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Post Info TOPIC: What am I missing? (Cranks, won’t start)


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What am I missing? (Cranks, won’t start)
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This is a bit of a long story, but hopefully someone can see what I am missing……

Two years ago, I was given a 2006 TTR250 for use as an instructor at an off road school.   It was a perfect bike spending 50+ hours a week teaching novices to ride - competent at everything and comfortable for my old bones!

The bike had been in “storage” for a few years (meaning, sitting in a sea can), however it had been given a once over and ridden about 1000 km on the street before coming to me.  Somewhere along its life, someone had added full lights and had it made street legal.  I rode it for five month off road exclusively during 2020.  Over last winter, I gave it a major service, set up the ergonomics for me, put on fresh tires and renewed all the consumables including rebuilding the carb from a kit.

The bike ran flawlessly starting in the spring of 2021.  In July, I had been out for about 2-hours with a group of students with no issues.   I parked the bike, we had lunch and then in the afternoon, it would not start.   The engine cranked well, but would not fire.   I did all the “field triage” I could think of, but no luck.  I attempted a few things, but it would never fire up.  The bike is now back in my shop for the winter and I seem to have hit a bit of a wall with the bike cranking but not starting.  So far all of these things check out:

New plug and good solid spark

Intake tract clear

Fresh fuel and good flow

Valves within specs

Timing appears good

Carb thoroughly cleaned

All the primary electrics bench test fine

All my attempts netted only a couple of ear ringing, flame spitting backfires from the exhaust. I have attempted to start with starting fluid and got a couple of backfires from the intake side. I have access to a couple of donor bikes, so I can start swapping out parts as required.

Am I missing something obvious? Any suggestions appreciated!

 

 

 



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Oh, I should add: the compression is good.

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For a TTR to suddenly not run in the manner you described makes me think this is an intermittent electrical issue because you said there is good spark.  Assuming you already checked the spark plug cap & wire, I would recommend checking all safety switches you have (ie. clutch, neutral, ON/OFF switch, etc.) for good continuity.  Timing issues can cause these symptoms, but you said you already checked it. 



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-Jeff



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Hello Gents,

 

I actually have the same issue, it does not start at all but cranks.

What I have tried is remove the air filter, and block the airbox with my hand, upon cranking a few times the bike starts up then suddenly stops. 

I have cleaned the carburetor serval times , New values, new timing chain but won't start.

 

One thing I noticed however, the thread on the head of the engine does not lock tight, could this be a cause?(Find attached)

Can the lower gasket (engine lower base gasket) cause compression issues?

 

Kind Regards

 

 

Kind Regards



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Super Guru

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I am sure you have checked but, just in case, make sure that not only do the camshaft marks line up exactly at TDC (single not double line on flywheel) but the cam lobes are pointing outwards as shown in the photo below.

Camshafts.jpg



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vwanjau wrote:

Hello Gents,

 I actually have the same issue, it does not start at all but cranks.

What I have tried is remove the air filter, and block the airbox with my hand, upon cranking a few times the bike starts up then suddenly stops. 

I have cleaned the carburetor serval times , New values, new timing chain but won't start. 

One thing I noticed however, the thread on the head of the engine does not lock tight, could this be a cause?(Find attached)

Can the lower gasket (engine lower base gasket) cause compression issues? 


From what you describe, it sounds as if you have a carburation problem. 

Lots of information here that might help you. 

If you open the drain valve on the float bowl does the fuel flow freely?

Have you checked the float level is correct?

When you cleaned the carb, did you ream the pilot jet?

Have you checked the inlet stub for a leak?

Regarding the cam cap bolts, I think you need to get them Helicoiled before damage is done to the other bolts. See here

A damaged base gasket won't cause compression issues, just an oil leak wink

Brian



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Exeter, Devon, UK

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TTRfan wrote:

I am sure you have checked but, just in case, make sure that not only do the camshaft marks line up exactly at TDC (single not double line on flywheel) but the cam lobes are pointing outwards as shown in the photo below.

Camshafts.jpg


 Brian, if the cam lobes are not pointing outwards, would the engine fire up and work? Would the operation be erratic? 



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Hi Super Guru,

I will give it a try on what you have recommended.

Thanks

Kind Regards

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Newbie

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Thank you very much for your suggestions and even the small highjack was helpful ;)  It has been extremely cold the last week (-32C this morning!) , so it took more time to work through all the ideas.

 

Unfortunately, no luck so far.   I lifted the entire ignition system from a donor bike which I will install once the weather warms up.  

 

I have to admit that it is making me wish that Yamaha still built a comparable and competent bike for sale here.  

 

Thanks, again.

 

Paul

 



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Bjorn, is your plug wet after your attempts at starting. If not then you have fueling issues.

When you say good fuel flow, do you mean from the tank?

My float in the bowl sometimes sticks. I know this because when I open the drain in the float bowl nothing comes out. But if I keep the drain open and tap it a few times with a heavy socket extension, fuel flows out. I can then strat it first time.



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