A forum for owners of Yamaha TTR250 trail and enduro bikes!

If you haven't already done so it would be worth taking the cam cover off and checking the camshafts are properly aligning at TDC. Also, as John suggests, also check the valve clearances.

I expect you have found the "show and tells" here http://ttr250.activeboard.com/f604245/repair-and-maintenance-quotstickiesquot/ 

Brian

Any luck with this yet?

 I noticed my decompression plug is leaking, but it's just the rubber plug. The switch was removed by the PO.

Should I have a headlight and taillight off of just ignition switch power or will it only run when the bike is running off of the stator?

also, what wires should be live at the cdi with the switch on but bike not running? I know the red black comes from the run switch, but it isnt live except when i use the start switch  shouldn't it be live at the cdi all the time? Its red white on the other side of the run switch, never live except when the start switch is used. I expected the cdi to get a live power wire when the ignition is on, but it doesn't.

Hi Brian - you sound very knowledgeable mechanically so I am in danger of trying to teach my grandmother to suck eggs!

However, as I am sure you know, our TTR engines need three things (at least) to run:

a) good quality (and preferably fresh!) petrol, (does petrol flow out freely when you loosen the drain plug on the carb float bowl?) 

b) compression, and

c) a spark delivered to the compressed fuel/air mix at the appropriate time, or very close to it.

Given those three items, an engine will run although we mustn't forget that your battery needs to be good enough to spin up the engine at a decent rate!

Did you try John's suggestion to take the plug out and put your thumb over the spark plug hole? Turning over the engine should easily spit your thumb off from the hole. In my experience, if it does this, there is enough compression for the bike to start. If it doesn't then the valves and rings need closer inspection.

Steve's suggestion ref the Woodruff key is a good one as a sheared key would almost certainly result in the ignition timing being out. It has to be said that this would be a rare occurrence but, if you have tried most everything else, it won't take long to throw the TTR over on its side (so as not to have to drain the oil) and pull the generator cover and check that nothing untoward has happened inside.

Am I right in thinking that you have had the head off and checked the valves are seating OK?

Brian

General response: yes I've checked the above suggestions.

Ttrfan, i used the diagram to go over the bike before i posted because the diagram links the diode to the running circuit. The red black is not live, it's the other side of the red/white from the run switch which is negative trigger. The run switch isnt live,the brown goes to blue white in the start button. As the diagram shows, it's live power is fed through the starter relay. The relay is only live when the start button is pressed. It looks like yamaha decided to use negative triggers instad of positive. If that's the case, the diode is critical as it won't feed voltage without the diode. In this case it doesn't matter that it drops the voltage .6 volt, it's used to control electron flow to the run switch making more potential electron flow and causing it to move towards the CDI. In that case it would be positive on the top side of the diode. I was hoping to verify, but someone would have to observed that other than me to verify that. Basically, will your ttr start without the diode would be the basic question.

In my current situation the red white will show about 1 volt positive when the starter is pressed, then jumpto 12v and fall to zero within a split second. I suspect if the diode were in line it would it would give it more negative potential and eliminate the backflow of 12v+ that keeps it from getting to 12v.

if the starter relay is faulty and should feed 12v with or without the diode, then i have a faulty starter relay if the diode isn't dropping my voltage potential. Red white on the starter relay turns to red black after the plug. If anyone can test if the starter relay red white has 12v with the key on and the bike not running, it would answer my question of having a faulty coil in the starter relay that feeds 12v to the running circuit. Theres a catch though..... do you still have 12v after you pull the diode off?

Continuing on, here is the results of everything I've looked at. The movement of the crank to the upper head (what I'm cranking) confirms wodruff key is locked in. Valves are opening and closing in time as they should. 

i have fuel squirt from the carb, as well using start spray. 

The bike just has no life. It cranks like it has no will to start. 

It has spark, though I'd consider it weak. I changed the ignition coil and it didn't change the intensity of it. The pickup coils read 208 ohm as they should. It's a mystery. The plug is brand new, dry as a bone. I squirt starter fluid directly in and it doesn't change a thing. 

BOught it a few days ago non running. I disconnected the cam cover vent hose and while turning ovr it produces a light amount of smoke so it is igniting.

Yes the proper buttons are in there. 

Wow Brian

This is a hard one

The fuel is right, the timing is right, spark is right, clearances are right, but still no running bike I take it the spark plug (though sparking) is the right one?

Correct plug, so we can eliminate that, very confusing

Sure we will get to sort this out

Anyone else have some ideas?

I am pretty sure the two carb pipes are just breathers as they are open at the top where they attach to the airbox and have one-way valves at the bottom as indicated by the arrows in the photo below:

Rings are seized on the piston. The engine sat for 3 years before i got it. ive dremeled them clean and the piston so it's going back together and we will see it run! 

 So the rings weren't worn badly before the engine sat for three years, hence why the normal signs of worn rings were not there  only after sitting did they stick and no compression  

-- Edited by One1 on Saturday 11th of March 2017 06:42:45 AM

Resurfacing the piston. 

All done :) 

everything went well.

Shouldn't be an issue from here. The rings were carbon locked from sitting and in the fully compressed state. I'm ready to take the twins out for a spin tomorrow.

-- Edited by One1 on Saturday 11th of March 2017 08:22:30 AM

I think Brian may be referring to the twin TTRs Steve

So the TTR now starts and runs OK Brian?

Thanks for the feedback and photos - nice to have the mystery solved 

I hope you found the advice from members helpful even if it didn't pinpoint your actual problem 

Brian

Thanks for all the helpful guesses. Yes it runs but I tore it down for the rebuild. I'm doing a solid graphite gunmetal high gloss frame. Just did a test spot to see how it'll look. I'm pleased. Should be done by tonight with the bike. I buy and rebuild ttr125's about one per week and resell them, but this 250 is for me. I've been wanting an enduro forever. I'll update tonight. 

Cool

Going to give that type of spray a try

one of mine ttrs does not have these tubes at all and it starts without problems.

Congratulations on your success.

It looks like you're in need of some new rubber now.

Martyn

New tires installed, and engine cases plus swing arm painted. Along with the rear brake. It's came a long way this week. I rode it today and love it! As a reminder when i bought it a week ago it didnt have a hope of running and looked like this  

Yes. I thought so as well.