'82 ATC200 - backfire/won't start

[speedyj]

So I've been riding my newly (~3 months) acquired '82 ATC 200 day and night for some time now. Rebuilt carb, sealed up the crankcase to stop the seepage. It ran *mint* - never even needed to the use choke that often until 3 weeks ago when it got cold up here (Ontario) - idled like a dream, revved up - everything was mint.....just perfect and I couldn't have asked for more.

2 nights ago I was out in the snow doing slides - caught something under the snow - rolled her over - stalled. I pushed her back over.....2 pulls.... away she goes. Get her out of the ditch under her own power and ride a mile back home. Park her for the night. It ran mint all the way home.

Yesterday I go out the shop and start her up - 10 pulls and nothing...not even a hint of ignition. 2 more and she backfires rather hot out the carb. ??? I fiddled with the throttle car - nothing. Flooded? Nope. Every 5 or 6 pulls and I get a nice clean backfire.

I yank the filter off the intake. When I pull it over I see a nice clean cloud of fuel mixture coming back out the intake! WTF?? Stock Keihin carb with new rebuilt kit. Choke not stuck.

My instant thoughts:

broken/skipped timing chain (never checked by me since I've owned it) - intake valve stuck closed??
Broken valve spring - intake valve stuck closed

but...

Verified facts thus far: (before I tear into the block)

I have a hot clean blue spark
The carb I checked and it seems fine - float not stuck, not flooding
I pulled the valve inspection cover off and the exhaust valve is moving
Tested CDI resistance - within normal limits
Tested spark plug boot resistance - within normal limits
I have great compression when I pull it over - normal (not more or less)
Plug was dark (oily?) and wet (fuel) when pulled

I'm a half-newbie at this - any hints would be appreciated. Just seems weird that it was all of a sudden. I don't ride the sh*t out of my bikes but this one seems odd.

Thanks folks!!

[Flossyb20]

If you have fuel spitting back out of the intake, then your carb is flooded. I doubt the rollover messed up your timimg, especially if you were able to drive off. Most likely there was a little trash in the bottom of your bowl or gas tank, and clogged something up. Take your carb off and clean it out, also check that your screen filter in the gas tank is still there/good. You may also want to get a few sparkplugs for that thing...they're like 3.00 each and well worth it. Those old 200 4 strokes go through plugs like crazy in the cold!

[Flossyb20]

Sorry, just noticed you're backfiring issue...what's happening is your pulling so much gas into the cylinder that every so many pulls it has to go somewhere, and ignites based solely on the compression of your engine, which tells me everything is mechanically right with the motor. The reason for the backfire is that there is so much fuel build up that when the gas does ignite, it burns crazy slow because of the lack of O2 in the chamber, that is until the intake valve opens up, hence the backfire. Like I said before, clean out the carb, pay special attention to the float needle and idle jet. When you have the carb off, pull the spark plug out and give her a few pulls to clean out all of the gas. Put a NEW plug in, the fresh, clean carb on, and I guarantee you you'll be back doin donuts in no time!

[TurboTacoma]

Flossyb20: Good advise!

I was going to recommend taking the carb off too! To clean and make sure it is clear of fuel and any debris. A fresh plug too.... Yes the older bikes eat plugs if fouled out to many times or really bad. ( You beat me to it!) Again what I would of suggested!

[speedyj]

Ok guys. I have a brand new replacement carb in the plastic still - I'm going to put it in and get back to you all - thanks guys. Ya a new years' eve task and I have a very understanding wife Oh - and new fresh plug installed - no difference.

[speedyj]

Live update:

Swapped in new carb (and plug) - same issue - fresh fuel back through intake & backfire....

[speedyj]

Spark is weaker than I thought but still there....

[ATCrider42]

How about your kill switch? Do you have a good ground on it? When you rolled it did it get bumped and possibly broke? You may have just gotten snow and ice build up in and around the switch which is diffusing the ground on the switch. Kinda sounds a possibility.

[speedyj]

So tomorrow morning I'm going to check all the wiring and take the switch out of the picture. I've already checked the grounds and will ensure everything has continuity and go from there.

[shortline10]

Sounds like the stator is bad to me . Very common prob with the 200cc honda's . But check all wire connections first .