Yamaha DT 125, 1988 model, HELP it wont start

[jim]

Ok it has a good engine and produces a spark. It is not the ignition coil of the carb. Anybody got any ideass?? i would appreciate the feedback.IF you need to know more just ask me on this forum i will reply ASAP. Thanks alot, much appreciated.

[Scooby]

What about your battery? Might have enough to create a spark but might not be fully charged so won't run the bike.
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A big enough hammer fixes anything!

[jimmy]

battery is fine

[McJamweasel]

Check the fuel line/filter.
____________________
BCF: Be yourself, just don't be an arse.

[jim]

fuel lione and filter ok no blockages, carb stripped and cleaned, jets clear, could it be the electronic igniton faulty?

[Kickstart]

Hi

Could be a cdi fault. Get an inductive timing light (ie, the type where the sensor just clips over the HT lead) and see what the timing is like while the bike is being kicked over. If the timing is wrong, but consistant then check that the rotor is in place correctly. Normally it is keyed in place, but the key can shear off allowing it to have moved a bit.

How fresh is the petrol? Are the reed valves sealing properly? Has it got decent compression (ie, piston and rings good)

All the best

Keith

[Scooby]

What would we do without Keith hey.......... 8)
____________________
A big enough hammer fixes anything!

[jim]

keith, many thanks for your kind interest, the engine has been recon lately, all in good nick, i am going to admit defeat and take it to the local dealer, ouch,, a shame you dont live closer. anyway cheers again, all the best.......

[Kickstart]

Hi

Has it run properly since it was pulled apart? Years ago I spent ages trying to start a bike I had fitted a new piston to. Turned out I had snapped a piston ring when reassembling it. Quite easy to do.

All the best

Keith

[zaknafien]

Keith needs the name under his changed from "Scooby Slapper" to "The Fixer"
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02 Firestorm.

[McJamweasel]

Or Jim.
As in 'l Fix It
____________________
BCF: Be yourself, just don't be an arse.

[jim]

Yes it has run since rebuild but not for long, approx 30 minutes total, it was rebuilt because it burnt a hole in the piston crown, dont know why, no excess carbon build up or anything, possible faulty ignition timing?

[Kickstart]

Hi

I would be tempted to pull the top end off the engine to check, but not sure how difficult that is on the DT. Also worth checking the reed valves (old RDs used steel reeds, which could prove expensive if they broke).

I have known 3 bikes have problems with the ignitions. One was the Gilera which basically shorted out the electronic rev counter. The 2nd was the RS, which is an unknown problem (I will find out when I have some known good bits to swap around), and the other was on an MBX125, and that might have been from using the wrong plug (Autolite kart race plug, when very well but fouled up quickly round town). On the first 2 of these I kept on getting a healthy spark, and the bike would run, but the Gilera would die as soon as you gave it any throttle.

Burning a hole in a piston is normally down to pre ignition of some type. Possibly as you say due to carbon build up (which gets hot enough to ignite fuel, plus takes up volume so raises the compression). However this is normally due to ignition timing being out or too high compression. Ignition timing can normally (on a 2 squeak) go out due to a fault in the ignition, or maybe it the rotor manages to more. The rotor is normally keyed to the crank, but the key can shear off allowing the rotor to move on the crank

All the best

Keith

[Ropehead]

Jim i'v got some TZR. 1989 parts for sale as u probable know most parts are the same

All very tidy and in good working order:-

dtr 3db1 -88-89
tzr 2rk -87-89

- Wiring Loom.
- CDI unit.
- Generator & flywheel.
For a pic go to
https://www.findit.co.uk/motorbikes/parts/265429.htm

Ropehead@lycos.co.uk

[jim]

cheers ropehead, but thanks to keiths advice i have now got it running, many thanks for your consideration.