72 T500 no spark

jabcb · Post by **jabcb** » Thu Mar 03, 2011 9:47 pm

Coil primary resistance of 4.5 ohms is OK.
The points toward the front of the bike are for the left cylinder (left cylinder when you sit on the bike).

Hate to have to ask this, but are you sure the points actually close completely? What gap did you set the points to?

With ignition on & lights off. One point open & the other closed.
For side with open points:
coil voltage for orange wire should be close to 12.4v (small voltage drop from battery to coil)
coil voltage for other wire should be about the same (no voltage drop across the coil)
voltage on coil side of points should also be about the same (no voltage drop from coil to points)
For side with closed points:
coil voltage for orange wire should be close to 12.4v (small voltage drop from battery to coil)
coil voltage for other wire should be close to 0v (large voltage drop across the coil)
voltage on coil side of points should be about 0v (small voltage drop from coil to points & points are grounded)

With ignition on & lights off. Both points open.
The battery isn't powering anything and all of the above readings should be 12.4v

smokin · Post by **smokin** » Thu Mar 03, 2011 11:20 pm

Have you tried checking the condensers?

Tamadrmr26 · Post by **Tamadrmr26** » Fri Mar 04, 2011 10:06 am

i gapped them to about .014 in. i will regap them and test the voltage again since i have never done this before and could've easily screwed up somewhere. also, to clarify, on the left hand grip i have the horn, the turn signal switch, high/low beam and one more switch. is that the kill switch or headlight switch with the red dot?

how would i go about checking the condensors?

thanks again for the help

jabcb · Post by **jabcb** » Fri Mar 04, 2011 12:27 pm

The kill switch is beside the throttle. It works by cutting off the power to the coils. All the voltages you tested will be 0v when you use the kill switch.

The other switch on the left hand grip turns probably turns the lights on & off. Depends on what your bike has.

The condensers are not causing the voltage reading problem.

Focus on getting the points to close correctly & getting the correct voltages.

Post your results when you get that fixed and somebody will help with the rest of the steps.

Tamadrmr26 · Post by **Tamadrmr26** » Sat Mar 05, 2011 12:25 pm

ok, i did a lot of reading up about the points ignitions. im understanding how they work now. i cleaned up the points pretty well and they seem to be closing and sitting flush. i am still getting the current flowing through from both sides. i noticed if i disconnect the yellow wire from the moveable point i no longer have continuity when the points are open. is this because the condensor is grounded and transfering that ground through that wire to the moveable point, which from what i can see, is supposed to be insulated by the small plastic/fiber washers and the plastic/fiber tube? should it work like that or does this mean i have a short?

Coyote · Post by **Coyote** » Sat Mar 05, 2011 1:45 pm

There should be no continuity when the points are open. I you have it, something is wrong with your pigtail assembly. I wish someone would come up with an explosed view of how that goes togetther.

Tamadrmr26 · Post by **Tamadrmr26** » Sat Mar 05, 2011 2:18 pm

ok, the pigtail assembly meaning where the wire from the condensor connects to the moveable point spring and such? i thought that might be where the problem was. i just picked up a small lift since im tired of bending over and laying on the ground trying to figure this out. im gonna get it on there and get a better look at how it all fits together. a nice big diagram of that would be great. i'll try and get some close up pictures at least.

jabcb · Post by **jabcb** » Sat Mar 05, 2011 2:55 pm

Do you have the parts assembled as I've shown?

Where I've marked "check voltage here", you should get:
1) close to 12.4v when the points are open
2) about 0v when the points are closed

PointDiagram1.jpg

Tamadrmr26 · Post by **Tamadrmr26** » Sat Mar 05, 2011 2:56 pm

i took some close up pictures. hopefully this works...

Tamadrmr26 · Post by **Tamadrmr26** » Sat Mar 05, 2011 3:00 pm

it looks like on mine the yellow wire is attaching on the nut side instead of near the head of the bolt. awesome diagram.

jabcb · Post by **jabcb** » Sat Mar 05, 2011 3:08 pm

With the left points open & the right one closed as you've shown,
what are the voltages when you measure them per my sketch?

alanr · Post by **alanr** » Sat Mar 05, 2011 3:21 pm

just wondering how old are the plugs.if you have power through the coils then the next stop is plugs.Alan

titan performance · Post by **titan performance** » Sat Mar 05, 2011 4:31 pm

Is it worth checking just how well the plug caps are screwing into the HT leads? After all, they are near 40 years old in all likelihood....I sometimes snip off a half inch at the end of the HT leads and re-attach the caps....

jabcb · Post by **jabcb** » Sat Mar 05, 2011 5:03 pm

Alanr & titan performance, as I understand the situation:
1) The coils have 4.5 ohm primary resistance, so they look to be OK.
2) Has voltage at the coils but no voltage drop across the coils -- doesn't matter if the points are open or closed.

First step is to get good coils voltage drop & current through the coils.
Then worry about plugs, condensers & plug caps.

Its a bit difficult to figure this out through forum postings.

Tamadrmr26 · Post by **Tamadrmr26** » Sun Mar 06, 2011 3:24 pm

i tested the voltages on the moveable point where you specified. im getting 12.4v no matter if its open or closed.

if i take the wire from the condensor off of the moveable point i get 12.4v when the points are closed and nothing when they're open.

plugs are brand new.

72 T500 no spark

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