Help! Bike suddenly stopped....

[simon43]

I was riding my bike as normal, absolutely no problems. Then the engine backfired once and stopped. 

 

The battery was strong and I tried the electric start quite a few times. The engine turned over but did not start. 

 

I checked that there was sufficient fuel in the tank ==> all OK. 

 

I took out the spark plug which was not oiled up. I attached the HT lead and pressed the starter button and got a strong spark. 

 

The problem suggested (to me) a fuel blockage. I pushed the bike to a local work shop where they managed to start the engine once, but after pushing the kill switch, the engine then refused to start again! 

 

They stripped down and cleaned the carb, reassembled everything and then tried to start the bike again, including pushing it at speed on the road (another bike rider alongside pushing with his foot). The bike still refused to start! 

 

They and I are at a loss to think what could be the problem. 

 

Any suggestions what to check next? Electrics seem OK, carb is clean, plenty of fuel in the tank.....

[jollyhangmon]

Does the kickstand have a safety kill-switch? Had one of these on a then 18 years old Yamaha XT failing progressively after some rough offroad rides, kept on shutting down the gig but not always, took us ages to nail da biatch ... 

[simon43]

Does the kickstand have a safety kill-switch

 

Yes it does.  But with the bike on the kickstand I'm getting a strong spark from the plug to the cylinder head, (after removing the spark plug and attaching the HT lead).

[tifino]

4 minutes ago, jollyhangmon said:

Does the kickstand have a safety kill-switch? Had one of these on a then 18 years old Yamaha XT failing progressively after some rough offroad rides, kept on shutting down the gig but not always, took us ages to nail da biatch ... 

 

funny if it had a kill-safety interlock, like under tractor mower seats!

p.s. for a Thai bike - this would actually be a good idea...to keep their asses on their seats...

[jollyhangmon]

Wait a sec, I mean the side-stand & the safety-switch is to avoid blasting off with the sidestand out (but in my case killed the engine sometimes while up in regular driving position) ... so you probably talking about the 'main-' or 'middle'-stand where it would be okay to still have a spark with the ride being on it ...
However, yes, with a perfect spark that can't be the problem anyway ... 

[jollyhangmon]

16 minutes ago, tifino said:

 

funny if it had a kill-safety interlock, like under tractor mower seats!

p.s. for a Thai bike - this would actually be a good idea...to keep their asses on their seats...

 

... agreed to one of these on the local rides, no bad idea - would rein in some acrobats here, hehe ...
On an Enduro or dirtbike offroad on the other hand you wouldn't be happy though as you are up from your seat half the time catching bumps with knees and arms rather than with your nuts ... 

[Maybole]

The backfire suggests the timing has slipped.

[OneMoreFarang]

10 hours ago, Maybole said:

The backfire suggests the timing has slipped.

My first idea was the kick-stand. But there is a spark so that is not the problem.

And my second idea is the timing. Let me elaborate.

The bike needs air/fuel and it needs a spark. But that is not enough. The spark must come in the correct moment (not exact but not too far off).

If the timing is very much off then there is still a spark but this spark just happens at the wrong moment and the bike won't run.

I guess I would first try to spray something in the carburetor (don't remember the name, technicians know that stuff which helps to start the engine). If that brings no result check the timing.

 

 

[Bung]

Tell us what bike it is. Sounds like you are losing spark sometimes. When you lose it the air/fuel keeps feeding the engine then you get a spark again it backfires. I would check all your electrical connections, especially the kick stand cut out. Sometimes they cut in and out which would cause your problems. Some bikes have a neutral switch (bike can run on the side stand but cuts out when you put it in gear). Also, try a new spark plug if it's old and check the kill switch. 

[simon43]

I appreciate all the advice ?

 

I do not think it is  spark problem. The bike backfired just once before stopping.  When the mechanic managed to start the engine again it seemed to run fine , but refused to start again after he stopped the egine after running it for a few minutes.  There were no more backfires at all.  The spark seems strong and consistent.

 

To my naive mind, it seems exactly like fuel starvation.  But the mechanic stripped down the carb, cleaned all the jets etc.  I recharged the battery overnight, the engine turns over strongly, but absolutely nothing!

 

Although it sounds like fuel starvation to me, the fact that the engine quickly stopped after one misfire doesn't sound like fuel starvation caused it to stop.  Typically, the engine would run badly, gradually getting starved of fuel  and would finally stop.This stopped within 5 seconds from normal running.

 

 

[CharlieH]

Broken down to basics....

 

Fuel delivery - OK

Spark - Ok

Compression -OK

Timing - Ok

 

If all those are functioning and as it should be its either an interruption in electric by a device like a safety switch/device or a fuel stop of some kind. (IMHO)

(checked no crap in tank/line blocking fuel flow ?)

[Vacuum]

11 hours ago, Maybole said:

The backfire suggests the timing has slipped.

The timing is probably a 'electronic' one, they don't "slip".

[simon43]

I'm still thinking about fuel starvation.  Even if the timing had slipped, the presence of fuel and spark would cause some ignition or backfire from the engine. I'm getting spark and absolutely no ignition or backfire.

 

The mechanic opened the carb, took out the jets, cleaned everything in petrol and rebuilt it.  If I unscrew the drain screw at the bottom of the carb, then petrol comes out of the plastic drain tube.  I can't see how the petrol/air mixture cannot be entering the cylinder head and being there when the spark is generated...

[simon43]

As an afterthought, even though I have turned the engine many times with the starter motor, the spark plug is not 'wet' with unignited fuel.... surely it should be wet if petrol were reaching it. Hmmm....

[OneMoreFarang]

39 minutes ago, Vacuum said:

12 hours ago, Maybole said:

The backfire suggests the timing has slipped.

The timing is probably a 'electronic' one, they don't "slip".

This is why it would help a lot to know what bike we are talking about...

[simon43]

Sorry - it's a Honda XL125 off-road bike, single cyclinger.

[papa al]

√ air-filter

?

[jollyhangmon]

26 minutes ago, simon43 said:

As an afterthought, even though I have turned the engine many times with the starter motor, the spark plug is not 'wet' with unignited fuel.... surely it should be wet if petrol were reaching it. Hmmm....

 

Morning sirs, yes that's a good point, I also think it should be wet ... seems like really no fuel's getting into the cylinder ?!

[Bung]

XL125? What year?? I think they are very old (1970's) and have points ignition? 

[simon43]

OK, I am making some fault-finding progress ?

 

FYI, this bike is an XR125L, made around 2002.

 

I took out the spark plug, dribbled a thimbleful of neat petrol into the hole, put the plug back and tried to start the engine.

 

This time, the petrol ignited for a second or two!  That suggests to me that the spark and timing and mechanics are fine, and that indeed it is a petrol starvation problem.

 

But how?  The carb has been stripped and cleaned.....

 

But what are the 2 electrical wires that are connected to this carb????  They are connected close to the interface of the carb and the cylinder head, (ie the opposite end of the carb from the air filter).

 

Has this carb got some form of electronic valve that regulates the passing of the petrol/air mixture into the cylinder head?

 

I'm trying to Google for this information right now.  It would make absolute sense to me if there were an electronic valve whose fuse had blown.

[CanuckThai]

Check your fuel, might not be the case, but the symptoms sound familiar.  When we buy fuel, shortly after a rain storm, from our local gas monkeys, water is in both petrol and diesel.  Enough water that I have to "purge" the diesel filter (alarm indicator + loss of power) water separator/filter, and also add clean petrol to the mc's (wife's honda seems more susceptible to water in fuel)  She can end up killing the battery, trying to start, with no success.  Fresh gas (clean water free petrol) does the trick...

[CharlieH]

"But how?  The carb has been stripped and cleaned....."

 

yes but if the issue is before the carb in the delivery process somewhere between tank and carb. Either electrical control or a restriction ?

[simon43]

I Googled and found out that the electrical bit is the carb heater - not sure whether failure of this would effect starting or not....

[Vacuum]

11 minutes ago, simon43 said:

The carb has been stripped and cleaned.....

I had to clean my carb 3 times before it worked. Do it yourself and check every orifice you can see with a thin hose, and use your lungs to be sure there's a free passage.

[jollyhangmon]

38 minutes ago, simon43 said:

I Googled and found out that the electrical bit is the carb heater - not sure whether failure of this would effect starting or not....

 

... interesting, never heard of a carb-heater before TBH, had to google that apparatus and it mostly referred to aircrafts which makes sense ...

 

Maybe therein lies the problem, was your bike a plane before maybe, ever tried to get it airborne?

Because then you simply have the wrong type of fuel in right now ... ? 

 

Seriously, don't think that heater-thingy would disable the whole thing if faulty ... like someone noted above, does the carb even get fuel down from the tank? Is there a little lever somewhere on it where if you push it fuel comes out below ... sorry, no experience with the Honda bits really, don't know if that exists on their carbs but I know it from Yamahas as well as older KTM's as probably still used by Austrian army ... 

[simon43]

The heater resistance indicates that it's not broken, but I can't detect 12 volts on the supply wire to the heater.  I jumped 12 volts from the battery to the heater but it didn't chnage anything.  I don't think lack of the heater will be the problem.

 

But I'm 99% sure that it is a fuel starvation problem which suddenly occurred.  What sort of carb failure could do this?  The jets were all blown through and all looked good.

 

There is another hose pipe that comes off near to the carb/cylinder head intake and then goes to some mechanical unit mounted near the petrol tank.  No idea what that's for...

[Vacuum]

4 minutes ago, simon43 said:

The jets were all blown through and all looked good.

There are several other orifices than the jets that could be clogged up. Open the carb up and have look.

[Daffy D]

Could be an air leak creating a weak mixture. Would also explain the backfire.

 

Just as another thought are you getting any intake suction when placing your hand over the carb.

 

 

[simon43]

Just as another thought are you getting any intake suction when placing your hand over the carb.

 

Can you please explain this check a little more?  Where do I place my hand etc?

[Daffy D]

Over the intake hole of the carb as you turn the engine, preferably with the ignition off. There should be a strong suck on your hand.

 

May have to move the air filter pipe out of the way.