Non-FJ, Dirt Bike Problem (LONG)

[SlowOldGuy]

How would you diagnose the following?

Went dirt riding with my son on Sunday.  He has a Yamaha TTR-90 and I have a TTR-230, both are 2005 models.  In preparation, I did a lot of maintenance on Saturday.  Cleaned and oiled the foam air filters, changed oil, adjusted chains and suspensions.  The batteries are both stock and are getting weak.  Not a problem for the 90 since it has a kickstarter, but my 230 is electric start only so I had it on the charger most of the weekend.  Both bikes ran fine on Saturday.  They are typically very cold natured but started easily after the air filter maintenance, so I suspected that I might have over-oiled the filters a bit, but I figured that would redistribute over night and not be a problem on Sunday.

We tow the 1.5 hours to the Red River M/C park and unload.  Both bikes start fine and run well.  The area is very sandy and my son is not that experienced so the initial going was slow, mostly first and second gear slogging though the sand trying not to fall down.

After about 30 minutes of riding, I stopped to let Dillon catch up.  The bike was idling just fine then suddenly it just died.  It would crank over slowly due to the weak battery, but wouldn't fire off.  I checked for fuel flow by disconnecting the fuel line to the carb and had a nice stream of fuel so no tank obstruction.

After sitting for about 5 minutes, I tried the starter again and it fired up.  Some popping as I revved it, but it cleared out and ran all the way back to our camp.  I initially thought it was a rich mixture problem due to an over-oiled air filter.  My thinking was it ran okay until it got too hot, due to the low speeds and idling, then the thinner air caused it to die.  When it cooled off, it was able to fire again.

Back at the truck, I removed the side cover and washed some of the oil out of the air filter with gas.  The engine started and ran fine when the air filter was reinstalled so we went out on another ride.  After a few miles of riding open terrain, we came to a section of hills that slowed me down.  Again, first and second gear stuff with some idling waiting for my son to catch up.  We were in the middle of nowhere when the symptom came back.  The bike would die when it got hot.  It would crank but not fire until it cooled down some.  I was beginning to think it was the old battery, but then after a short wait, it would start. 

One of the confusing parts was it was initially slow to rev when it finally re-started.  Like it needed to clear out.  It got worse throughout the ride dieing more frequently and hardly wanting to run at all.  When it would start, it would initially idle but if I gave it any throttle at all, it would immediately die.  With enough cooldown time I could get it started and revved out enough to finally get up to speed and get back to the truck.

It seemed to be heat related because if I maintained enough speed, it happened less frequently.  The only problem with was too much sand slowing me down and waiting for Dillon.  Temperature was in the mid-90s so that didn't help.

Back at the truck, I decided to take a look at the plug to see if it was a mixture problem.  Just one minor issue.  I had a 13/16th and a 5/8th sockets, but had forgotten the stupid 18mm plug socket which Yamaha seems to prefer.  I must have asked 30 people for a plug socket, but no one had an 18mm. 

We gave up at this point, loaded up and headed home.  At home, the plug looked fine.

I was able to fix the problem but would like to hear what others think.

DavidR.

[weymouth399]

Hi David

Before going very far I would replace the battery just for giggles first.

It sounds to me possibly like a stater pick up problem. Check the ohms of resistance in pick ups coils cold.
Then get it hot again and check them hot  (parking lot, road out front of house) coils go bad hot normaly and work cold. hope this helps.

Bob

[Dan Filetti]

Hi David

Before going very far I would replace the battery just for giggles first.

It sounds to me possibly like a stater pick up problem. Check the ohms of resistance in pick ups coils cold.
Then get it hot again and check them hot  (parking lot, road out front of house) coils go bad hot normaly and work cold. hope this helps.

Bob

2X to what Bob says.  Battery to remove the variable, as it's on its last legs anyway, not a bad thing any way you look at it.  Seriously though, go with a good battery.  I bought a Walmart job for my CRF250X and it barely lasted a month...  Replaced it with a good $55. Yuasa, and it's been great ever since.

Also, as was the case with my hiccuping FJ, lo those many years ago, coils can and do fail when hot, but work fine when cold.  The timing light shown against the stator showed this to me clear as a bell, but with the TTR being a 1 cylinder, it might be a bit tougher to diagnose with a timing light.   By the by, I could be wrong, but I think it was your suggestion to use the timing light to check for spark issues...

Did you say you were able to fix this, so it's a quiz?  Or you resolved it temporarily and you're looking for help still?

Dan

[Arnie]

David,

After inspecting the plug for obvious richness, I'd suspect the coil.  Nothing else that would be heat related other than maybe a connector.

Arnie

[RichBaker]

I had a similar problem with my WR450.... weak battery was the problem. After I replaced it, she was fine. It never has a chance to charge when you're running the low speeds, so when the voltage gets too low it won't run the ignition.

[SlowOldGuy]

Yes, this is a test of sorts.  Just seeing what the varied opinions think.  I realize it's tough when you're just reading a description of the symptom and did not actually experience it.  

Initially it seemed like a fuel delivery/carb problem. I could get it fired and idling, but any throttle at all would make it die immediately.  Once I got it to "clear out" (for lack of a better trem) and rev up, I almost ride it normally as long as I kept some speed.  

It was kind of carb-like when it would die. It would begin to sputter, then bog down, not wanting to take any throttle, then shut off completely and roll to a stop.

It was not the battery or the coil.

DavidR.

(yes, Dan, that was me that suggested using a timing light, still one of my favorite ignition diagnostic devices)

[Arnie]

OK, not fuel related, nor battery, nor coil. 
Hmmm, its gotta be electrical and my next guess would be a bad connector.  This could be the spark lead at either end where the cable connects to the plug cap or to the coil cap, or one of the supply or ground leads to the coil.

Cheers,
Arnie

[fj1289]

Ball bearings -- it's all ball bearings!




Seriously, rectifier partially fail?  Only putting out 2/3 of the normal current - too little at low speeds to keep up with the demand, but OK at higher RPMs?


Or, you being the carb guru, some excess oil blocked the pilot air jet?

[SlowOldGuy]

Okay, thanks for playing guys, I appreciate the responses.  As always, the information from this group is exceptional.

It was not the air filter.
I suspected a low battery since it would crank over slowly, but it was not the battery.
Seemed like a carb problem.  But fuel delivery was fine and adjusting the idle mixture didn't affect anything.

Once it cooled down, I could get it started and it ran fine.  Until it got hot again.  Seemed electrical when it would die suddenly.

It was the spark plug.  The plug was the original one installed at the factory.  It's a 5 year old bike, but I really haven't run it a lot.  When I got the plug out at home, it looked fine to me; nice color and no indication of fouling.  Back in my 2-stroke days, plug problems were common, but not with a modern 4-stroke. 

Here's the embarrassing part: I had an extra plug with me for both bikes, but didn't have the stupid 18mm socket.  I had practically an entire toolbox and probably could have rebuilt most of the engine if necessary, but didn't have anything in 18mm.  I could get pliers on the plug, but didn't have enough room to turn it.  Extremely frustrating.

When I got home, I fired it up and the problem occurred almost immediately.  R&R the plug and instant cure!  Motor fires right up, idles smooth and good throttle response.  I've already added an extra 18mm socket to my "dirt bike toolbag."

What is interesting about the situation is how much this seemed like a carb problem.  I've never experienced these symptoms before so it was frustrating trying to figure it out.  Also, my son used to think I can fix anything, now he's not so sure.  Although I was redeemed somewhat after fixing it at home.  I had the correct part, just missing the correct tool.

Anyway, I just thought I would throw this out there as a lesson for anyone suffering a similar symptom in the future.  We tend to give a lot of advice but receive far too little feedback.

Thanks again,
DavidR.

[andyb]

Simple stuff first

Gets ya every time!

[racerman_27410]

K.I.S.S  troubleshooting  method wins again

the right tools are sooooo very important.


KOOKALOO!

Frank

[mst3kguy]

sounds like carbs to me.
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i don't really believe that.  in fact, i didn't even read the whole post.  i've just always wanted to say that to you, david.  ( :

[Dan Filetti]

occam's razor wins again!!

[junkyardroad]

Interesting.

The battery in my Honda XR650l is 9 1/2 years old. And it still has the original spark plug in it. Runs great.

The biggest problem with Honda dirtbikes is that they always land on top of you, then compound the issue by staying running.