Ok, so I have a strange situation with my 1982 Maico 490 Piston Port engine. You can see the situation in the following video.
You can skip to around 3:38 to hear it.
Diamond Mill MMXI Some background.
1. Started occuring recently; within the last few rides and doesn't occur all the time.
2. Carb doesn't matter. Occurs on both Bing and Mikuni and never occured on either carb before.
3. Sometimes you can shut the fuel off and it will eventually clear up, othertimes not.
4. Drift starting and getting the engine running will always clear it up.
5. Can occur suddenly, engine may just shut off. However, the usual case is that it seems to loose power under heavy load (i.e. hill climb), bog out and then it's in this situation.
6. The engine does not backfire nor does it back kick. So, while it appears to be a rich condition it doesn't give a kick back you would expect from a flooded engine.
7.In starting like in the video, throttle MUST be WIDE OPEN. Which makes it seem like a very rich or flooded (or air clogged) condition.
8. Air filter is not the issue. Have taken off the air filter at the time this occured and put a new one on even without oil and it still occured.
Here are some of my thinkings, trying to narrow it down so was looking before I tear the engine apart if anyone may already know the issue.
1. Timing.
I checked the timing, it's at 2mm. Possibly could be the issue that it's retarded a little, but the specification states timing is 2.1mm, and generally they say +/- .1mm.
2. Ignition.
It's new. I just tested it again, OHMs are within 225. I did find water was in the ignition cover when I took it off though, unfortunately, not sure where that came from since the thing was sealed pretty tight. No gas at least.
3. Rings.
I did a new top end 2 years back, it has been riden a bunch, probably could use a new set of rings. However, not so sure that it would create this condition.
4. Seals.
Possible that the seal under load sucks in oil. I know my oil level is not going down and it's not execessively smoking so its' not sucking oil under normal conditions. the seals or perhaps the splines on the primary drive maybe suck oil every so often to where it can't start like this and that's why I need WOT.
5. Coil.
Well, I didn't test the coil yet, possible it's bad. Still think it's something in the engine itself since it gets into a condition under load and won't recover without getting higher RPM, spark flowing to clear it.
6. Exhaust or Silencer.
Possible my exhaust is so carboned up that sucks in some bad stuff under load, prolly needs cleaned either way but if its not going to fix the issue I dont want to do this and then go test again, would rather know the issue fix it and have it ready next time I ride it. Possible silencer needs repacked, but I have never seen an unpacked silencer have anything to do with something like this at all.
7. Overheating and can't get combustion? Well, it clears up with drift starting so I don't think this is an issue.
My thought is maybe the timing needs advanced to 2.1mm instead of 2mm and I am going to try that. Second thought is maybe sucking oil sometimes, but can't tell since oil level doesnt go down. However, if anyone has experienced this before and has an idea like me know.