Weak spark only runs on full choke

[Omegati]

1980 GS1000GL:
Died while out on a ride; coaxed it home with full choke and very little throttle.
Rebuilt the carbs with no change. New plugs with no change.
Checked spark - and it is yellow and very weak on all plugs.
Starts and runs on full choke, but dies as soon as any throttle is introduced.
Checked coil primaries and they are in-spec at 4.4 ohms.
checked coil secondaries at infinite resistance (resistance from plug 1 to plug 4,and plug 2 to plug 3).
Manual spec. is 33 ohms for secondaries.
I disassembled the internals of the plug caps and found RF resistors on 1 and 4 with infinite resistance.
Can't find any RF resistors on 2 and 3.
I read somewhere that it is possible to trim the high-tension leads, but the caps appear firmly attached to the wires.
Any Ideas? - how do I get the plug caps off the wire to inspect/trim/ measure resistance at the spark plug end of the high-tension lead?
Where do I buy new RF resistors?

Thanks for any help!

Eric

 

[Nessism]

Try unscrewing the caps from the wires. The cap has a threaded stud that threads into the wire.

NGK makes nice replacement plug caps that sell for about $6/each. Well worth the money.

Edit: updated to correct mistake in second sentence.

 

[tom203]

"Manual spec. is 33 (k)ohms for secondaries."

yes, over the plug caps . Remove the plug caps and stick meter probes in wires,and measure plug wire to plug wire: should be in 12000 ohm range

 

[Redman]

1980 GS1000GL:
..............
checked coil secondaries at infinite resistance (resistance from plug 1 to plug 4,and plug 2 to plug 3).
Manual spec. is 33 ohms for secondaries.
I disassembled the internals of the plug caps and found RF resistors on 1 and 4 with infinite resistance.
Can't find any RF resistors on 2 and 3.
,,,,,,,,,,,,,

Welcome to TheGSR.

That would be 30K (33?), kilo ohms.
5K for cap, + about 20K for one wire and coil and other wire, + 5K for other cap = 30K

CAn pull-twist the caps off the wires. Can then ohm check each cap.
NGK caps can be found at about any motorcycle parts supplier (doesnt need to be Suzuki specific) for 4 - 5 bucks each. 1 & 4 are different than 2 & 3 (longer).

You say you disassembled the caps, so puzzled about you asking if can remove from the wire.

Yes, look at end of wire, should be all the conductors all the way to the end, if some lot shorter than others then some of them have been zapped away. Trim about 1/4-3/8" off the end to get fresh conductors.

On 1100G the NGK numbers are XB05F and VB05F. I would think are same on 1000G but not sure.

 

[Redman]

Weither it is 30 or 33, is not my point.
My point is that it is Kilo ohms.
And each cap is 5K ohms.
ANd caps are removable, and easily replaceable, and probably one of the most common ignition problems.

Yah, that infinite reading on each cap-to-cap , yah, that is the from the infinite you measured on a cap.

My expereince is the caps go higher than the 5K, say 8 or 10K over time and heat and usage over years, and things still run. THen they go higher and higher to 20 or 25 or 30K each quickly and then open-infinite quickly after that.

I would say, 20 bucks worth of new caps, and you will be back in business.

 

[Omegati]

Thank you, thank you, thank you!
I didn't know the caps unscrewed. When I said I disassembled caps, I meant I unscrewed the brass piece inside that captures the spark plug electrical contact.
The long caps on 2 and 3 have springs inside that pushed out the RF resistors. The short caps, I had to tap the cap onto a hard surface to get the resistor to come out. It is the RF resistors that go bad causing resistance to go to megohms or infinite. Measured the resistance through the cap without the RF resistor and it was half an ohm. Resistance through the HT leads and coil secondaries is 12K ohms. HT leads are copper core, so I am thinking that the 12K is the Coil secondary winding.
Thanks again!

Eric

 

[Steve]

Just in case you are not worried about RF suppression, you can substitute a piece of solid wire in place of the resistor and restore operation. Some have used welding rod, others have used a piece of solid 10ga wire, others have used a short section from a heavy-duty coat hanger. At least it will get you back on the road while waiting for your proper resistor caps from NGK.

By the way, there are two models that you need to get. XB05F is the longer one for the inner plugs, VB05F is the shorter one for the outer plugs.

.

 

[Brendan W]

Have you checked the coil supply voltage and the condition of the fusebox?
The coil plugs can hide a mess of corrosion.
The contacts on the ignition switch and the kill switch can also rob a volt or three.
Well worth a clean.