Hi, I wonder if you knowledgeable people can help me out.
I run a 71 RT2 / RT2MX in a Champion frame and I have had many a problem with it. A lot is me learning and enjoying the process but sometimes I get stumped.

Recently due to the state of the MX barrell (it was tuned, unreliable and a challenge to race with my mortal skills) I switched to a good RT2 barrell and head. Things went well on a brief test but trackside she just would not play. Massive backfires when trying to start, wet plugs, missing - popping, cutting out etc

I have first of all tried re-jetting (running a larger VM34) and now I'm going through the iginition, trying to identify the problem.

So far I've replaced wiring, connectors, grounds/earths,checked timing is at RT2 tolerance, changed coil and have another replacement cdi on the way (changed before in 2019)

Is there anything obvious when combining the hitachi pointless system with the non MX head and barrell? 

many thanks. 
Ren

I ran an RT2MX ignition on my DT1 with GYT race kit top end back in the day & worked perfect. No reason for it not to work on your 360. Just be sure its not stuffed the cank key & gone willy nilly on timing backfiring & all. Not much inertia on the small rotors so an unlikely thing to happen but i had that happen on a yz80 so suppose possible. It's likely a suspect charge coil is the culprit but think they have two so more likely the higher resistance one. But in saying 'that' those pulser coils are suspect too. To be honest or just my opinion i think you'd enjoy it more with the heavy flywheel original mag or go for a "79 DT250 CDI mag or DT400 from the late years that have the better pulser--better system. On one of mine i'm running a super simple system of a DT360A stator plate & charge coil & one wire up to an RG50/JR50/or any suzy with same coil [coil cdi box combines] & starts & runs sweet. That's a full flywheel DT360A system of course.
Anyway--tried a clean plug or new plug?, had to ask. Just reading back again it does sound like rotor crank key to check first. Then run it in the dark & look for sparks shorting somewhere. Can't beat having individual connectors too, & ditch those multi plugs as could be just one bad or loose pin or even a bad crimp joint. Had that on an MX250 "74 with the same exact mag.
Other thing that just came to mind is with the Std cylinder with the low exhaust port it makes it harder to kick through compression & if it kicks back [shouldn't as pulser retards to start] but 'if' it does it's bad news for the kick gears & is harder on them regardless due to less flywheel help to swing through. I was forgetting you probably have the decomp to soften the blow. Might be best to bring timing back to 2.5 btdc. i dunno, just thinking out loud.

Sounds sort of like CDI has gone south.  I think there are places that make parts and repair those early Hitachi units. 

Any chance you have a stock enduro ignition you have or could borrow to swap to?  That would tell you if it's ignition pretty quick. 
 

Just going way off left field for a minute i guess you're running a chamber exhaust so no chance the muffler on the end has collapsed & constipating it under throttle pushing it even harder to get out--but blocking worse & that's causing plug to go oily & black then short out when black gos baked on to the insulator. If ya using the original exhaust [maybe not in an aftermarket frame] could it be blocking up in the built in spark arrestor. sorry--just having thoughts.

Thank you. I have another CDI on the way, I sort of hope thats the problem - but I would be surprised as it was only fitted in 2019.
Aside from vibration/degradation - any ideas what else could screw up a cdi?  

Thanks, for these ideas. I did check the pipe (aftermarket low slung) and the silencer seemed normal. I will remove and check the front pipe / gasket. I will also check the key on the crank is fine.

I wish I had an answer.  Here's a video of three later 175 CDI's.  All three are using the same CDI box.  All three stators have correct ohm readings. 

The first two are MX175 which uses a slightly smaller flywheel.  Same flywheel was used in video.  Other flywheel makes no difference. 

First one won't rev at all.  Throttle is being opened fully and it just goes bah-bah-bah.  Second ignition revs erratically.  Bike is unrideable with either one. 

Third ignition is the original flywheel and stator and runs great.  Hits redline almost instantly and rides great.  All tests run within about 1/2 hour, no other changes to bike. 

All three have GREAT spark when kicking over with plug out of engine.  I tried to measure stator readings with oscilloscope and could not find anything really significant.  Video uses the same CDI box for all 3 tests...  but I tried 4 different CDI boxes.  No change. 

What adds to the madness is I have come across CDI bikes that have similar symptoms and a CDI box fixes the issue.  Simply cleaning the (already looked clean!) CDI wire connections between CDI box and stator with Caig Deoxit has also fixed issues on different bikes. 

Another old CDI box trick is heat it in the oven and sometimes that brings it back to life. 

The old Yamaha CDI test procedures were pretty basic and then the next step was "replace with known good".  That process is good to remember for your sanity!  Because yes, it could also be a clogged exhaust or something more "conventional".  So if you can borrow a complete ignition that is known to be good, in my experience it's worthwhile to swap it out and see what happens. 

Hope you solve it soon! 

Thanks again Mark. I'll let you know how I get on - I have a good list to go at. As I get going what is the advice for removing the internal flywheel? I've just done 1 or 2 external in the past - is this much the same, i.e. grip, nut, puller etc....

Use a correct and quality puller...  not the "jaw type" is my best advice. 

Thanks again for your words. I have replaced the cdi (twice after the first supplied was unable to raise a spark) and on first test the bike started 2nd kick and idled. I aim to rebuild and test under load this weekend.
But the initial developments are encouraging.