Something odd with my engine. ?

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Texhun

Texhun

New Member
Aug 2, 2011
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Rosebud Texas
My engine runs great, startsup perfect and couldn't idle any smoother. But what boggles me is it runs like an HT, vibrating, rattling and so-on. But there has been quite a few times where it will smooth out having almost no vibration, have an enormous amount of power and run smooth as silk, why it does this I don't know, it's not 4stroking and that I'm certain. I'm not sure but maybe it's from a weak CDI or sparkplug and all the sudden it gets the right amount of juice? I changed the cable after being worn out and abused after 2 years and my plug is fairly new but it still does the same thing. Any ideas? Am I running rich, is it a weak spark?
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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"Runs like and HT"- what do you mean?
"HT's" can and do run fine (most of them anyway)
What kind of engine is it?
 
Texhun

Texhun

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Aug 2, 2011
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Rosebud Texas
It's a 66cc K-80 from BGF. It runs like my first 2 engines did, that feeling of unnerving vibration as your revs go up with the speed and when it does that thing there's almost no vibration to be heard of. I know it's sounds odd and it's a little hard for me to explain. Like I said earlier it's not 4stroking, it just all the sudden runs faster and gets super smooth like the crank all the sudden got balanced and the vibes are almost completely gone. If I can just figure out what's causing it to keep from running smooth and faster like that. I'm almost thinking it's a combination of running rich and having bad spark. I'm running a RT carb with a #70 and a champion plug. On a cold start it 4strokes for about 3-4 seconds when I let the choke off and that's it. Then I can run all day and just randomly while I'm riding it goes super smooth for about 8 seconds then goes back to normal.
 
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Allen_Wrench

Allen_Wrench

Resident Mad Scientist
Feb 6, 2010
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Sounds like you got gremlins in there. The good gremlin is fighting the bad gremlin. You need to help the good one win.

(This is where my daughter Kassandra says to my wife "Daddy's writing crazy stuff again".)
 
tooljunkie

tooljunkie

Member
Apr 4, 2012
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my 48 grubee does this also,i raised the clip (dropping the needle) and it runs smoother for a longer stretch,as the rpm's are climbing,then it fourstrokes til i slow down and accelerate again.its rich,i know it is,by reading the plug.at wide open its worse,but 43 kph is too fast on the gravel road i drive on anyway.
jetting is the key,reading the plug is the trick to getting to the right jet size.
 
Al.Fisherman

Al.Fisherman

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Sep 9, 2009
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Texhun said:
It's a 66cc K-80 from BGF. It runs like my first 2 engines did, that feeling of unnerving vibration as your revs go up with the speed and when it does that thing there's almost no vibration to be heard of. I know it's sounds odd and it's a little hard for me to explain. Like I said earlier it's not 4stroking, it just all the sudden runs faster and gets super smooth like the crank all the sudden got balanced and the vibes are almost completely gone. If I can just figure out what's causing it to keep from running smooth and faster like that. I'm almost thinking it's a combination of running rich and having bad spark. I'm running a RT carb with a #70 and a champion plug. On a cold start it 4strokes for about 3-4 seconds when I let the choke off and that's it. Then I can run all day and just randomly while I'm riding it goes super smooth for about 8 seconds then goes back to normal.
Click to expand...
Were all engines on the same frame? Are you using any insulation between the mount and frame?
 
Texhun

Texhun

New Member
Aug 2, 2011
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Rosebud Texas
Same frame, same setup, same mounts, an no I havn't used insulation on any the engines mounts I've had and this is the only engine that's had a issue like this. I just bought some drill bits from HB. I'm gonna try to drill out my RT's #60 jet out to about #68 and see how it does and then I'll try using the #65 an see what it does.
 
rustycase

rustycase

Gutter Rider
May 26, 2011
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There have been a number of qualified builders who have declared the 66 is generally not as well balanced as the 48. I have not yet fired my 66.

And I've had my cns equipped 48 do some REALLY stoopid things when trying WOT runs.
Occasionally, at WOT it would go into a mode like a compression release was triggered.
NO indication of head gasket leakage before, or after then blazing 24mph run dragging my carcass...
I'm beginning to suspect a intermittently defective CDI coil.
The feeling is kinda like when my Ford runs up against the rpm limiter, at 93mph and the motor goes to stumbling, and just won't do a bit more... all because of the electronics!
I'm going to swap out my coil for another, in a few days.

Good luck!
rc
 
Texhun

Texhun

New Member
Aug 2, 2011
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Rosebud Texas
CDI coil....hmmm. It just might be it. Thanks RC, I'm gonna order one and see what happens this one has well over 1700 miles and who knows how many thousands of hours on it. After 2 years it just might be going out finally.
 
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