Yamaha DT50 won't start

[Whealie]

The is s the second time this has happened. First time I changed the rectifier. I have a spare so could change it again but if it is that, what is happening to it?

If it isn't that, what can it be? There is a spark. There is fuel. You don't need much else on a 3-year old 2-stroke. Was working Sunday. Got it out, kicked it, it started and died, twice now nothing.

 

[scouseviking]

What year is the bike, my son has a DT80LC and if its points ignition, it could very well be the condenser that sits next to the points if its not one of those electronic ignition thingies.

 

[Philwhiskeydrinker]

Chris, just because it has a spark doesn't mean it has a good strong spark.

Open the plug gap a bit to see if you still have a spark strong enough to jump the gap.

Good call re the condensor.

Phil

sent from my 'phone

 

[Lutin]

Good calls re the spark and condenser.

Just because you get a spark in air at, obviously, atmospheric pressure, does not mean that the spark is strong enough to jump the gap at the increased pressure in the cylinder. And remember that air is an insulator, there is only a spark as the voltage is so high. So, increase the pressure and I suppose that you'd get an increase in insulation properties as well. Oh, and hydrocarbons are insulators as well.

Condensers are almost always ignored by people as they cannot see anything wrong with them, so assume that they are fine. It's a shame that they don't turn bright blue when they fail, as I'm sure this would have saved hours of grief for people over the years.

Whilst I'm here, the coil hasn't got damp has it? This would be exacerbated (good word that) if the insulation around the HT end were dirty and/or cracked. Can't see it being damaged on such a young bike, but you never know.

 

[Whealie]

It's 32 years old (twice as old as my daughter, who is supposed to be doing her CBT on it tomorrow).

The bike fell over and petrol leaked out two days ago. Could that have done some damage.

Will look for a condenser (no sure what I am looking for but will look anyway). Not sure what I do about it if it is shot.

 

[Lutin]

Here's a picture of a points and condenser setup. It's off a car but basically the same thing. The condenser is the silver cylinder at the top of the picture with the red wire coming from it. The wire goes to the non-earth side of the points, and the body of the condenser is the earth.

It's difficult to test a condenser and the usual thing is to replace it. It might have a value marked on it, otherwise try and get one that will fit - ie is not too big physically. A bit of a bodge maybe, but if it works you're sorted.

 

[nigelphoto]

Its getting its own back because you painted it black

 

[Whealie]

Can't see that on Tapatalk. It's the bit the HT lead comes out of to the Spark plug?

 

[Lutin]

Can't see that on Tapatalk. It's the bit the HT lead comes out of to the Spark plug?

Err, no. I'm think we're getting confused here.

Does the bike have a points system?

 

[Whealie]

No mention of points in Haynes.

What you have in the pic is the rectifier left (square the size of a 50p piece), the regulator and then the whatever with the HT lead down to the spark plug. I think the spark is actually intermittent, only occasionally sparking. But it's hard to tell 1. In bright sunlight 2. Holding with one hand while trying to kick-start.

Rectifier and spark plug are new.

 

[Lutin]

Ah, right. This must be one of those systems that uses a magneto type system.

Do you have a wiring diagram for the bike?

 

[hotbulb]

Old 2-strokes are VERY fussy about plugs. Have you tried it with a brand, spanking. ..straight out of the pack... new plug? Is the HT lead from coil to plug in perfect condition?

Sent from my GT-I8160 using Tapatalk

 

[Whealie]

The plug is a week old. The HT lead looks old but not broken. Will scan the Haynes wiring diagram. Just better put the tools away and lock up the garage.

 

[Lutin]

Hmm, found a wiring diagram for a Yamaha QT50 moped which might be similar.

 

[Whealie]

PDFs not allowed as attachments

 

[Whealie]

Hope this works - full size as a Jpeg though.

Yamaha DT50 wiring diagram by whealie, on Flickr

 

[hotbulb]

Doesn't appear to have points. .....is this any help?

Sent from my GT-I8160 using Tapatalk

 

[Philwhiskeydrinker]

Chris, have you tested the primary and secondary resistance of the coil?
Have you tried spraying the electrics with wd40?
It might be worth fitting a new plug cap and ht lead in any case, at the very least, remove the old one, cut the ends off and reattach.

Welcome to the temperamental world of old 2 strokes

Another thing, have you checked the pilot screw setting on the carb?

Phil

sent from my 'phone

 

[Whealie]

Well when I go to Wemoto to buy parts, points are an option.

http://www.wemoto.com/bikes/yamaha/dt_50_mx/81-86/

 

[Whealie]

How easy is it to replace all the wiring and upgrade to 12v anyway?

A 12-volt conversion is pretty standard on old Vespas.