[all4nick4]

Hey guys/gals long time reader, 1st time for a post as this is the 1st time i couldn't find my answer in existing threads so here goes... I've got an 04 300ex, owned it since new, bikes still pretty mint, original everything except all the typical bolt-ons(Umi CDI, FMF full exhaust, k&n filter w/outerwear, 400ex carb swap, gear change, holeshot rears) this is the first problem I've ever had with it, except one other thing just recently. Bikes been rock solid, maintained religiously. I'll try to not drag on here but I've got a cranks but wont start, I'll get a random burble and 3 times now it started and I was able to rev the snot outta it for a free seconds and then it dies. It started and ran perfect as it always has 2 days prior, we rolled it outtaa the way in backyard, went to start next day and nothing. Now a bit of background on me I'm a 20yr+ diesel mechanic so in know my way around an engine and troubleshooting very well. This ones got me stumped, all the typical things have been checked, I'll run thru em...
-plug changed 3 times lol (originally it acted just like it has before the one time it fouled a plug while jetting 400ex carb swap)
- has excellent blue consistent spark
-compression test is 145(yes I know manual says 175 or 185+/- 10psi I think, but 145 is plenty, hell 120 is plenty, it only had 155/160 from new)
-pouring gas down plug hole no change
-spraying brake clean in carb throat, no change
-battery is new cranks like crazy
-airbox off, no change
-checked and reset valves(first time they actually we're out a bit from new) no change
-added fresh gas from different station, even tho it was fresh gas already(bikes never had ethanol regular since new), assured full gas flow from petcock
-pulled new 400ex carb and recleaned it all anyway(it is a Chinese copy, which I believe is the cause why I had trouble jetting it based on recommendations here, but I got it figured last year and it's been great once I figured out I had to jet it way richer than what prolly a Honda 400ex carb would have needed)
-did find cracked open carb vent hoses and fuel supply line l, figured AHAHA THATS IT! Nope no change.
Only thing I haven't checked yet is the cam timing, is it possible the chain stretched suddenly with no prior symptoms of a loose chain and jumped so many teeth it won't even start, sure but highly unlikely as it ran perfect 3 days prior.
I do believe there's 1 or 2 things I'm forgetting to mention that I've tried as well
So I beg for all your collective experience here, HELP! IM PULLING MY FRICKIN HAIR OUT WITH THIS THING!
I will be checking the timing but before I crack open a factory sealed engine I figured I better ask for help here first, so any ideas, thx for ur time.

 

[all4nick4]

Update, I decided to watch the spark from plug for an extended period of cranking and I noticed something, now I swear I cranked it long enough before to create this but maybe I didn't, basically after 3secs of cranking my nice blue spark suddenly quits, then reactivating the starter, same thing, nice blue spark for couple secs then it quits. I thought this could be enough time to just not allow it to fire and maybe explain why I get a burble sometimes and 3 times it did fire but only for a few secs, now what are your thoughts on what could cause this, I seen another thread here where guy had same issues with disappearing spark and the pulse generator was suggested but even more likely is maybe the CDI? What are your thoughts on this

 

[all4nick4]

I see no help has been offered, I figured it out, I by chance unplugged Umi CDI and plugged back in and bike started! Thought it was fixed, but it ran like crap and cut out, stalling. Went and dug up original CDI and plugged it in, voila! Bike runs proper again. So I'll be ordering an amr stage 3 CDI off eBay as it's the only one I can find available these days for the 300ex that does also has an improved timing curve, I'm doing this as the OEM one sucks with low rev limit. Over 10yrs ago I bought the Umi CDI (which from what I can tell only raised rev limit 1000rpm) from Royal distributing (the only aftermarket powersports chain in Canada). I've always wanted to try a CDI that also improved timing. Does anyone have any suggestions for a CDI that may provide the most performance for a 300ex? I've always tried to eek out every bit of bolt on performance from this quad. Now that it's fixed I'm finally going to order a big bore kit and stage 1 or 2 cam that I've been wanting to do for years. Hopefully this thread can proved help to so done else in the future when troubleshooting a no start. It) seems the CDI would provide spark but then break down and either misfire the spark or it would cut out completely. I think this is a rare occurrence, but it's bound to of happened for will happen to someone else. I do t think I'll be posting here ever again as no help was offered at all. Thx