HELP!! 1975 Suzuki GT-250 Question About Coils

[bubbaboss]

Hi i have a 1975 GT-250 and i wanted to know how i can tell if the Coils are Blown or Finsihed?

The Voltage gets from the points to the Coils Fne.. But i don't see any Spark when i kick the bike over..
Mind you they were just resting on the Head.

I tested the Coils with an OHMN Meter and i don't see any OPEN or Broken Internal connections...

I see Now Real Signs of then Being Blown!!

When i use the OHMN Meter across the Black to the end of the Spark Plug cap it shows a connetion or closed circuit, the same for the otherside with the white wire.,, Is this Normal?
For Fun i Stuck My Voltmeter in the Plug Cap and Touched Ground with the other end, as i slowly cranked the bike by foot i noticed the Volt Meter Jump to 12 Volts? is this Normal?

IS THERE ANY WAY I CAN RIG SOMETHIN UP WITH A BATTERY AND TEST THE COILS OF THE BIKE..
I would hate to Buy New Coild for Nothing...

Any Help is Welcome...

[jabcb]

For Fun i Stuck My Voltmeter in the Plug Cap and Touched Ground with the other end, as i slowly cranked the bike by foot i noticed the Volt Meter Jump to 12 Volts? is this Normal?

Don't do this again. This test is a good way to destroy your meter.

Its a good idea to check some known voltages, like the battery, to make sure the meter is still ok.

[H2RICK]

Don't do this again. This test is a good way to destroy your meter.

++++1.

Bubbaboss, the high tension side (spark plug wire) of your coils is putting out about 15K (or 15,000) volts DC. Most meters can't handle anything near to that.

[alanr]

Im not an expert but the replies are more concerned with your meter and offer no help with your problem,I had the same on an old T350 and after putting new plugs and still no spark just replaced the coils.problem solved.you can try this and that but replacement is the quickest.if the voltage gets to the coils but no spark with new plugs there is only one problem,coils.replace.

[jabcb]

Sorry for the short response. Didn't have time for a more complete answer.

The GT250B wiring diagram is shown in here:
download/file.php?id=826
Your GT250M is slightly different. It doesn't have a voltage regulator while the B model does.

Unplug the connector for the coils from the wiring harness.

To check the coil primary side:
measure resistance between the O/W wire & W wire (try other O/W wire if you didn't get a reading)
measure resistance between the O/W wire & B wire (try other O/W wire if you didn't get a reading)
You should get around 4 ohms

To check coil secondary side:
for both coils, measure resistance between O/W wire & spark plug cap. (try other O/W wire you didn't get a reading)
You should get around 15k ohms

The specs for the coils are shown on page 15 of:
http://www.ozebook.com/compendium/suzi/suzidata1.htm

You should also see if you can get a spark by removing the spark plug, grounding it to the cylinder head, and manually opening the points with a screw driver. Make sure the points are completely closed before doing this test.

[bubbaboss]

Hi Guys, thanks for the reply.... The Tester is still ok..thanks for the concern.. LOL

I will test the ohms of the coil windings themselves.... and see what i get.

I think it may be fried, but i don't want to Buy New ones for no reason either.

I will post my results...

If they are Burned out, can i make up my own form another motorbike that has good coils, and just match by Suzuki Connector Plug ends to it etc..

OK.. i got 2.3 and 5.3 ohms,, and on the plug side i got 22.8k ohms and 36.9k ohms... specs. say(4-6ohms and 15k to 25k ohms)

I Guess they need changing Right??? let meknow, i have Zero Experise with Coils, but i am willing to learn.. LOL

Thanks

[jabcb]

Do the coils looks exactly the same?
The 2.3 ohm reading could be the result of the PO having replaced that coil with different coil that has lower primary resistance.
If its the original coil, 2.3 ohms would indicate that coil is toast.

The spark plug caps probably have a resistor in them that might be shot. Remove the caps & check the coil secondary resistance again.

The GT250, T250, T350, T500 use the same coil assemblies. Might also be the same for some other models.

NOS coils are still available but are quite pricey.

Rex Caunt Racing sells new aftermarket coils that fit the stock coil brackets. I have them on my GT250. Cost around $20 each.
He has 2 & 4 ohm coils, so make sure to get the 4 ohm coils.
You can get the coils via his website or sometimes via eBay.
http://rexcauntracing.com/pages/htcoils.html

[bubbaboss]

Yes!! they look like the Original Coils.
I Will Remove the plug caps and test the ohms again...

In the meantime i have a friend who owns a small engine repair business, i will see if i can find coils from another Suzuki, or Other Japanese Motorbike to replace these coils... he has a pile of Old Parts.

Just So i do it Right, whats the Polarity of the 4 wires i see at the Coil Connector? Black, White, and the O/W
I think Black and White are (-)Ground and the O/W is(+) Postive... Am I right on that?

I will let you know how i make out.

Thanks

[jabcb]

Correct. Bike is negative grounded; so the Black & White wires are (-) ground.

[bubbaboss]

OK.. i retested i get 2.7 and 5.1 ohms,,, and i get 22.8k and 36.9k ohms with Plug Caps On.

With Plug caps off i get 11.8k and 12.7k ohms ??

What does that mean? why such a change in reading with the plug caps off??

Which Reading do i use a spec for the coil were it says 15k to 25k ohms... is that with the plug cap on or off ??

Should i take the plug cap apart and try and clean the parts inside?

Just want to make sure and LEARN PROPERLY Once, exactly how to test a coil.. and the pulg caps play in all this too.

Thanks

[tz375]

Plug caps fro teh street are usually fitted with a resistor to reduce electronic noise. Most I see are 5,000 ohms but they are available at 10,000 ohms as well. Sounds like your plug caps need to be replaced and teh coils appear to be out of spec as well.

I would toss them and fir a pair from Rex Caunt (smaller and cheaper) or Dyna (larger and more expensive). They are probably other sources as well, but I wouldn't bother with more old used coils.

[jabcb]

+1 on tz375's recommendation.

Both of your caps are toast. Same for one or both of the coils.
Also, you aren't going to save much if anything with used coils.

The Rex Caunt coils bolt up to the stock coil bracket.
Last time I looked, didn't find any Dyna coils with the correct bolt spacing & primary resistance.

My GT250 has Rex Caunt coils, NGK resistor caps (5k ohm) & non-resistor NGK plugs.
Runs good.

[bubbaboss]

OK... thanks for the info... I will look into New Coils for the bike.