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Discussion Starter #1
Bike sat in a barn for 20+ years got it running but backfired and throws flames when I try to give it gas quick if I go slow it will climb the rpm but a quick snap it backfires I pulled the carbs and cleaned them the best I could put them back on and still backfires the same way I’m not sure what to try to stop it
 

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That’s a long time. Exactly what did you do to the carbs to clean them? A full disassembly and ultrasonic cleaning (boiling them) of the metal bits might be in order. Also, check all of the fuel and air lines for blockage.
 

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ok, lets make sure you are using the right terminology for what is happening...

Backfire through the carbs themselves OR Backfire out the muffler??
The way you wrote it, I'm thinking out the muffler...but just to make sure...

Here's a page that should get you started.

When it comes to carb cleaning, even after you've cleaned 'em,
they still have to be set correctly...there's a few great posts on that on our site.
Read 'em all, and then go through them one at a time until ou find the fix that works for you.
Probably gonna be the air/fuel ratio screw...but may be your exhaust setup...
or lack of an exhaust setup...holes in it or no muffler at all/aftermarket muffler
may be your whole issue.

Also, new plugs & wires ain't a bad idea...that'll cut out a few variables,
so you're not trying to work off 20+ yr old data.
 

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Discussion Starter #5
That’s a long time. Exactly what did you do to the carbs to clean them? A full disassembly and ultrasonic cleaning (boiling them) of the metal bits might be in order. Also, check all of the fuel and air lines for blockage.
I cleaned all the jets and used a carb cleaner I don’t have anything to do a ultrasonic clean I can soak them it you think that will help
 

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Sometimes even someone experienced with CV carbs has to take them apart a second time, we see it here all the time. Find a good video on cleaning shadow carbs or do a search here on the subject.
 

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If the factory air intake tubing has been removed or modified they run crappy.
 

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Discussion Starter #8
Well along with backfire it won’t rev up if I give it gas quick it backfires and wants to die out but it I go really slow I can get it up the rpms I’m not sure what causes that tho
 

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Well, when you get on the gas quick, the resulting vacuum pulls the slide valves open. This pulls the needles up and gives an extra shot of fuel. There may be a hole in your carb diaphragms, or the slides are binding up.
 

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Discussion Starter #10
Well, when you get on the gas quick, the resulting vacuum pulls the slide valves open. This pulls the needles up and gives an extra shot of fuel. There may be a hole in your carb diaphragms, or the slides are binding up.
I just replaced slides the whole assembly when I watch them they open right up but it spits and spatters still
 

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Diaphragms as well? But if they’re opening nice and smooth, that’s probably not the problem. When they do open, do you see fuel coming up from the needle jet?
 

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Discussion Starter #12
Diaphragms as well? But if they’re opening nice and smooth, that’s probably not the problem. When they do open, do you see fuel coming up from the needle jet?
Actually yes I know that’s not good because unburnt fuel causes a backfire but how do I fix that
 

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A high float level allows fuel to be drawn up the main jet easier. Maybe that is what is happening.
 

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In this case, that’s what is supposed to happen. The needles open in response to a quick demand for more air from the engine. More air requires an extra shot of fuel to keep the engine from leaning out. So you might be getting too much, or too little, out of those needle jets.
 
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