My EVO is back firing when I back off. I had no baffles in it and no worries, I put T-makers on with baffles and it now back fires, also did the same with stock pipes, so I don't think it's an exhaust leak, I also put new gaskets in with new pipes.

When I'm de-accelerating if I give it a little choke it doesn't back fire. The mixture screw is about 3/4 turn out to run right when idling.

So I think it's running lean???

Needs bigger jet??? main??? pilot???

It's an S&S E series carb. So if I need bigger jet are they hard to do in S&S carbs??? I have done my own jetting on dirt bikes but never a harley.....

thanks in advance............

Haven't checked plugs, pipes are black I think will have close look. what do you think of the mixture screw only 3/4 out and idling smooth???
thanks scotty

easy to do

what size are your jets currently? 29.5 or 31 for pilot, or intermediate as S +S like to call them, and 72 or 74 main would be pretty normal for not too radical 80 evo

turn off fuel
remove fuel bowl( 4 screws)(perhaps remove a/c to ease this)
the long skinny jet offset from the middle is the low speed
take care with large flat gasket as the jet goes thru it, but cannot pass thru it, so the gasket must be removed first
both main and pilot jet are stamped with size(in thou)

is it one big pop, or lots of little pops

given that the throttle is closed when this occurs, it mey be only the mixture screw setting
did you try turning it out a little?
what is off idle response like?
the effectiveness of the transition ports is a very good indicator of whether or not the jet is correctly sized

1 to 1 1/2 turns would be very normal
3/4 is not totally unheard of, but if that is really the correct setting for that set up, hard to think the jet was too small
there can be an issue of the pumper rod making contact with the pumper diaphragm with the throttle closed
this "jiggling" leads to a bit of extra fuel flow that can have an effect

Thanks for replies.....

OZ ~ I wont rule out pipes not sealing totally yet, but leaning away from that because when I give a little choke it stops back firing.....

Dyna ~ I will check jet size's as soon as I get half an hour.
It's lots of pops most small with a few big one's, ie gun shot sound.
the 3/4 turn out for mixture is right for smooth idle, I would have though that's not enough, hence why I think it's running lean???
I went through same problem with my KLX450 when I went to high performance pipe, I went from 148 main to 155, and 45 to 48 pilot and that fixed it on that bike.
Whats the story on the jiggling, because if I hold just a little throttle on it doesn't back fire....

To check for intake and exhaust leaks start a COLD engine and spray exhaust with soapy water - look for bubbles, spray intake with Airostart or carby cleaner and listen for idle increase. You could spray the exhaust with carby cleaner but then you would be looking for a flash of flame and calling 000.
Sprays are COLD and WILL damage a HOT engine!!!!

Mine pops all the time this time of year, But im IN Vic.

Thanks OZ, Dyna, Scotty and deadly, it sounds like I've got a good starting place on the weekend, appreciate it...