Bike accelerating without using throttle

herbilious

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Joined
May 15, 2019
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14
Hi, I've got a relatively new (3rd tank of break-in) 66c motor that has a weird issue. I just installed a new expansion chamber banana exhaust because I broke the stock one, and something I've noticed is that once I start the motor and let out the clutch, the bike accelerates relatively fast without me touching the throttle. I've checked that the barrel in the carb is sitting correctly and that the throttle isn't getting stuck. I'm not sure if this has been happening for a while and I only noticed now because of the increased power, but it's dangerous and makes it difficult to ride the bike. The carb is tight around the intake, and the intake is tight to the cylinder.

P.S. I've been having a very hard time with my clutch and finding the sweet spot where it doesn't slip or not engage, but after installing the new exhaust It doesn't slip anymore. Could this be related to my throttle issue?
 


Lukesky36

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Oct 3, 2018
Messages
464
Turn the idle screw down or rich the fuel mixture with the needle if that does not help check the throttle adjustments nuts screw them all in and start again
 

herbilious

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May 15, 2019
Messages
14
Turn the idle screw down or rich the fuel mixture with the needle if that does not help check the throttle adjustments nuts screw them all in and start again
I've unscrewed the idle screw until the point of it falling out, and my fuel is on the richest mixture.
 

mark20

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Sep 26, 2018
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561
I've unscrewed the idle screw until the point of it falling out, and my fuel is on the richest mixture.
is the throttle cable seated all the way? it could be pulling on the needle causing it not to go all the way down (ie it will start going without throttle)
when you attached thecalbe to the needle housing (the round thing that has a needle) did it go all the way down into the carb (ie did it go ALL he way down, or did it stop half way?)
 

herbilious

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May 15, 2019
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14
is the throttle cable seated all the way? it could be pulling on the needle causing it not to go all the way down (ie it will start going without throttle)
when you attached thecalbe to the needle housing (the round thing that has a needle) did it go all the way down into the carb (ie did it go ALL he way down, or did it stop half way?)
The problem was that my carb pin was bent, so I hammered it back into shape and it fixed the issue.
 

Spare_Parts

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Nov 29, 2017
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2,024
Bent needle = new carb time.

Also you need to up jet. The expansion chamber is making the engine run lean which will make it rev. 2 strokes like lean until they burn a piston.
 

herbilious

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May 15, 2019
Messages
14
Bent needle = new carb time.

Also you need to up jet. The expansion chamber is making the engine run lean which will make it rev. 2 strokes like lean until they burn a piston.
So I need to get a jet with a bigger number. Do you know how I could find the stock jet size?
 

gary55

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Nov 27, 2012
Messages
3,945
The problem was that my carb pin was bent, so I hammered it back into shape and it fixed the issue.
Thanks for letting us know it was just the needle. 1 more thing I can add to my things to look for while trouble shooting a run away engine. Once the bike is warmed up if it isn't balking before it revs up then taking a long time to return to idle the jet is probably fine especially since you are probably close to sea level. From what I've heard the banana pipes don't have that great of a effect. If it is doing what I described abv. you may be able to adjust it out with clip location, if no change with clip adjustment then jetting would needed. Stock jet is #70.
 

herbilious

New Member
Joined
May 15, 2019
Messages
14
Thanks for letting us know it was just the needle. 1 more thing I can add to my things to look for while trouble shooting a run away engine. Once the bike is warmed up if it isn't balking before it revs up then taking a long time to return to idle the jet is probably fine especially since you are probably close to sea level. From what I've heard the banana pipes don't have that great of a effect. If it is doing what I described abv. you may be able to adjust it out with clip location, if no change with clip adjustment then jetting would needed. Stock jet is #70.
Thank you for all the information. I changed the needle clip to the 2nd richest notch and the bike is running great and the plug looks fairly tan. I dont mean to change the thread topic too much, but after this tank I'll be going from 1:20 oil ratio to 1:40. Would this have an effect on the fuel/air mix since theres more actual fuel being used?
 
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