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Post by jbenp on Oct 17, 2014 23:45:21 GMT -5
Hi there,
This is my first time posting to this forum. I am having issues with my 2009 Sym scooter that has had its engine upgraded to 70cc and has an aftermarket airfilter. All other parts on this scooter are stock.
The issue is when I am reaching top speed ~35mph that there is a drop in power and a backfire. It happens a bit less as I ease off the throttle and stops when I am at ~75% throttle.
I have thoughts that it might be the carburetor or the exhaust but thought I would check here before shelling out any cash.
I appreciate any advice you have to give.
Cheers
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Post by alleyoop on Oct 17, 2014 23:51:37 GMT -5
Did you up jet the carb, backfire is a LEAN condition and it is really lean if it backfires. So do not run it at Wide Open Throttle until you up jet the carb. Get at least a #75 and a #80 main jet, if . Alleyoop
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Post by jbenp on Oct 18, 2014 12:37:58 GMT -5
Thanks for the advice Alleyoop. I will give that a go and let you know what happens. From reading on the Sym website the main jet is a # and the slow jet is 35#. I will see if there are larger ones that will fit the carb. Is there any point in upgrading the exhaust pipe as well? cheers
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Post by alleyoop on Oct 18, 2014 12:52:19 GMT -5
I do not think the stock 50cc sym carb has a # main and a #35 pilot, what website were you reading this? The thing to do if someone says this is to take the bowl off and see if the jets are marked with the size. When they say 70cc upgrade it is really a 63cc bbk they always round up on to make them more appealing. To big of a main jet and or pilot jet will flood the thing, It may run but with loss of power. Just so you are aware a 150cc with a 24mm carb come with a #35 Pilot jet, so you can see someone is blowing smoke out their rear. I am just stating facts you can do what you want. Alleyoop
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Post by jbenp on Oct 19, 2014 9:47:11 GMT -5
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Post by jbenp on Nov 9, 2014 17:30:05 GMT -5
It seems that the jet was too big. I had swapped out the main jet (it was a # ). I put in a # and it made the issue worse. So, I changed it to a #82 and that seems to have fixed the issue. I can actually hit 40mph on a slight hill and 50mph on the flat. Thanks for all the help Alleyoop!
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Post by alleyoop on Nov 9, 2014 17:50:34 GMT -5
Great, that indicates it did not have a # main jet but a smaller one probably in the 70 range. Ride Safe Alleyoop
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