odd plugs ??

My bike was running pretty well, firing on all four the other day. So i took the plugs out to read em (they all looked ok to me!
I noticed that my #4 was a ngk B7ES and the other three were B8ES.
So i put a B8ES into #4. NOW #4 AIN'T FIRING !!
Will it do any long term damage if i just put the B7 back in #4 or is there a more serious problem ?

Bill, unusual question/prob. NGK #'s tell a story. 7 is hotter than 8.and heat changes are relativly small.(often 1 step cooler is recommeneded for prolonged/high speed riding). to drop a cyl just because of 1 heat range is odd. Is #4 now fouled? did you replace w/ a new plug? Have you thought to look for leaking plug cap/wire? Hope these give you opts' to look for G.

it's maybe a little sooty compared to the rest.
I'll go check for a spark now to see if it's a bad plug or not
thanks

the only time i've seen this is when a mechanic at a shop i worked at one summer put 7's in a gpz1100 that was having fuel inject probs and would foul 8's once a week ...this was his hillbilly solution since we were broke ....he thought the 7 was hotter and would resist fouling....can't remember any improvement...sounded good at the time....we would put em in and roll another one......

I don't think you have a heat range problem. First, check your plug gap. 2nd, check your resistor caps and if they are mounted well on the cables. Than check your cable to coil connection. Because almost all of our cables are solid core wires the wires themselves do not go bad. I normally run hotter plugs on the outside two cylinders than on the inside two by one heat range.

Black sooty plugs... could be low voltage to the +12 Vdc inputs of the Coils. Very common on vintage bikes.

As I did, try the very popular WG Coil(s) Repowering mod. Dirt cheap at about $10.00 USD in parts. See here:

WG MOD

This is how I implemented mine:

K1

Best of success.

Yah, but the sut is only on one plug????

otakar... one plug. Ooops missed that one. :blush:

So, if the plug is good now we are down to carburetion... a bit rich? The usual suspects would be:
1) Are all the jets the same size?
2) Is the Fuel Service Level correct.
3) Is the Carb slide synced with the other slides?

Best of success.

I had a similar problem on my 76 KZ900. I had one cylinder that would always fowl out and start cutting out until I would be running on just three. I checked everything and rebuilt the carbs. I even installed a electronic ignition. After about 3 years of putsing around with it, I found out that it was in the choke plunger on that one carb. All I started doing, was "POPPING" the choke handle up and down two to three times to seat the plunger more positively, and the problem went away. to this day, if I just turn off the choke just by pressing it down I will have this problem. If I simply open and close it two to three times the problem is gone.

If not already done, would assure valve clearances adjusted to specs.

Imo, both spark quality and compression should be assured before addressing carbs.

Good Luck!

Well I checked for a spark with a b8(and had one) so i put the b7 back in to #4 and......
still no #4 fire !!!
So it ain't to do with the plug heat.

here's what i'm thinking now. I tore into the wiring harness behind the headlight the other day to sort some lighting issues out

I didn't have a taillight so i spliced the blue taillight wire into a bigger thicker white wire (didn't know where else to put it to get the tail working)
could this wire fiddle have caused a short that stops #4 from firing.
All the lights/blinkers work now.
(this harness is really bodged together. it's the reason i got the bike cheap, because the harness had been cutup in the headlight by an angry neighbor)

this is the only thing i can think why #4 should suddenly stop firing ???

i'm the elec dummy here and anything is possible...but i think they would fail in pairs.....if you had a coil problem.....patton is saying to check valves and it cant hurt..... too bad you did'nt have a cheap extra coil from e-bay or somwhere to swap out and see if persists....your tail light fix should not matter and is just coincidence imo.....good luck