I'm having an issue with the bike cutting out. It happens mostly around 6000 rpm like it's misfiring. I checked the coil windings and measured .4 ohms on the primary and 6.5k on the secondary. This is close to what the manual says it should be primary .17 - .23 and 5k - 7.6k secondary. I then tried to measure the peak input voltage to the primary which should be 120vdc according to the manual. I don't get anywhere near that more like half a volt. So I'm not sure if I have a bad coil or the ECU is flakey. Yeah I've bypassed the side stand switch so I'm pretty certain that's not the problem. So I'm appealing to the collective brain trust to help shed some light on my problem.

 

Did u try a new plug?

Are u sure your suppose to get 120vdc, that seems a like a high voltage for dc. And I don't see how the coil would cause a 'rpm' dependant miss. If it ain't making voltage, it is not working everywhere. But I am not an 'expert', but I am an EE.

 

New plug was first thing I tried and 120vdc does seem on the high side but that's what the service manual said it should be. I'm not it's rpm dependent 6 grand is where is more noticeable. I think the coil is breaking down under load. I tried hitting with a heat gun while checking resistance of the primary and secondary neither one changed much. So I'm debating to just bite the bullet buy a new coil and try it. At least I'll know if it is or isn't the problem. I also come from an electronics background 40 years as a telecom tech.

 

I can't think of a reason to have a constant 120vdc on the primary. The only thing the primary should see is a pulse coming from the CDI. when the engine is turning over. I may be wrong on that. If I am wrong, maybe a misprint and should be 12.0 vdc.
What other mods have been done to the engine? This sounds like a lean miss from opening up the air flow through the engine and not increasing fuel flow.

I also have electronics back ground.

Ride on
Brewster

 

It's not constant its only present for a milli second or less so have to use max min feature on my multimeter, fluke 87 V. Which may not be fast enough to capture a good reading. At first I thought it was just a clogged main jet, so I've cleaned and inspected them at least twice. Along with a new air filter. The only other thing in the fuel delivery I haven't checked is the fuel filters. There's two of them one for main and one for reserve. It acts the same regardless of where I have the fuel tap main or reserve. So I've sorta ruled out a fuel issue.

 

"Response time is the length of time an input must stay at a new value to be recorded. A shorter response time captures shorter events, but with decreased accuracy. Changing the response time erases all recorded readings. Model 83 has 100 millisecond response time; Model 87 has 100 millisecond, and 250 μs (peak) response times. The 250 μs response time is indicated by "p" on the display."

Is your Fluke 87V set to the 250us minimum response time? I didn't see in the manual how that was done. I don't know what pulse width to expect from the CDI.
A weak spark usually shows up under load or high rpm's. Your mid range cutout is typical of a lean mixture caused by more air flow through the engine. I'm assuming that your bike isn't FI. The idle and main jet circuits function ok but the needle restricts the fuel flow in mid range. When the air box lid is removed and/or a better breathing exhaust is put on, the stock non-adjustable needle must be replaced.

Ride on
Brewster

 

It has a DJ 2206 needle and 128 main FMF slip on stock header. Had this setup almost since I rode off the deal showroom without an issue so to start having fueling problems now when nothing's changed seems kinda remote.

 

Ok. Now I see why you are looking at the ignition system.

Ride on
Brewster

 

Sounds like a bad CDI maybe?, I had one that went and would cause a miss at high load/high RPM.
I seem to remember it's a common problem on one of the big thumpers, xr600's maybe

 

The pulse done by the cdi is less than 20us, with 140V amplitude nominal. The output voltage is 0V except for that pulse. The service manual calls for 120V min, and requires using a "Peak Voltage Adapter" special tool between coil primary and tester (which is to be set on DC volts). Without that peak adapter, you won't be able to get any meaningful result on a voltmeter. You either need that adpater or use a scope.

I bet that said peak voltage adapter is just a 200V diode with a 100nF high voltage capacitor or something like that. Could be built by yourself if you have some knowledge in these components.

Thus the testing you did is not meaningful at all to determine whether your cdi box is good or not. Since your bike runs at least some, your cdi is most probably good. Yet it sometimes occur that they develop intermittent malfunctions like you have, so you cannot rule it out completely at this stage. Same thing with the coil, even if you tested it with heat applied and found no correlation, it may have internal shorts or opens that develop only with specific usage scenarios. Thus only a swap with a known good one will provide a definite diagnostic here (hint: you might be able to buy a used coil for cheap on eBay).