TT500 won't fire...

[Wired1]

I've just bought a 1980 TT500 serial 1T1-232493 on both the frame and the motor (that makes a change).
It has been sitting for a while and won't fire up. There is no spark at either the points or at the plug, and my experience doesn't make it past CDI so I'm not 100% sure how it works. The wiring is very simple - two wires from the alternator feeding only the coil via the points. The wiring is also there for the 6 volt headlight and tail light but these aren't fitted so it's just the basics.
I suspect it's the condenser by the points as in my experience these babies fail after about 25 years of service but I'm keen to hear what the experts think. I'm guessing I should be able to measure a voltage from the alternator so I'll try that tomorrow.
Another possibility that I have struck before in proper wiring (ie mains stuff) is that the alternator may have lost it's residual magnetism from sitting too long and won't generate anything until it's been primed with a quick DC current through it.

[saul]

love those bikes mate good luck

[tri boy]

Exciter coil "kick through" test should show 100v approx. (best tested with peak voltage meter, but an analogue meter should do).
Can't recall specific resistance readings, but a Yamaha shop should be able to supply readings over the phone.
Ign coil would also be suspect. Do the usual points clean n tests for contact/gap/earth insulation.
Best test for condenser is charge it up, and get the apprentice to catch it. If he squeals like a pig, then it's fine.

[Wired1]

Exciter coil "kick through" test should show 100v approx. (best tested with peak voltage meter, but an analogue meter should do).
Can't recall specific resistance readings, but a Yamaha shop should be able to supply readings over the phone.
Ign coil would also be suspect. Do the usual points clean n tests for contact/gap/earth insulation.
Best test for condenser is charge it up, and get the apprentice to catch it. If he squeals like a pig, then it's fine.

So the exciter coil - is that the one on the end of the flywheel? It goes from there to the points and then to the coil. I figure the points close to charge up the coil then open to force the coil to discharge through the spark plug. What does the small condenser do?

[Ixion]

Sort of. The exciter coil provides a small electric current to "charge" the coil. When the points open, the collapse of the magnetic field causes a very high (hundreds of volts) back voltage . This back voltage then provides the HT spark.(coil is actually a simple transformer).

On a more 'street' bike the charge voltage for the coil is provided by the battery , which makes testing much easier. Magnetos can be a pain when they do not work. But very nice indeed when they do.

The condensor (= capacitor) is to prevent sparking across the points, which would otherwise rapidly erode them. But if it is "leaky" or shorted, it will short out the points.

If you are sure that the bike was running when abandoned, the problem is likely either the condensor, or the points. (though I have seen the demagnetism problem you mention. Usually easily tested by clicking a screwdriver on the flywheel)

But it may have been abandoned when it lost its spark, perhaps ?



Ah youff. One forgets what they do not know of.

[Wired1]

Thanks, I'll have a go at it tomorrow and report any success or failures. The guy I bought the bike off said it was running 6 months ago and he sounds genuine so I'll go with that.
If the condensor cap is faulty, do they fail to a short circuit? if so I could disconnect it fo a simple test. I could also use an external power source to replace the alternator as it's not there for timing like on a CDI bike.
I'd like to hear it run before I pull it apart!

[Ixion]

They fail all sorts of ways. Normally, with a battery , the failure is not enough to prevent starting, causes misfires and such. But a mag is more fussy.

I'm not sure if it would run with no condensor. Your friendly lawnmower shop should have something suitable for a few bucks.

Dunno if using a battery would work safely, you might burn out the coil, htey are often special coils. Check the manual if there is one.

And stone the points. Even if they look OK, they can get a coating film of oxide that is non conducting.

[tri boy]

It is possible to "tickle" the circuit with an external AC 110V power source, and by passing the condenser is also acceptable, but don't do either for too long.
Also disconnect any kill switches, as these can cause greif if old, and weathered. TT's are great old beasts, and the grunt from them was linear and strong.
Good luck.

[Motu]

They are a pretty simple system and seldom give trouble,condenser failure is very rare - in all my years of fixing vehicles genuine condenser failures I could count on the fingers of one hand.I'd disconnect the kill switch first as Tri boy says,kill switches on dirt bikes cause many problems.Clean the points,set the gap and time,check the mechanical advance is working well.They are AC,so don't hook up a battery.

Quick check to see if there is anything going on - get an old analogue multimeter,set to any DC range...red into spark lead,neg to earth.If the needle flicks then there is some activity - you have a voltage problem,clean all connections.I'd be looking at the points if it's been sitting around - remove and clean by running emery tape through,then spray with cleaner.Next is bad HT connection into coil.

[slowpoke]

Oh to be a spotty school boy again, gazing upon the wondrousnous of a bare alloy tanked TT500. They have got to be one of the all time best looking bikes. Who cares if they are heavy, underpowered pig's in comparison to today's weaponry, if I could have a selection of bikes in the shed one of these would definitely be in there.
Good luck with it.

[Wired1]

I've been out in the shed all morning and here's the update:
Thanks for all the help by the way, just to narrow it down a bit this bike has no kill switch, no key, no lights, in fact nothing except the alternator, points, coil and spark plug so not much to go wrong you would think (I'm not sure how you stop it but that's a problem I look forward to solving soon).
There are two wires from the alternator thing, black and white. The white one was supplying the lights and is not connected to anything. The Black one splits into two, one to the points and one to the coil orange.

There is continuity between the coil orange lead and ground, the coil HT lead and ground (with the spark plug cap removed from the HT lead) and the points to ground. With the plug out I measure a voltage spike at the HT lead of over 50 volts on my analogue multimeter, and a similar voltage at the coil input (orange) to ground for each kick over.

Has anyone got a wiring diagram for this bike? it would be interesting to see how it should have been wired originally and I'd like to know where to put a kill switch!

[Ixion]

That doesn't sound right. Or, at any rate, it's certainly not normal. The effect of the way it is would be to produce a spark when the points close , rather than when they open (becasue the points will, in effect , be shorting the coil).

Normal would be black lead from alternator (excitor coil) to orange coil lead.
The other thin wire on the coil to the points.

When you say "There is continuity between the coil orange lead and ground", is that with the points closed? That would make sense with the circuit you describe. And there should be no continuity with the points open .

Voltage on the HT lead should be far greater than 50 volts. More like 50000 volts.

[Motu]

The analogue meter won't actually show the voltage reading - it will just kick on any voltage scale....and it won't damage the meter either,my meter is over 25 years old,I've been using it this way for years,and it still works.

So that means everything is working,but just not good enough.It means the stator coils are generating current,it's building a field around the primary coils,the points open and interrupt the flow,the field is collapsing and inducing a secondary kick.All the things you need for spark.Now work on getting every step in the chain up to scratch and a big fat blue one will be your reward.

[Ixion]

Um, you have tried a new spark plug, eh?

[Wired1]

Thanks again guys, I'll head back out the the shed and go through it again. I've been searching the web for info on this and can;t find any decent TT500 websites or info, I would have thought there would be a site somewhere.

The TT500 coil only has one orange input lead, the other end of this coil is already grounded so it must be right the way it is wired. I have found a couple of wiring diagrams for other bikes that use this method too so I'll assume it's right and just clean up the points & plug etc.