Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: opfermanmotors on February 10, 2011, 11:57:37 PM
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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 (http://www.youtube.com/watch?v=WUk7fqL0HzM#ws)
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.
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maybe a blockage in the fuel tank breather or something blocking the fuel flow.
I would say check your float valve but you reckon it happens with different carbs fitted
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I'll check that out, take off the breather and next time it happen may be pop off the fuel line.
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I am not saying this is it, but here's a similar story of a similar situation. My KX125 two winters ago it was doing the exact same thing. Turned out to be a mouse nest in the pipe. Seriously. While the bike sat unused over winter the little sob squeezed in somehow and built the nest and sometimes it would move up and block the pipe where it narrowed in the area the silencer bolts on. Took a while to find the problem. After and hour with a hose I got all the nest and a dead mouse out of the pipe :D .
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Sounds like the symptoms of a Motoplat going bad.
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Sounds like the symptoms of a Motoplat going bad.
X2.Geez,I hate to agree with Sachs :D They were famous for poor coil connections as well but no doubt you've done that already.
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It has a brand new PVL on it :) So I hope they don't go bad that fast! The Ohm Meter reads it is still in correct spec.
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To get it into this state, you can for example, put it into a higher gear and then go from a dead start, but don't get the bike up to rpm (i.e. once it's moving don't use the clutch). Just let the bike keep bogging until it eventually stalls. It'll be in this state then. I think that's the case that can happen, I might be wrong on that one, but for sure going up a hill climb and bogging it will get into this state. And like I said sometimes sporaticallly just shuts off and is in this state if you are idling after riding.
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One other thing I was thinking is that when I took off the side cover for the magneto there was some water in there. this is two fold, one possibility is that perhaps sometimes it gets a short, but still only in some scenarios which I would think it would ahve shorted more often and not "clear up" by revving it. My other thought is, what if there was an air leak on that seal and every so often under load sucked in some water? I had sealed that magneto cover so good it had somehow gotten a decent bit of water in there and it was sealed in there. I haven't taken it out since I've cleared this but that could be the reason and given the sound it does make sense.
When I saw that I thought it might be it but the thing is when it started occuring I didn't ride the bike for a while so the water would have had to stay in there. Around the time it started happening now I think about it was the time we went to trask and it was wet and I did do 1 river crossing which could be wehre the water got from. I just don't like thinking there is an air leak, but maybe it's not bad and only sucks in water :) Anyhow, I didnt like to mention this in the first post b/c didnt want to jump to this conclusion without eliminating other possibilities.
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Ford,resistance is futile, you will be absorbed into the Aryan collective. :-X
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I once had an SWM TL250 trials bike and at one vintage event I snuck across a pond between sections and the engine started to misbehave like your Maico.I checked everything and could not narrow down the problem.I eventually sold the bike to a collector without ever really figuring that one out.I still tend to believe that you have an ignition related problem that seems to intensify under load (heat).
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Ford,resistance is futile, you will be absorbed into the Aryan collective. :-X
Noooooooooooooooooooooo ???
I'd still tend to lean the same way though.If there's one thing I've learned over the years with bike electronica-and maybe the only thing-is that just because it reads good,doesn't mean it is.Especially when taking resistance readings who's values vary by temp as per manual charts.I've been stung by perfect readings before when finally,out of desperation,you swap a good reading part for one that reads the same and voila,problem solved.
You rarely run into this on cars for some reason.
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Possibly, the only reason I am trying to rule it out though is b/c it is brand new. The last one did go bad but it was also the wrong one. It wouldn't run at low RPM when the last one went bad.
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If you've changed the coil already maybe a bad magneto or slightly high resistance when hot/under load?
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Possibly, the only reason I am trying to rule it out though is b/c it is brand new.
I have seen faulty new electrics before.
As ford said sometimes they can read good but are not.
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Watching the video, you seem to do alot of riding in a gear higher and slowly lugging the motor...not something a big bore mxer is designed for.Sounds like it's just loading up and needs to be cleared out.
If they are lugged to long the crank get full of unused fuel.
It;s a simple case of starting the bike and holding it wide open, eventualy it will rev out nice and clean. This can take up to a minute.
Does this happen when you are riding in wide open territory or just single trails?
I had exactly the same thing happen to my sons KX 60 when he was first learning to ride a geared/clutch bike.
Have you checked your reeds for wear.
or
You need to replace your clutch side hand grip :o :o :o
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Actually, that's first gear and it is geared low. I know the video makes it sound like it's bogging but it's actually pulling quite strong at above idle RPM, but it will lug pretty low. I would like to say it's loading up or getting gased up like you say. The only reason I don't go with that explaination though is because it didn't always do this and nothing changed. Seems like it bogs and looses power where it didnt used to.
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Ok, just watched the vid again and it's an '82 not '83 so disregard the reed statement ::)
I still think it's just loading up, Why now and not before? not sure, perhaps engine wear.
Does it happen on the wide open sections or just the single trail sections?
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The engine was completely rebuilt the year before, so only after a year of riding this occured. But maybe it needs new rings, I guess it's possible since it is a weisco and not a Mahle. Happens on hill climbs usually, which you can be wideopen on. However, sometimes you can just be sitting idle and it just shuts off and this occurs.
It seems to me like it loaded up, just not sure why its not back firing and why its hard to clear out even with gas off. Just seems strange to me like its fixible since it didnt occur before, definately feels like a power loss sometimes.
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Is there any chance your float needle is intermittently sticking open and your overflow tube is blocked?
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Nope, would have to have occured at the same time on two previously working carbs, Mikuni (brand new) and Bing.
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Any updates? :)
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Haven't riden the bike recently :) My only thought is that I am hoping that it was the water sitting in the ignition cover. I have to ride it to rule that out as the issue that either it was sucking in water there or the water was causing an electrical problem. There was a good bit of water that was sealed in the ignition cover.
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Wipe some grease around your magneto side crankshaft seal.If the seal is leaking your Maico will run fine until all the grease is sucked into the crankcase.