutch lever into the loom. I do not know where it goes. I have never had to pull the clutch in to start the bike.

I should weather permitting get back to the bike on Wednesday to try again.

Thanks again for all the suggestions i will sort this b@**er out!

zedhead

[Stu]

I haven,t re-read the thread again so dont shoot me

have you checked the coils? they could be breaking down with heat and load