Sudden surge in idol

Johnny trigger

New Member
Jan 22, 2020
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Hey guys. I have new 80cc kit. Iv done total maybe 10 miles on her. Always a bear to start up... anyway once she goes ill leave it idol a minute after a short ride and couple times The engine just took off. Sounded like it was going full throttle. I ran hit kill switch. Any ideas... thanks.. jon
 

Morbius18

New Member
Feb 18, 2020
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2
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40
Hey guys. I have new 80cc kit. Iv done total maybe 10 miles on her. Always a bear to start up... anyway once she goes ill leave it idol a minute after a short ride and couple times The engine just took off. Sounded like it was going full throttle. I ran hit kill switch. Any ideas... thanks.. jon
You have an air leak. One way to test is to idle it and spray carb cleaner around the intake and cylinder gaskets. Mine was a bad base gasket and crank seal below the crank gear.
 

Morbius18

New Member
Feb 18, 2020
6
2
3
40
The proper way to test it is to block off the intake and exhaust by sandwiching a rubber block off strip between the cylinder and intake/exhaust. An old tire inner tube will work.

Then you have to have a vacuum/pressure pump and see if it leaks.

For large leaks, a leakdown tester from harbor freight works. I fill the cylinder to a low psi and take soap water with a brush and put it along all the seals.

It's not a simple thing to vacuum and pressure test two strokes.
 

Johnny trigger

New Member
Jan 22, 2020
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After it starts it runs and idols great no surge. After its fully primed i still cant get any fuel through to the plug it stays dry. Carb is cleaned and seald to the manifold and the manifold sealed the cylinder. only thing i come up with is crack the cases and reseal with HONDABOND
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,120
163
63
Santa Barbara, CA
Check for air leaks around the head gasket, start it up and put your hand around the head and see if you can feel any air shooting out from around the head. I've seen those cheap stock heads warp from heat or are even made warped. I recommend getting a high compression head with large cooling fins like a fredhead but you can get another stock one for about $8.
 

Johnny trigger

New Member
Jan 22, 2020
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As of right now it wont start. I tried to seal the gasket with copper spray gasket over the metal one. When it did run i didnt feel any air or see anything. Would the high compression be a good purchase? Thanks for your help
 

Johnny trigger

New Member
Jan 22, 2020
25
15
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35
Update. High compression head. HD carburetor. Offsett intake and i sealed up tha base gasket as well as the intake and exhaust with Hondabond. Now pedal 10 feet starts right up and nice idol... thanks guys... cheers
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,120
163
63
Santa Barbara, CA
Update. High compression head. HD carburetor. Offsett intake and i sealed up tha base gasket as well as the intake and exhaust with Hondabond. Now pedal 10 feet starts right up and nice idol... thanks guys... cheers
Sweet. It had to be an air leak, the new head will not only seal much better but it will dissipate heat much better letting the engine run cooler.
 
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