Engine problem thread for the Corvid 19

Loop

Active Member
May 27, 2020
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Ok, so I had an issue yesterday the motor lost power and got to the point that it even had no compression at all. Today I went to the shed after letting it sit all night so I didn’t lose my temper lol.
And I tried kicking it over and the compression is back, so that may have been overheating ( I noticed my gas isn’t blue for some reason even though it came from the proper can) I pulled the plug, the cap was broken of course so I need to get a new one I think I have a plug wire set here I can get a cap from. I put it together and barely got a spark but that is probably the broken cap.
Anywho I took the exhaust off and looked inside and this is what I saw,,
8710E514-4C3D-4B73-A67A-7EA4021E82B0.png
D211FAA9-ACDE-49A9-83A9-6516A7B23D68.png

any thoughts?
 

FOG

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Mar 3, 2019
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Looks like it got too hot and seized the piston. At an elevated temperature the piston expands to the point where it gets too big and more or less gets stuck in the bore. They can even lock up completely.

I know this from an RD400 that locked up on me at 75 mph. That was a slide for life. Once they cool and the piston contracts and you can usually start 'em up and cripple home, but they're wounded.

This is typically caused by the carb jetting being too lean. Lean mixtures run fast and hot and can even melt a hole right thru the top of the piston! My brother killed a Zundapp that way when we were young and dumb...

Looking at the plug is a good way know. Light gray is is dangerous and you can also use magnification to look for aluminum globules on the plug too. Bad sign. Using a lot of oil in the pre-mix tends to make them look black. What you want is tan.

Parts are cheap tho so I wouldn't even try to salvage the top end, but if you want to, you can actually sand the rough spots off the piston. There will normally be aluminum deposits on the bore too and it's just amazing how well muriatic acid cleans that up. Rings are probably not salvageable tho. They lose their temper after overheating. You can tell if they've gone soft when they bend instead of breaking.
 

Loop

Active Member
May 27, 2020
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S.Knoxville
image.jpg

that’s the plug, I think it probably overheated, the new carb is probably the culprit, I guess I’ll try to get a new top end for it.
any suggestions for where to get it and what kind to order? It’s a flying horse motor if that matters.
 

Greg58

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May 1, 2011
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Also take the engine off the bike and wash out the crankcase with mixed fuel, pour it through a old tee shirt streached over a bucket to see what comes out.
 
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Loop

Active Member
May 27, 2020
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S.Knoxville
Looks like it got too hot and seized the piston. At an elevated temperature the piston expands to the point where it gets too big and more or less gets stuck in the bore. They can even lock up completely.
The piston never seized, it just lost compression.
 

Loop

Active Member
May 27, 2020
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Update,
Ok I put the new cdi on today, drained the gas in the tank and as I suspected it was yellow. Somehow my mix can was filled but had little to no oil in it, the overheating makes sense now. I oiled it, a little heavy just to be safe (8oz/gallon) and I had to tighten the choke lever, it was super loose put the air filter back on and it took a little work to start it but it started, I had to adjust the idle a bit not sure where it is supposed to be set it was really high out of the box btw I turned it down so it sounds more like it used to and ride up and down the road a few times, It feels good but probably has lost a bit of power because of that overheating. And the exhaust is out of place a bit now i need to readjust it.
The oil issue was my fault, I should have checked it better but was In a hurry last week.

I plan on building a second off road type later on and there will be a pre ride checklist lol.
 

Loop

Active Member
May 27, 2020
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S.Knoxville
I think the new carb may be part of the issue, it seems to not want to be adjusted and surges easily when warmed up but bogs more often than I like.
 

Loop

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May 27, 2020
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So I’ve been away for a bit, stupid outside world lol. Anywho today I put the original carb back on, and apparently all the running issues I replaced it for was due to the crap fuel valve on the tank and the bad fuel line. With the new coil in place it runs like the day it was new started up first kick and once I adjusted the idle screw (my lil man decided to turn it all the way in ) it ran fine. I just need to put air in the rear tire and figure out a way to reduce the vibration in the front fender. And power the headlight better the new led ring needs more juice.
 

Tyler6357

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Mar 15, 2012
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Santa Barbara, CA
So I’ve been away for a bit, stupid outside world lol. Anywho today I put the original carb back on, and apparently all the running issues I replaced it for was due to the crap fuel valve on the tank and the bad fuel line. With the new coil in place it runs like the day it was new started up first kick and once I adjusted the idle screw (my lil man decided to turn it all the way in ) it ran fine. I just need to put air in the rear tire and figure out a way to reduce the vibration in the front fender. And power the headlight better the new led ring needs more juice.
Good news about replacing the fuel line. Be damn careful with fenders, they have been known to vibrate loose, going into the wheel and spokes, followed by very bad things happening. Also, the cheap aluminum ones can break even if they are tight.
 

Loop

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May 27, 2020
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Yeah, but it just doesn’t look right without them, I’m seriously considering some way to mount them so they are not releasing
 

Tyler6357

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Mar 15, 2012
1,143
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Santa Barbara, CA
If they are easy to bend, I would reinforce them with something stronger, make some kind of mount with lock nuts or use blue loctite or something like that. I don't have fenders on either of my bikes so I'm not the best person to tell you how to do it but I don't ride in the rain or even on wet streets. I understand you wanting them, just secure them good. Check out this thread:
 

Loop

Active Member
May 27, 2020
113
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S.Knoxville
I saw a little bracket at the hardware store the other day that would go around the fork and bolt the fender to it, I’ll have to drill the fender and I’ll probably use nylon washers for the connection.
 
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