66/80cc Grubee High RPM Engine Cutout

Maskot

New Member
Apr 22, 2011
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Wellington, FL
Right as the engine starts to vibrate every nut loose, it cuts off and revs down to idle then after 2-3 seconds the power comes back.

Fuel flow is good, spark plug is black :p, don't know jet size, probably too big, stock everything, NT carb, 1:35~40 fuel mix, 89 octane pure gasoline, does the same thing when moving or not.

I think it's either the spark or the exhaust.

If a thread already exists for this, please lock and post a link to it, thanks.
 
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Chaz

Well-Known Member
Jun 3, 2012
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Vancouver, British Columbia
Two quick thoughts. Maybe vibration is foaming the fuel in the carb bowl. Possibly vibration is irritating some iffy electrical connection, particularly the magneto connection.
 

crassius

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Sep 30, 2012
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fuel foaming in carb - something loose or sometimes happens with long, offset, intake
 

Maskot

New Member
Apr 22, 2011
46
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0
Wellington, FL
Two quick thoughts. Maybe vibration is foaming the fuel in the carb bowl. Possibly vibration is irritating some iffy electrical connection, particularly the magneto connection.
I'm convinced it's fuel foaming, I have the engine mounted to the frame on dampers that allow it to rock side to side and prevents vibrations. I'm going to take those out, lock the thread bolts into the engine and tighten the mounts down with lock washers nice and tight. If this doesn't work, I think I'll try to make a custom shock mount for the carb to the frame and use rubber tubing to bridge the small gap to the engine intake.
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
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Vancouver, British Columbia
Yeah, ditch those dampers and see how she goes. Sounds like you gotta whole lotta shakin goin on. Hope that does it for you. Let us know.

I have an older motor and it vibrates but smooths out at my higher cruising rpm.
 

Maskot

New Member
Apr 22, 2011
46
0
0
Wellington, FL
Yeah, ditch those dampers and see how she goes. Sounds like you gotta whole lotta shakin goin on. Hope that does it for you. Let us know.

I have an older motor and it vibrates but smooths out at my higher cruising rpm.
After the hard mount, I realized why I put the shock mounts in, All of the capillaries in my hands are shredded. It did fix the problem however and I'm happy for that.
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
70
48
Vancouver, British Columbia
Glad to hear you got it sorted but too bad about the bad vibes. Maybe time to get one of the new balanced engines. Also you could try banging some fishing weights into the handlebars to reduce it somewhat. I haven't done this but I hear it helps. Best to research for options.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
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sometimes moving the rear mount up or down just a 1/4inch and front mount the other way to keep it tight will stop some of the vibration