Autonerdz forums

Hey guys, been a while since I have posted but I have another stumper that I hope you all may be able to help with.

A guy brought me this bike to Dyno Tune so we ordered him a jet kit and proceeded to tune the bike. The Air/Fuel ratio seemed to pretty much stay the same no matter how much fuel I added or took away. Also something odd that I have never seen...the plugs were white indicating a lean mixture but my AFR was reading nearly 11:1(very rich). My gears got to turning and I thought that this is most likely ignition. The bike is putting down roughly 35 hp. They are roughly 55 hp out of the box. So I am running nearly 20hp shy of factory numbers.

I have a couple of waveforms that I have saved and will attach for you guys to check out. I normally dont like to jump to the most expensive part to replace but I think it may be a possible CDI box failure.

I started with the scope on the secondary side of the coil and have worked my way backwards towards the CDI box. The coils all ohm out within spec on the primary and secondary side according to the service manual. (.2-.5ohms primary side) (35K ohms on the secondary side)

The trigger coils also fall into spec at 523 & 528 ohms.

All wires from the CDI to the coils have been check and show good continuity and have no shorts to ground.

So my thought is that if I have good information/signal going into the CDI box and getting poor signal out...seems like a CDI?

The attached file with the primary coil voltage and secondary voltage are both under load and both seem bad to me. (Don't look like good waveforms) Front and rear coils are almost identical which also points to the CDI because my thought is...what are the odds of two coils failing at the same time??

Still not a master at the scope which is why I am asking what you guys think! 

Hi, first of all that it is not CDI ignition but Transistorized ignition. You can tell that from your capture. I believe you may have used the wrong probe setting for you secondary leads as the voltage is way too high. Do you have the colored leads and did you by chance select the "black secondary probe" setting? I personally do not see a problem with coil output, primary looks good. The only thing I see is the secondary is suggesting to have a lean condition because of the sloping up of the burn line. Are you using a 4 gas analyzer or a wideband to determing afr? Is 11-1 at wide open top rpm?  If using the 4 gas what is your 02, co and co2 readings. Down that amount of hp I would think would require a dead hole or some major mechanical problems. If you want a quick and dirty test for afr problems stick it on the dyno and do a lean/rich test quickly by opening up the airbox lid slightly (lean) and partially duct tapping off the intake snorkel (rich). Only do enough to make a small change in power output. If it goes up in one of the tests, try slightly more. If it goes up again you for sure have found at least one problem. Can you do an in cylinder compression test? Can you post the Dyno graph?

James H wrote on Oct 20^th, 2017 at 3:11pm:


That is exactly what he did.


Russ,

Use the colored secondary probe from your probe library section.  if you have nothing in the library section, install the Autonerdz PicoScope add-on.

RedlinePowersports wrote on Oct 21^st, 2017 at 6:45am:


Much better! Do you have other coils you could sway onto this?

Just noticed in your first post you said primary resistance of the coils is .2 to .5 ?. Primary side of the coils should be 2 to 2.5 ohms. Any non CDI (they always have very low pri resistance - read high amperage) coil off any bike will work.
When did the problem start? Since you put in a jet kit? After the customer did some modification? Did it happen suddenly or deteriorated over time. Is it consistent? How much mileage? This will help with a diagnostic direction.

Your peak torque looks about right at 3000 rpm but just falls off too quick. In my opinion I would think a air flow or air fuel ratio problem as an ignition problem I would think would show up at peak torque. Do you have a plugged carb slide vent preventing them from opening?

RedlinePowersports wrote on Oct 21^st, 2017 at 10:29am:


Smart move. We do the same here and it has saved a lot of stress when dealing with a customer. Showing them what they really have vs. what they think they have works wonders!

RedlinePowersports wrote on Oct 21^st, 2017 at 10:29am:


This has come up a lot here. Someone thinks a tune is the issue when it's something else.

RedlinePowersports wrote on Oct 21^st, 2017 at 10:29am:


We have a saying if you add 10% fuel, take away fuel 10%, add  10 to 15 degrees lead ignition timing and take away 10 to 15 degrees lead ignition timing and little or no response it's not the tune.

RedlinePowersports wrote on Oct 21^st, 2017 at 10:29am:




RedlinePowersports wrote on Oct 21^st, 2017 at 10:29am:


You will only see the coil output that high when there is an open circuit either because of an issue or you made it one by pulling a plug wire off and making a larger gap.

Just putting the curved clamp on the plug wire and the ground wire to the chassis of the bike.

RedlinePowersports wrote on Oct 20^th, 2017 at 1:46pm:


Good thread, but one quesiton?, how is the AfR determined, is this with a scanner or what?  11/1 verses White plug, someone is not telling the truth and it is not the plug, don't need a Pico or scanner for that, but suppose timing could do that.  Is this unit injected or old school float ect?

After liestening to James, hate too say too much and sound stupid, he is all over this, James, as Spence stated I second Nice.

Stitch