Spark Problem

[BritinNH]

Hi anyone got any suggestions for a little problem i have.
Went to start the bike for the first time since i put it back
together.
Now if you have all 4 spark plugs in she wont start so i pull one to check spark, ground it on cylinder and she starts right up, put the plug back in wont start, pull the opposite plug starts right up , plug in no start.
Doesnt seem to make any difference which plug you pull out, with 3 it starts but with 4 it wont.

thanks

[DiverRay]

Check that you have the plugs wired to the correct piston! IIRC, the left side coil fires piston 2&3, and the right side coil fires 1&4. The second thing to check is the resistance of the spark plug caps. They should be 5K Ohms if they are stock. If ONE cap is 6K Ohms or higher, the coil will only fire one plug in open air. Third check, unscrew the plug cap, and cut 1/4" off the end of the coil wire, reinstall the cap. If you have some oxidation of the copper wire, it will also cause a missfire.
You DO have new plugs in, correct?

[Cobia]

Could it be that you have the coil wires on backward, you know, the gray and the orange ones? Could be grounding out the whole ignition system? Don't know.....JAT.

[BritinNH]

Yep brand new plugs ,new ingnition wires , new 5K NGK spark plug caps too,tested resistances everything looks good

[TopCatGr58]

Still sounds like a weak spark situation, it'll fire in air but not under compression. You've got a 79, so it has the ballast resistor if it has OEM coils. You stated new wires...so thinking you did the new wires in old coils repair. Did you test the primary and secondary resistances on the OEM coils while the wires were disconnected, or at least before you put the new plug caps on??

Also, how much voltage are you reading at the ballast resistor....harness side before it goes into the resistor, as well as after the resistor. SHould be 12 going in, and about 9 going out. IF the voltage going in is much less, then that can also be causing a poor spark. A quick test would be to bypass the BR and see if it will start on all 4 plugs. IF SO...then it's a weak spark for some reason. IF it won't start...then I don't know??

T.C.

[BritinNH]

Thanks TC ,yep i did remove the original wires and replaced with solid core
accels , in the excitement of my 4 year old going to see the fireworks last night i forgot to switch off the ignition so as soon as i charge her up again
ill take a look at what you suggest.

[petejw]

might also be worth while checking your
ballast resistor located under the tank, you can
bypass it for a short time by connecting the two
wires together.