No spark after rebuild - problem solved!

[Madbuffalo]

When I went out to start the bike this morning for the first time after the engine rebuild there was no spark. I've been checking things all day and at this point am just out of ideas. Advice/ideas welcome... please! Here's what I've checked/done:

- Initially I had spark on only the center point and spark plug. It seemed overly strong and erratic on the point.

- Replaced the condensers with the ones I had on before the rebuild (since I knew they worked when I took it all apart), cleaned the points, and sprayed electric cleaner on the entire area. Point gaps are good too.

- Rechecked, no spark on anything.

- Tested points wires all the way back to the coils with resistance tester - all good.

- Tested on/off switch and key switch - good.

- Followed positive wire from battery to key switch to coils. Measured 0 ohms resistance through each wire. With 12.7V in battery orange wires at coils were reading 11.0V. If I disconnected the voltage regulator I got 12.4V at the coils.

- Currently no spark on anything.

[Joiseygirl]

Hmmmm....seems to me like you've lost your spark.

(Sorry, the made me do it)

[jabcb]

Do you get any spark with the voltage regulator disconnected?

What voltage drops do you get across the coils with the points open & closed?

Wiring diagram for GT750:
http://smokeriders.com/diagrams/index.p ... /GT750.gif

The voltage regulator powers the alternator's field coil. Looks to be drawing way to much current. Could you have hooked it up incorrectly or shorted out one of the wires?

[Madbuffalo]

No spark with the voltage regulator disconnected either. How do I check voltage drop across the coils? Could you go into a bit more detail on your alternator comment? Sorry, electrical work is definately not one of my strengths although my knowledge on the subject has been improving involuntarily. Thanks for the help and the fast response!

[Cliff]

Is there power to the points? With the key "On" and the kill switch in "Run" check the voltage at each set of points when they are open. If no voltage, disconnect the wire and check for voltage at the wire. It could be that the points are grounding out because of some oil/solvent/cleaner or whatever has shorted them out to ground. Also check the contacts. They should be clean and dry. A quick check of the contacts is put a match book cover between the contacts when they are closed, pull out the matchbook and look for any stains or dirt on the cardboard.
Cliff.

[jabcb]

The GT triples have a three-phase alternator with an electromagnet (field coil). The voltage regulator controls the amount of current sent to the field coil. The alternator outputs varies according to engine speed and current sent to the field coil.

Look at the wiring diagram.
Three wires connect to the voltage regulator:
O (orange wire) is the hot from the ignition switch
B/W (black wire with white tracer) is the ground
G (green wire) powers the field coil in the alternator.

For specs on GT series ignition coils & alternator, look at page 15 in:
http://www.ozebook.com/compendium/suzi/suzidata1.htm

Per Suzuki:
1) the ignition coils should have a resistance of 3 to 6 ohms (typically 4 to 4.5 ohms from what I've seen)
2) the alternator field coil is referred to as the rotor coil
field coils for Kokusan alternators have a resistance of 2 to 5 ohms (used on GT380 & GT550)
field coils for Nippon Denso alternators have a resistance of 10 to 20 ohms (used on GT380, GT550, GT750)

For your GT750, the field coil would have a greater resistance than one ignition coil.
I would expect the voltage drop for powering the coils to be greater than for powering the alternator.

If I understand your description,
1) have 12.7V at battery
2) have 12.4V at orange wire on coil with voltage regulator disconnected (no power to alternator field coil)
3) have 11.0V at orange wire on coil with voltage regulator connected (power going to alternator field coil)

Since you've done a lot of work there are a few possibilities, including:
1) points, condensers, voltage regulator & alternator are all OK. Have a problem in the wiring.
2) separate problems in the ignition system & charging system (voltage regulator or alternator)

Good starting points for testing with battery connected:
1) with voltage regulator disconnected, check voltage at points when points are open & closed as suggested by Cliff
2) with voltage regulator disconnected, check voltage drop across coils with points open & closed
(multimeter red lead connects to orange wire on coil, & black lead connects to other wire on coil)
And tests with battery disconnected:
1) disconnect coils, check resistance from connector to points (black, white & black/yellow wires)
2) disconnect voltage regulator, check resistance from connector green wire to ground
3) disconnect voltage regulator, check resistance of voltage regulator
orange to black/white connectors should be high
green to black/white should be high
orange to green should be around 0 ohms

This is all I can think of at the moment. Hopefully this will get you pointed in the right direction.

Some background info if you are interested:
For diagrams of different types of alternators:
http://home.earthlink.net/~trinomial/chgtypes.html" onclick="window.open(this.href);return false;
Article on how three-phase alternators work (see Figure 3 for your bike):
http://www.electrosport.com/technical-r ... stem-works" onclick="window.open(this.href);return false;

[tz375]

You did fit a good ground lead from the motor to the frame didn't you? And it had a good clean connection at both ends? The motor is rubber mounted, and that basically leaves the clutch cable to act as a ground unless there's a good ground lead.

No spark at all tends to indicate that the power is not getting to the points. Check power to the points as indicated by the previous posts. With all those washers and things, it's not hard to connect the points wires in a way that they either short out or don't make a connection.

If you have power to the leads at the points but nothing to the moving points, that may be an issue.

[oldjapanesebikes]

And the engine kill switch didn't get toggled by accident ?

[Madbuffalo]

Thanks for all the ideas thus far. I'll do some more tests tomorrow night based on these comments and post again.

[Madbuffalo]

Now running on 1 cylinder! After running the tests I hit the starter button and saw spark on the right point and almost instantly the bike started up which nearly gave me a heart attack being that the gas tank, air box, seat, etc. are off the bike and wires are hanging out everywhere. The spark seems to come and go on that point now. But this is good. It gives me hope!

Here are the results from the tests:

Cliff
With the key on check the voltage to the points when in open position - 11.2V at each.
Check the contacts - Thorougly recleaned and gapped. O ohms when closed, infinite ohms when open.

jabcb
1) With V.R. disconnected check voltage at points - 12.4V at each. 12.5V in battery.
2) With V.R. disconnected check voltage drop across coils with points open and closed - Where should I connect the meter leads? To have voltage in the coils I need the wires connected so I can't put the meter leads in the connector to test. Confused.
1) Disconnect coils, check resistance from connector to points - O ohms through points wires. 4.4 ohms through each coil.
2) Disconnect V.R. check resistance from connector green wire to ground - 24.5 ohms.
3) Disconnect V.R. check resistance of voltage regulator - O-B/W = 97ohms, G-B/W = 97ohms, O-G = 0ohms.

Great links.

tz375
Do you have a good ground - Original engine-frame ground seems good. Replaced incorrect frame-battery ground with 10gauge wire during the rebuild. Getting 0ohms resistance from any point on engine to battery negative and starter is working so I think the ground is good.

Any further ideas based on these results? Thanks again!

[jabcb]

The resistance numbers look reasonable.

The voltage readings at open points aren't consistent with the combination of:
A) other points being closed, and
B) ignition coil resistance being a good bit lower than the alternator field coil.

How many points were closed when you took the 11.2V & 12.4V readings at an open points?

Current values through the ignition coils will help to sort this out. Coil resistance is 4.4 ohms. Need voltage drop across coils when the points are closed.

For checking voltage drop across the coils, take an uninsulated thin wire & twist it around the meter lead tip. Extend the thin wire to create a lead tip that's small enough to insert into the back of the connector. Might have to bend the wire a little so that it touches metal inside the connector. Make the thin lead tip as short as practical.

[Madbuffalo]

The voltage readings at open points aren't consistent with the combination of:
A) other points being closed, and
B) ignition coil resistance being a good bit lower than the alternator field coil.

How many points were closed when you took the 11.2V & 12.4V readings at an open points?
11.2V - V.R. connected, tested open point with other 2 points closed
12.4V - V.R. disconnected, all points held open with wood splinters (I didn't want to fry them while testing).
Oops, I didn't realize the other points made a difference! I will re-test without the wood and check voltage drop across coils tonight and post what I find.

Since spark seems to be coming and going on the points I'm wondering if I should change over the points/plate tonight too. It was the only electrical component replaced during the engine rebuild. It came from my parts engine with significantly less miles so I had assumed it was in better shape than mine. I've been hesitant to put the original one back on because I've never done timing on my own and don't have a dial indicator, yet. Red helped with the rebuild but lives 200 miles away.

[jabcb]

Well, that makes a big difference. The voltage readings make a lot more sense now.

Do you know why your parts engine was retired? Did it run when it was retired?
Did you use the points/plate wiring from you bike or from the parts engine?

You've tried different condensers. Points look good. You have 11.2V on the open points, so they are presumably wired up correctly. Its probably worth doing a little more testing before you swap out the points/plate.

One of the possibilities is that you used the points/plate wiring from the parts engine & there is something wrong with that wiring. I've not worked on GT750 points, but I think you can change the points/plate wiring out without removing the points/plate.

[Madbuffalo]

Well, that makes a big difference. The voltage readings make a lot more sense now.
When doing any scientific testing they say you have to account for human error, which in my case is a very high variable. I'm learning though.

Do you know why your parts engine was retired? Did it run when it was retired?
The engine and all the mechanicals were taken from a bike at some point to build a go-kart that never happened. I ended up buying the whole lot a few years back for $100 and was told it was a working engine, although I have since found issues with it (broken clutch, broken exhaust studs, etc.) so it's hard to say if it was in fact a running engine or not.

Did you use the points/plate wiring from you bike or from the parts engine?
Points, plate, wiring from parts engine. Condensers first from parts engine, now switched back to originals from my engine.

You've tried different condensers. Points look good. You have 11.2V on the open points, so they are presumably wired up correctly. Its probably worth doing a little more testing before you swap out the points/plate. OK, agreed.

One of the possibilities is that you used the points/plate wiring from the parts engine & there is something wrong with that wiring. Wiring is removable, I'll try changing it back tonight.

[Cliff]

Let's start from the beginning. The bike won't start. Only runs on one cylinder.
"Initially I had spark on only the center point and spark plug. It seemed overly strong and erratic on the point.
- Replaced the condensers with the ones I had on before the rebuild (since I knew they worked when I took it all apart), cleaned the points, and sprayed electric cleaner on the entire area. Point gaps are good too.
- Rechecked, no spark on anything."
Then after some screwing around you had:
"Now running on 1 cylinder! After running the tests I hit the starter button and saw spark on the right point and almost instantly the bike started up which nearly gave me a heart attack being that the gas tank, air box, seat, etc. are off the bike and wires are hanging out everywhere. The spark seems to come and go on that point now. But this is good. It gives me hope!"


You had spark on the center cylinder only, then none and now on the only on the right. This may be a dumb question, but how did you check for spark? Removed the plugs, pushed on the high tension leads from the coils and grounded out the plugs against the head I assume?
Try doing this. Find the push on connector for the wires going to the points and pull it apart. Are the two halves clean and dry inside? If the are, push them back together. With the plugs removed, high tension leads on the plugs, plugs grounded out against the head, key "On", kill switch in "Run", manually open and close one set of points. Just use a small slotted screwdriver blade, put it in between the two contacts of the points and open and close then breaking the contact. What happens? Any spark at the plugs? If there is, which plug is firing? Make sure the left set of points is firing the left cylinder, same with the center and right.
Long story short, are the points and plugs wired up correctly? You're working with three separate, independant iginition systems. If there's a wire crossed somewhere, at least two of them won't work!!
One other thing to check for is a good ground. Run a temporary ground wire from a side cover bolt back to the neg. post on the battery and see what happens!
Good luck, and keep us posted!!
Cliff.
P.S. Started my Buffalo tonight for the first time time this year and the center cylinder is not firing!! You're not alone!!