vape CDI failing on only one cylinder? this is a new one

[m in sc]

so, on the 70 r5 i have recently had the RH cyl hav issue, i figured it was just carb stuff but i went thru everything, and to make along story short, even swapped another r5 carb onto it known good, and still same issues. 

compression is good. 120 each cyl even +/- 4 psi

fire up and idles. rides ok..for about 5 mins then the RH cyl starts failing. misfiring at idle, then just cutting out and eventually not firing.
cools down, fresh plug, fired back up 'resets'
new crank & seals a year ago, no excessive smoking, def doesnt appear to be a crank seal. plug not oil fouled.

changed wires. caps. same thing

swapped wires left to right. SAME THING, stays on RH cyl. this is what i have a hard time understanding.

you can run it hot, (fan in front of motor) with a plug on the head and watch it start to fire intermittently on the rh side.
this bike does NOT have a zeeltronic on it (the 72 does).

ive NEVER seen one of these fail, much less like this.

i have a spare new rotor and pickup, but thats it. It cant be the coil as it doesn't matter if i swap wire sides

anybody ever seen this before on an mzb/vape? unit was installed new in spring 23. its acting just like a cingle coil going out on a stock rd ignition system and dropping one side. its sooo weird

[1976RD400C]

Seems like the rotor may have problems. You have the 2 raised square pieces, on the rotor, 180* apart that trigger the pick-up coil, one for left cylinder, one for right. The right hand one may have a problem, when hot, it's not causing the pick-up coil to send a signal. You could remove the rotor and turn it 180* and reinstall (set up the rotor install using the other cylinder) and see if the problem switches to the left side.

[gargantua350]

I know you a talking about vape but my HPI ignition failed on me and I found out the rotor magnet was cracked.  This was a no spark condition on both not one side.  Could it be spark leakage on the side that is failing?  If you start it up in a darkened room can you see the spark arc to ground?

[m in sc]

thats a good theory, but to your pount if it loses one, it should lose both. however,  76rd400 made a good point.  while its nearly impossible for a trigger to fall off or break, I think it was def something affecting the trigger process at the rh cyl side. took cover off and the trigger to rotor gap was a mile wide. closed it up to .020" and seems to have cured it.

[RDRoy]

Check the coil resistance after it warms up.

[SoCal250]

Check the coil resistance after it warms up.

Nope, already ruled that out with tests

changed wires. caps. same thing

swapped wires left to right. SAME THING, stays on RH cyl. this is what i have a hard time understanding.

[m in sc]

was for sure pickup air gap.had it out for about 30 miles ran awesome.  like said, that was a new one on me. ill def take it out a few more times but ive never had it affect just one side before. im guessing that it was juat on the cusp on the left trigger, but the right one was beyond and when warmed up would miss on that cycle. wild.

[Kawtriplefreak]

Glad you got it sorted.

[m in sc]

sounds like some crazy FB group diagnosis come to life... but took it back out, running like a top. go figure totally my own miss.

[Striker1423]

Air gap ha? You know what's funny? I just had that issue on my damn lawnmower. I had to replace the coil because of this shit. I thought I needed a battery. But, I'm glad the engine didn't start because I woulda had a fire.

Anyway, air gap wasn't quite right and the engine was really hard to start.

[m in sc]

lol. man.

[Striker1423]

Actually, I wonder. You may recall me complaining here and there about how much better the left side runs than the right on my RD? I honestly wonder if the airgap is off for my vape as well?

[m in sc]

the airgap def helped. however the issue came back, but nowhere near as aggressively.  but still there, killed a rh plug at lunch today for no obvious reason. I can't find a def smoking gun, but im goung to check the rh crank seal. even though its only a year old, and everything else has been exhaustively checked. the plug didn't look overly oily but maybe juat enough to kill it

[RDryan]

As a fellow member running this same Vape ignition I do find this thread interesting albeit scary. I'll have to try to remember it if I run into this problem. So with nothing to add I can only ask how do you go about checking the rh crank seal?

[m in sc]

pretty sure I found the culprit.  weirdly it didn't smoke more on the rh side but I think it was just  enough to foul the plug.  as said, the airgap was large, adjusting it down helped, but probably juat by giving a better signal to fire thr plug better to help prolong the fouling.

the wear it's bad enough to feel the curve of the grooves.  its wild.  I rebuilt this motor a year ago. weirdly don't remember this being that bad. luckily I had a spare. so, not the ignition,  not the carb. I think this might be the downside of running synthetic  trans oil. can't really tell when the seal is seeing on the plug.