DT 125, Cut out, now wont start!

Mr.Ormes · Nova Slayer Joined: 30 Mar 2009 Karma :

Hi,

Last night I though I'd take my DT for a run, considering it has been at 2 years and the only run its had was to the MOT station last week.

The last work I done to it after the MOT was rear wheel off for a new back tyre and I put a powervalve cover on it (it was running without for 50 or so miles) Now I dont think this cover has any specific way of going on as theres only one bolt hole meaning it can only go on one way!

I'm riding along, get 3 or 4 miles away from my house and something doesnt feel right...power and everything was still there though, so I proceed to pull over so I could check the chain tension etc and as I get down to first gear to go into a junction the bike cut out. I quickly pushed the bike into the junction and check fuel was on, kill switches, HT cap firmly on etc. Everything seemed fine, so I try and kick it over a few times, then it backfired ~ (not a bang, it was more of a sneeze) and I repeated this a few times, untill giving up and pushing the bike to a friends near by.

I'm kinda worried as My good old DT has been probably the most reliable bike I've had. Any help, much appreciated! Thumbs Up

This is the picture of the cover, (I only replaced the cover on the right hand side, nothing else.

https://img684.imageshack.us/img684/364/dsc00263xlr.jpg

Thanks in advance, Dave.
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DT 125 1995
Thumpstar 120
Suzuki ZR 50

FBSF · Nitrous Nuisance Joined: 23 Mar 2011 Karma :

Have you checked to see if there is a spark?

Take the plug out of the head, and with the HT lead still connected (and gloves on) put the central electrode onto an engine nut (away from the head - don't wanna be igniting petrol at this point).

If you kick it over with the ignition on, you should see a spark. If not, then it might be a coil/CDI issue...

If there is a reasonable bluish spark, then I'd be taking the carb off to make sure there isn't a blockage, and that fuel is getting through to it.

Final thought - does there still seem to be compression when you kick it over, or has it got easier? If the latter, you might have a holed piston...

The powervalve should only really affect where in the range the power is produced - even without one in there it should still start.

Mr.Ormes · Nova Slayer Joined: 30 Mar 2009 Karma :

I checked the plug today, a lovely beautiful blue spark there, and I took the carb off at the road side, cleaned the main jet out and any gunk in the bottom of the float bowl/needle etc...put everything back together it still didnt run, but doesnt backfire anymore.

I thought I'd trickle some fuel into the head then kick the bike over to see if that made any difference and none, not even so much as a cough into life, same with bump starting it, doesnt seem to want to go.

Battery has since gone flat, however the magneto gives enough residual energy to get the bike started then charge the bike so I dont see this being a problem.

Thanks. Dave
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DT 125 1995
Thumpstar 120
Suzuki ZR 50

FBSF · Nitrous Nuisance Joined: 23 Mar 2011 Karma :

Unfortunately trickling fuel into it won't help - it's only when converted into a fine spray as the carb does that it will ignite.

Is there compression when you kick it over? if you were running without a powervalve cover for a while, then added one, it could have changed the fuel mixture from rich to lean - and this could have holed the piston...

I'd be tempted to whip the head off and check the piston - make sure there is no pitting or any sign of holes...

From memory, aren't the powervalves asymetric? I mean that they turn in their hole (if the servo is fitted thus changing the port duration. Could it be that it's in the "high" position, making starting difficult?

Might be worth getting the carb on a bench and clearing out the pilot and needle jet tube with an air line or similar (or a can of compressed air) - the main jet only really comes into play from about 1/2 throttle onwards.

The other thing it might be is that the carb float heights are incorrect, so fuel isn't getting to the jets correctly, even though there may have been some in there when you drained it.

Maybe check the float needle while you are at it?

Other than that the only thing I can think of is that the timing has somehow slipped so although you have a nice spark, it might not be at the correct time in the cycle - which could have explained the backfire?

bikersupermot... · Could Be A Chat Bot Joined: 26 Jul 2008 Karma :

1st thing id do ... put in a new spark plug!. see how you go with that, they can fail, in that they ll spark out of the engine, but under pressure it wont or wont spark properly to run the bike.

also make sure that the fuell is getting to the carb okies...esp with it having been sat for a while.

good luck with it! -)
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