At Wits End! 2000 YFM250 Bear Tracker Will NOT Start! - ANY and ALL Help/Advice MUCH Appreciated!

[rebeltaz]

I've got a Bear Tracker I'm working on. The guy said that it was running until they ran it through water and it backfired and would not start again. He said when it backfired, it blew a hole in the muffler. Yeah... customers tend to lie, but... anyway.
 

• I replaced the starter clutch set to begin with so I could spin the engine and see what else was wrong.
• I cleaned the kill switch and got it to spark.
• I rebuilt the carburetor - there is no way this thing was running, but... yeah.
• I have verified that it has compression (over 150psi).
• I have verified that there are no leaks (with a leak down test).
• I have verified that the cam is in time.
• I have verified the the cam gear has not spun on the camshaft.
• I have verified that the valves are adjusted correctly.
• I have verified that the valves are in fact opening and closing.
• I have verified that the flywheel hadn't sheared the key (both when I replaced the starter clutch and I made sure that when the top-dead center mark is lined up, the piston is, in fact, at tdc).
• I have verified that it still has spark.
• I loosened the exhaust manifold, in case the muffler was clogged (even though you can feel the pressure as the engine spins over)/

It refuses to start. Even on starter fluid. EXCEPT... If I hold my hand over the intake, it has twice popped off like it wants to start, but that is it.

I have no clue what else I could even try! I am hoping someone will have that Ah Ha! moment...

[Mech]

Checked fuel's getting into the carb ? Loosen the drain bung and see if fuel comes out, after it's empty crank it over and check that more comes out. Tests the flow and pump.

Take the spark plug lead's fittings off(if you can) in case they are shorting.. Use a tiny split pin jambed up the wire to the plug.

Loosen the exhaust at the head perhaps. Blocked exhaust stops the suck too.

It's got a new plug huh ?

And fresh fuel ?

[rebeltaz]

14 hours ago, Mech said:

Checked fuel's getting into the carb ? Loosen the drain bung and see if fuel comes out, after it's empty crank it over and check that more comes out. Tests the flow and pump.

Take the spark plug lead's fittings off(if you can) in case they are shorting.. Use a tiny split pin jambed up the wire to the plug.

Loosen the exhaust at the head perhaps. Blocked exhaust stops the suck too.

It's got a new plug huh ?

And fresh fuel ?

Hi! Yeah... I did make sure that gas is getting to the carburetor. But aside from that, I"ve tried starter fluid straight into the intake.

I did also loosen the exhaust in case it was clogged. It's got suction - I can feel it with my hand over the intake and it'll pull a paper towel in on each intake stroke.

Three new plugs, just in case one was defective.

....

[davefrombc]

Have you checked it is sparking top dead center on compression stroke rather on exhaust ( timing 180 degrees out). It is an easy mistake to  miss even among the most experienced techs .

 

[Mech]

The dunking in water might have caused a crack or track down the sparkplug cap.. It might look like it's sparking good when the plugs out, but be shorting when there's compression on the plug. If it's possible take the cap off the end of the lead. Even taking the waterproofing rubber boot off might make a difference or allow you to hear the spark jumping down the porcelain.

It could have done the same thing to the ignition coil. Once there's compression on the plug the spark has a harder time jumping, and can short somewhere else.

[rebeltaz]

7 hours ago, davefrombc said:

Have you checked it is sparking top dead center on compression stroke rather on exhaust ( timing 180 degrees out). It is an easy mistake to  miss even among the most experienced techs .

 

This is a dumb question, but how do I check that it's not 180 out and how would it have even gotten that way without it having been put back together wrong?

1 hour ago, Mech said:

The dunking in water might have caused a crack or track down the sparkplug cap.. It might look like it's sparking good when the plugs out, but be shorting when there's compression on the plug. If it's possible take the cap off the end of the lead. Even taking the waterproofing rubber boot off might make a difference or allow you to hear the spark jumping down the porcelain.

It could have done the same thing to the ignition coil. Once there's compression on the plug the spark has a harder time jumping, and can short somewhere else.

I will take a look at that when I come back Monday, but I want to think they looked ok...

[Mech]

The track isn't something you are likely to see.. Take the rubber boots off, if not the whole plug cap, and look and listen for sparks.

If you have a timing light, put a screwdriver through it's pickup, and poke around down the plug porcelain looking for a flash of the light. Check around the coil and plug lead the same way..

[Mech]

If you've got a timing light, check it's firing on the mark.. I doubt it will be 180 out, but I've seen them sparking out of time because the wires going into the engine/stator/pickup were saturated and shorting together.. They generally did run though, with a lot of backfiring and missing. They soon dried out also.

[rebeltaz]

I do have timing light. I'll check both of those Monday. Fingers crossed!

[Cj Winds]

Is the spark plug wet or dry after repeated attempts of starting the engine? If the plug is wet, the engine could be getting too much fuel. Try draining the carb and disconnecting the fuel line to the carb. Then try starting it and while starting it try spraying different amounts of starting fluid into intake.

[Savage3]

Based on information provided,  timing is off. Not sparking at the correct time. Go back and recheck.

[Savage3]

8 minutes ago, Savage3 said:

Based on information provided,  timing is off. Not sparking at the correct time. Go back and recheck

This assumes all other information provided is correct.

Is there enough spark to fire under compression? Etc...

[rebeltaz]

3 hours ago, Cj Winds said:

Is the spark plug wet or dry after repeated attempts of starting the engine? If the plug is wet, the engine could be getting too much fuel. Try draining the carb and disconnecting the fuel line to the carb. Then try starting it and while starting it try spraying different amounts of starting fluid into intake.

Spark plug is completely dry.

58 minutes ago, Savage3 said:

This assumes all other information provided is correct.

Is there enough spark to fire under compression? Etc...

I have checked three times. I agree that that is what it sounds like, but if it is, I can't see it. As for the spark, it looks like a good strong spark to me and I have even left one spark plug in the cylinder; put another spark plug in the spark plug boot; and touched the electrode of that plug to the anode of the other spark plug. I an still getting a strong spark. So, for that to happen, it has to be sparking in the cylinder under pressure. 

[Savage3]

Well, if the spark plug is completely dry, that means fuel is not making it to cylinder. However, it should start with fluid injected directly into cylinder. (Go back and revisit fuel problem as well.)

So, if spark is good, timing is off. Ya don't necessarily need a timing light, remove valve cover, put cylinder at top dead center and see if timing marks line up. You should be able to see marks on flywheel.

Up top, inside valve cover, they usually have a mark on timing gear as well.

Remember, TDC must be on compression stroke! It can be 180 degrees out as the other member mentioned. Very important!

[rebeltaz]

50 minutes ago, Savage3 said:

Well, if the spark plug is completely dry, that means fuel is not making it to cylinder. However, it should start with fluid injected directly into cylinder. (Go back and revisit fuel problem as well.)

So, if spark is good, timing is off. Ya don't necessarily need a timing light, remove valve cover, put cylinder at top dead center and see if timing marks line up. You should be able to see marks on flywheel.

Up top, inside valve cover, they usually have a mark on timing gear as well.

Remember, TDC must be on compression stroke! It can be 180 degrees out as the other member mentioned. Very important!

re: spark plug dry... yeah, that's what I would think, too. But, even if the fuel is completely missing - either carburetor issue or even no gas tank at all! - I should (and always do) be able to get the engine to fire off until the starter fluid burns off. 

re: timing... Like I said... I've literally triple checked timing. All of the marks line up and the piston is in fact at tdc when the flywheel marks line up. 

I asked earlier, but how do I know if it's 180 degrees out? And if it were, how could that even be possible without someone accidentally on purpose doing that? I mean... I get jumping time by a tooth or two, but with all of the pins, guides and keys intact, who on earth could the timing jump by 180 degrees? 

[Mech]

Hmmm.. You sound thorough and competent, I'm assuming that you are checking things carefully.

For the spark to be 360 degrees out I agree that it would have to have the cam retimed, and even then it may or not cause a 360 degree off situation. Some cdi systems that run off the crank, that is get their low voltage off the stator, need more than one rotation before they will fire. They have to see several low voltage pulses before the trigger coil will fire them. If the cam timing hasn't been changed though that will not have happened. If it was firing 360 degrees off it should fire out the inlet too.

The dry plug either means it's getting no fuel, or it is but it's getting burnt off but not firing up because of bad timing.

You could pour about a teaspoonful of fuel down the plug hole and try starting it. I don't trust starting fluid. it can flood plugs.

The timing could be off if the voltages coming out of the stator were getting shorted together. I've seen that. Check the wiring pug going into the engine isn't full of mud or wet.

Remove the plug cap in case it's shorting. Your putting the two plugs in series was a good test for strong spark, and it will have tested the coil's not shorting, but it won't have tested the plug cap. I  should point out though that they probably wouldn't recommend that as a test in case it causes a short in the coil.

Check the sparkplug cap, put fuel into the cylinder. If it fires then you need to figure out why it's not getting fuel. Carby, airleak, blocked exhaust.  

Edited February 13, 2022 by Mech

[Savage3]

Check the woodruff key on the crankshaft, ensure it has not sheered.

[rebeltaz]

1 hour ago, Mech said:

Hmmm.. You sound thorough and competent, I'm assuming that you are checking things carefully.

For the spark to be 360 degrees out I agree that it would have to have the cam retimed, and even then it may or not cause a 360 degree off situation. Some cdi systems that run off the crank, that is get their low voltage off the stator, need more than one rotation before they will fire. They have to see several low voltage pulses before the trigger coil will fire them. If the cam timing hasn't been changed though that will not have happened. If it was firing 360 degrees off it should fire out the inlet too.

The dry plug either means it's getting no fuel, or it is but it's getting burnt off but not firing up because of bad timing.

You could pour about a teaspoonful of fuel down the plug hole and try starting it. I don't trust starting fluid. it can flood plugs.

The timing could be off if the voltages coming out of the stator were getting shorted together. I've seen that. Check the wiring pug going into the engine isn't full of mud or wet.

Remove the plug cap in case it's shorting. Your putting the two plugs in series was a good test for strong spark, and it will have tested the coil's not shorting, but it won't have tested the plug cap. I  should point out though that they probably wouldn't recommend that as a test in case it causes a short in the coil.

Check the sparkplug cap, put fuel into the cylinder. If it fires then you need to figure out why it's not getting fuel. Carby, airleak, blocked exhaust.  

re: plug wiring... yep, it was muddy... had to clean all of that (and the kill switch) to get spark in the first place.

re: plugs in series... isn't that basically what a spark tester does, though?

re: fuel in the cylinder... Yep... done that too (fuel in the cylinder). Still no fire. 

55 minutes ago, Savage3 said:

Check the woodruff key on the crankshaft, ensure it has not sheered.

When I replaced the starter clutch, it wasn't and, unless I somehow fugged that up putting it back together - which I don't think would even be possible - it should still be good. Besides, like I said, I have made sure that when the tdc timing mark is lined up, the piston is, in fact, at top dead center.

[Mech]

"re: plugs in series... isn't that basically what a spark tester does, though?"

A spark plug tester puts compression on the plug while you check it's sparking. A cdi tester just simulates the electrical system of the vehicle. A coil tester simulates the vehicle too, either a cdi vehicle or a traditional coil vehicle. The later two do say to use an air gap of about six mill to test the spark, but most vehicle manufacturers warn against cranking things over with the spark plug leads off lest the high voltage causes a short or damages the electronics in the cdi or ignitor.

I'm about out of ideas for you. Compression, fuel and properly timed spark.

So no backfiring, no smell of burnt fuel, dry plug.. all I can think of is that it's not drawing fuel in..  Blocked exhaust..  You'd think it would be in the muffler, but perhaps the header's double walled and it's collapsed the inner or something highly unusual.

[Mech]

I wonder if there's something in the bottom of the plug hole preventing the mix getting to the plug... mud maybe, cobweb of soot.... Never seen it but...

It's strange that fuel down the plug hole didn't even get it to kick. No air or no  ignition of the mix.

[Mech]

i just had a look at the wiring circuits of a couple of yfm250/350 manuals I have, older models though, and they both have a power feed into the cdi when the starter's being operated. 

On a car they feed starter signal into the ecu because the timing pickups and airflow sensors aren't accurate at cranking revs, so the starter signal sets the timing fixed at a suitable point for starting.

On that thing, it could be either providing power to charge the capacitor, or to alter the timing.. If it has a feed from the starting circuit. Probably worth checking that signal's getting in there if it has it.

[Cookie]

This might sound silly but more than once, I’ve installed the plunger down into a carb and it gets hung up. Since you can’t see it, it could be effectively “wide open” throttle trying to start. The mixture would be way off and it could explain the dry spark plug and no light off even with gas/ starting fluid. Look into the carb, make sure it’s not wide open/ full throttle. FWIW, my other machine a Timberwolf 250 won’t start without choke. Is the choke ON? Hope that helps.

[Cj Winds]

Do you have the intake system installed with the air filter installed?

 

[Savage3]

Let's start at the beginning.  The original post states the machine is getting fuel, (by starting fluid at a minimum) spark, and compression. 

Operationally, the engine should start based on the facts provided. However,  the machine needs spark at the proper time.

Now, unless the owner missed something during his diagnosis, failed to provide information, or misdiagnosed something.

The only alternative is spark at the incorrect time or spark not happening under compression. 

 

 

 

[rebeltaz]

47 minutes ago, Mech said:

So no backfiring, no smell of burnt fuel, dry plug.. all I can think of is that it's not drawing fuel in..  Blocked exhaust..  You'd think it would be in the muffler, but perhaps the header's double walled and it's collapsed the inner or something highly unusual.

Nope. Only once in a blue moon will it even act like it wants to fire off. I loosened the exhaust manifold to make sure it wasn't a clogged muffler, but it didn't change anything. Maybe I didn't loosen it fr enough? I don't know, but I would have thought just breaking the seal would have been enough if that were the cause. I'll quadruple check that again tomorrow...

39 minutes ago, Mech said:

I wonder if there's something in the bottom of the plug hole preventing the mix getting to the plug... mud maybe, cobweb of soot.... Never seen it but...

It's strange that fuel down the plug hole didn't even get it to kick. No air or no  ignition of the mix.

I ran a camera down the spark plug hole to take a look at the cylinder walls, so nothing blocking that. 

4 minutes ago, Cookie said:

This might sound silly but more than once, I’ve installed the plunger down into a carb and it gets hung up. Since you can’t see it, it could be effectively “wide open” throttle trying to start. The mixture would be way off and it could explain the dry spark plug and no light off even with gas/ starting fluid. Look into the carb, make sure it’s not wide open/ full throttle. FWIW, my other machine a Timberwolf 250 won’t start without choke. Is the choke ON? Hope that helps.

Yep. Done that before myself, but no. It's good here. And nope. Not on choke, either. Trust me... at this point NOTHING sounds silly!

Just now, Cj Winds said:

Do you have the intake system installed with the air filter installed?

 

I have tried it with the air box installed and removed. Typically, though, an engine will at least start without the air filter. Depending on the tuning, it might not run right or open up right without the air filter restriction, but I've never come across one that wouldn't at least start. But yeah... I have tried that as well. 

 

I just want to go on record as thanking each and every one of you. Believe me, I do not like to ask for help - I like to figure things out myself - but when I do have to ask... you can bet it's a doozy!

[Cj Winds]

Just to give anther 2 cents, About 6 months ago I worked on a Yamaha 250 from the 1990's and it had good compression and spark and fuel but the engine would not start. When this happens I first try several attempts with different shots of starting fluid but this did not work. Then I check the output of the stator and its resistance and DVA voltages were good. It even had good spark with a spark plug installed. I changed the stator knowing that sometimes they test good but are the problem and the atv ran great with a new stator.

Now this person states the plug is dry. If you spray lots of starting fluid in and the plug is still dry, you need to figure out why the plug stays dry. 

[rebeltaz]

6 minutes ago, Savage3 said:

Let's start at the beginning.  The original post states the machine is getting fuel, (by starting fluid at a minimum) spark, and compression. 

Operationally, the engine should start based on the facts provided. However,  the machine needs spark at the proper time.

Now, unless the owner missed something during his diagnosis, failed to provide information, or misdiagnosed something.

The only alternative is spark at the incorrect time or spark not happening under compression. 

I'm going to check again - this will make four times - but unless I am completely off my rocker, timing looks right. I agree with you in your diagnosis, but unless someone has been in this before me without telling me (a high probability in my area) timing is right.

Misdiagnosed something is not outside the realm of possibility. I do do this for a living, but I am human like everyone and do make mistakes. That's why I am open to any and all suggestions and perfectly willing to check and recheck things I know I've already checked. 

As for failed to provide information.... lol... I am always afraid that I provide too much information and that people just skim over it. If there is anything I have left out, I would be more than happy to offer anything I might have missed. 

[Savage3]

1 minute ago, rebeltaz said:

I'm going to check again - this will make four times - but unless I am completely off my rocker, timing looks right. I agree with you in your diagnosis, but unless someone has been in this before me without telling me (a high probability in my area) timing is right.

Misdiagnosed something is not outside the realm of possibility. I do do this for a living, but I am human like everyone and do make mistakes. That's why I am open to any and all suggestions and perfectly willing to check and recheck things I know I've already checked. 

As for failed to provide information.... lol... I am always afraid that I provide too much information and that people just skim over it. If there is anything I have left out, I would be more than happy to offer anything I might have missed. 

You're doing great man! We just need to keep trying, you know the deal! We all miss the simple problem now and then.

I'm just trying to help through a process of elimination. 👍

[Savage3]

9 minutes ago, rebeltaz said:

I'm going to check again - this will make four times - but unless I am completely off my rocker, timing looks right. I agree with you in your diagnosis, but unless someone has been in this before me without telling me (a high probability in my area) timing is right.

Misdiagnosed something is not outside the realm of possibility. I do do this for a living, but I am human like everyone and do make mistakes. That's why I am open to any and all suggestions and perfectly willing to check and recheck things I know I've already checked. 

As for failed to provide information.... lol... I am always afraid that I provide too much information and that people just skim over it. If there is anything I have left out, I would be more than happy to offer anything I might have missed. 

You're doing great man! We just need to keep trying, you know the deal! We all miss the simple problem now and then.

I'm just trying to help through a process of elimination. 👍

[Mech]

Ha.. I'm a mech too Rebel and I know what it can be like.. and as has been said, and you know, it's sometimes the simplest thing. You certainly thorough, and methodical.. 

Check if there's a starter feed into the cdi unit..