08-11-2015, 08:49 AM | #1 |
Not Yet Wild
Join Date: Sep 2011
Location: Butterfield, MN
Posts: 43
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Backfire/Afterfire
What causes backfire on fast deceleration and afterfire when the motor shuts off? Is it running to lean or to rich? Its a Predator 420 and i currently have the stock main jet in that it comes with from Harbor Freight, aftermarket air filter, and pretty free flowing exhaust (14" tractor muffler). Its kinda annoying. Thanks
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08-11-2015, 10:27 AM | #2 |
Getting Wild
Join Date: Sep 2013
Location: Texas
Posts: 106
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Re: Backfire/Afterfire
Running lean, Had same issue on a VC 420, Was surprised how far I needed to crank open the mixture screw.
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08-11-2015, 11:17 AM | #3 |
Gone Wild
Join Date: Oct 2010
Location: Pittsburgh Pa
Posts: 1,551
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Re: Backfire/Afterfire
Running lean. They are lean from the factory. Then you open up the air filter and exhaust and that makes it even more lean.
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08-11-2015, 11:18 AM | #4 |
Not Yet Wild
Join Date: Sep 2011
Location: Butterfield, MN
Posts: 43
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Re: Backfire/Afterfire
Ahhhh.... Gotcha. Thanks
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08-11-2015, 06:25 PM | #5 |
Vegas modded 420
Join Date: Jun 2009
Location: West MI
Posts: 15,433
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Re: Backfire/Afterfire
You need to get the idle mix screw working, sometimes you have to enlarge the idle jet. The main is mostly at 1/4 throttle and more. If it goes flat after half throttle or runs better WOT with the choke on a little, or the plug is white, you need a larger main or enlarge it.
Lean idle causes hard starting, wont start warm with no choke, wont idle slow, pops/backfires when you let off the gas as speed. |
08-20-2015, 09:41 PM | #6 |
Not Yet Wild
Join Date: Sep 2011
Location: Butterfield, MN
Posts: 43
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Re: Backfire/Afterfire
Is there an idle mix screw on a factory carb?
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08-23-2015, 06:05 PM | #7 |
Vegas modded 420
Join Date: Jun 2009
Location: West MI
Posts: 15,433
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Re: Backfire/Afterfire
Yes but they plug it to cover it, or break it off. Its on the side near the spacer. If you had the head of the engine towards you, you would see it.
Brass screw on the left: http://www.ezbore.net/v/vspfiles/photos/REA035041-2.jpg The plug is easy to drill out, if broken off you will see a stub of brass there you have to remove. |
08-23-2015, 06:12 PM | #8 |
Not Yet Wild
Join Date: Sep 2011
Location: Butterfield, MN
Posts: 43
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Re: Backfire/Afterfire
I found it... they broke the head off of it. Where can I get a screw with a head on it? And is there an easy way to get this broken off one out?
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08-28-2015, 06:33 PM | #9 |
Vegas modded 420
Join Date: Jun 2009
Location: West MI
Posts: 15,433
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Re: Backfire/Afterfire
I took a dremel with a tiny blade on it and cut a slot into the end of it. Then I took a solder gun and got it hot, that released the loctite and it screwed out easily. Then got on ebay and ordered a carb kit with a screw it was cheap. You may be able to get just the screw now I don't know. You need the screw and spring. This one had gobs of loctite on it, I could have screwed it out and left it.
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09-01-2015, 06:05 AM | #10 |
Getting Wild
Join Date: Sep 2010
Location: Sanford, North Carolina
Posts: 88
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Re: Backfire/Afterfire
I have the VC carb on mine. I had to put a 115 jet in it to get the spark plug color right. I adjusted the idle mixture screw until the idle smoothed out, but mine still back fires when I let off the gas going down a hill and sometimes when I shut it off! Should I open up the idle jet a little?
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