Weak, tiny spark, kz750 twin

I got it all put together and started cranking it over.:woohoo:

Did that for an hour and it wont start :blink:

Spark plug have gas on them, so it is getting gas.

13.1 volts at the coil input/hot

Cranks over and DOES spark, just very weak and puny.

Just replaced the condenser, they are cheap.

Hooking up to jumpers to give the battery a boost has no effect on spark quality.

Come on and throw some ideas at me guys! I am near my wits end with this damn thing!
Wiring makes my head hurt...:pinch:

Are the sparks hot blue or cool orange?

I assume you've replaced the spark plugs and that they're the proper one's for the bike?

They are blue, and just strong enough to be seen outside in the shade. Been foolin with this thing all day. The plugs are both old, I should replace them, but they are clean. Both of the are sparking weak on either lead.

Just to rule this out: #1 cylinder is indeed on the left, as you are sitting on the bike?

Also, does the coil have a hot and a ground that HAS to be hooked a certain way? Because I get the same weak spark either way, but just grassping at straws here..

If not already done, would ohm-test coil primary and secondary.

Good Fortune!

Refresh my memory.. What numbers am I looking for on the multi meter?

Including information about bike year and model may elicit better responses.
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Just guessing, would guess coil primary at 3Ω with points ign or 2.2Ω ohm with Kaw elec ign, and secondary with either ign at way high ohms such as maybe 15k~18k ohms.

Should find an FSM most helpful.

Good Fortune!

Ok datgummit! Now the coil is VERY hot to the touch, AND now I got NO spark!

Resistance hot to ground tab is 7 ohms and R to leads maxed out my Snap-On multimeter.

Pretty safe to say my $20 ebay coil is poo-poo.

Patton wrote: If not already done, would ohm-test coil primary and secondary.

Good Fortune!

I would punt the old coil into the can and buy the new Four-Ohm EMGO coil at Z1 for the bargain price of $36. The 750 twins with points run a four Ohm coil. I am running one on my 750 twin and it really cranks spark. Old coils do not age well. Guess how I know...

Will do, and thanks for the help guys.

Helpful thread. Thanks. I have a similar problem on my 1979 KZ750B (or 1980 KZ750G). I'm not sure which the motor came out of. It turns over ok, but won't fire. Getting gas, but spark is very faint. My voltage INTO the coil was also over 12 volts, so I assume the points system is ok. I may just have to break down and buy a new coil myself.

ElSombreroNegro wrote: I got it all put together and started cranking it over.:woohoo:

Did that for an hour and it wont start :blink:

Spark plug have gas on them, so it is getting gas.

13.1 volts at the coil input/hot

Cranks over and DOES spark, just very weak and puny.

Just replaced the condenser, they are cheap.

Hooking up to jumpers to give the battery a boost has no effect on spark quality.

Come on and throw some ideas at me guys! I am near my wits end with this damn thing!
Wiring makes my head hurt...:pinch:

Just in case...

Did you happen to take apart the timing advance mechanism?
If so, and if it's like the inline-four motors, there is a chance that the rotor is installed backwards. This would make the spark fire just before bottom-dead-center, rather than before top-dead-center. This can explain having gas and spark, but no fire.

Just checking.

Oh, and I agree, don't waste time with old coils. That can get you stranded, usually in the rain.

Yeah, I had thought about that and triple checked to be sure. It has a keyway and I found it only goes on the one way. The new coil should be in today! We will see how that pans out.

Thanks again for the help guys. Will post how it turns out.. Personaly, I hate to be left hanging on a subject..