New plunger black plugs

Maxbou92 wrote:

Thats the dyno guy method!!?? I don’t know why he did that.. 102.5 and 105 in center !

You need a better dyno guy..

wrote:

I don’t know voltage. They are Oem coils!!  If I look at the dyno curve. It looks good to have bad fire , what do you think ?! 





 

You should check the voltage because as it may have something to do with your combustion issue. Like I said old wiring may be to blame, look up "WG coil mod" on here. You mentioned everything else but the voltage at the coils, and a cheap multi meter is a essential tool for working on these old bikes.

Weak spark can also show up as a black plug (see "WG coil mod")

That dip in the dyno curve is a very typical low RPM transition from low to high circuits on theses carbs, and its very hard to tune that out. Its easier on fuel injection to make those kind of changes. That dip in my opinion is not a "miss fire".

Your main issue is the black plugs so you need to concentrate on that first, its either too much fuel or not enough burn, or a combination of the two. 

You mentioned running a B7 spark plug, they run B8's on 750's because they typically run hotter than a 650 does. I believe your issue with the black plugs is not a spark plug heat range problem.
 

I will check for Wg coil!! I have new one on ebay(cheap).. never put them on the bike. And I have B8es spark plug!! What are you thinking about 102.5 and 105 in center ?! Why he did that ?

wrote:

I will check for Wg coil!! I have new one on ebay(cheap).. never put them on the bike. And I have B8es spark plug!! What are you thinking about 102.5 and 105 in center ?! Why he did that ?

 

Maybe you misunderstood the difference between coil and coil mod. The coil mod is a trick in the wiring harness to use a relay circuit to send more voltage directly to the coils.

I just used B7/B8 abbreviations, I know it has ES in there. Warren3200gt suggested running B7ES plugs because they run a bit hotter (stock KZ650 plug) which may burn better. May be something to try.

Some people think that running a richer main jet in the center cylinders on a air cooled motor helps because the center cylinders may run hotter. I am not sold on this and would just stick with the same main jet across all 4.

What coils mod are you using?

Maxbou92 wrote:

What coils mod are you using?









 

www.kzrider.com/forum/4-electrical/297304-wired-george-coil-mod  

kzrider.com/forum/4-electrical/231761-wg...-is-it-to-accomplish

Get a multi meter and check your power output at the coils first.

I have one on my bike that has a original wire harness on it. Its just a splice in and a relay that fits under the side cover, took mine from 10V to 12V.

 

 

Are you up in Quebec? I am in Ontario.


 

A lot of the V's 2 and 4 cylinders used different mains front to back but had different emulsion or "type" carbs. I know early Yamaha XS1100's has larger sized mains on 2/3 but they also had different emulsion tubes too. This was not found to really make a difference and subsequent change back to uniform jetting across the bank was readopted. But like Zed mentioned some older mechanics adopt this forgotten tech and apply it without really knowing why? An ole wives tale. I don't know for whatever reason you're fighting the obvious "easy out" and just go back to the carbs designed as Warren has mentioned? Didn't you also have some 29 smoothbores, a while back, you were trying to adapt initially?   

Injected, a tip for cleaning those connector blocks/terminals. I've been using a 50/50 solution of CLR and water for years. Just grab a jar and dangle the connectors on the mix overnight. Instant gratification and doesn't attack those plastic blocks. Will tint/cloud the rubber covers on male/female terminals if left in the emulsion for like a week though. Cheap/effective and Earth friendly.

Yes im in quebec!!  So I need to start the bike and test one of the 2 wires that coming to the coils ?

I had cv34mm stock one before. No air box on the bike when I bought it.. so Ive find 28ss to be able to run the old 750 with pods filter

Maxbou92 wrote:

Yes im in quebec!!  So I need to start the bike and test one of the 2 wires that coming to the coils ?

With the ignition on without the the engine running. 
The coils each have two wires. 
One is the live feed the other is the trigger to "fire" the coil. 
Find the live feed and measure the voltage the coil is receiving from the battery via all the loom, kill switch etc. 
Multimeter to volts, red to live coil feed, black to battery negative. 
Ideally it should read the same as if you were reading the battery voltage across the battery terminals. However after 40 odd years of old wiring loom, corroded switch terminals etc it'll likely be a fair bit lower. 
The coil relay mod allows full battery voltage to feed the coils but still maintains it being switchable with the ignition key. 
Try not to leave the ignition on for more than a few minutes without the engine running or the coils can overload and burn out. 
 

wrote:

Yes im in quebec!!  So I need to start the bike and test one of the 2 wires that coming to the coils ?
 

Yes, there is a power wire (red/yellow) and a ground wire (green or black) at the coils. Just turn the key on, no need to start it.

While your at it you might even want to test that your battery is charging properly, it should read 14 to 14.5V at 4000 RPM.