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

grandad · Veteran Member

could it be coil???

TTRfan · Super Guru

Need more info to diagnose please.

Does it carry on like that or does the TTR run OK again for another 10 miles after left to stand for a while? Thinking maybe blocked tank breather.....

Is the battery OK after the 10 miles - does it have enough juice to spin the engine over quickly? Thinking maybe regulator/rectifier not charging.

Brian

grandad · Veteran Member

Thanks for your reply Brian, the tank is breathing ok , I slackened the cap off and it was still the same, charge is ok as I can carry on riding even with my heated grip on and at the end of the day still have a full battery , the problemim is after say ten minutes running it starts to miss a little when accelerating and occasionally backfires and when coming to a stop it wont tick over, press the starter and it fires up no problem but dies if left to tick over, start it up the next day and run till warm it will tick over and sounds good,

TTRfan · Super Guru

Faulty plug, coil, or connection in the ignition circuit?

Valve clearances?

Try draining the float bowl to flush it out - just in case......

Air filter clean and fitted properly?

Intake stub intact and rubber not parted from metal stub - not easy to spot!

Check the easy things first wink

Brian

grandad · Veteran Member

Brian I'm mick, if you recall I've just fit new rings sprag clutch manifold rubber and timing cover so most of the things you've mentioned are new, carb was cleaned out and checked valve clearances are spot on, all ignition joints are clean, coil was my first question!! Another thought could I have upset ignition timing when I swapped stator and pickup over into new timing cover??

TTRfan · Super Guru

Hi Mick

This is what your stator should look like.

Stator 002.jpg

There isn't much opportunity to get the ignition pickup fitted wrongly. Could you have trapped a wire possibly?

Another possibility is that the timing chain may have jumped a tooth in the rebuild process - I have done that myself and the TTR started and ran but misfired as it revved. It may be worth taking the cam cover off and check the sprocket marks are still lining up.

Otherwise, would you like to borrow a coil to try?

Brian

grandad · Veteran Member

Brian, went trail riding today did 130 miles 95 of it off road and bike ran ok apart from a few times when it missed a few beats and wouldnt rev out, at one point when it cut out it woulnt start on the button sounded like a flat battery but lights were on anyway it bump started ok, but the last hr was hell it woulnt tick over or rev and when I pressed the starter it sounded like it was trying to fire before TDC and kick back a few times before starting and sometimes got a knocking sound coming from the engine when setting off,

Regards
mick

TTRfan · Super Guru

I am not an auto electrician but your TTR's symptoms seem to indicate that your battery went flat during the ride. They are similar to what happened on one of my TTRs when I stupidly forgot to connect up the rec/reg after doing some fettling. Also happened on a Royal Enfield Bullet I used to own when the rec/reg fried itself.

It may be worth investing in a SparkBright Monsoon battery voltage monitor - see here.

Brian

ttboof · Super Guru

you have got a tough one here .

I would say you Possibly have two separate problems .

the miss fire is going to be fuel ,air ,valves , electrical

the starting problem sounds like the Batt getting down like Brian said , could also be a poor connection or even a stuck brush or solenoid , with the stater if the lights dim right out when you press the button its an indication of low voltage or a large current draw that is the voltage is dropping , if you press the button and there is little action and the lights stay fairly bright it indicates a low load eg stuck brush ,faulty solenoid or poor connection .

the battery has no influence on the ignition ,as a ttr can run ok with out a battery (but not recommended leaves the regulator to dump all the excess current

with the miss fire it could be the coil , pick up coil or cdi unit but its rare . a loose connection is more common and there is the old nemmis the Kill switch they a classic one with them is you set off with a dry bike but a build up of dust ext in the switch gets wet a bit of a current leak starts across the crap and it starts playing up

again the carby and inlet stub come into it if its running lean the engine plays up a bit and gets hotter than usual and is hard to start and can ping at low speeds eg when initially setting off

the problems you are having are a matter of a careful look at what's going on , even the way the bike miss fires can help if its electrical it will tend to be a sudden on off as apposed to fuel is more of a die off and come back

a thorough break down of the symptoms really helps track down the culprit , hope this helps in some way because you should be out enjoying the ttr

ive tried to pass on some of the things I use out in the field when in away from the tools and test equipment .if you an break down the symptoms im sure the ttr forum crew will fix her up